Delmarva Power & Light 10-K 9 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2017USD ($)shares
Entity Registrant Name	EXELON CORP
Entity Central Index Key	1,109,357
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding	965,029,399
Entity Public Float | $	$ 34,604,071,959
Exelon Generation Co L L C [Member]
Entity Registrant Name	EXELON GENERATION CO LLC
Entity Central Index Key	1,168,165
Entity Filer Category	Non-accelerated Filer
Commonwealth Edison Co [Member]
Entity Registrant Name	COMMONWEALTH EDISON CO
Entity Central Index Key	22,606
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	127,021,256
PECO Energy Co [Member]
Entity Registrant Name	PECO ENERGY CO
Entity Central Index Key	78,100
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	170,478,507
Baltimore Gas and Electric Company [Member]
Entity Registrant Name	BALTIMORE GAS AND ELECTRIC
Entity Central Index Key	9,466
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	1,000
Pepco Holdings LLC [Member]
Entity Registrant Name	PEPCO HOLDINGS LLC
Entity Central Index Key	1,135,971
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	252,815,448
Potomac Electric Power Company [Member]
Entity Registrant Name	POTOMAC ELECTRIC POWER CO
Entity Central Index Key	79,732
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	100
Delmarva Power and Light Company [Member]
Entity Registrant Name	DELMARVA POWER & LIGHT CO /DE/
Entity Central Index Key	27,879
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	1,000
Atlantic City Electric Company [Member]
Entity Registrant Name	ATLANTIC CITY ELECTRIC CO
Entity Central Index Key	8,192
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	8,546,017

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues
Operating Revenue				$ 17,360	$ 16,324	$ 18,395
Regulated Operating Revenue				16,171	15,036	11,052
Electric operating revenues	[1]			14,840	13,869	9,876
Natural gas operating revenues	[1]			1,333	1,166	1,176
Operating revenues from affiliates				7	10	9
Total operating revenues				33,531	31,360	29,447
Operating expenses
Competitive businesses purchased power and fuel				9,668	8,817	10,007
Cost of Purchased Power				4,367	3,823	3,077
Operating and maintenance				10,126	10,048	8,322
Depreciation and amortization				3,828	3,936	2,450
Taxes other than income				1,731	1,576	1,200
Total operating expenses				29,720	28,200	25,056
Gain (Loss) on Disposition of Other Assets				3	(48)	18
Bargain purchase gain				233	0	0
Gain on deconsolidation of business				213	0	0
Operating Income (Loss)				4,260	3,112	4,409
Other income and (deductions)
Interest Expense				(1,524)	(1,495)	(992)
Interest expense to affiliates				(36)	(41)	(41)
Other, net				1,056	413	(46)
Total other income and (deductions)				(504)	(1,123)	(1,079)
Income before income taxes				3,756	1,989	3,330
Income before income taxes				3,756	1,989	3,330
Income taxes				(125)	761	1,073
Income (Loss) from Equity Method Investments				(32)	(24)	(7)
Net Income (Loss)				3,849	1,204	2,250
Net Income Loss Attributable To Noncontrolling Interest And Preferred Stock Dividends And Other Adjustments				79	70	(19)
Net income attributable to common shareholders				3,770	1,134	2,269
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax				(56)	(48)	(46)
Actuarial loss reclassified to periodic cost, net of tax				197	184	220
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax				(10)	181	99
Unrealized gain (loss) on cash flow hedges, net of taxes			$ 0	(3)	(2)	(9)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax				6	1	0
Unrealized gain (loss) on foreign currency translation, net of taxes				7	10	(21)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax				4	(4)	(3)
Other comprehensive income (loss)				171	(36)	60
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest				4,020	1,168	2,310
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest				77	70	(19)
Comprehensive income				$ 3,943	$ 1,098	$ 2,329
Average shares of common stock outstanding:
Basic				947	924	890
Diluted				949	927	893
Earnings per average common share:
Earnings Per Share, Basic				$ 3.98	$ 1.23	$ 2.55
Diluted (in usd per share)				3.97	1.22	2.54
Dividends per common share (in usd per share)				$ 1.31	$ 1.26	$ 1.24
Predecessor [Member]
Other income and (deductions)
Income (Loss) from Equity Method Investments						$ 0
Exelon Generation Co L L C [Member]
Operating revenues
Operating Revenue				$ 17,351	$ 16,312	18,386
Operating revenues from affiliates				1,115	1,439	749
Total operating revenues				18,466	17,751	19,135
Operating expenses
Cost of Purchased Power				9,671	8,818	10,007
Purchased power from affiliate				19	12	14
Operating and maintenance				5,594	4,978	4,688
Operating and maintenance from affiliates				697	663	620
Depreciation and amortization				1,457	1,879	1,054
Taxes other than income				555	506	489
Total operating expenses				17,993	16,856	16,872
Gain (Loss) on Disposition of Other Assets				2	(59)	12
Bargain purchase gain				233	0	0
Gain on deconsolidation of business				213	0	0
Operating Income (Loss)				921	836	2,275
Other income and (deductions)
Interest Expense				(401)	(325)	(322)
Interest expense to affiliates				(39)	(39)	(43)
Other, net				948	401	(60)
Total other income and (deductions)				508	37	(425)
Income before income taxes				1,429	873	1,850
Income taxes				(1,375)	290	502
Income (Loss) from Equity Method Investments						(8)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)	(25)	(8)
Net Income (Loss)				2,771	558	1,340
Income (Loss) Attributable to Noncontrolling Interest, before Tax				77	62	(32)
Net income attributable to membership interest				2,694	496	1,372
Pension and non-pension postretirement benefit plans:
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)	(25)	(8)
Unrealized gain (loss) on cash flow hedges, net of taxes				(3)	(2)	3
Other Comprehensive Income Unrealized Income Loss On Equity Investments Arising During Period Net Of Tax				4	(4)	(3)
Unrealized gain (loss) on foreign currency translation, net of taxes				7	10	(21)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax				1	1	0
Other comprehensive income (loss)				15	9	(27)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest				2,786	567	1,313
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest				75	62	(32)
Comprehensive income				2,711	505	1,345
Commonwealth Edison Co [Member]
Operating revenues
Electric operating revenues				5,521	5,239	4,901
Operating revenues from affiliates				15	15	4
Total operating revenues				5,536	5,254	4,905
Operating expenses
Purchased power				1,533	1,411	1,301
Purchased power from affiliate				108	47	18
Operating and maintenance				1,157	1,303	1,372
Operating and maintenance from affiliates				270	227	195
Depreciation and amortization				850	775	707
Taxes other than income				296	293	296
Total operating expenses				4,214	4,056	3,889
Gain (Loss) on Disposition of Other Assets				1	7	1
Operating Income (Loss)				1,323	1,205	1,017
Other income and (deductions)
Interest Expense				(348)	(448)	(319)
Interest expense to affiliates				(13)	(13)	(13)
Other, net				22	(65)	21
Total other income and (deductions)				(339)	(526)	(311)
Income before income taxes				984	679	706
Income taxes				417	301	280
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				567	378	426
Pension and non-pension postretirement benefit plans:
Comprehensive income				567	378	426
PECO Energy Co [Member]
Operating revenues
Electric operating revenues				2,369	2,524	2,485
Natural gas operating revenues				494	462	545
Operating revenues from affiliates				7	8	2
Total operating revenues				2,870	2,994	3,032
Operating expenses
Purchased power				648	598	735
Purchased fuel				186	162	235
Purchased power from affiliate				135	287	220
Operating and maintenance				657	665	684
Operating and maintenance from affiliates				149	146	110
Depreciation and amortization				286	270	260
Taxes other than income				154	164	160
Total operating expenses				2,215	2,292	2,404
Gain (Loss) on Disposition of Other Assets				0	0	2
Operating Income (Loss)				655	702	630
Other income and (deductions)
Interest Expense				(115)	(111)	(102)
Interest expense to affiliates				(11)	(12)	(12)
Other, net				9	8	5
Total other income and (deductions)				(117)	(115)	(109)
Income before income taxes				538	587	521
Income taxes				104	149	143
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				434	438	378
Net income attributable to common shareholders				434	438	378
Pension and non-pension postretirement benefit plans:
Comprehensive income				434	438	378
Baltimore Gas and Electric Company [Member]
Operating revenues
Electric operating revenues				2,484	2,603	2,490
Natural gas operating revenues				676	609	631
Operating revenues from affiliates				16	21	14
Total operating revenues				3,176	3,233	3,135
Operating expenses
Purchased power				566	528	602
Purchased fuel				183	162	205
Purchased power from affiliate				384	604	498
Operating and maintenance				563	605	565
Operating and maintenance from affiliates				153	132	118
Depreciation and amortization				473	423	366
Taxes other than income				240	229	224
Total operating expenses				2,562	2,683	2,578
Gain (Loss) on Disposition of Other Assets				0	0	1
Operating Income (Loss)				614	550	558
Other income and (deductions)
Interest Expense				(95)	(87)	(83)
Interest expense to affiliates				(10)	(16)	(16)
Other, net				16	21	18
Total other income and (deductions)				(89)	(82)	(81)
Income before income taxes				525	468	477
Income taxes				218	174	189
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				307	294	288
Dividends, Preferred Stock				0	8	13
Net income attributable to common shareholders				307	286	275
Pension and non-pension postretirement benefit plans:
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest				307	294	288
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest				0	8	13
Comprehensive income				307	286	275
Pepco Holdings LLC [Member]
Operating expenses
Purchased power from affiliate		$ 0				0
Pepco Holdings LLC [Member] | Predecessor [Member]
Operating revenues
Electric operating revenues		1,096				4,770
Natural gas operating revenues		57				165
Operating revenues from affiliates		0				0
Total operating revenues		1,153				4,935
Operating expenses
Purchased power		471				1,986
Purchased fuel		26				87
Operating and maintenance		294				1,156
Operating and maintenance from affiliates		0				0
Depreciation and amortization		152				624
Taxes other than income		105				455
Total operating expenses		1,048				4,308
Gain (Loss) on Disposition of Other Assets		0				46
Operating Income (Loss)		105				673
Other income and (deductions)
Interest Expense		(65)				(280)
Other, net		(4)				88
Total other income and (deductions)		(69)				(192)
Income before income taxes		36				481
Income taxes		17				163
Income (Loss) from Equity Method Investments		0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		0				0
Net Income (Loss)		19				327
Net income attributable to membership interest		19				327
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		19				318
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest		0				9
Pension and non-pension postretirement benefit plans:
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		0				0
Actuarial loss reclassified to periodic cost, net of tax		1				9
Unrealized gain (loss) on cash flow hedges, net of taxes		0				(1)
Other comprehensive income (loss)		1				10
Comprehensive income		$ 20				337
Pepco Holdings LLC [Member] | Successor [Member]
Operating revenues
Electric operating revenues			3,506	4,468
Natural gas operating revenues			92	161
Operating revenues from affiliates			45	50
Total operating revenues			3,643	4,679
Operating expenses
Purchased power			925	1,182
Purchased fuel			36	71
Purchased power from affiliate			486	463
Operating and maintenance			1,144	918
Operating and maintenance from affiliates			89	150
Depreciation and amortization			515	675
Taxes other than income			354	452
Total operating expenses			3,549	3,911
Gain (Loss) on Disposition of Other Assets			(1)	1
Operating Income (Loss)			93	769
Other income and (deductions)
Interest Expense			(195)	(245)
Other, net			44	54
Total other income and (deductions)			(151)	(191)
Income before income taxes			(58)	578
Income taxes			3	217
Income (Loss) from Equity Method Investments			0	(1)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			0	1
Net Income (Loss)			(61)	362
Net income attributable to membership interest			(61)	362
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			(61)	362
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest			0	0
Pension and non-pension postretirement benefit plans:
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			0	1
Actuarial loss reclassified to periodic cost, net of tax			0	0
Unrealized gain (loss) on cash flow hedges, net of taxes				0
Other comprehensive income (loss)			0	0
Comprehensive income			$ (61)	362
Potomac Electric Power Company [Member]
Operating revenues
Electric operating revenues				2,152	2,181	2,124
Operating revenues from affiliates				6	5	5
Total operating revenues				2,158	2,186	2,129
Operating expenses
Purchased power				359	411	719
Purchased power from affiliate				255	295	0
Operating and maintenance				396	607	435
Operating and maintenance from affiliates				58	35	4
Depreciation and amortization				321	295	256
Taxes other than income				371	377	376
Total operating expenses				1,760	2,020	1,790
Gain (Loss) on Disposition of Other Assets				1	8	46
Operating Income (Loss)				399	174	385
Other income and (deductions)
Interest Expense				(121)	(127)	(124)
Other, net				32	36	28
Total other income and (deductions)				(89)	(91)	(96)
Income before income taxes				310	83	289
Income taxes				105	41	102
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				205	42	187
Pension and non-pension postretirement benefit plans:
Comprehensive income				205	42	187
Delmarva Power and Light Company [Member]
Operating revenues
Electric operating revenues				1,131	1,122	1,132
Natural gas operating revenues				161	148	164
Operating revenues from affiliates				8	7	6
Total operating revenues				1,300	1,277	1,302
Operating expenses
Purchased power				282	369	555
Purchased fuel				71	60	79
Purchased power from affiliate				179	154	0
Operating and maintenance				283	422	303
Operating and maintenance from affiliates				32	19	1
Depreciation and amortization				167	157	148
Taxes other than income				57	55	51
Total operating expenses				1,071	1,236	1,137
Gain (Loss) on Disposition of Other Assets				0	9	0
Operating Income (Loss)				229	50	165
Other income and (deductions)
Interest Expense				(51)	(50)	(50)
Other, net				14	13	10
Total other income and (deductions)				(37)	(37)	(40)
Income before income taxes				192	13	125
Income taxes				71	22	49
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				121	(9)	76
Pension and non-pension postretirement benefit plans:
Comprehensive income				121	(9)	76
Atlantic City Electric Company [Member]
Operating revenues
Electric operating revenues				1,184	1,254	1,291
Operating revenues from affiliates				2	3	4
Total operating revenues				1,186	1,257	1,295
Operating expenses
Purchased power				541	614	708
Purchased power from affiliate				29	37	0
Operating and maintenance				279	410	268
Operating and maintenance from affiliates				28	18	3
Depreciation and amortization				146	165	175
Taxes other than income				6	7	7
Total operating expenses				1,029	1,251	1,161
Gain (Loss) on Disposition of Other Assets				0	1	0
Operating Income (Loss)				157	7	134
Other income and (deductions)
Interest Expense				(61)	(62)	(64)
Other, net				7	9	3
Total other income and (deductions)				(54)	(53)	(61)
Income before income taxes				103	(46)	73
Income taxes				26	(4)	33
Income (Loss) from Equity Method Investments				0	0	0
Net Income (Loss)				77	(42)	40
Pension and non-pension postretirement benefit plans:
Comprehensive income				$ 77	$ (42)	$ 40
[1]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net Income (Loss)	$ 3,849	$ 1,204	$ 2,250
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	5,427	5,576	3,987
Impairment losses of long-lived assets, intangibles and regulatory assets	573	306	36
Deconsolidation, Gain (Loss), Amount	(213)	0	0
Gain (Loss) on Disposition of Assets	(3)	48	(18)
Business Combination, Bargain Purchase, Gain Recognized, Amount	(233)	0	0
Deferred income taxes and amortization of investment tax credits	(361)	664	752
Net fair value changes related to derivatives	151	24	(367)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(616)	(229)	131
Other non-cash operating activities	721	1,333	1,109
Changes in assets and liabilities:
Accounts receivable	(426)	(432)	240
Inventories	(72)	7	4
Accounts payable and accrued expenses	(390)	771	(121)
Increase (Decrease) in Premiums Receivable	28	(66)	58
Increase (Decrease) Cash Collateral from Counterparties	(158)	931	347
Income taxes	299	576	97
Pension and non-pension postretirement benefit contributions	(405)	(397)	(502)
Increase (Decrease) in Prepaid Taxes	0	(1,250)	0
Other assets and liabilities	(691)	(621)	(387)
Net Cash Provided by (Used in) Operating Activities	7,480	8,445	7,616
Cash flows from investing activities
Capital expenditures	(7,584)	(8,553)	(7,624)
Payments to Acquire Businesses, Net of Cash Acquired		(6,962)	0
Proceeds from Sale and Collection of Lease Receivables	0	360	0
Proceeds from nuclear decommissioning trust fund sales	7,845	9,496	6,895
Investment in nuclear decommissioning trust funds	(8,113)	(9,738)	(7,147)
Acquisitions of businesses, net	(208)	(6,934)	(40)
Proceeds from sales of long-lived assets	219	61	147
Change in restricted cash	(50)	(42)	66
Other investing activities	(43)	(153)	(119)
Net cash flows used in investing activities	(7,934)	(15,503)	(7,822)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt	(261)	(353)	80
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	621	240	0
Repayments of Debt, Maturing in More than Three Months	(700)	(462)	0
Issuance of long-term debt	3,470	4,716	6,709
Retirement of long-term debt	(2,490)	(1,936)	(2,687)
Proceeds from Issuance of Common Stock	0	0	1,868
Redemption of preference stock	0	(190)	0
Dividends paid on common stock	(1,236)	(1,166)	(1,105)
Proceeds from employee stock plans	(150)	(55)	(32)
Proceeds from Noncontrolling Interests	396	372	32
Other financing activities	(83)	(85)	(99)
Net cash flows provided by financing activities	717	1,191	4,830
Increase (Decrease) in cash and cash equivalents	263	(5,867)	4,624
Cash and cash equivalents at beginning of period	635	6,502	1,878
Cash and cash equivalents at end of period	898	635	6,502
Parent Company [Member]
Cash flows from operating activities
Net Income (Loss)	3,770	1,134	2,269
Changes in assets and liabilities:
Net Cash Provided by (Used in) Operating Activities	1,921	1,029	3,071
Cash flows from investing activities
Payments to Acquire Businesses, Net of Cash Acquired	0
Other investing activities	(5)	5	(55)
Increase (Decrease) Due from Affiliates	(129)	1,390	(1,217)
Net cash flows used in investing activities	(1,851)	(7,324)	(934)
Cash flows from financing activities
Issuance of long-term debt	0	1,800	4,200
Retirement of long-term debt	(569)	(46)	(2,263)
Contributions from member	1,879	1,912	3,209
Proceeds from Issuance of Common Stock	0	0	1,868
Dividends paid on common stock	(1,236)	(1,166)	(1,105)
Proceeds from employee stock plans	(150)	(55)	(32)
Other financing activities	(9)	(20)	(58)
Net cash flows provided by financing activities	(14)	623	2,674
Increase (Decrease) in cash and cash equivalents	56	(5,672)	4,811
Cash and cash equivalents at beginning of period	18	5,690	879
Cash and cash equivalents at end of period	74	18	5,690
Increase (Decrease) Due from Affiliates	(129)	1,390	(1,217)
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net Income (Loss)	2,771	558	1,340
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	3,056	3,519	2,589
Impairment losses of long-lived assets, intangibles and regulatory assets	510	243	12
Deconsolidation, Gain (Loss), Amount	(213)	0	0
Gain (Loss) on Disposition of Assets	(2)	59	(12)
Business Combination, Bargain Purchase, Gain Recognized, Amount	(233)	0	0
Deferred income taxes and amortization of investment tax credits	(2,022)	(269)	49
Net fair value changes related to derivatives	167	40	(249)
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	(616)	(229)	131
Other non-cash operating activities	112	15	268
Changes in assets and liabilities:
Accounts receivable	(276)	(152)	194
Receivables from and payables to affiliates, net	(7)	(21)	15
Inventories	(29)	(4)	16
Accounts payable and accrued expenses	2	29	(149)
Increase (Decrease) in Premiums Receivable	28	(66)	58
Increase (Decrease) Cash Collateral from Counterparties	(129)	923	407
Income taxes	496	182	(18)
Pension and non-pension postretirement benefit contributions	(148)	(152)	(245)
Other assets and liabilities	(168)	(231)	(207)
Net Cash Provided by (Used in) Operating Activities	3,299	4,444	4,199
Cash flows from investing activities
Capital expenditures	(2,259)	(3,078)	(3,841)
Proceeds from nuclear decommissioning trust fund sales	7,845	9,496	6,895
Investment in nuclear decommissioning trust funds	(8,113)	(9,738)	(7,147)
Acquisitions of businesses, net	(208)	(293)	(40)
Proceeds from sales of long-lived assets	218	37	147
Change in restricted cash	(17)	(35)	35
Other investing activities	(58)	(240)	(118)
Net cash flows used in investing activities	(2,592)	(3,851)	(4,069)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	(620)	620	0
Repayments of Debt, Maturing in More than Three Months	(200)	(162)	0
Proceeds from Debt, Maturing in More than Three Months	121	240	0
Issuance of long-term debt	1,645	388	1,309
Retirement of long-term debt	(1,261)	(202)	(89)
Proceeds from (Repayments of) Restricted Cash, Financing Activities	(50)
Repayments of Related Party Debt	0	0	(550)
Increase (Decrease) in Due to Affiliates	(1)	(1,191)	1,252
Distributions to member	(659)	(922)	(2,474)
Contributions from member	102	142	47
Proceeds from Noncontrolling Interests	396	372	32
Other financing activities	(54)	(19)	(6)
Net cash flows provided by financing activities	(581)	(734)	(479)
Increase (Decrease) in cash and cash equivalents	126	(141)	(349)
Cash and cash equivalents at beginning of period	290	431	780
Cash and cash equivalents at end of period	416	290	431
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net Income (Loss)	567	378	426
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	850	775	707
Deferred income taxes and amortization of investment tax credits	659	439	353
Other non-cash operating activities	164	215	416
Changes in assets and liabilities:
Accounts receivable	(59)	(25)	(93)
Receivables from and payables to affiliates, net	8	3	(19)
Inventories	4	1	(40)
Accounts payable and accrued expenses	(297)	339	68
Increase (Decrease) Cash Collateral from Counterparties	(26)	7	(33)
Income taxes	(308)	306	192
Pension and non-pension postretirement benefit contributions	(41)	(38)	(150)
Other assets and liabilities	6	105	69
Net Cash Provided by (Used in) Operating Activities	1,527	2,505	1,896
Cash flows from investing activities
Capital expenditures	(2,250)	(2,734)	(2,398)
Acquisitions of businesses, net		0
Change in restricted cash	(66)	0	2
Other investing activities	20	49	34
Net cash flows used in investing activities	(2,296)	(2,685)	(2,362)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	0	(294)	(10)
Issuance of long-term debt	1,000	1,200	850
Retirement of long-term debt	(425)	(665)	(260)
Dividends paid on common stock	(422)	(369)	(299)
Other financing activities	(15)	(18)	(16)
Contributions from parent	651	315	202
Net cash flows provided by financing activities	789	169	467
Increase (Decrease) in cash and cash equivalents	20	(11)	1
Cash and cash equivalents at beginning of period	56	67	66
Cash and cash equivalents at end of period	76	56	67
PECO Energy Co [Member]
Cash flows from operating activities
Net Income (Loss)	434	438	378
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	286	270	260
Deferred income taxes and amortization of investment tax credits	19	78	90
Other non-cash operating activities	54	65	70
Changes in assets and liabilities:
Accounts receivable	(44)	(71)	37
Receivables from and payables to affiliates, net	(6)	6	3
Inventories	1	6	10
Accounts payable and accrued expenses	6	67	(25)
Income taxes	34	8	(9)
Pension and non-pension postretirement benefit contributions	(24)	(30)	(40)
Other assets and liabilities	(5)	(8)	(4)
Net Cash Provided by (Used in) Operating Activities	755	829	770
Cash flows from investing activities
Capital expenditures	(732)	(686)	(601)
Acquisitions of businesses, net		0
Change in restricted cash	0	(1)	(1)
Other investing activities	4	20	14
Increase (Decrease) Due from Affiliates	131	(131)	0
Net cash flows used in investing activities	(597)	(798)	(588)
Cash flows from financing activities
Issuance of long-term debt	325	300	350
Retirement of long-term debt	0	(300)	0
Dividends paid on common stock	(288)	(277)	(279)
Other financing activities	(3)	(4)	(4)
Contributions from parent	16	18	16
Net cash flows provided by financing activities	50	(263)	83
Increase (Decrease) in cash and cash equivalents	208	(232)	265
Cash and cash equivalents at beginning of period	63	295	30
Cash and cash equivalents at end of period	271	63	295
Increase (Decrease) Due from Affiliates	131	(131)	0
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net Income (Loss)	307	294	288
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	473	423	366
Impairment losses of long-lived assets, intangibles and regulatory assets	7	52	0
Deferred income taxes and amortization of investment tax credits	145	118	165
Other non-cash operating activities	65	88	137
Changes in assets and liabilities:
Accounts receivable	(5)	(98)	84
Receivables from and payables to affiliates, net	(4)	3	(2)
Inventories	(9)	1	18
Accounts payable and accrued expenses	(15)	138	(3)
Increase (Decrease) Cash Collateral from Counterparties	0	0	(27)
Income taxes	60	18	(54)
Pension and non-pension postretirement benefit contributions	(53)	(49)	(17)
Other assets and liabilities	(150)	(43)	(173)
Net Cash Provided by (Used in) Operating Activities	821	945	782
Cash flows from investing activities
Capital expenditures	(882)	(934)	(719)
Acquisitions of businesses, net		0
Change in restricted cash	26	0	26
Other investing activities	7	24	18
Net cash flows used in investing activities	(849)	(910)	(675)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	32	(165)	90
Issuance of long-term debt	300	850	0
Retirement of long-term debt	(41)	(379)	(75)
Repayments of Related Party Debt	(250)	0	0
Redemption of preference stock	0	(190)	0
Dividends paid on common stock	(198)	(179)	(158)
Other financing activities	(5)	(11)	(13)
Contributions from parent	184	61	7
Dividends paid on preferred securities	0	(8)	(13)
Net cash flows provided by financing activities	22	(21)	(162)
Increase (Decrease) in cash and cash equivalents	(6)	14	(55)
Cash and cash equivalents at beginning of period	23	9	64
Cash and cash equivalents at end of period	17	23	9
Pepco Holdings LLC [Member] | Predecessor [Member]
Cash flows from operating activities
Net Income (Loss)			327
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			(9)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization			624
Impairment losses of long-lived assets, intangibles and regulatory assets			0
Gain (Loss) on Disposition of Assets			(46)
Deferred income taxes and amortization of investment tax credits			134
Net fair value changes related to derivatives			0
Other non-cash operating activities			167
Changes in assets and liabilities:
Accounts receivable			(105)
Receivables from and payables to affiliates, net			0
Inventories			0
Accounts payable and accrued expenses			(41)
Income taxes			8
Pension and non-pension postretirement benefit contributions			(21)
Other assets and liabilities			(99)
Net Cash Provided by (Used in) Operating Activities			939
Cash flows from investing activities
Capital expenditures			(1,230)
Proceeds from sales of long-lived assets			54
Purchases of investments			0
Change in restricted cash			6
Other investing activities			9
Net cash flows used in investing activities			(1,161)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt			34
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less			300
Repayments of Debt, Maturing in More than Three Months			0
Issuance of long-term debt			558
Retirement of long-term debt			(430)
Increase (Decrease) in Due to Affiliates			0
Distributions to member			0
Dividends paid on common stock			(275)
Proceeds from employee stock plans			(18)
Other financing activities			(26)
Contributions from parent			0
Proceeds from Issuance of Preferred Stock and Preference Stock			54
Net cash flows provided by financing activities			233
Increase (Decrease) in cash and cash equivalents			11
Cash and cash equivalents at beginning of period	170	26	15
Cash and cash equivalents at end of period		170	26
Proceeds from Issuance of Preferred Stock and Preference Stock			54
Pepco Holdings LLC [Member] | Successor [Member]
Cash flows from operating activities
Net Income (Loss)	362
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	675
Impairment losses of long-lived assets, intangibles and regulatory assets	52
Gain (Loss) on Disposition of Assets	(1)
Deferred income taxes and amortization of investment tax credits	252
Net fair value changes related to derivatives	0
Other non-cash operating activities	59
Changes in assets and liabilities:
Accounts receivable	(26)
Receivables from and payables to affiliates, net	(2)
Inventories	(37)
Accounts payable and accrued expenses	(106)
Income taxes	79
Pension and non-pension postretirement benefit contributions	(99)
Other assets and liabilities	(258)
Net Cash Provided by (Used in) Operating Activities	950
Cash flows from investing activities
Capital expenditures	(1,396)
Proceeds from sales of long-lived assets	1
Purchases of investments	0
Change in restricted cash	1
Other investing activities	(2)
Net cash flows used in investing activities	(1,396)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt	328
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	0
Repayments of Debt, Maturing in More than Three Months	(500)
Issuance of long-term debt	202
Retirement of long-term debt	(169)
Increase (Decrease) in Due to Affiliates	0
Distributions to member	(311)
Dividends paid on common stock	0
Proceeds from employee stock plans	0
Other financing activities	(2)
Contributions from parent	758
Proceeds from Issuance of Preferred Stock and Preference Stock	0
Net cash flows provided by financing activities	306
Increase (Decrease) in cash and cash equivalents	(140)
Cash and cash equivalents at beginning of period	170
Cash and cash equivalents at end of period	30	170
Proceeds from Issuance of Preferred Stock and Preference Stock	0
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net Income (Loss)	205	42	187
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	321	295	256
Impairment losses of long-lived assets, intangibles and regulatory assets	14	0	0
Gain (Loss) on Disposition of Assets	1	(8)	(46)
Deferred income taxes and amortization of investment tax credits	113	153	150
Other non-cash operating activities	(5)	183	54
Changes in assets and liabilities:
Accounts receivable	(20)	(41)	(43)
Receivables from and payables to affiliates, net	0	44	0
Inventories	(24)	1	(5)
Accounts payable and accrued expenses	(63)	32	(21)
Income taxes	81	110	(46)
Pension and non-pension postretirement benefit contributions	(72)	(32)	(14)
Other assets and liabilities	(142)	(128)	(99)
Net Cash Provided by (Used in) Operating Activities	407	651	373
Cash flows from investing activities
Capital expenditures	(628)	(586)	(544)
Acquisitions of businesses, net		0
Proceeds from sales of long-lived assets	1	12	54
Purchases of investments	0	(30)	0
Change in restricted cash	(2)	(31)	3
Other investing activities	(1)	(12)	10
Net cash flows used in investing activities	(630)	(647)	(477)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt	3	(41)	(40)
Issuance of long-term debt	202	4	208
Retirement of long-term debt	(13)	(11)	(22)
Dividends paid on common stock	(133)	(136)	(146)
Other financing activities	(1)	(3)	(9)
Contributions from parent	161	187	112
Net cash flows provided by financing activities	219	0	103
Increase (Decrease) in cash and cash equivalents	(4)	4	(1)
Cash and cash equivalents at beginning of period	9	5	6
Cash and cash equivalents at end of period	5	9	5
Delmarva Power and Light Company [Member]
Cash flows from operating activities
Net Income (Loss)	121	(9)	76
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	167	157	148
Impairment losses of long-lived assets, intangibles and regulatory assets	6	0	0
Deferred income taxes and amortization of investment tax credits	89	109	73
Other non-cash operating activities	9	114	33
Changes in assets and liabilities:
Accounts receivable	(22)	(5)	(24)
Receivables from and payables to affiliates, net	11	13	3
Inventories	(5)	0	6
Accounts payable and accrued expenses	(8)	(4)	(8)
Increase (Decrease) Cash Collateral from Counterparties	0	1	(1)
Income taxes	26	28	(26)
Pension and non-pension postretirement benefit contributions	(2)	(22)	0
Other assets and liabilities	(71)	(72)	(14)
Net Cash Provided by (Used in) Operating Activities	321	310	266
Cash flows from investing activities
Capital expenditures	(428)	(349)	(352)
Acquisitions of businesses, net		0
Proceeds from sales of long-lived assets	0	9	0
Change in restricted cash	0	0	5
Other investing activities	(1)	4	2
Net cash flows used in investing activities	(429)	(336)	(345)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt	216	(105)	(1)
Issuance of long-term debt	0	175	200
Retirement of long-term debt	(40)	(100)	(100)
Dividends paid on common stock	(112)	(54)	(92)
Other financing activities	0	(1)	(2)
Contributions from parent	0	152	75
Net cash flows provided by financing activities	64	67	80
Increase (Decrease) in cash and cash equivalents	(44)	41	1
Cash and cash equivalents at beginning of period	46	5	4
Cash and cash equivalents at end of period	2	46	5
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net Income (Loss)	77	(42)	40
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	146	165	175
Impairment losses of long-lived assets, intangibles and regulatory assets	7	0	0
Deferred income taxes and amortization of investment tax credits	32	22	31
Other non-cash operating activities	17	155	37
Changes in assets and liabilities:
Accounts receivable	14	(8)	(67)
Receivables from and payables to affiliates, net	0	13	1
Inventories	(7)	(1)	(1)
Accounts payable and accrued expenses	(2)	9	9
Income taxes	(11)	174	(34)
Pension and non-pension postretirement benefit contributions	(20)	(17)	(2)
Other assets and liabilities	(47)	(85)	67
Net Cash Provided by (Used in) Operating Activities	206	385	256
Cash flows from investing activities
Capital expenditures	(312)	(311)	(300)
Acquisitions of businesses, net		0
Proceeds from sales of long-lived assets	0	2	0
Change in restricted cash	3	(2)	(6)
Other investing activities	(1)	2	0
Net cash flows used in investing activities	(310)	(309)	(306)
Cash flows from financing activities
Proceeds from (Repayments of) Short-term Debt	108	(5)	(122)
Issuance of long-term debt	0	0	150
Retirement of long-term debt	(35)	(48)	(58)
Dividends paid on common stock	(68)	(63)	(12)
Other financing activities	0	(1)	(2)
Contributions from parent	0	139	95
Net cash flows provided by financing activities	5	22	51
Increase (Decrease) in cash and cash equivalents	(99)	98	1
Cash and cash equivalents at beginning of period	101	3	2
Cash and cash equivalents at end of period	$ 2	$ 101	$ 3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016
Current assets
Cash and cash equivalents		$ 898		$ 635
Restricted cash and cash equivalents		207		253
Accounts receivable, net
Customer		4,401		4,158
Other		1,132		1,201
Mark-to-market derivative assets		976		917
Energy Marketing Contracts Assets, Current		60		88
Inventories, net
Energy Related Inventory, Other Fossil Fuel		340		364
Materials and supplies		1,311		1,274
Regulatory assets		1,267		1,342
Prepaid utility taxes		0		1,250
Other		1,242		930
Total current assets		11,834		12,412
Property, plant and equipment, net		74,202		71,555
Deferred debits and other assets
Regulatory assets		8,021		10,046
Nuclear decommissioning trust funds		13,272		11,061
Investments		640		629
Goodwill		6,677		6,677
Mark-to-market derivative assets		337		492
Unamortized energy contract assets		395		447
Pledged assets for Zion Station decommissioning		0		113
Other		1,322		1,472
Deferred Costs and Other Assets		30,664		30,937
Assets	[1]	116,700		114,904
Current liabilities
Short-term borrowings		929		1,267
Long-term debt due within one year		2,088		2,430
Accounts payable		3,532		3,441
Accrued expenses		1,835		3,460
Regulatory liabilities		523		602
Mark-to-market derivative liabilities		232		282
Unamortized energy contract liabilities		231		407
Energy Marketing Accounts Payable		352		428
Payables to Customers		87		151
Other		982		981
Accounts Payable, Related Parties, Current		5		8
Total current liabilities		10,796		13,457
Long-term debt		32,176		31,575
Long-term debt to financing trusts		389		641
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		11,222		18,138
Asset retirement obligations		10,029		9,111
Pension obligations		3,736		4,248
Non-pension postretirement benefit obligations		2,093		1,848
Spent nuclear fuel obligation		1,147		1,024
Regulatory liabilities		9,865		4,187
Mark-to-market derivative liabilities		409		392
Unamortized energy contract liabilities		609		830
Payable for Zion Station decommissioning		0		14
Other		2,097		1,827
Total deferred credits and other liabilities		41,207		41,619
Liabilities	[1]	84,568		87,292
Shareholders’ equity
Common stock		18,964		18,794
Treasury stock, at cost (2 shares and 35 shares at December 31, 2017 and 2016, respectively)		(123)		(2,327)
Retained earnings		13,503		12,030
Accumulated other comprehensive loss, net		(2,487)		(2,660)
Total shareholders’ equity		29,857		25,837
Member’s equity
Noncontrolling interests		2,275		1,775
Total equity		32,132		27,612
Liabilities and Equity		116,700		114,904
Variable Interest Entity, Consolidated, Carrying Amount, Assets	[2]	9,947		9,517	[3]
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	[2]	3,618		3,598	[3]
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		416		290
Restricted cash and cash equivalents		138		158
Accounts receivable, net
Customer		2,653		2,433
Other		321		558
Mark-to-market derivative assets		976		917
Due from Affiliate, Current		140		156
Energy Marketing Contracts Assets, Current		60		88
Inventories, net
Energy Related Inventory, Other Fossil Fuel		264		292
Materials and supplies		937		935
Other		915		701
Total current assets		6,820		6,528
Property, plant and equipment, net		24,906		25,585
Deferred debits and other assets
Nuclear decommissioning trust funds		13,272		11,061
Investments		433		418
Goodwill		47		47
Mark-to-market derivative assets		334		476
Assets for Plan Benefits, Defined Benefit Plan		1,502		1,595
Unamortized energy contract assets		395		447
Deferred income taxes		16		16
Pledged assets for Zion Station decommissioning		0		113
Other		662		688
Deferred Costs and Other Assets		16,661		14,861
Assets	[4]	48,387		46,974
Current liabilities
Short-term borrowings		2		699
Long-term debt due within one year		346		1,117
Accounts payable		1,773		1,610
Accrued expenses		1,020		989
Mark-to-market derivative liabilities		211		263
Unamortized energy contract liabilities		43		72
Energy Marketing Accounts Payable		352		428
Other		265		313
Accounts Payable, Related Parties, Current		123		137
Notes Payable, Related Parties, Current		54		55
Total current liabilities		4,189		5,683
Long-term debt		7,734		7,202
Long-term debt to financing trusts		910		922
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		3,798		5,585
Asset retirement obligations		9,844		8,922
Non-pension postretirement benefit obligations		916		930
Spent nuclear fuel obligation		1,147		1,024
Due to Affiliate, Noncurrent		3,065		2,608
Mark-to-market derivative liabilities		174		153
Unamortized energy contract liabilities		48		80
Payable for Zion Station decommissioning		0		14
Other		658		595
Total deferred credits and other liabilities		19,650		19,911
Liabilities	[4]	32,483		33,718
Shareholders’ equity
Retained earnings		4,310		2,275
Accumulated other comprehensive loss, net		(37)		(54)
Member’s equity
Membership interest		9,357		9,261
Total member’s equity		13,630		11,482
Noncontrolling interests		2,274		1,774
Total equity		15,904		13,256
Liabilities and Equity		48,387		46,974
Variable Interest Entity, Consolidated, Carrying Amount, Assets		9,906		9,441
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		3,516		3,414
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents		76		56
Restricted cash and cash equivalents		5		2
Accounts receivable, net
Customer		559		528
Other		266		218
Due from Affiliate, Current		13		356
Inventories, net
Inventories, net		152		159
Regulatory assets		225		190
Other		68		45
Total current assets		1,364		1,554
Property, plant and equipment, net		20,723		19,335
Deferred debits and other assets
Regulatory assets		1,054		977
Investments		6		6
Goodwill		2,625		2,625
Receivable from affiliates		2,528		2,170
Assets for Plan Benefits, Defined Benefit Plan		1,188		1,343
Other		238		325
Deferred Costs and Other Assets		7,639		7,446
Assets		29,726		28,335
Current liabilities
Long-term debt due within one year		840		425
Accounts payable		568		645
Accrued expenses		327		1,250
Regulatory liabilities		249		329
Mark-to-market derivative liabilities		21		19
Customer deposits		112		121
Other		103		84
Accounts Payable, Related Parties, Current		74		65
Total current liabilities		2,294		2,938
Long-term debt		6,761		6,608
Long-term debt to financing trusts		205		205
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		3,469		5,364
Asset retirement obligations		111		119
Non-pension postretirement benefit obligations		219		239
Regulatory liabilities		6,328		3,369
Mark-to-market derivative liabilities		235		239
Other		562		529
Total deferred credits and other liabilities		10,924		9,859
Liabilities		20,184		19,610
Shareholders’ equity
Common stock		1,588		1,588
Other paid-in capital		6,822		6,150
Retained Earnings, Unappropriated		(1,639)		(1,639)
Retained Earnings, Appropriated		2,771		2,626
Total shareholders’ equity		9,542		8,725
Member’s equity
Liabilities and Equity		29,726		28,335
PECO Energy Co [Member]
Current assets
Cash and cash equivalents		271		63
Restricted cash and cash equivalents		4		4
Accounts receivable, net
Customer		327		306
Other		105		131
Due from Affiliate, Current		0		4
Due from Affiliates		0		131
Inventories, net
Energy Related Inventory, Other Fossil Fuel		31		35
Materials and supplies		30		27
Regulatory assets		29		29
Prepaid utility taxes		8		9
Other		17		18
Total current assets		822		757
Property, plant and equipment, net		8,053		7,565
Deferred debits and other assets
Regulatory assets		381		1,681
Investments		25		25
Receivable from affiliates		537		438
Assets for Plan Benefits, Defined Benefit Plan		340		345
Other		12		20
Deferred Costs and Other Assets		1,295		2,509
Assets		10,170		10,831
Current liabilities
Long-term debt due within one year		500		0
Accounts payable		370		342
Accrued expenses		114		104
Regulatory liabilities		141		127
Customer deposits		66		61
Other		23		30
Accounts Payable, Related Parties, Current		53		63
Total current liabilities		1,267		727
Long-term debt		2,403		2,580
Long-term debt to financing trusts		184		184
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,789		3,006
Asset retirement obligations		27		28
Non-pension postretirement benefit obligations		288		289
Regulatory liabilities		549		517
Other		86		85
Total deferred credits and other liabilities		2,739		3,925
Liabilities		6,593		7,416
Shareholders’ equity
Common stock		2,489		2,473
Retained earnings		1,087		941
Accumulated other comprehensive loss, net		1		1
Total shareholders’ equity		3,577		3,415
Member’s equity
Liabilities and Equity		10,170		10,831
Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents		17		23
Restricted cash and cash equivalents		1		24
Accounts receivable, net
Customer		375		395
Other		94		102
Due from Affiliate, Current		1
Inventories, net
Energy Related Inventory, Natural Gas in Storage		37		30
Materials and supplies		40		38
Regulatory assets		174		208
Prepaid utility taxes		69		15
Other		3		7
Total current assets		811		842
Property, plant and equipment, net		7,602		7,040
Deferred debits and other assets
Regulatory assets		397		504
Investments		5		12
Assets for Plan Benefits, Defined Benefit Plan		285		297
Other		4		9
Deferred Costs and Other Assets		691		822
Assets	[5]	9,104		8,704
Current liabilities
Short-term borrowings		77		45
Long-term debt due within one year		0		41
Accounts payable		265		205
Accrued expenses		164		175
Regulatory liabilities		62		50
Customer deposits		116		110
Other		24		26
Accounts Payable, Related Parties, Current		52		55
Total current liabilities		760		707
Long-term debt		2,577		2,281
Long-term debt to financing trusts		0		252
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,244		2,219
Asset retirement obligations		23		21
Non-pension postretirement benefit obligations		202		205
Regulatory liabilities		1,101		110
Other		56		61
Total deferred credits and other liabilities		2,626		2,616
Liabilities	[5]	5,963		5,856
Shareholders’ equity
Common stock		1,605		1,421
Retained earnings		1,536		1,427
Total shareholders’ equity		3,141		2,848
Member’s equity
Liabilities and Equity		9,104		8,704
Variable Interest Entity, Consolidated, Carrying Amount, Assets				26
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities				42
Pepco Holdings LLC [Member]
Member’s equity
Variable Interest Entity, Consolidated, Carrying Amount, Assets		41		49
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		102		143
Pepco Holdings LLC [Member] | Successor [Member]
Current assets
Cash and cash equivalents		30		170
Restricted cash and cash equivalents		42		43
Accounts receivable, net
Customer		486		496
Other		206		283
Inventories, net
Energy Related Inventory, Natural Gas in Storage		7		6
Materials and supplies		151		116
Regulatory assets		554		653
Other		75		71
Total current assets		1,551		1,838
Property, plant and equipment, net		12,498		11,598
Deferred debits and other assets
Regulatory assets		2,493		2,851
Investments		132		133
Goodwill		4,005		4,005
Assets for Plan Benefits, Defined Benefit Plan		490		509
Deferred income taxes		4		6
Notes, Loans and Financing Receivable, Gross, Noncurrent		4		4
Other		70		81
Deferred Costs and Other Assets		7,198		7,589
Assets	[6]	21,247		21,025
Current liabilities
Short-term borrowings		350		522
Long-term debt due within one year		396		253
Accounts payable		348		458
Accrued expenses		261		272
Regulatory liabilities		56		79
Unamortized energy contract liabilities		188		335
Customer deposits		119		123
Payables to Customers		42		101
Other		81		47
Accounts Payable, Related Parties, Current		90		94
Total current liabilities		1,931		2,284
Long-term debt		5,478		5,645
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		2,070		3,775
Asset retirement obligations		16		14
Non-pension postretirement benefit obligations		105		134
Regulatory liabilities		1,872		158
Unamortized energy contract liabilities		561		750
Other		389		249
Total deferred credits and other liabilities		5,013		5,080
Liabilities	[6]	12,422		13,009
Shareholders’ equity
Retained earnings		(10)		(61)
Member’s equity
Membership interest		8,835		8,077
Total member’s equity		8,825		8,016
Total equity		8,825		8,016
Liabilities and Equity		21,247		21,025
Variable Interest Entity, Consolidated, Carrying Amount, Assets	[2]	41		49
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	[2]	102		143
Potomac Electric Power Company [Member]
Current assets
Cash and cash equivalents		5		9
Restricted cash and cash equivalents		35		33
Accounts receivable, net
Customer		250		235
Other		87		150
Inventories, net
Inventories, net		87		63
Regulatory assets		213		162
Other		33		32
Total current assets		710		684
Property, plant and equipment, net		6,001		5,571
Deferred debits and other assets
Regulatory assets		678		690
Investments		102		102
Assets for Plan Benefits, Defined Benefit Plan		322		282
Other		19		6
Deferred Costs and Other Assets		1,121		1,080
Assets		7,832		7,335
Current liabilities
Short-term borrowings		26		23
Long-term debt due within one year		19		16
Accounts payable		139		209
Accrued expenses		137		113
Regulatory liabilities		3		11
Customer deposits		54		53
Payables to Customers		42		68
Current portion of DC PLUG obligation		28		0
Other		28		29
Accounts Payable, Related Parties, Current		74		74
Total current liabilities		550		596
Long-term debt		2,521		2,333
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,063		1,910
Non-pension postretirement benefit obligations		36		43
Regulatory liabilities		829		20
Other		300		133
Total deferred credits and other liabilities		2,228		2,106
Liabilities		5,299		5,035
Shareholders’ equity
Common stock		1,470		1,309
Retained earnings		1,063		991
Total shareholders’ equity		2,533		2,300
Member’s equity
Liabilities and Equity		7,832		7,335
Delmarva Power and Light Company [Member]
Current assets
Cash and cash equivalents		2		46
Accounts receivable, net
Customer		146		136
Other		38		63
Due from Affiliate, Current		0		3
Inventories, net
Energy Related Inventory, Natural Gas in Storage		7		7
Materials and supplies		36		32
Regulatory assets		69		59
Other		27		24
Total current assets		325		370
Property, plant and equipment, net		3,579		3,273
Deferred debits and other assets
Regulatory assets		245		289
Investments		0		0
Goodwill		8		8
Assets for Plan Benefits, Defined Benefit Plan		193		206
Other		7		7
Total Deferred Debits And Other Assets		453		510
Assets		4,357		4,153
Current liabilities
Short-term borrowings		216		0
Long-term debt due within one year		83		119
Accounts payable		82		88
Accrued expenses		35		36
Regulatory liabilities		42		43
Customer deposits		35		36
Payables to Customers		0		13
Other		8		8
Accounts Payable, Related Parties, Current		46		38
Total current liabilities		547		381
Long-term debt		1,217		1,221
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		603		1,056
Non-pension postretirement benefit obligations		14		19
Regulatory liabilities		593		97
Other		48		53
Total deferred credits and other liabilities		1,258		1,225
Liabilities		3,022		2,827
Shareholders’ equity
Common stock		764		764
Retained earnings		571		562
Total shareholders’ equity		1,335		1,326
Member’s equity
Liabilities and Equity		4,357		4,153
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		2		101
Restricted cash and cash equivalents		6		9
Accounts receivable, net
Customer		92		125
Other		56		44
Inventories, net
Inventories, net		29		22
Regulatory assets		71		96
Other		2		2
Total current assets		258		399
Property, plant and equipment, net		2,706		2,521
Deferred debits and other assets
Regulatory assets		359		405
Investments		0		0
Assets for Plan Benefits, Defined Benefit Plan		73		84
Notes, Loans and Financing Receivable, Gross, Noncurrent		4		4
Other		45		44
Deferred Costs and Other Assets		481		537
Assets	[7]	3,445		3,457
Current liabilities
Short-term borrowings		108		0
Long-term debt due within one year		281		35
Accounts payable		118		132
Accrued expenses		33		38
Regulatory liabilities		11		25
Customer deposits		31		33
Payables to Customers		0		20
Other		8		8
Accounts Payable, Related Parties, Current		29		29
Total current liabilities		619		320
Long-term debt		840		1,120
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		493		917
Non-pension postretirement benefit obligations		14		34
Regulatory liabilities		411		0
Other		25		32
Total deferred credits and other liabilities		943		983
Liabilities	[7]	2,402		2,423
Shareholders’ equity
Common stock		912		912
Retained earnings		131		122
Total shareholders’ equity		1,043		1,034
Member’s equity
Liabilities and Equity		3,445		3,457
Variable Interest Entity, Consolidated, Carrying Amount, Assets		29		32
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities		90		126
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents		126	[8]	150	[9],[10]
Restricted cash and cash equivalents		64	[8]	59	[9],[10]
Accounts receivable, net
Customer		138	[8]	371	[9],[10]
Other		25	[8]	48	[9],[10]
Mark-to-market derivative assets	[9],[10]			31
Inventories, net
Materials and supplies		205	[8]	199	[9],[10]
Other		45	[8]	50	[9],[10]
Total current assets		603	[8]	908	[9],[10]
Property, plant and equipment, net		6,186	[8]	5,415	[9],[10]
Deferred debits and other assets
Nuclear decommissioning trust funds		2,502	[8]	2,185	[9],[10]
Goodwill	[9],[10]			47
Mark-to-market derivative assets	[9],[10]			23
Other		274	[8]	315	[9],[10]
Assets		9,565	[8]	8,893	[9],[10]
Current liabilities
Long-term debt due within one year		102	[8]	181	[9],[10]
Accounts payable		114	[8]	269	[9],[10]
Accrued expenses		65	[8]	119	[9],[10]
Mark-to-market derivative liabilities	[9],[10]			60
Unamortized energy contract liabilities		18	[8]	15	[9],[10]
Other		7	[8]	30	[9],[10]
Total current liabilities		306	[8]	674	[9],[10]
Long-term debt		1,154	[8]	641	[9],[10]
Deferred credits and other liabilities
Asset retirement obligations		2,035	[8]	1,904	[9],[10]
Pension obligations	[9],[10],[11]			9
Unamortized energy contract liabilities		5	[8]	22	[9],[10]
Other		112	[8]	106	[9],[10]
Liabilities		3,612	[8]	3,356	[9],[10]
Variable Interest Entity, Primary Beneficiary [Member] | Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		126		150
Restricted cash and cash equivalents		58		27
Accounts receivable, net
Customer		138		371
Other		25		48
Mark-to-market derivative assets				31
Inventories, net
Materials and supplies		205		199
Other		41		44
Total current assets		593		870
Property, plant and equipment, net		6,186		5,415
Deferred debits and other assets
Nuclear decommissioning trust funds		2,502		2,185
Goodwill				47
Mark-to-market derivative assets				23
Other		243		277
Assets		9,524		8,817
Current liabilities
Long-term debt due within one year		67		99
Accounts payable		114		269
Accrued expenses		64		116
Mark-to-market derivative liabilities				60
Unamortized energy contract liabilities		18		15
Other		7		30
Total current liabilities		270		589
Long-term debt		1,088		540
Deferred credits and other liabilities
Asset retirement obligations		2,035		1,904
Pension obligations	[11]			9
Unamortized energy contract liabilities		5		22
Other		112		106
Liabilities		3,510		3,170
Variable Interest Entity, Primary Beneficiary [Member] | Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents				0
Restricted cash and cash equivalents				23
Accounts receivable, net
Customer				0
Other				0
Mark-to-market derivative assets				0
Inventories, net
Materials and supplies				0
Other				0
Total current assets				23
Property, plant and equipment, net				0
Deferred debits and other assets
Nuclear decommissioning trust funds				0
Goodwill				0
Mark-to-market derivative assets				0
Other				3
Assets				26
Current liabilities
Long-term debt due within one year				41
Accounts payable				0
Accrued expenses				1
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities				0
Other				0
Total current liabilities				42
Long-term debt				0
Deferred credits and other liabilities
Asset retirement obligations				0
Pension obligations	[11]			0
Unamortized energy contract liabilities				0
Other				0
Liabilities				42
Variable Interest Entity, Primary Beneficiary [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Current assets
Cash and cash equivalents		0	[8]	0	[9]
Restricted cash and cash equivalents		6	[8]	9	[9]
Accounts receivable, net
Customer		0	[8]	0	[9]
Other		0	[8]	0	[9]
Mark-to-market derivative assets	[9]			0
Inventories, net
Materials and supplies		0	[8]	0	[9]
Other		4	[8]	5	[9]
Total current assets		10	[8]	14	[9]
Property, plant and equipment, net		0	[8]	0	[9]
Deferred debits and other assets
Nuclear decommissioning trust funds		0	[8]	0	[9]
Goodwill	[9]			0
Mark-to-market derivative assets	[9]			0
Other		31	[8]	35	[9]
Assets		41	[8]	49	[9]
Current liabilities
Long-term debt due within one year		35	[8]	40	[9]
Accounts payable		0	[8]	0	[9]
Accrued expenses		1	[8]	2	[9]
Mark-to-market derivative liabilities	[9]			0
Unamortized energy contract liabilities		0	[8]	0	[9]
Other		0	[8]	0	[9]
Total current liabilities		36	[8]	42	[9]
Long-term debt		66	[8]	101	[9]
Deferred credits and other liabilities
Asset retirement obligations		0	[8]	0	[9]
Pension obligations	[9],[11]			0
Unamortized energy contract liabilities		0	[8]	0	[9]
Other		0	[8]	0	[9]
Liabilities		102	[8]	143	[9]
Variable Interest Entity, Primary Beneficiary [Member] | Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		0		0
Restricted cash and cash equivalents		6		9
Accounts receivable, net
Customer		0		0
Other		0		0
Mark-to-market derivative assets				0
Inventories, net
Materials and supplies		0		0
Other		0		0
Total current assets		6		9
Property, plant and equipment, net		0		0
Deferred debits and other assets
Nuclear decommissioning trust funds		0		0
Goodwill				0
Mark-to-market derivative assets				0
Other		23		23
Assets		29		32
Current liabilities
Long-term debt due within one year		31		35
Accounts payable		0		0
Accrued expenses		1		2
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities		0		0
Other		0		0
Total current liabilities		32		37
Long-term debt		58		89
Deferred credits and other liabilities
Asset retirement obligations		0		0
Pension obligations	[11]			0
Unamortized energy contract liabilities		0		0
Other		0		0
Liabilities		90		$ 126
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] | Exelon Generation Co L L C [Member]
Deferred debits and other assets
Assets		9,524
Deferred credits and other liabilities
Liabilities		$ 3,510
[1]	Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[3]	Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.
[4]	Generation’s consolidated assets include $9,524 million and $8,817 million at December 31, 2017 and 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,510 million and $3,170 million at December 31, 2017 and 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[5]	BGE’s consolidated assets include $26 million at December 31, 2016 of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $42 million at December 31, 2016 of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. BGE no longer has interests in any VIEs as of December 31, 2017. See Note 2 - Variable Interest Entities.
[6]	PHI’s consolidated total assets include $41 million and $49 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $102 million and $143 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities.
[7]	ACE’s consolidated assets include $29 million and $32 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $90 million and $126 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 - Variable Interest Entities.
[8]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity
[9]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[10]	Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.
[11]	Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 16 - Retirement Benefits for additional details.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares $ / shares in Millions	Dec. 31, 2017	Dec. 31, 2016
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Treasury Stock, Shares held	2,000,000	35,000,000

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands		Total	Pepco Holdings LLC [Member]	Commitments [Member]Pepco Holdings LLC [Member]	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]		Noncontrolling Interest [Member]	Preference Stock Not Subject To Mandatory Redemption [Member]	Exelon Generation Co L L C [Member]	Exelon Generation Co L L C [Member]Undistributed Earnings [Member]	Exelon Generation Co L L C [Member]Accumulated Other Comprehensive Income (Loss) [Member]		Exelon Generation Co L L C [Member]Noncontrolling Interest [Member]	Exelon Generation Co L L C [Member]Membership Interest [Member]	Commonwealth Edison Co [Member]	Commonwealth Edison Co [Member]Common Stock [Member]	Commonwealth Edison Co [Member]Other Additional Capital [Member]	Commonwealth Edison Co [Member]Retained Earnings, Unappropriated [Member]	Commonwealth Edison Co [Member]Retained Earnings Appropriated [Member]	PECO Energy Co [Member]	PECO Energy Co [Member]Common Stock [Member]	PECO Energy Co [Member]Retained Earnings [Member]	PECO Energy Co [Member]Accumulated Other Comprehensive Income (Loss) [Member]		Baltimore Gas and Electric Company [Member]	Baltimore Gas and Electric Company [Member]Parent [Member]	Baltimore Gas and Electric Company [Member]Common Stock [Member]	Baltimore Gas and Electric Company [Member]Common Stock [Member]Parent [Member]	Baltimore Gas and Electric Company [Member]Retained Earnings [Member]	Baltimore Gas and Electric Company [Member]Membership Interest [Member]	Baltimore Gas and Electric Company [Member]Membership Interest [Member]Parent [Member]	Baltimore Gas and Electric Company [Member]Preference Stock Not Subject To Mandatory Redemption [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Deferred Compensation, Share-based Payments [Member]Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Common Stock [Member]		Pepco Holdings LLC [Member]Retained Earnings [Member]	Pepco Holdings LLC [Member]Undistributed Earnings [Member]	Pepco Holdings LLC [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Additional Paid-in Capital [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member]Common Stock [Member]	Potomac Electric Power Company [Member]Retained Earnings [Member]	Delmarva Power and Light Company [Member]	Delmarva Power and Light Company [Member]Common Stock [Member]	Delmarva Power and Light Company [Member]Retained Earnings [Member]	Atlantic City Electric Company [Member]	Atlantic City Electric Company [Member]Common Stock [Member]	Atlantic City Electric Company [Member]Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 24,133,000,000			$ 16,709,000,000	$ (2,327,000,000)	$ 10,910,000,000	$ (2,684,000,000)		$ 1,332,000,000	$ 193,000,000
Beginning Balance (in shares) at Dec. 31, 2014		894,568
Beginning Balance at Dec. 31, 2014																		$ 7,907,000,000	$ 1,588,000,000	$ 5,468,000,000	$ (1,639,000,000)	$ 2,490,000,000	$ 3,121,000,000	$ 2,439,000,000	$ 681,000,000	$ 1,000,000		$ 2,753,000,000		$ 1,360,000,000		$ 1,203,000,000	$ 2,563,000,000		$ 190,000,000												$ 2,087,000,000	$ 1,010,000,000	$ 1,077,000,000	$ 1,178,000,000	$ 537,000,000	$ 641,000,000	$ 877,000,000	$ 678,000,000	$ 199,000,000
Beginning Balance (Predecessor [Member]) at Dec. 31, 2014																																				$ 4,322,000,000			$ 3,803,000,000	[1]	$ 565,000,000		$ (46,000,000)
Beginning Balance at Dec. 31, 2014												$ 14,051,000,000	$ 3,803,000,000	$ (36,000,000)		$ 1,333,000,000	$ 8,951,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) | Predecessor [Member]																																				327,000,000					327,000,000
Net Income (Loss)		$ 2,250,000,000					2,269,000,000			(32,000,000)	13,000,000	1,340,000,000	1,372,000,000			(32,000,000)		426,000,000			426,000,000		378,000,000		378,000,000			288,000,000				288,000,000	288,000,000														187,000,000		187,000,000	76,000,000		76,000,000	40,000,000		40,000,000
Stock Issued During Period, Shares, Share-based Compensation, Gross		1,430
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 70,000,000			70,000,000	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,170
Employee stock purchase plan issuances | Predecessor [Member]																																				3,000,000			3,000,000
Employee stock purchase plan issuances		$ 32,000,000			32,000,000	0	0	0		0	0
Stock Issued During Period, Shares, New Issues		57,500
Stock Issued During Period, Value, New Issues		$ 1,868,000,000			1,868,000,000
Tax benefit on stock compensation | Predecessor [Member]																																				(5,000,000)
Tax benefit on stock compensation		(3,000,000)			(3,000,000)
Changes in equity of noncontrolling interests		4,000,000								4,000,000						0
Noncontrolling Interest, Change in Redemption Value		4,000,000								4,000,000		4,000,000				4,000,000
Noncontrolling interest acquired												1,000,000				(2,000,000)	1,000,000
Common stock dividends | Predecessor [Member]																																				(275,000,000)					(275,000,000)
Common stock dividends		(1,111,000,000)					(1,111,000,000)											(299,000,000)				(299,000,000)	(279,000,000)		(279,000,000)			(158,000,000)				(158,000,000)	(158,000,000)														(146,000,000)		(146,000,000)	(92,000,000)		(92,000,000)	(12,000,000)		(12,000,000)
Preferred and preference stock dividends		(13,000,000)									(13,000,000)																	(13,000,000)				(13,000,000)	(13,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(2,474,000,000)	(2,474,000,000)
Adjustments to Additional Paid in Capital, Other																		202,000,000		202,000,000								7,000,000		7,000,000			7,000,000														112,000,000	112,000,000		75,000,000	75,000,000		95,000,000	95,000,000
Income Tax Effects Allocated Directly to Equity, Other												47,000,000					47,000,000						16,000,000	16,000,000		0
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				10,000,000							10,000,000
Other comprehensive income (loss), net of income taxes		$ 60,000,000						60,000,000				(27,000,000)		(27,000,000)
Distribution to member													0
Stock Issued During Period, Value, Dividend Reinvestment Plan | Predecessor [Member]																																				11,000,000			11,000,000
Ending Balance (in shares) at Dec. 31, 2015		954,668
Ending Balance at Dec. 31, 2015																		8,243,000,000	1,588,000,000	5,677,000,000	(1,639,000,000)	2,617,000,000	3,236,000,000	2,455,000,000	780,000,000	1,000,000		2,877,000,000		1,367,000,000		1,320,000,000	2,687,000,000		190,000,000												2,240,000,000	1,122,000,000	1,118,000,000	1,237,000,000	612,000,000	625,000,000	1,000,000,000	773,000,000	227,000,000
Ending Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413,000,000			3,832,000,000	[1]	617,000,000		(36,000,000)
Ending Balance at Dec. 31, 2015												12,942,000,000	2,701,000,000	(63,000,000)		1,307,000,000	8,997,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				15,000,000			15,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,294,000,000			18,676,000,000	(2,327,000,000)	12,068,000,000	(2,624,000,000)	[2]	1,308,000,000	193,000,000			(63,000,000)	[2]											1,000,000	[2]
Other Additional Capital																		7,000,000		7,000,000
Retained Earnings, Appropriated																					(426,000,000)	426,000,000
Net Income (Loss) | Predecessor [Member]																																				19,000,000					19,000,000
Employee stock purchase plan issuances | Predecessor [Member]																																				3,000,000			3,000,000
Tax benefit on stock compensation | Predecessor [Member]																																				(1,000,000)
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				1,000,000							1,000,000
Ending Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439,000,000			3,838,000,000	[1]	636,000,000		(35,000,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				3,000,000			3,000,000
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		8,243,000,000	1,588,000,000	5,677,000,000	(1,639,000,000)	2,617,000,000	3,236,000,000	2,455,000,000	780,000,000	1,000,000		2,877,000,000		1,367,000,000		1,320,000,000	2,687,000,000		190,000,000												2,240,000,000	1,122,000,000	1,118,000,000	1,237,000,000	612,000,000	625,000,000	1,000,000,000	773,000,000	227,000,000
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413,000,000			3,832,000,000	[1]	617,000,000		(36,000,000)
Beginning Balance at Dec. 31, 2015												12,942,000,000	2,701,000,000	(63,000,000)		1,307,000,000	8,997,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)		$ 1,204,000,000	$ (66,000,000)				1,134,000,000			62,000,000	8,000,000	558,000,000	496,000,000			62,000,000		378,000,000			378,000,000		438,000,000		438,000,000			294,000,000				294,000,000	294,000,000														42,000,000		42,000,000	(9,000,000)		(9,000,000)	(42,000,000)		(42,000,000)
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,868
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 85,000,000			85,000,000	0	0			0	0
Employee stock purchase plan issuances, shares		1,242
Employee stock purchase plan issuances		$ 55,000,000			55,000,000	0	0			0	0
Tax benefit on stock compensation		(18,000,000)			(18,000,000)
Noncontrolling Interest, Change in Redemption Value		157,000,000						0		157,000,000		(157,000,000)				(157,000,000)	0
Noncontrolling Interest, Period Increase (Decrease)		5,000,000			0					5,000,000		5,000,000				5,000,000
Noncontrolling interest acquired		239,000,000			(4,000,000)					243,000,000		239,000,000				243,000,000	4,000,000
Common stock dividends		(1,172,000,000)					(1,172,000,000)											(369,000,000)				(369,000,000)	(277,000,000)		(277,000,000)			(179,000,000)				(179,000,000)	(179,000,000)														(169,000,000)		(169,000,000)	(54,000,000)		(54,000,000)	(63,000,000)		(63,000,000)
Preferred and preference stock dividends		(8,000,000)									(8,000,000)																	(8,000,000)				(8,000,000)	(8,000,000)
Stock Redeemed or Called During Period, Value		(193,000,000)									(193,000,000)																	(190,000,000)							(190,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared		0										(922,000,000)	(922,000,000)			0
Temporary Equity, Other Changes												(157,000,000)
Adjustments to Additional Paid in Capital, Other		0										170,000,000					170,000,000	315,000,000		315,000,000								61,000,000	$ (7,000,000)	61,000,000	$ (7,000,000)		61,000,000	$ (7,000,000)	0												187,000,000	187,000,000		152,000,000	152,000,000		139,000,000	139,000,000
Income Tax Effects Allocated Directly to Equity, Other		0						0		0		98,000,000	0				98,000,000						18,000,000	18,000,000
Consolidated VIE dividend to noncontrolling interests																0
Other comprehensive income (loss), net of income taxes		$ (36,000,000)						(36,000,000)	[2]			9,000,000		9,000,000	[2]											0	[2]
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016		$ 25,837,000,000																8,725,000,000	1,588,000,000	6,150,000,000	(1,639,000,000)	2,626,000,000	3,415,000,000	2,473,000,000	941,000,000	1,000,000		2,848,000,000		1,421,000,000		1,427,000,000	2,848,000,000		0												2,300,000,000	1,309,000,000	991,000,000	1,326,000,000	764,000,000	562,000,000	1,034,000,000	912,000,000	122,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016,000,000						$ (61,000,000)	0	$ 8,077,000,000
Ending Balance at Dec. 31, 2016												13,256,000,000	2,275,000,000	(54,000,000)		1,774,000,000	9,261,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Additional Paid in Capital | Successor [Member]																																														$ 3,835,000,000
Common stock | Successor [Member]																																														3,000,000
Beginning Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439,000,000			$ 3,838,000,000	[1]	$ 636,000,000		(35,000,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) | Successor [Member]																																				(61,000,000)						(61,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(400,000,000)								(400,000,000)
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid | Successor [Member]																																				53,000,000								53,000,000
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				1,251,000,000								1,251,000,000
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016		$ 25,837,000,000																8,725,000,000	1,588,000,000	6,150,000,000	(1,639,000,000)	2,626,000,000	3,415,000,000	2,473,000,000	941,000,000	1,000,000		2,848,000,000		1,421,000,000		1,427,000,000	2,848,000,000		0												2,300,000,000	1,309,000,000	991,000,000	1,326,000,000	764,000,000	562,000,000	1,034,000,000	912,000,000	122,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016,000,000						(61,000,000)	0	8,077,000,000
Ending Balance at Dec. 31, 2016												13,256,000,000	2,275,000,000	(54,000,000)		1,774,000,000	9,261,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]				$ 33,000,000																																35,000,000	$ (62,000,000)							35,000,000	$ (62,000,000)
Stockholders' Equity, Other																																						$ 29,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		27,612,000,000			18,794,000,000	(2,327,000,000)	12,030,000,000	(2,660,000,000)	[2]	1,775,000,000	0			(54,000,000)	[2]											1,000,000	[2]
Other Additional Capital																		158,000,000		158,000,000
Retained Earnings, Appropriated																		2,626,000,000			(378,000,000)	378,000,000
Additional Paid in Capital | Predecessor [Member]																																														3,829,000,000
Additional Paid in Capital																		6,150,000,000
Common stock | Predecessor [Member]																																														$ 3,000,000
Common stock		18,794,000,000																1,588,000,000					2,473,000,000					1,421,000,000																			1,309,000,000			764,000,000			912,000,000
Net Income (Loss) | Successor [Member]																																				362,000,000						362,000,000
Net Income (Loss)		$ 3,849,000,000	$ 364,000,000				3,770,000,000			79,000,000	0	2,771,000,000	2,694,000,000			77,000,000		567,000,000			567,000,000		434,000,000		434,000,000			307,000,000				307,000,000	307,000,000														205,000,000		205,000,000	121,000,000		121,000,000	77,000,000		77,000,000
Stock Issued During Period, Shares, Share-based Compensation, Gross		5,066
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 56,000,000			56,000,000	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,324
Employee stock purchase plan issuances		$ 150,000,000			150,000,000	0	0	0		0	0
Stock Issued During Period, Value, Treasury Stock Reissued		1,150,000,000				2,204,000,000	(1,054,000,000)
Changes in equity of noncontrolling interests												18,000,000				18,000,000
Noncontrolling Interest, Change in Redemption Value		0
Noncontrolling Interest, Period Increase (Decrease)		(20,000,000)			0					(20,000,000)
Noncontrolling interest acquired		407,000,000			(36,000,000)	0	0	0		443,000,000	0	407,000,000	0	0		443,000,000	36,000,000
Common stock dividends		(1,243,000,000)					(1,243,000,000)											(422,000,000)				(422,000,000)	(288,000,000)		(288,000,000)			(198,000,000)				(198,000,000)	(198,000,000)														(133,000,000)		(133,000,000)	(112,000,000)		(112,000,000)	(68,000,000)		(68,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(311,000,000)						(311,000,000)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared										0		(659,000,000)	(659,000,000)	0
Adjustments to Additional Paid in Capital, Other																		651,000,000		651,000,000								184,000,000		184,000,000		0	184,000,000		0												161,000,000	161,000,000
Income Tax Effects Allocated Directly to Equity, Other		0										99,000,000					99,000,000						16,000,000	16,000,000												7,000,000								7,000,000
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Other comprehensive income (loss), net of income taxes		$ 171,000,000						173,000,000	[2]	(2,000,000)		15,000,000		17,000,000	[2]	(2,000,000)										0	[2]
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid												33,000,000					33,000,000
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				751,000,000								751,000,000
Ending Balance (in shares) at Dec. 31, 2017		965,168
Ending Balance at Dec. 31, 2017		$ 29,857,000,000																9,542,000,000	$ 1,588,000,000	6,822,000,000	(1,639,000,000)	2,771,000,000	3,577,000,000	$ 2,489,000,000	$ 1,087,000,000	1,000,000		3,141,000,000		$ 1,605,000,000		$ 1,536,000,000	$ 3,141,000,000		$ 0												2,533,000,000	$ 1,470,000,000	$ 1,063,000,000	1,335,000,000	$ 764,000,000	$ 571,000,000	1,043,000,000	$ 912,000,000	$ 131,000,000
Ending Balance (Successor [Member]) at Dec. 31, 2017																																				$ 8,825,000,000						$ (10,000,000)	$ 0	$ 8,835,000,000
Ending Balance at Dec. 31, 2017												$ 15,904,000,000	$ 4,310,000,000	(37,000,000)		$ 2,274,000,000	$ 9,357,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		32,132,000,000			$ 18,964,000,000	$ (123,000,000)	$ 13,503,000,000	$ (2,487,000,000)	[2]	$ 2,275,000,000	$ 0			$ (37,000,000)	[2]											$ 1,000,000	[2]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Additional Capital																		21,000,000		$ 21,000,000
Retained Earnings, Appropriated																		2,771,000,000			$ (567,000,000)	$ 567,000,000
Additional Paid in Capital																		6,822,000,000
Common stock		$ 18,964,000,000																$ 1,588,000,000					$ 2,489,000,000					$ 1,605,000,000																			$ 1,470,000,000			$ 764,000,000			$ 912,000,000
[1]	At March 23, 2016 and December 31, 2015, PHI's (predecessor) shareholders' equity included $3,835 million and $3,829 million of other paid-in capital, and $3 million and $3 million of common stock, respectively.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	Distribution to member includes $235 million of net assets associated with PHI's unregulated business interests and $165 million of cash, each of which were distributed by PHI to Exelon.

Consolidated Statement of Chan7

Consolidated Statement of Changes in Shareholders Equity (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Other comprehensive income, income taxes	$ (53)
Exelon Generation Co L L C [Member]
Other comprehensive income, income taxes	3
PECO Energy Co [Member]
Other comprehensive income, income taxes	$ 0

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies (All Registrants)	Significant Accounting Policies (All Registrants) Description of Business (All Registrants) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy distribution and transmission businesses. Prior to March 23, 2016 , Exelon's principal, wholly owned subsidiaries included Generation, ComEd, PECO and BGE. On March 23, 2016 , in conjunction with the Amended and Restated Agreement and Plan of Merger (the PHI Merger Agreement), Purple Acquisition Corp, a wholly owned subsidiary of Exelon, merged with and into PHI, with PHI continuing as the surviving entity as a wholly owned subsidiary of Exelon. PHI is a utility services holding company engaged through its principal wholly owned subsidiaries, Pepco, DPL and ACE, in the energy distribution and transmission businesses. Refer to Note 4 — Mergers, Acquisitions and Dispositions for further information regarding the merger transaction. Name of Registrant Business Service Territories Exelon Generation Generation, physical delivery and marketing of power across multiple geographical regions through its customer-facing business, Constellation, which sells electricity to both wholesale and retail customers. Generation also sells natural gas, renewable energy and other energy-related products and services. Six reportable segments: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions Commonwealth Edison Company Purchase and regulated retail sale of electricity Northern Illinois, including the City of Chicago Transmission and distribution of electricity to retail customers PECO Energy Company Purchase and regulated retail sale of electricity and natural gas Southeastern Pennsylvania, including the City of Philadelphia (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Pennsylvania counties surrounding the City of Philadelphia (natural gas) Baltimore Gas and Electric Company Purchase and regulated retail sale of electricity and natural gas Central Maryland, including the City of Baltimore (electricity and natural gas) Transmission and distribution of electricity and distribution of natural gas to retail customers Pepco Holdings LLC Utility services holding company engaged, through its reportable segments Pepco, DPL and ACE Service Territories of Pepco, DPL and ACE Potomac Electric Purchase and regulated retail sale of electricity District of Columbia, and major portions of Montgomery and Prince George’s Counties, Maryland. Transmission and distribution of electricity to retail customers Delmarva Power & Light Company Purchase and regulated retail sale of electricity and natural gas Portions of Delaware and Maryland (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Portions of New Castle County, Delaware (natural gas) Atlantic City Electric Company Purchase and regulated retail sale of electricity Portions of Southern New Jersey Transmission and distribution of electricity to retail customers Basis of Presentation (All Registrants) This is a combined annual report of all Registrants. The Notes to the Consolidated Financial Statements apply to the Registrants as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, the Registrants are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. As a result of the acquisition of PHI, Exelon’s financial reporting reflects PHI’s consolidated financial results subsequent to the March 23, 2016 , acquisition date. Exelon has accounted for the merger transaction applying the acquisition method of accounting, which requires the assets acquired and liabilities assumed by Exelon to be reported in Exelon’s financial statements at fair value, with any excess of the purchase price over the fair value of net assets acquired reported as goodwill. Exelon has pushed-down the application of the acquisition method of accounting to the consolidated financial statements of PHI such that the assets and liabilities of PHI are similarly recorded at their respective fair values, and goodwill has been established as of the acquisition date. Accordingly, the consolidated financial statements of PHI for periods before and after the March 23, 2016 , acquisition date reflect different bases of accounting, and the results of operations and the financial positions of the predecessor and successor periods are not comparable. The acquisition method of accounting has not been pushed down to PHI’s wholly owned subsidiary utility registrants, Pepco, DPL and ACE. For financial statement purposes, beginning on March 24, 2016 , disclosures related to Exelon now also apply to PHI, Pepco, DPL and ACE, unless otherwise noted. Through its business services subsidiary, BSC, Exelon provides its subsidiaries with a variety of support services at cost, including legal, human resources, financial, information technology and supply management services. The costs of BSC, including support services, are directly charged or allocated to the applicable subsidiaries using a cost-causative allocation method. Corporate governance-type costs that cannot be directly assigned are allocated based on a Modified Massachusetts Formula, which is a method that utilizes a combination of gross revenues, total assets and direct labor costs for the allocation base. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. PHISCO, a wholly owned subsidiary of PHI, provides a variety of support services at cost, including legal, accounting, engineering, distribution and transmission planning, asset management, system operations, and power procurement, to PHI and its operating subsidiaries. These services are directly charged or allocated pursuant to service agreements among PHISCO and the participating operating subsidiaries. Exelon owns 100% of its significant consolidated subsidiaries, including PHI, either directly or indirectly, except for ComEd, of which Exelon owns more than 99% . As of December 31, 2017 , Exelon owned none of BGE's preferred securities, which BGE redeemed in 2016. Exelon has reflected the third-party interests in ComEd, which totaled less than $1 million at December 31, 2017 and December 31, 2016 , as equity, in its consolidated financial statements. BGE is subject to certain ring-fencing measures established by order of the MDPSC. As part of this arrangement, BGE common stock is held directly by RF Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (BGE Utility), an unrelated party, holds a nominal non-economic interest in RF Holdco LLC with limited voting rights on specified matters. PHI is subject to some ring-fencing measures established by orders of the DCPSC, DPSC, MDPSC and NJBPU, pursuant to which all of the membership interest in PHI is held directly by PH Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (PH Utility), Inc., an unrelated party, holds a nominal non-economic interest in PH Holdco LLC with limited voting rights on specified matters. PHI owns 100% of its subsidiaries including Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and ExGen Renewables Partners, LLC, of which Generation holds a 50.01% and 51% interest, respectively. The remaining interests in these consolidated VIEs are included in noncontrolling interests on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 2 — Variable Interest Entities for further discussion of Exelon’s and Generation’s consolidated VIEs. The Registrants consolidate the accounts of entities in which a Registrant has a controlling financial interest, after the elimination of intercompany transactions. A controlling financial interest is evidenced by either a voting interest greater than 50% in which the Registrant can exercise control over the operations and policies of the investee, or the results of a model that identifies the Registrant or one of its subsidiaries as the primary beneficiary of a VIE. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or cost method accounting is applied. The Registrants apply proportionate consolidation when they have an undivided interest in an asset and are proportionately liable for their share of each liability associated with the asset. The Registrants proportionately consolidate their undivided ownership interests in jointly owned electric plants and transmission facilities. Under proportionate consolidation, the Registrants separately record their proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. The Registrants apply equity method accounting when they have significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. The Registrants apply equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd, PECO and BGE. Under equity method accounting, the Registrants report their interest in the entity as an investment and the Registrants’ percentage share of the earnings from the entity as single line items in their financial statements. The Registrants use cost method accounting if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under cost method accounting, the Registrants report their investments at cost and recognize income only to the extent dividends or distributions are received. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC. Use of Estimates (All Registrants) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and other postretirement benefits, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates. Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been reclassified between line items for comparative purposes. The reclassifications did not affect any of the Registrants’ net income, cash flows from operating activities or financial positions. Accounting for the Effects of Regulation (Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) The Registrants apply the authoritative guidance for accounting for certain types of regulation, which requires them to record in their consolidated financial statements the effects of cost-based rate regulation for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates designed to recover costs can be charged to and collected from customers. Exelon and the Utility Registrants account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon believes that it is probable that its currently recorded regulatory assets and liabilities will be recovered and settled, respectively, in future rates. Exelon and the Utility Registrants continue to evaluate their respective abilities to continue to apply the authoritative guidance for accounting for certain types of regulation, including consideration of current events in their respective regulatory and political environments. If a separable portion of the Registrants' business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their results of operations and financial positions. See Note 3 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, the Registrants classify regulatory assets and liabilities with a recovery or settlement period greater than one year as both current and non-current in their Consolidated Balance Sheets, with the current portion representing the amount expected to be recovered from or settled to customers over the next twelve-month period as of the balance sheet date. Income tax-related regulatory assets and liabilities are classified entirely as non-current on the Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. The Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order. Revenues (All Registrants) Operating Revenues Operating revenues are recorded as service is rendered or energy is delivered to customers. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records its best estimate of its electric distribution, energy efficiency and transmission revenue impacts resulting from changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. PECO, BGE, Pepco, DPL and ACE record their best estimate of the transmission revenue impacts resulting from changes in rates that they each believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 3 — Regulatory Matters and Note 5 — Accounts Receivable for further information. RTOs and ISOs In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly activity. In addition, capacity revenue and expense classification is based on the net sale or purchase position of Exelon in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 3 — Regulatory Matters and Note 12 — Derivative Financial Instruments for further information. Income Taxes (All Registrants) Deferred Federal and state income taxes are recorded on significant temporary differences between the book and tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred on the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. In accordance with applicable authoritative guidance, the Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) and recognize penalties related to unrecognized tax benefits in Other, net on their Consolidated Statements of Operations and Comprehensive Income. In the first quarter of 2016, PHI, Pepco, DPL and ACE changed their accounting for classification of interest on uncertain tax positions. PHI, Pepco, DPL and ACE have reclassified interest on uncertain tax positions as Interest expense from Income tax expense in the Consolidated Statements of Operations and Comprehensive Income. GAAP does not address the preferability of one acceptable method of accounting over the other for the classification of interest on uncertain tax positions. However, PHI, Pepco, DPL and ACE believe this change is preferable for comparability of their financial statements with the financial statements of the other Registrants in the combined filing, for consistency with FERC classification and for a more appropriate representation of the effective tax rate as they manage the settlement of uncertain tax positions and interest expense separately. PHI, Pepco, DPL and ACE applied the change retrospectively. The reclassification in the Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2015 was $34 million and $4 million for PHI and Pepco, respectively. The impact on all other PHI Registrants for the year ended December 31, 2015 was less than $1 million . Pursuant to the IRC and relevant state taxing authorities, Exelon and its subsidiaries file consolidated or combined income tax returns for Federal and certain state jurisdictions where allowed or required. See Note 14 — Income Taxes for further information. Taxes Directly Imposed on Revenue-Producing Transactions (All Registrants) The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. See Note 24 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes that are presented on a gross basis. Cash and Cash Equivalents (All Registrants) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (All Registrants) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2017 and 2016 , Exelon Corporate’s restricted cash and cash equivalents primarily represented restricted funds for payment of medical, dental, vision and long-term disability benefits. Generation’s restricted cash and cash equivalents primarily included cash at various project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities, see Note 13 — Debt and Credit Agreements for additional information on Generation’s project- specific financing structures. ComEd’s restricted cash primarily represented cash collateral held from suppliers associated with ComEd’s energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and certain funds set aside for the remediation of one of ComEd's MGP sites. PECO’s restricted cash primarily represented funds from the sales of assets that were subject to PECO’s mortgage indenture. BGE’s restricted cash primarily represented funds restricted for certain energy conservation incentive programs. PHI Corporate's restricted cash and cash equivalents primarily represented funds restricted for the payment of merger commitments and cash collateral held from its utility suppliers. Pepco's restricted cash and cash equivalents primarily represented funds restricted for the payment of merger commitments and collateral held from its utility suppliers. DPL's restricted cash and cash equivalents primarily represented cash collateral held from suppliers associated with procurement contracts. ACE's restricted cash and cash equivalents primarily represented funds restricted at its consolidated variable interest entity for repayment of transition bonds and cash collateral held from suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. Allowance for Uncollectible Accounts (All Registrants) The allowance for uncollectible accounts reflects the Registrants’ best estimates of losses on the customers' accounts receivable balances. For Generation, the allowance is based on accounts receivable aging historical experience and other currently available information. ComEd, PECO, BGE, Pepco, DPL and ACE estimate the allowance for uncollectible accounts on customer receivables by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Risk segments represent a group of customers with similar credit quality indicators that are comprised based on various attributes, including delinquency of their balances and payment history. Loss rates applied to the accounts receivable balances are based on a historical average of charge-offs as a percentage of accounts receivable in each risk segment. Utility Registrants' customer accounts are generally considered delinquent if the amount billed is not received by the time the next bill is issued, which normally occurs on a monthly basis. Utility Registrants' customer accounts are written off consistent with approved regulatory requirements. Utility Registrants' allowances for uncollectible accounts will continue to be affected by changes in volume, prices and economic conditions as well as changes in ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU regulations. See Note 3 — Regulatory Matters for additional information regarding the regulatory recovery of uncollectible accounts receivable at ComEd and ACE. Variable Interest Entities (All Registrants) Exelon accounts for its investments in and arrangements with VIEs based on the authoritative guidance which includes the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity has a controlling financial interest, meaning (1) has the power to direct the activities that most significantly impact the VIE's economic performance, and (2) has the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary. See Note 2 — Variable Interest Entities for additional information. Inventories (All Registrants) Inventory is recorded at the lower of weighted average cost or net realizable value. Provisions are recorded for excess and obsolete inventory. Fossil Fuel Fossil fuel inventory includes natural gas held in storage, propane and oil. The costs of natural gas, propane and oil are generally included in inventory when purchased and charged to purchased power and fuel expense at weighted average cost when used or sold. Materials and Supplies Materials and supplies inventory generally includes transmission, distribution and generating plant materials. Materials are generally charged to inventory when purchased and expensed or capitalized to property, plant and equipment, as appropriate, at weighted average cost when installed or used. Emission Allowances Emission allowances are included in inventory (for emission allowances exercisable in the current year) and other deferred debits (for emission allowances that are exercisable beyond one year) and charged to purchased power and fuel expense at weighted average cost as they are used in operations. Marketable Securities (All Registrants) All marketable securities are reported at fair value. Marketable securities held in the NDT funds are classified as trading securities, and all other securities are classified as available-for-sale securities. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Regulatory Agreement Units are included in regulatory liabilities at Exelon, ComEd and PECO and in Noncurrent payables to affiliates at Generation and in Noncurrent receivables from affiliates at ComEd and PECO. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Non-Regulatory Agreement Units are included in earnings at Exelon and Generation. Unrealized gains and losses, net of tax, for Exelon's available-for-sale securities are reported in OCI. Exelon’s and Generation’s NDT funds, which are designated to satisfy future decommissioning obligations, are classified as either noncurrent or current assets, depending on the timing of the decommissioning activities and income taxes on trust earnings. Beginning January 1, 2018, the authoritative guidance eliminates the available-for-sale classification for equity securities and requires that all equity investments (other than those accounted for using the equity method of accounting) be measured and recorded at fair value with any changes in fair value recorded through earnings. The new authoritative guidance does not impact the classification or measurement of investments in debt securities. See Note 3 — Regulatory Matters for additional information regarding ComEd’s and PECO’s regulatory assets and liabilities and Note 11 — Fair Value of Financial Assets and Liabilities and Note 15 — Asset Retirement Obligations for information regarding marketable securities held by NDT funds. Property, Plant and Equipment (All Registrants) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. The Utility Registrants also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation, Exelon Corporate and PHI and AFUDC for regulated property at ComEd, PECO, BGE, Pepco, DPL and ACE. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to Operating and maintenance expense as incurred. Third parties reimburse the Utility Registrants for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, plant and equipment. DOE SGIG and other funds reimbursed to the Utility Registrants have been accounted for as CIAC. For Generation, upon retirement, the cost of property is generally charged to accumulated depreciation in accordance with the composite and group methods of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to Operating and maintenance expense as incurred. For the Utility Registrants, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation consistent with the composite and group methods of depreciation. Depreciation expense at ComEd, BGE, Pepco, DPL and ACE includes the estimated cost of dismantling and removing plant from service upon retirement. Actual incurred removal costs are applied against a related regulatory liability or recorded to a regulatory asset if in excess of previously collected removal costs. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. See Note 6 — Property, Plant and Equipment , Note 9 — Jointly Owned Electric Utility Plant and Note 24 — Supplemental Financial Information for additional information regarding property, plant and equipment. Nuclear Fuel (Exelon and Generation) The cost of nuclear fuel is capitalized within Property, plant and equipment and charged to fuel expense using the unit-of-production method. Prior to May 16, 2014, the estimated disposal cost of SNF was established per the Standard Waste Contract with the DOE and was expensed through fuel expense at one mill ($0.001) per kWh of net nuclear generation. Effective May 16, 2014, the SNF disposal fee was set to zero by the DOE and Exelon and Generation are not accruing any further costs related to SNF disposal fees until a new fee structure goes into effect. Certain on-site SNF storage costs are being reimbursed by the DOE since a DOE (or government-owned) long-term storage facility has not been completed. See Note 23 — Commitments and Contingencies for additional information regarding the SNF disposal fee. Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to Operating and maintenance expense or capitalized to Property, plant and equipment (based on the nature of the activities) in the period incurred. New Site Development Costs (Exelon and Generation) New site development costs represent the costs incurred in the assessment and design of new power generating facilities. Such costs are capitalized when management considers project completion to be probable, primarily based on management’s determination that the project is economically and operationally feasible, management and/or the Exelon Board of Directors has approved the project and has committed to a plan to develop it, and Exelo

Variable Interest Entities (All

Variable Interest Entities (All Registrants)	12 Months Ended
	Dec. 31, 2017
Variable Interest Entity [Abstract]
Variable Interest Entity Disclosure [Text Block]	Variable Interest Entities (All Registrants) A VIE is a legal entity that possesses any of the following characteristics: an insufficient amount of equity at risk to finance its activities, equity owners who do not have the power to direct the significant activities of the entity (or have voting rights that are disproportionate to their ownership interest), or equity owners who do not have the obligation to absorb expected losses or the right to receive the expected residual returns of the entity. Companies are required to consolidate a VIE if they are its primary beneficiary, which is the enterprise that has the power to direct the activities that most significantly affect the entity’s economic performance. At December 31, 2017 , Exelon, Generation, PHI and ACE collectively consolidated five VIEs or VIE groups for which the applicable Registrant was the primary beneficiary. At December 31, 2016 , Exelon, Generation, BGE, PHI and ACE collectively consolidated nine VIEs or VIE groups for which the applicable Registrant was the primary beneficiary ( see Consolidated Variable Interest Entities below) . As of December 31, 2017 and 2016 , Exelon and Generation collectively had significant interests in seven and eight other VIEs, respectively, for which the applicable Registrant does not have the power to direct the entities’ activities and, accordingly, was not the primary beneficiary ( see Unconsolidated Variable Interest Entities below) . Consolidated Variable Interest Entities The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at December 31, 2017 and 2016 are as follows: December 31, 2017 Successor Exelon (a) Generation PHI (a) ACE Current assets $ 630 $ 620 $ 10 6 Noncurrent assets 9,317 9,286 31 23 Total assets $ 9,947 $ 9,906 $ 41 $ 29 Current liabilities $ 306 $ 270 $ 36 32 Noncurrent liabilities 3,312 3,246 66 58 Total liabilities $ 3,618 $ 3,516 $ 102 $ 90 December 31, 2016 Successor Exelon (a)(b) Generation BGE PHI (a) ACE Current assets $ 954 $ 916 $ 23 $ 14 $ 9 Noncurrent assets 8,563 8,525 3 35 23 Total assets $ 9,517 $ 9,441 $ 26 $ 49 $ 32 Current liabilities $ 885 $ 802 $ 42 $ 42 $ 37 Noncurrent liabilities 2,713 2,612 — 101 89 Total liabilities $ 3,598 $ 3,414 $ 42 $ 143 $ 126 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity. Except as specifically noted below, the assets in the table above are restricted for settlement of the VIE obligations and the liabilities in the table can only be settled using VIE resources. As of December 31, 2017 , Exelon's and Generation's consolidated VIEs consist of: Investments in Other Energy Related Companies During 2015, Generation sold 69% of its equity interest in a company to a tax equity investor. The company holds an equity method investment in a distributed energy company that is an unconsolidated VIE (see unconsolidated VIE section for additional details). Generation and the tax equity investor contributed a total of $227 million of equity in proportion to their ownership interests to the company. The company meets the definition of a VIE because it has a similar structure to a limited partnership and the limited partners do not have kick-out rights with respect to the general partner. Generation is the primary beneficiary because Generation manages the day-to-day activities of the entity. During 2015, Generation formed a limited liability company to build, own, and operate a backup generator. While Generation owns 100% of the backup generator company, it was determined that the entity is a VIE because the customer absorbs price variability from the entity through the fixed price backup generator agreement. Generation provides operating and capital funding to the backup generator company. During the fourth quarter of 2017 Generation acquired a controlling financial interest in an energy development company. The company is in the development stage and requires additional subordinated financial support from the equity holders to fund activities. Generation is the majority owner with a 62% equity interest and has the power to direct the activities that most significantly affect the economic performance of the company. Renewable Energy Project Companies In July 2017, Generation entered into an arrangement to sell a 49% interest in ExGen Renewable Partners, LLC (the Renewable JV) to an outside investor for $400 million of cash plus immaterial working capital and other customary post-closing adjustments. The Renewable JV meets the definition of a VIE because the Renewable JV has a similar structure to a limited partnership and the limited partners do not have kick out rights with respect to the general partner. Generation is the primarily beneficiary because Generation manages the day-to-day activities of the entity; therefore, Generation will continue to consolidate the Renewable JV. The Renewable JV is a collection of wind and solar project entities and some of these project entities are VIEs that are consolidated by the Renewable JV. The details relating to these VIEs are discussed below. Generation owns a number of limited liability companies that build, own, and operate solar and wind power facilities some of which are owned by the Renewable JV. While Generation or the Renewable JV owns 100% of the solar entities and 100% of the majority of the wind entities, it has been determined that certain of the solar and wind entities are VIEs because the entities require additional subordinated financial support in the form of a parental guarantee of debt, loans from the customers in order to obtain the necessary funds for construction of the solar facilities, or the customers absorb price variability from the entities through the fixed price power and/or REC purchase agreements. Generation is the primary beneficiary of these solar and wind entities that qualify as VIEs because Generation controls the design, construction, and operation of the facilities. Generation provides operating and capital funding to the solar and wind entities for ongoing construction, operations and maintenance and there is limited recourse related to Generation related to certain solar and wind entities. While Generation or the Renewable JV owns 100% of the majority of the wind entities, six of the projects have noncontrolling equity interests of 1% held by third parties and one of the projects has noncontrolling equity interests related to its Class B Membership Interest (see additional details below). The entities with noncontrolling equity interests of 1% held by third parties meet the definition of a VIE because the entities have noncontrolling equity interest holders that absorb variability from the wind projects. Generation’s or the Renewable JV's current economic interests in five of these projects is significantly greater than its stated contractual governance rights and all of these projects have reversionary interest provisions that provide the noncontrolling interest holder with a purchase option, certain of which are considered bargain purchase prices, which, if exercised, transfers ownership of the projects to the noncontrolling interest holder upon either the passage of time or the achievement of targeted financial returns. The ownership agreements with the noncontrolling interests state that Generation or the Renewable JV are to provide financial support to the projects in proportion to its current 99% economic interests in the projects. Generation provides operating and capital funding to the wind project entities for ongoing construction, operations and maintenance and there is limited recourse to Generation related to certain wind project entities. However, no additional support to these projects beyond what was contractually required has been provided during 2017. Generation is the primary beneficiary of these wind entities because Generation controls the design, construction, and operation of the facilities. In December 2016, Generation sold 100% of the Class B Membership Interests to a tax equity investor and retained 100% of the Class A Membership Interests of its equity interest in one of its wind entities that was previously consolidated under the voting interest model. The wind entity meets the definition of a VIE because the company has a similar structure to a limited partnership and the limited partners do not have kick-out rights with respect to the general partner. While Generation is the minority interest holder, Generation is the primary beneficiary, because Generation manages the day-to-day activities of the entity. Therefore, the entity continues to be consolidated by Generation. The renewable energy project companies VIE group was previously separated into two VIE groups for solar project limited liability companies and wind project companies as of December 31, 2016 . Retail Power and Gas Companies In March 2014, Generation began consolidating retail power and gas VIEs for which Generation is the primary beneficiary as a result of energy supply contracts that give Generation the power to direct the activities that most significantly affect the economic performance of the entities. Generation does not have an equity ownership interest in these entities, but provides approximately $30 million in credit support for the retail power and gas companies for which Generation is the sole supplier of energy. These entities are included in Generation’s consolidated financial statements, and the consolidation of the VIEs do not have a material impact on Generation’s financial results or financial condition. CENG CENG is a joint venture between Generation and EDF. On April 1, 2014, Generation, CENG, and subsidiaries of CENG executed the Nuclear Operating Services Agreement (NOSA) pursuant to which Generation now conducts all activities associated with the operations of the CENG fleet and provides corporate and administrative services to CENG and the CENG fleet for the remaining life of the CENG nuclear plants as if they were a part of the Generation nuclear fleet, subject to the CENG member rights of EDF. As a result of executing the NOSA, CENG qualifies as a VIE due to the disproportionate relationship between Generation’s 50.01% equity ownership interest and its role in conducting the operational activities of CENG and the CENG fleet conveyed through the NOSA. Further, since Generation is conducting the operational activities of CENG and the CENG fleet, Generation qualifies as the primary beneficiary of CENG and, therefore, is required to consolidate the results of operations and financial position of CENG. Exelon and Generation, where indicated, provide the following support to CENG (see Note 26 — Related Party Transactions for additional information regarding Generation's and Exelon’s transactions with CENG): • under power purchase agreements with CENG, Generation purchased or will purchase 50.01% of the available output generated by the CENG nuclear plants not subject to other contractual agreements from January 2015 through the end of the operating life of each respective plant. However, pursuant to amendments dated March 31, 2015, the energy obligations under the Ginna Nuclear Power Plant (Ginna) PPAs were suspended during the term of the Reliability Support Services Agreement (RSSA), through the end of March 31, 2017. With the expiration of the RSSA, the PPA was reinstated beginning April 1, 2017. (see Note 3 — Regulatory Matters for additional details), • Generation provided a $400 million loan to CENG. As of December 31, 2017 , the remaining obligation is $333 million , including accrued interest, which reflects the principal payment made in January 2015, • Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF against third-party claims that may arise from any future nuclear incident (as defined in the Price-Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this Indemnity Agreement. (See Note 23 — Commitments and Contingencies for more details), • Generation and EDF share in the $637 million of contingent payment obligations for the payment of contingent retrospective premium adjustments for the nuclear liability insurance, and • Exelon has executed an agreement to provide up to $245 million to support the operations of CENG as well as a $165 million guarantee of CENG’s cash pooling agreement with its subsidiaries. As of December 31, 2016 , Exelon and Generation had the following consolidated VIEs that are no longer VIEs as of December 31, 2017 : Retail Gas Group During 2009, Constellation formed a retail gas group to enter into a collateralized gas supply agreement with a third-party gas supplier. The retail gas group was determined to be a VIE because there was not sufficient equity to fund the group’s activities without additional credit support and a $75 million parental guarantee provided by Generation. As the primary beneficiary, Generation consolidated the retail gas group. During the second quarter of 2017, the collateral structure was terminated with the third-party gas supplier except for the $75 million parental guarantee provided by Generation. Although the parental guarantee remains, this is considered customary and reasonable for the unsecured position Generation has with the third-party gas supplier. As a result of the termination, the retail gas group no longer met the definition of a VIE. However, the retail gas group continues to be consolidated by Generation under the voting interest model. Other Generating Facilities Prior to 2017, Generation owned 90% of a biomass fueled, combined heat and power company. In the second quarter of 2015, the entity was deemed to be a VIE because the entity required additional subordinated financial support in the form of a parental guarantee provided by Generation for up to $ 275 million in support of the payment obligations related to the Engineering, Procurement and Construction contract for the facility in support of one of its other generating facilities. During the third quarter of 2017, the ownership of the entity increased to 99% , all payment obligations related to the EPC contract were satisfied, and the parental guarantee provided by Generation was terminated. As a result, the entity is now sufficiently capitalized and no longer meets the definition of a VIE. However, the biomass facility continues to be consolidated by Generation under the voting interest model. As of December 31, 2017 and 2016 , Exelon's and ACE's consolidated VIE consists of: ACE Transition Funding A special purpose entity formed by ACE for the purpose of securitizing authorized portions of ACE’s recoverable stranded costs through the issuance and sale of transition bonds. Proceeds from the sale of each series of transition bonds by ATF were transferred to ACE in exchange for the transfer by ACE to ATF of the right to collect a non-bypassable Transition Bond Charge from ACE customers pursuant to bondable stranded costs rate orders issued by the NJBPU in an amount sufficient to fund the principal and interest payments on transition bonds and related taxes, expenses and fees. During the three years ended December 31, 2017 , 2016 and 2015 , ACE transferred $48 million , $60 million and $61 million to ATF, respectively. As of December 31, 2016 , Exelon and BGE had the following consolidated VIE that is no longer a VIE as of December 31, 2017 : RSB BondCo LLC. In 2007, BGE formed RSB BondCo LLC (BondCo), a special purpose bankruptcy remote limited liability company, to acquire and hold rate stabilization property and to issue and service bonds secured by the rate stabilization property. In June 2007, BondCo purchased rate stabilization property from BGE, including the right to assess, collect, and receive non-bypassable rate stabilization charges payable by all residential electric customers of BGE. These charges were assessed in order to recover previously incurred power purchase costs that BGE deferred pursuant to Senate Bill 1. In the second quarter of 2017 the rate stabilization bonds were fully redeemed and BGE remitted its final payment to BondCo. Upon redemption of the bonds, BondCo no longer meets the definition of a variable interest entity. BondCo’s assets were restricted and could only be used to settle the obligations of BondCo. Further, BGE was required to remit all payments it received from customers for rate stabilization charges to BondCo. During 2017, 2016 and 2015, BGE remitted $22 million , $86 million and $86 million , respectively, to BondCo. For each of the consolidated VIEs noted above, except as otherwise noted: • the assets of the VIEs are restricted and can only be used to settle obligations of the respective VIE; • Exelon, Generation, BGE, PHI and ACE did not provide any additional material financial support to the VIEs; • Exelon, Generation, BGE, PHI and ACE did not have any material contractual commitments or obligations to provide financial support to the VIEs; and • the creditors of the VIEs did not have recourse to Exelon’s, Generation’s, BGE’s, PHI's or ACE's general credit. As of December 31, 2017 and 2016 , ComEd, PECO, Pepco and DPL do not have any material consolidated VIEs. Assets and Liabilities of Consolidated VIEs Included within the balances above are assets and liabilities of certain consolidated VIEs for which the assets can only be used to settle obligations of those VIEs, and liabilities that creditors, or beneficiaries, do not have recourse to the general credit of the Registrants. As of December 31, 2017 and 2016 , these assets and liabilities primarily consisted of the following: December 31, 2017 Successor Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 126 $ 126 $ — $ — Restricted cash 64 58 6 6 Accounts receivable, net Customer 138 138 — — Other 25 25 — — Inventory Materials and supplies 205 205 — — Other current assets 45 41 4 — Total current assets 603 593 10 6 Property, plant and equipment, net 6,186 6,186 — — Nuclear decommissioning trust funds 2,502 2,502 — — Other noncurrent assets 274 243 31 23 Total noncurrent assets 8,962 8,931 31 23 Total assets $ 9,565 $ 9,524 $ 41 $ 29 Long-term debt due within one year $ 102 $ 67 $ 35 $ 31 Accounts payable 114 114 — — Accrued expenses 65 64 1 1 Unamortized energy contract liabilities 18 18 — — Other current liabilities 7 7 — — Total current liabilities 306 270 36 32 Long-term debt 1,154 1,088 66 58 Asset retirement obligations 2,035 2,035 — — Unamortized energy contract liabilities 5 5 — — Other noncurrent liabilities 112 112 — — Noncurrent liabilities 3,306 3,240 66 58 Total liabilities $ 3,612 $ 3,510 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. December 31, 2016 Successor Exelon (a)(b) Generation BGE PHI (a) ACE Cash and cash equivalents $ 150 $ 150 $ — $ — $ — Restricted cash 59 27 23 9 9 Accounts receivable, net Customer 371 371 — — — Other 48 48 — — — Mark-to-market derivative assets 31 31 — — — Inventory Materials and supplies 199 199 — — — Other current assets 50 44 — 5 — Total current assets 908 870 23 14 9 Property, plant and equipment, net 5,415 5,415 — — — Nuclear decommissioning trust funds 2,185 2,185 — — — Goodwill 47 47 — — — Mark-to-market derivative assets 23 23 — — — Other noncurrent assets 315 277 3 35 23 Total noncurrent assets 7,985 7,947 3 35 23 Total assets $ 8,893 $ 8,817 $ 26 $ 49 $ 32 Long-term debt due within one year $ 181 $ 99 $ 41 $ 40 $ 35 Accounts payable 269 269 — — — Accrued expenses 119 116 1 2 2 Mark-to-market derivative liabilities 60 60 — — — Unamortized energy contract liabilities 15 15 — — — Other current liabilities 30 30 — — — Total current liabilities 674 589 42 42 37 Long-term debt 641 540 — 101 89 Asset retirement obligations 1,904 1,904 — — — Pension obligation (c) 9 9 — — — Unamortized energy contract liabilities 22 22 — — — Other noncurrent liabilities 106 106 — — — Noncurrent liabilities 2,682 2,581 — 101 89 Total liabilities $ 3,356 $ 3,170 $ 42 $ 143 $ 126 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity. (c) Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 16 - Retirement Benefits for additional details. Unconsolidated Variable Interest Entities Exelon’s and Generation’s variable interests in unconsolidated VIEs generally include equity investments and energy purchase and sale contracts. For the equity investments, the carrying amount of the investments is reflected on Exelon’s and Generation’s Consolidated Balance Sheets in Investments. For the energy purchase and sale contracts (commercial agreements), the carrying amount of assets and liabilities in Exelon’s and Generation’s Consolidated Balance Sheets that relate to their involvement with the VIEs are predominately related to working capital accounts and generally represent the amounts owed by, or owed to, Exelon and Generation for the deliveries associated with the current billing cycles under the commercial agreements. Further, Exelon and Generation have not provided material debt or equity support, liquidity arrangements or performance guarantees associated with these commercial agreements. As of December 31, 2017 and 2016 , Exelon and Generation had significant unconsolidated variable interests in seven and eight VIEs, respectively, for which Exelon or Generation, as applicable, was not the primary beneficiary. These interests include certain equity method investments and certain commercial agreements. Exelon and Generation only include unconsolidated VIEs that are individually material in the tables below. However, Generation has several individually immaterial VIEs that in aggregate represent a total investment of $ 8 million . These immaterial VIEs are equity and debt securities in energy development companies. The maximum exposure to loss related to these securities is limited to the $ 8 million included in Investments on Exelon’s and Generation’s Consolidated Balance Sheets . The following tables present summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2017 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 625 $ 509 $ 1,134 Total liabilities (a) 37 228 265 Exelon's ownership interest in VIE (a) — 251 251 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 251 251 Contract intangible asset 8 — 8 Debt and payment guarantees — — — Net assets pledged for Zion Station decommissioning (b) 2 — 2 December 31, 2016 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 638 $ 567 $ 1,205 Total liabilities (a) 215 287 502 Exelon's ownership interest in VIE (a) — 248 248 Other ownership interests in VIE (a) 423 32 455 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 264 264 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 9 — 9 __________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $39 million and $113 million as of December 31, 2017 and December 31, 2016 , respectively; offset by payables to ZionSolutions LLC of $37 million and $104 million as of December 31, 2017 and December 31, 2016 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE. For each unconsolidated VIE, Exelon and Generation assessed the risk of a loss equal to their maximum exposure to be remote and accordingly, Exelon and Generation have not recognized a liability associated with any portion of the maximum exposure to loss. In addition, there are no agreements with, or commitments by, third parties that would materially affect the fair value or risk of their variable interests in these variable interest entities. As of December 31, 2017 , Exelon's and Generation's unconsolidated VIEs consist of: Energy Purchase and Sale Agreements Generation has several energy purchase and sale agreements with generating facilities. Generation has evaluated the significant agreements, ownership structures and risks of each entity, and determined that certain of the entities are VIEs because the entity absorbs risk through the sale of fixed price power and renewable energy credits. Generation has reviewed the entities and has determined that Generation is not the primary beneficiary of the VIEs because Generation does not have the power to direct the activities that most significantly impact the VIEs economic performance. ZionSolutions Generation has an asset sale agreement with EnergySolutions, Inc. and certain of its subsidiaries, including ZionSolutions, LLC (ZionSolutions), which is further discussed in Note 15 — Asset Retirement Obligations . Under this agreement, ZionSolutions can put the assets and liabilities back to Generation when decommissioning activities under the asset sale agreement are complete. Generation has evaluated this agreement and determined that, through the put option, it has a variable interest in ZionSolutions but is not the primary beneficiary. As a result, Generation has concluded that consolidation is not required. Other than the asset sale agreement, Exelon and Generation do not have any contractual or other obligations to provide additional financial support and ZionSolutions’ creditors do not have any recourse to Exelon’s or Generation’s general credit. Investment in Distributed Energy Companies In July 2014, Generation entered into an arrangement to purchase a 90% equity interest and 90% of the tax attributes of a distributed energy company. Generation contributed a total $ 85 million of equity. The distributed energy company meets the definition of a VIE because the company has a similar structure to a limited partnership and the limited partners do not have kick-out rights of the general partner. Generation is not the primary beneficiary; therefore, the investment continues to be recorded using the equity method. During 2015, a company that is consolidated by Generation as a VIE entered into an arrangement to purchase a 90% equity interest and 99% of the tax attributes of another distributed energy company (see additional details in the Consolidated Variable Interest Entities section above). The equity holders (of which Generation is one) contributed to the distributed energy company a total of $ 227 million of equity in proportion to their ownership interests. The equity holders provided a parental guarantee of up to $ 275 million in support of equity contributions to the distributed energy company. As all equity contributions were made as of the first quarter of 2017, there is no further payment obligation under the parental guarantee. The distributed energy company meets the definition of a VIE because the company has a similar structure to a limited partnership and the limited partners do not have kick-out rights of the general partner. Generation is not the primary beneficiary; therefore, the investment is recorded using the equity method. Both distributed energy companies from the 2015 and 2014 arrangements are considered related parties to Generation. As of December 31, 2016 , Exelon and Generation had the following unconsolidated VIE that is no longer a VIE as of December 31, 2017 : Investment in Energy Generating Facility As of December 31, 2016, Generation had an equity investment in an energy generating facility. The entity was a VIE because Generation guaranteed the debt of the entity, provided equity support, and provided operating services to the entity. Generation was not the primary beneficiary of the entity because Generation did not have the power to direct the activities that most significantly impacted the VIE’s economic performance. During 2017, Generation sold its equity investment in the entity; therefore, the entity is no longer a VIE as of December 31, 2017. ComEd, PECO and BGE The financing trust of ComEd, ComEd Financing III, and the financing trusts of PECO, PECO Trust III and PECO Trust IV, are not consolidated in Exelon’s, ComEd’s, or PECO’s financial statements. These financing trusts were created to issue mandatorily redeemable trust preferred securities. ComEd and PECO have concluded that they do not have a significant variable interest in ComEd Financing III, PECO Trust III, or PECO Trust IV as each Registrant financed its equity interest in the financing trusts through the issuance of subordinated debt and, therefore, has no equity at risk. The financing trust of BGE, BGE Capital Trust II, was created for the purpose of issuing mandatorily redeemable trust preferred securities. In the third quarter of 2017, BGE redeemed the securities pursuant to the optional redemption provisions of the Indenture, under which the subordinated debt securities were issued, and dissolved BGE Capital Trust II. Prior to dissolution, the BGE Capital Trust II was not consolidated in Exelon's or BGE's financial statements. BGE concluded it did not have a significant variable interest in BGE Capital Trust II as BGE financed its equity interest in the financing trust through the issuance of subordinated debt and, therefore, had no equity at risk. See Note 13 — Debt and Credit Agreements for additional information.

Regulatory Matters (All Registr

Regulatory Matters (All Registrants)	12 Months Ended
	Dec. 31, 2017
Regulated Operations [Abstract]
Regulatory Matters (All Registrants)	3 . Regulatory Matters (All Registrants) The following matters below discuss the status of material regulatory and legislative proceedings of the Registrants. Illinois Regulatory Matters Tax Cuts and Jobs Act (Exelon and ComEd). On January 18, 2018, the ICC approved ComEd's petition filed on January 5, 2018 seeking approval to pass back to customers beginning February 1, 2018 $201 million in tax savings resulting from the enactment of the TCJA through a reduction in electric distribution rates. The amounts being passed back to customers reflect the benefit of lower income tax rates beginning January 1, 2018 and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. Refer to Note 14 - Income Taxes for more detail on Corporate Tax Reform. Electric Distribution Formula Rate (Exelon and ComEd). ComEd’s electric distribution rates are established through a performance-based formula rate. ComEd is required to file an annual update to the performance-based formula rate on or before May 1, with resulting rates effective in January of the following year. This annual electric distribution formula rate update is based on prior year actual costs and current year projected capital additions (initial revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred for that year (annual reconciliation). Throughout each year, ComEd records regulatory assets or regulatory liabilities and corresponding increases or decreases to Operating revenues for any differences between the revenue requirement in effect and ComEd’s best estimate of the revenue requirement expected to be approved by the ICC for that year’s reconciliation. The regulatory asset associated with electric distribution formula rate is amortized to Operating revenues in ComEd's Consolidated Statement of Operations and Comprehensive Income as the associated amounts are recovered through rates. Changes to the distribution formula rate as a result of FEJA are discussed below. For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's electric distributions formula rate filings: Annual Electric Distribution Filings 2017 2016 2015 ComEd's requested total revenue requirement increase (decrease) $ 96 $ 138 $ (50 ) Final ICC Order Initial revenue requirement increase $ 78 $ 134 $ 85 Annual reconciliation increase (decrease) 18 (7 ) (152 ) Total revenue requirement increase (decrease) $ 96 $ 127 (a) $ (67 ) Allowed Return on Rate Base: Initial revenue requirement 6.47 % 6.71 % 7.05 % Annual reconciliation 6.45 % 6.69 % 7.02 % Allowed ROE: Initial revenue requirement 8.40 % 8.64 % 9.14 % Annual reconciliation 8.34 % (b) 8.59 % (b) 9.09 % (b) Effective date of rates January 2018 January 2017 January 2016 __________ (a) On March 22, 2017, the ICC issued an order approving ComEd's proposal to reduce the 2016 revenue requirement by $18 million , which was reflected in customer rates beginning in April 2017. This reduction is not reflected in the 2016 revenue requirement amounts above. (b) Includes a reduction of 6 basis points in 2017 and 5 basis points in 2016 and 2015 for a reliability performance metric penalty. Illinois Future Energy Jobs Act (Exelon, Generation and ComEd) Background On December 7, 2016, FEJA was signed into law by the Governor of Illinois. FEJA went into effect on June 1, 2017, and includes, among other provisions, (1) a ZES providing compensation for certain nuclear-powered generating facilities, (2) an extension of and certain adjustments to ComEd’s electric distribution formula rate, (3) new cumulative persisting annual energy efficiency MWh savings goals for ComEd, (4) revisions to the Illinois RPS requirements, (5) provisions for adjustments to or termination of FEJA programs if the average impact on ComEd’s customer rates exceeds specified limits, (6) revisions to the existing net metering statute to (i) mandate net metering for community generation projects, and establish billing procedures for subscribers to those projects, (ii) provide immediately for netting at the energy-only rate for nonresidential customers, and (iii) transition from netting at the full retail rate to the energy-only rate for certain residential net metering customers once the net meter customer load equals 5% of total peak demand supplied in the previous year and (7) support for low income rooftop and community solar programs . Zero Emission Standard FEJA includes a ZES that provides compensation through the procurement of ZECs targeted at preserving the environmental attributes of zero-emissions nuclear-powered generating facilities that meet specific eligibility criteria. On September 11, 2017, the ICC approved the IPA's ZES Procurement Plan filed with the ICC on July 31, 2017. Bidders interested in participating in the procurement process had 14 days following the ICC's approval of the plan to submit the required eligibility information and become qualified bidders. Generation’s Clinton and Quad Cities nuclear plants timely submitted the required eligibility information to the ICC and responded to follow up questions. Winning bidders will contract directly with Illinois utilities, including ComEd, for 10-year terms extending through May 31, 2027. The ZEC price will be based upon the current social cost of carbon as determined by the Federal government and is initially established at $16.50 per MWh of production, subject to annual future adjustments determined by the IPA for specified escalation and pricing adjustment mechanisms designed to lower the ZEC price based on increases in underlying energy and capacity prices. Illinois utilities will be required to purchase all ZECs delivered by the zero-emissions nuclear-powered generating facilities, subject to annual cost caps. For the initial delivery year, June 1, 2017 to May 31, 2018, the ZEC annual cost cap is set at $235 million (ComEd’s share is approximately $170 million ). For subsequent delivery years, the IPA-approved targeted ZEC procurement amounts will change based on forward energy and capacity prices. ZECs delivered to Illinois utilities in excess of the annual cost cap will be paid in subsequent years if the payments do not exceed the prescribed annual cost cap for that year. ComEd recovers all costs associated with purchasing ZECs through a rate rider that provides for an annual reconciliation and true-up to actual costs incurred by ComEd to purchase ZECs, with any difference to be credited to or collected from ComEd’s retail customers in subsequent periods with interest. ComEd began billing its retail customers under its new ZEC rate rider on June 1, 2017. On February 14, 2017, two lawsuits were filed in the Northern District of Illinois against the IPA alleging that the state’s ZEC program violates certain provisions of the U.S. Constitution. One lawsuit was filed by customers of ComEd, led by the Village of Old Mill Creek, and the other was brought by the EPSA and three other electric suppliers. Both lawsuits argue that the Illinois ZEC program will distort PJM's FERC-approved energy and capacity market auction system of setting wholesale prices, and seek a permanent injunction preventing the implementation of the program. Exelon intervened and filed motions to dismiss in both lawsuits. In addition, on March 31, 2017, plaintiffs in both lawsuits filed motions for preliminary injunction with the court; the court stayed briefing on the motions for preliminary injunction until the resolution of the motions to dismiss. On July 14, 2017, the district court granted the motions to dismiss. On July 17, 2017, the plaintiffs appealed the decision to the Seventh Circuit. Briefs were fully submitted on December 12, 2017, the Court heard oral argument on January 3, 2018. At the argument, the Court asked for supplemental briefing, which was filed on January 26, 2018. Exelon cannot predict the outcome of these lawsuits. It is possible that resolution of these matters could have a material, unfavorable impact on Exelon’s and Generation’s results of operations, cash flows and financial positions. See Note 8 — Early Nuclear Plant Retirements for additional information regarding the economic challenges facing Generation’s Clinton and Quad Cities nuclear plants and the expected benefits of the ZES. ComEd Electric Distribution Rates FEJA extended the sunset date for ComEd’s performance-based electric distribution formula rate from 2019 to the end of 2022, allowed ComEd to revise the electric distribution formula rate to eliminate the ROE collar, and allowed ComEd to implement a decoupling tariff if the electric distribution formula rate is terminated at any time. ComEd revised its electric distribution formula rate to eliminate the ROE collar, which eliminates any unfavorable or favorable impacts of weather or load from ComEd’s electric distribution formula rate revenues beginning with the reconciliation filed in 2018 for the 2017 calendar year. Elimination of the ROE collar effectively offsets the favorable or unfavorable impacts to ComEd's electric distribution formula rate revenues associated with variations in delivery volumes associated with above or below normal weather, numbers of customers or usage per customer. ComEd began reflecting the impacts of this change in its electric distribution services costs regulatory asset in the first quarter 2017. As of December 31, 2017 , ComEd recorded an increase to its electric distribution services costs regulatory asset of approximately $32 million for this change. FEJA requires ComEd to make non-recoverable contributions to low income energy assistance programs of $10 million per year for 5 years as long as the electric distribution formula rate remains in effect. With the exception of these contributions, ComEd will recover from customers, subject to certain caps explained below, the costs it incurs pursuant to FEJA either through its electric distribution formula rate or other recovery mechanisms. Energy Efficiency Prior to FEJA, Illinois law required ComEd to implement cost-effective energy efficiency measures and, for a 10-year period ending May 31, 2018, cost-effective demand response measures to reduce peak demand by 0.1% over the prior year for eligible retail customers. Beginning January 1, 2018, FEJA provides for new cumulative annual energy efficiency MWh savings goals for ComEd, which are designed to achieve 21.5% of cumulative persisting annual MWh savings by 2030, as compared to the deemed baseline of 88 million MWhs of electric power and energy sales. FEJA deems the cumulative persisting annual MWh savings to be 6.6% from 2012 through the end of 2017. ComEd expects to spend approximately $350 million to $400 million annually through 2030 to achieve these energy efficiency MWh savings goals. In addition, FEJA extends the peak demand reduction requirement from 2018 to 2026. Because the new requirements apply beginning in 2018, FEJA extends the existing energy efficiency plans, which were due to end on May 31, 2017, through December 31, 2017. FEJA also exempts customers with demands over 10 MW from energy efficiency plans and requirements beginning June 1, 2017. On September 11, 2017, the ICC approved ComEd's 2018-2021 energy efficiency plan with minor modifications filed by ComEd with the ICC on June 30, 2017. As allowed by FEJA, ComEd cancelled its existing energy efficiency rate rider effective June 2, 2017. On August 1, 2017, ComEd filed with the ICC a reconciliation of revenues and costs incurred through the cancellation date. On August 30, 2017, the ICC approved ComEd's request, filed on August 1, 2017, to issue an $80 million credit on retail customers' bills in October 2017 for the majority of the over-recoveries with any final adjustment applicable to the over-recoveries to be billed or credited in the future. As of December 31, 2017 , ComEd’s over-recoveries associated with its former energy efficiency rate rider were $4 million and are expected to be refunded to customers in future rates. FEJA allows ComEd to defer energy efficiency costs (except for any voltage optimization costs which are recovered through the electric distribution formula rate) as a separate regulatory asset that is recovered through the energy efficiency formula rate over the weighted average useful life, as approved by the ICC, of the related energy efficiency measures. ComEd earns a return on the energy efficiency regulatory asset at a rate equal to its weighted average cost of capital, which is based on a year-end capital structure and calculated using the same methodology applicable to ComEd’s electric distribution formula rate. Beginning January 1, 2018 through December 31, 2030, the return on equity that ComEd earns on its energy efficiency regulatory asset is subject to a maximum downward or upward adjustment of 200 basis points if ComEd’s cumulative persisting annual MWh savings falls short of or exceeds specified percentage benchmarks of its annual incremental savings goal. ComEd is required to file an update to its energy efficiency formula rate on or before June 1 each year, with resulting rates effective in January of the following year. The annual update will be based on projected current year energy efficiency costs, PJM capacity revenues, and the projected year-end regulatory asset balance less any related deferred income taxes. The update will also include a reconciliation of any differences between the revenue requirement in effect for the prior year and the revenue requirement based on actual prior year costs and actual year-end energy efficiency regulatory asset balances less any related deferred income taxes. ComEd records a regulatory asset or liability and corresponding increase or decrease to Operating revenues for any differences between the revenue requirement in effect and ComEd’s best estimate of the revenue requirement expected to be approved by the ICC for that year’s reconciliation. On August 15, 2017, the ICC approved ComEd's new initial energy efficiency formula rate filed pursuant to FEJA. The order establishes the formula under which energy efficiency rates will be calculated going forward and the revenue requirement used to set the initial rates for the period October 1, 2017 through December 31, 2017. The initial revenue requirement is based on projected costs and projected PJM capacity revenues for the period from June 1, 2017 through December 31, 2017, and projected year-end 2017 energy efficiency regulatory asset balances (less related deferred income taxes). The approved energy efficiency formula rate also provides for revenue decoupling to effectively offset the favorable or unfavorable impacts to ComEd's energy efficiency formula rate revenues associated with variations in delivery volumes associated with above or below normal weather, numbers of customers or usage per customer. On September 11, 2017, the ICC approved ComEd's annual energy efficiency formula rate. The order establishes the revenue requirement used to set rates that will take effect in January 2018. The revenue requirement for 2018 is based on projected 2018 energy efficiency costs and PJM capacity revenues, and year-end 2018 energy efficiency regulatory asset balances (less related deferred income taxes). For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's requested energy efficiency revenue requirement: Annual Energy Efficiency Filings Initial 2017 ComEd's requested total revenue requirement (decrease) increase $ (7 ) (a) $ 12 Allowed Return on Rate Base: Initial revenue requirement 6.47 % 6.47 % Allowed ROE: Initial revenue requirement 8.40 % 8.40 % Effective date of rates (b) October 2017 January 2018 __________ (a) Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs. (b) An ICC order on the annual reconciliation of any differences between the revenue requirement in effect and the revenue requirement based on actual costs for 2017 and 2018 is expected in December 2018 and December 2019, respectively. Renewable Portfolio Standard Existing Illinois law requires ComEd to purchase each year an increasing percentage of renewable energy resources for the customers for which it supplies electricity. This obligation is satisfied through the procurement of RECs. FEJA revises the Illinois RPS to require ComEd to procure RECs for all retail customers by June 2019, regardless of the customers’ electricity supplier, and provides support for low-income rooftop and community solar programs, which will be funded by the existing Renewable Energy Resources Fund and ongoing RPS collections. FEJA also requires ComEd to use RPS collections to fund utility job training and workforce development programs in the amounts of $10 million in each of the years 2017, 2021, and 2025. ComEd recorded a $20 million noncurrent liability as of December 31, 2017 associated with this obligation. ComEd will recover all costs associated with purchasing RECs and funding utility job training and workforce development programs through a new RPS rate rider that provides for a reconciliation and true-up to actual costs, with any difference between revenues and expenses to be credited to or collected from ComEd’s retail customers in subsequent periods with interest. The first reconciliation and true-up for RECs will occur in 2021 and cover revenues and costs for the four-year period beginning June 1, 2017 through May 31, 2021. Subsequently, the RPS rate rider will provide for an annual reconciliation and true-up. ComEd began billing its retail customers under its new RPS rate rider on June 1, 2017 and recorded a related regulatory liability of $21 million as of December 31, 2017 . ComEd also recorded a regulatory liability of $41 million for alternative compliance payments received from RES to purchase RECs on behalf of the RES in the future. As of December 31, 2017 , ComEd had received $62 million of over-recovered RPS costs and alternative compliance payments from RES, which are deposited into a separate interest-bearing bank account pursuant to FEJA. The current portion is classified as Restricted cash and the non-current portion is classified as other deferred debits on Exelon's and ComEd's Balance Sheets. Customer Rate Increase Limitations FEJA includes provisions intended to limit the average impact on ComEd customer rates for recovery of costs incurred under FEJA as follows: (1) for a typical ComEd residential customer, the average impact must be less than $0.25 cents per month, (2) for nonresidential customers with a peak demand less than 10 MW, the average annual impact must be less than 1.3% of the average amount paid per kWh for electric service by Illinois commercial retail customers during 2015, and (3) for nonresidential customers with a peak demand greater than 10 MW, the average annual impact must be less than 1.3% of the average amount paid per kWh for electric service by Illinois industrial retail customers during 2015. On June 30, 2017, ComEd submitted a 10-year projection to the ICC of customer rate impacts for residential customers and nonresidential customers with a peak demand less than 10 MW . Such projections indicate that customer rate impacts will not exceed the limitations set by FEJA discussed below. Thereafter, beginning in 2018, ComEd must submit a report to the ICC for residential customers and nonresidential customers with a peak demand less than 10 MW by February 15th and June 30th of each year, respectively. For nonresidential customers with a peak demand greater than 10 MW, ComEd must submit a report to the ICC by May 1 of each year if a rate reduction will be necessary in the following year. For residential customers, the reports will include the actual costs incurred under FEJA during the preceding year and a rolling 10-year customer rate impact projection. The reports for nonresidential customers with a peak demand less than 10 MW will also include the actual costs incurred under FEJA during the preceding year, as well as the average annual rate increase from January 1, 2017 through the end of the preceding year and the average annual rate increase projected for the remainder of the 10-year period. If the projected residential customer or nonresidential customer with a peak demand less than 10 MW rate increase exceeds the limitations during the first four years, ComEd is required to decrease costs associated with FEJA investments, including reductions to ZEC contract quantities. If the projected residential customer or nonresidential customer with a peak demand less than 10 MW rate increase exceeds the limitations during the last six years, ComEd is required to demonstrate how it will reduce FEJA investments to ensure compliance. If the actual residential customer or nonresidential customer with a peak demand less than 10 MW rate increase exceeds the limitations for any one year, ComEd is required to submit a corrective action plan to decrease future year costs to reduce customer rates to ensure future compliance. If the actual residential customer or nonresidential customer rate exceeds the limitations for two consecutive years, ComEd can offer to credit customers for amounts billed in excess of the limitations or ComEd can terminate FEJA investments. If ComEd chooses to terminate FEJA investments, the ICC shall order termination of ZEC contracts and further initiate proceedings to reduce energy efficiency savings goals and terminate support for low-income rooftop and community solar programs . ComEd is allowed to fully recover all costs incurred as of and up to the date of the programs’ termination. Renewable Energy Resources (Exelon and ComEd). In accordance with FEJA, beginning with the plan or plans to be implemented in the 2017 delivery year, the IPA filed its long term renewable resource procurement plan (LT Plan) with the ICC on December 4, 2017. The LT Plan requires a certain percentage of electricity sales be met with a climbing percentage of REC procurement. The 2017 delivery year requirement was 13% , with the obligation increasing by at least 1.5% each year thereafter to at least 25% by the 2025 delivery year; and continuing at no less than 25% for each delivery year thereafter. Each RES and each Illinois utility, which includes ComEd, is responsible for the renewable resource obligation for the customers to which it supplies power. Over time, this will change and ComEd will procure renewable resources based on the retail load of substantially all customers in its service territory. For the delivery year beginning June 1, 2017, the LT Plan shall include cost effective renewable energy resources procured by ComEd for the retail load it supplies and for 50% of the retail customer load supplied by RES in ComEd's service territory on February 28, 2017. ComEd's procurement for RES supplied retail customer load will increase to 75% June 1, 2018 and to 100% beginning June 1, 2019. All goals are subject to rate impact criteria set forth by Illinois legislation. As of December 31, 2017 , ComEd had purchased renewable energy resources or equivalents, such as RECs, in accordance with the IPA Plan. ComEd currently retires all RECs upon transfer and acceptance. ComEd is permitted to recover procurement costs of RECs from retail customers without mark-up through rates. Pennsylvania Regulatory Matters Tax Cuts and Jobs Act (Exelon and PECO). PECO is working with the PAPUC and stakeholders on behalf of its distribution customers to determine the proper regulatory mechanisms and timing to reflect the tax benefits from the TCJA. 2015 Pennsylvania Electric Distribution Rate Case (Exelon and PECO). On March 27, 2015, PECO filed a petition with the PAPUC requesting an increase of $190 million to its annual service revenues for electric delivery, which requested an ROE of 10.95% . On September 10, 2015, PECO and interested parties filed with the PAPUC a petition for joint settlement for an increase of $127 million in annual distribution service revenue. No overall ROE was specified in the settlement. On December 17, 2015, the PAPUC approved the settlement of PECO’s electric distribution rate case, which included the approval of the In-Program Arrearage Forgiveness ("IPAF") Program. The approved electric delivery rates became effective on January 1, 2016. The IPAF Program provides for forgiveness of a portion of the eligible arrearage balance of its low-income Customer Assistance Program (CAP) accounts receivable at program inception. The forgiveness will be granted to the extent CAP customers remain current over the duration of the five-year payment agreement term. The Settlement guarantees PECO’s recovery of two-thirds of the arrearage balance through a combination of customer payments and rate recovery, including through future rates cases if necessary. The remaining one-third of the arrearage balance has been absorbed by PECO through bad debt expense on its Consolidated Statements of Operations. In October 2016, the IPAF was fully implemented. PECO recorded a regulatory asset representing previously incurred bad debt expense associated with the eligible accounts receivable balances, which is included in the Regulatory assets table below. Maryland Regulatory Matters Tax Cuts and Jobs Act (Exelon, BGE, PHI, Pepco and DPL). On January 12, 2018, the MDPSC issued an order that directed each of BGE, Pepco and DPL to track the impacts of the TCJA beginning January 1, 2018 and file by February 15, 2018 how and when they expect to pass through such impacts to their customers. On January 31, 2018, the MDPSC approved BGE’s petition to pass back to customers beginning February 1, 2018 $103 million in tax savings resulting from the enactment of the TCJA through a reduction in distribution rates, of which $72 million and $31 million were related to electric and natural gas, respectively. On February 5, 2018, Pepco filed with the MDPSC an update to its current distribution rate case to reflect $31 million in TCJA tax savings. By mid-February 2018, DPL is planning to file with the MDPSC seeking approval to pass back to customers beginning in 2018 $13 million in TCJA tax savings through a reduction in electric distribution rates. The amounts being passed back or proposed to be passed back to customers reflect the annual benefit of lower income tax rates and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. Refer to Note 14 — Income Taxes for more detail on Corporate Tax Reform. After the filings due by February 15, 2018, it is expected that the MDPSC will address the treatment of the TCJA tax savings tracked by BGE, Pepco and DPL for the period January 1, 2018 through the effective date of their respective $103 million , $31 million and $13 million customer rate adjustments described above. 2018 Maryland Electric Distribution Rates (Exelon, PHI and Pepco). On January 2, 2018, Pepco filed an application with the MDPSC to increase its annual electric distribution base rates by $41 million , reflecting a requested ROE of 10.1% . On February 5, 2018, Pepco filed with the MDPSC an update to its current distribution rate case to reflect $31 million in TCJA tax savings, thereby reducing the requested annual base rate increase to $11 million . Pepco expects a decision in the matter in the third quarter of 2018, but cannot predict how much of the requested increase the MDPSC will approve. 2017 Maryland Electric Distribution Rates (Exelon, PHI and Pepco). On March 24, 2017, Pepco filed an application with the MDPSC to increase its annual electric distribution base rates by $69 million , which was updated to $67 million on August 24, 2017, reflecting a requested ROE of 10.1% . The application included a request for an income tax adjustment to reflect full normalization of removal costs associated with pre-1981 property, which accounted for $18 million of the requested increase. On October 20, 2017, the MDPSC approved an increase in Pepco electric distribution rates of $34 million , reflecting a ROE of 9.5% . On October 27, 2017, the MDPSC issued an errata order revising the approved increase in Pepco electric distribution rates to $32 million . The errata order corrected a number of computational errors in the original order but did not alter any of the findings. The new rates became effective for services rendered on or after October 20, 2017. In its decision, the MDPSC denied Pepco’s request regarding the income tax adjustment without prejudice to Pepco filing another similar proposal with additional information. On November 20, 2017, an interested party in the proceeding filed a request for rehearing. On December 4, 2017, Pepco filed its response in opposition to the request for rehearing. Pepco cannot predict the outcome of this matter or when it will be decided. 2016 Maryland Electric Distribution Base Rates (Exelon, PHI and Pepco). On November 15, 2016, the MDPSC approved an increase in electric distribution base rates of $53 million based on a ROE of 9.55% . The new rates became effective for services rendered on or after November 15, 2016. MDPSC also approved Pepco's recovery of substantially all of its capital investment and regulatory assets associated with its AMI program as part of the newly effective rates as well as a recovery over a five-year period of transition costs related to a new billing system implemented in 2015. As a result, during the fourth quarter of 2016, Exelon, PHI and Pepco established a regulatory asset of $13 million , wrote-off $3 million in disallowed AMI costs and recorded a pre-tax credit to net income for $10 million . Additionally, the MDPSC denied Pepco's request to extend its Grid Resiliency Program surcharge for new system reliability and safety improvement projects, with costs for such programs to be recovered going forward through base rates. 2017 Maryland Electric Distribution Rates (Exelon, PHI and DPL). On July 14, 2017, DPL filed an application with the MDPSC to increase its annual electric distribution base rates by $27 million , which was updated to $19 million on November 16, 2017, reflecting a requested ROE of 10.1% . On December 18, 2017, a settlement agreement was filed with the MDPSC wherein DPL will be granted a rate increase of $13 million , and a ROE of 9.5% solely for purposes of calculating AFUDC and regulatory asset carrying costs. On January 5, 2018, the MDPSC held a hearing on the settlement agreement. DPL expects a decision in the matter in the first quarter of 2018, but cannot predict whether the MDPSC will approve the settlement agreement as filed or how much of the requested increase will be approved. 2016 Maryland Electric Distribution Base Rates (Exelon, PHI and DPL). On February 15, 2017, the MDPSC approved an increase in DPL electric distribution rates of $38 million reflecting a ROE of 9.6% . The new rates became effective for services rendered on or after February 15, 2017. The MDPSC also denied DPL’s request to continue its Grid Resiliency Program, through which DPL proposed to invest $5 million a year for two years to improve priority feeders and install single-phase reclosing fuse technology. The final order did not result in the recognition of any incremental regulatory assets or liabilities. 2015 Maryland Electric and Natural Gas Distribution Base Rates (Exelon and BGE). On November 6, 2015, and as amended through the course of the proceeding, BGE filed for electric and natural gas distribution base rate increases with the MDPSC, ultimately requesting annual increases of $116 million and $78 million , respectively, of which $104 million and $37 million were related to recovery of electric and natural gas smart grid initiative costs, respectively. BGE also proposed to recover an annual increase of approximately $30 million for Baltimore City underground conduit fees through a surcharge. On June 3, 2016, the MDPSC issued an order in which the MDPSC found compelling evidence to conclude that BGE's smart grid initiative overall was cost beneficial to customers. However, the June 3 order contained several cost disallowances and adjustments, including not allowing BGE to defer or recover through a surcharge the $30 million increase in annual Baltimore City underground conduit fees. On June 30, 2016, BGE filed a petition for rehearing of the June 3 order requesting that the MDPSC modify its order to reverse certain decisions including the decision associated with the Baltimore City underground conduit fees. OPC also subsequently

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (All Registrants)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Acquisition of James A. FitzPatrick Nuclear Generating Station (Exelon and Generation) On March 31, 2017, Generation acquired the 842 MW single-unit James A. FitzPatrick (FitzPatrick) nuclear generating station located in Scriba, New York from Entergy Nuclear FitzPatrick LLC (Entergy) for a total purchase price of $289 million , which consisted of a cash purchase price of $110 million and a net cost reimbursement to and on behalf of Entergy of $179 million . As part of the acquisition agreements, Generation provided nuclear fuel and reimbursed Entergy for incremental costs to prepare for and conduct a plant refueling outage; and Generation reimbursed Entergy for incremental costs to operate and maintain the plant for the period after the refueling outage through the acquisition closing date. These reimbursements covered costs that Entergy otherwise would have avoided had it shut down the plant as originally intended in January 2017. The amounts reimbursed by Generation were offset by FitzPatrick's electricity and capacity sales revenues for this same post-outage period. As part of the transaction, Generation received the FitzPatrick NDT fund assets and assumed the obligation to decommission FitzPatrick. The NRC license for FitzPatrick expires in 2034. In 2017, the final purchase price consideration of $289 million (including $235 million of cash and $54 million of nuclear fuel) was remitted to and on behalf of Entergy. The fair values of FitzPatrick’s assets and liabilities were determined based on significant estimates and assumptions that are judgmental in nature, including projected future cash flows (including timing), discount rates reflecting risk inherent in the future cash flows and future power and fuel market prices. The valuations performed in the first quarter of 2017 to determine the fair value of the FitzPatrick assets acquired and liabilities assumed were preliminary. Accounting guidance provides that the allocation of the purchase price may be modified up to one year from the date of the acquisition to the extent that additional information is obtained about the facts and circumstances that existed as of the acquisition date. During the third quarter of 2017, certain modifications were made to the initial preliminary valuation amounts for acquired property, plant and equipment, the decommissioning ARO, pension and OPEB obligations and related deferred tax liabilities, resulting in a $3 million net increase in assets acquired and liabilities assumed. Additionally, in the third quarter a purchase price settlement payment of $4 million was received from Entergy. These resulted in an adjustment to the after-tax bargain purchase gain recorded at Generation. For the year ended December 31, 2017 , the after-tax bargain purchase gain of $233 million is included within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income and primarily reflects differences in strategies between Generation and Entergy for the intended use and ultimate decommissioning of the plant. There are no further adjustments expected to be made to the allocation of the purchase price. See Note 15 - Asset Retirement Obligations and Note 16 - Retirement Benefits for additional information regarding the FitzPatrick decommissioning ARO and pension and OPEB updates. The following table summarizes the final acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the FitzPatrick acquisition by Generation as of December 31, 2017 : Cash paid for purchase price $ 110 Cash paid for net cost reimbursement 125 Nuclear fuel transfer 54 Total consideration transferred $ 289 Identifiable assets acquired and liabilities assumed Current assets $ 60 Property, plant and equipment 298 Nuclear decommissioning trust funds 807 Other assets (a) 114 Total assets $ 1,279 Current liabilities $ 6 Nuclear decommissioning ARO 444 Pension and OPEB obligations 33 Deferred income taxes 149 Spent nuclear fuel obligation 110 Other liabilities 15 Total liabilities $ 757 Total net identifiable assets, at fair value $ 522 Bargain purchase gain (after-tax) $ 233 _________ (a) Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23 - Commitments and Contingencies for additional background regarding SNF obligations to the DOE. For the year ended December 31, 2017 , Exelon and Generation incurred $57 million of merger and integration related costs which are included within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Acquisition of ConEdison Solutions (Exelon and Generation) On September 1, 2016, Generation acquired the competitive retail electricity and natural gas business of Consolidated Edison Solutions, Inc. (ConEdison Solutions), a subsidiary of Consolidated Edison, Inc. for a purchase price of $257 million including net working capital of $204 million . The renewable energy, sustainable services and energy efficiency businesses of ConEdison Solutions are excluded from the transaction. The fair values of ConEdison Solutions' assets and liabilities were determined based on significant estimates and assumptions that are judgmental in nature, including projected future cash flows (including timing), discount rates reflecting risk inherent in the future cash flows and future power and fuel market prices. The purchase price equaled the estimated fair value of the net assets acquired and the liabilities assumed and, therefore, no goodwill or bargain purchase was recorded as of the acquisition date. The purchase price allocation is now final. The following table summarizes the final acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the ConEdison Solutions acquisition by Generation: Total consideration transferred $ 257 Identifiable assets acquired and liabilities assumed Working capital assets $ 204 Property, plant and equipment 2 Mark-to-market derivative assets 6 Unamortized energy contract assets 100 Customer relationships 9 Other assets 1 Total assets $ 322 Mark-to-market derivative liabilities $ 65 Total liabilities $ 65 Total net identifiable assets, at fair value $ 257 Merger with Pepco Holdings, Inc. (Exelon) Description of Transaction On March 23, 2016 , Exelon completed the merger contemplated by the Merger Agreement among Exelon, Purple Acquisition Corp., a wholly owned subsidiary of Exelon (Merger Sub) and Pepco Holdings, Inc. (PHI). As a result of that merger, Merger Sub was merged into PHI (the PHI Merger) with PHI surviving as a wholly owned subsidiary of Exelon and Exelon Energy Delivery Company, LLC (EEDC), a wholly owned subsidiary of Exelon which also owns Exelon's interests in ComEd, PECO and BGE (through a special purpose subsidiary in the case of BGE). Following the completion of the PHI Merger, Exelon and PHI completed a series of internal corporate organization restructuring transactions resulting in the transfer of PHI’s unregulated business interests to Exelon and Generation and the transfer of PHI, Pepco, DPL and ACE to a special purpose subsidiary of EEDC. Regulatory Matters Approval of the merger in Delaware, New Jersey, Maryland and the District of Columbia was conditioned upon Exelon and PHI agreeing to certain commitments including where applicable: customer rate credits, funding for energy efficiency and delivery system modernization programs, a green sustainability fund, workforce development initiatives, charitable contributions, renewable generation and other required commitments. In addition, the orders approving the merger in Delaware, New Jersey, and Maryland include a “most favored nation” provision which, generally, requires allocation of merger benefits proportionally across all the jurisdictions. During the third and fourth quarters of 2016, Exelon and PHI filed proposals in Delaware, New Jersey and Maryland for amounts and allocations reflecting the application of the most favored nation provision, resulting in a total nominal cost of commitments of $513 million excluding renewable generation commitments (approximately $444 million on a net present value basis amount, excluding renewable generation commitments and charitable contributions). These filings reflected agreements reached with certain parties to the merger proceedings in these jurisdictions. In 2016, the DPSC and NJBPU approved the amounts and allocations of the additional merger benefits for Delaware and New Jersey, respectively. On April 12, 2017, the MDPSC issued an order approving the amounts of the additional merger benefits for Maryland, but amending the proposed allocations of the benefits. The amended allocations do not have a material effect on any of the Registrants' financial statements. No changes in commitment cost levels are required in the District of Columbia. During the second quarter of 2017, Exelon finalized the application of $8 million funding for low- and moderate-income customers in the Pepco Maryland and DPL Maryland service territories. This resulted in an adjustment to merger commitment costs recorded at Exelon Corporate, Pepco, and DPL. Exelon Corporate recorded an increase of $8 million and Pepco and DPL recorded a decrease of $6 million and $2 million , respectively, in Operating and maintenance expense. The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date: Expected Payment Period Successor Description Pepco DPL ACE PHI Exelon Rate credits 2016 - 2017 $ 91 $ 67 $ 101 $ 259 $ 259 Energy efficiency 2016 - 2021 — — — — 122 Charitable contributions 2016 - 2026 28 12 10 50 50 Delivery system modernization Q2 2017 — — — — 22 Green sustainability fund Q2 2017 — — — — 14 Workforce development 2016 - 2020 — — — — 17 Other 1 5 — 6 29 Total $ 120 $ 84 $ 111 $ 315 $ 513 Pursuant to the orders approving the merger, Exelon made $73 million , $46 million and $49 million of equity contributions to Pepco, DPL and ACE, respectively, in the second quarter of 2016 to fund the after-tax amounts of the customer bill credit and the customer base rate credit commitments. In addition, Exelon is committed to develop or to assist in the commercial development of approximately 37 MWs of new generation in Maryland, District of Columbia, and Delaware, 27 MWs of which are expected to be completed by 2018. These investments are expected to total approximately $137 million , are expected to be primarily capital in nature, and will generate future earnings at Exelon and Generation. Investment costs will be recognized as incurred and recorded on Exelon's and Generation's financial statements. Exelon has also committed to purchase 100 MWs of wind energy in PJM, to procure 120 MWs of wind RECs for the purpose of meeting Delaware's renewable portfolio standards, and to maintain and promote energy efficiency and demand response programs in the PHI jurisdictions. Pursuant to the various jurisdictions' merger approval conditions, over specified periods Pepco, DPL and ACE are not permitted to reduce employment levels due to involuntary attrition associated with the merger integration process and have made other commitments regarding hiring and relocation of positions. In July 2015, the OPC, Public Citizen, Inc., the Sierra Club and the Chesapeake Climate Action Network (CCAN) filed motions to stay the MDPSC order approving the merger. The Circuit Court judge issued an order denying the motions for stay on August 12, 2015. On January 8, 2016, the Circuit Court judge affirmed the MDPSC’s order approving the merger and denied the petitions for judicial review filed by the OPC, the Sierra Club, CCAN and Public Citizen, Inc. On January 19, 2016, the OPC filed a notice of appeal to the Maryland Court of Special Appeals, and on January 21, the Sierra Club and CCAN filed notices of appeal. On January 27, 2017, the Maryland Court of Special Appeals affirmed the Circuit Court's judgment that the MDPSC did not err in approving the merger. The OPC and Sierra Club filed petitions seeking further review in the Court of Appeals of Maryland, which is the highest court in Maryland. On June 21, 2017, the Court of Appeals granted discretionary review of the January 27, 2017 decision by the Maryland Court of Special Appeals. The Maryland Court of Appeals will review the OPC argument that the MDPSC did not properly consider the acquisition premium paid to PHI shareholders under Maryland’s merger approval st and ard and the Sierra Club’s argument that the merger would harm the renewable and distributed generation markets. The two lower courts examining these issues rejected these arguments, which Exelon believes are without merit. All briefs have been filed and oral arguments were presented to the court on October 10, 2017. Between March 25, 2016 and April 22, 2016, various parties filed motions with the DCPSC to reconsider its March 23, 2016 order approving the merger. On June 17, 2016, the DCPSC denied all motions. In August 2016, the District Legal Entity of Columbia Office of People’s Counsel, the District of Columbia Government, and Public Citizen jointly with DC Sun each filed petitions for judicial review of the DCPSC’s March 23, 2016 order with the District of Columbia Court of Appeals. On July 20, 2017, the Court issued an opinion rejecting all of appellants’ arguments and affirming the Commission’s decision approving the merger. Accounting for the Merger Transaction The total purchase price consideration of approximately $7.1 billion for the PHI Merger consisted of cash paid to PHI shareholders, cash paid for PHI preferred securities and cash paid for PHI stock-based compensation equity awards as follows: (In millions of dollars, except per share data) Total Consideration Cash paid to PHI shareholders at $27.25 per share (254 million shares outstanding at March 23, 2016) $ 6,933 Cash paid for PHI preferred stock 180 Cash paid for PHI stock-based compensation equity awards (a) 29 Total purchase price $ 7,142 __________ (a) PHI’s unvested time-based restricted stock units and performance-based restricted stock units issued prior to April 29, 2014 were immediately vested and paid in cash upon the close of the merger. PHI’s remaining unvested time-based restricted stock units as of the close of the merger were cancelled. There were no remaining unvested performance-based restricted stock units as of the close of the merger. PHI shareholders received $27.25 of cash in exchange for each share of PHI common stock outstanding as of the effective date of the merger. In connection with the Merger Agreement, Exelon entered into a Subscription Agreement under which it purchased $180 million of a new class of nonvoting, nonconvertible and nontransferable preferred securities of PHI prior to December 31, 2015. On March 23, 2016 , the preferred securities were cancelled for no consideration to Exelon, and accordingly, the $180 million cash consideration previously paid to acquire the preferred securities was treated as purchase price consideration. The preliminary valuations performed in the first quarter of 2016 were updated in the second, third, and fourth quarters of 2016. There were no adjustments to the purchase price allocation in the first quarter of 2017 and the purchase price allocation is now final. Exelon applied push-down accounting to PHI, and accordingly, the PHI assets acquired and liabilities assumed were recorded at their estimated fair values on Exelon’s and PHI's Consolidated Balance Sheets as follows: Purchase Price Allocation (a) Current assets $ 1,441 Property, plant and equipment 11,088 Regulatory assets 5,015 Other assets 248 Goodwill 4,005 Total assets $ 21,797 Current liabilities $ 2,752 Unamortized energy contracts 1,515 Regulatory liabilities 297 Long-term debt, including current maturities 5,636 Deferred income taxes 3,447 Pension and OPEB obligations 821 Other liabilities 187 Total liabilities $ 14,655 Total purchase price $ 7,142 __________ (a) Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances. On its successor financial statements, PHI has recorded, beginning March 24, 2016, Membership interest equity of $7.2 billion , which is greater than the total $7.1 billion purchase price, reflecting the impact of a $59 million deferred tax liability recorded only at Exelon Corporate to reflect unitary state income tax consequences of the merger. The excess of the purchase price over the estimated fair value of the assets acquired and the liabilities assumed totaled $4.0 billion , which was recognized as goodwill by PHI and Exelon at the acquisition date, reflecting the value associated with enhancing Exelon's regulated utility portfolio of businesses, including the ability to leverage experience and best practices across the utilities and the opportunities for synergies. For purposes of future required impairment assessments, the goodwill has been assigned to PHI's reportable units Pepco, DPL and ACE in the amounts of $1.7 billion , $1.1 billion and $1.2 billion , respectively. None of this goodwill is expected to be tax deductible. Immediately following closing of the merger, $235 million of net assets included in the table above associated with PHI's unregulated business interests were distributed by PHI to Exelon. Exelon contributed $163 million of such net assets to Generation. The fair values of PHI's assets and liabilities were determined based on significant estimates and assumptions that are judgmental in nature, including projected future cash flows (including timing), discount rates reflecting risk inherent in the future cash flows, future market prices and impacts of utility rate regulation. There were also judgments made to determine the expected useful lives assigned to each class of assets acquired. Through its wholly owned rate regulated utility subsidiaries, most of PHI’s assets and liabilities are subject to cost-of-service rate regulation. Under such regulation, rates charged to customers are established by a regulator to provide for recovery of costs and a fair return on invested capital, or rate base, generally measured at historical cost. In applying the acquisition method of accounting, for regulated assets and liabilities included in rate base or otherwise earning a return (primarily property, plant and equipment and regulatory assets earning a return), no fair value adjustments were recorded as historical cost is viewed as a reasonable proxy for fair value. Fair value adjustments were applied to the historical cost bases of other assets and liabilities subject to rate regulation but not earning a return (including debt instruments and pension and OPEB obligations). In these instances, a corresponding offsetting regulatory asset or liability was also established, as the underlying utility asset and liability amounts are recoverable from or refundable to customers at historical cost (and not at fair value) through the rate setting process. Similar treatment was applied for fair value adjustments to record intangible assets and liabilities, such as for electricity and gas energy supply contracts as further described below. Regulatory assets and liabilities established to offset fair value adjustments are amortized in amounts and over time frames consistent with the realization or settlement of the fair value adjustments, with no impact on reported net income. See Note 3 - Regulatory Matters for additional information regarding the fair value of regulatory assets and liabilities established by Exelon and PHI. Fair value adjustments were recorded at Exelon and PHI for the difference between the contract price and the market price of electricity and gas energy supply contracts of PHI’s wholly owned rate regulated utility subsidiaries. These adjustments are intangible assets and liabilities classified as unamortized energy contracts on Exelon’s and PHI’s Consolidated Balance Sheets as of December 31, 2017 . The difference between the contract price and the market price at the acquisition date of the Merger was recognized for each contract as either an intangible asset or liability. In total, Exelon and PHI recorded a net $1.5 billion liability reflecting out-of-the-money contracts. The valuation of the acquired intangible assets and liabilities was estimated by applying either the market approach or the income approach depending on the nature of the underlying contract. The market approach was utilized when prices and other relevant information generated by market transactions involving comparable transactions were available. Otherwise the income approach, which is based upon discounted projected future cash flows associated with the underlying contracts, was utilized. In certain instances, the valuations were based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key estimates and inputs include forecasted power prices and the discount rate. The unamortized energy contract fair value adjustment amounts and the corresponding offsetting regulatory asset and liability amounts are amortized through Purchased power and fuel expense or Operating revenues, as applicable, over the life of the applicable contract in relation to the present value of the underlying cash flows as of the merger date. As mentioned, under cost-of-service rate regulation, rates charged to customers are established by a regulator to provide for recovery of costs and a fair return on invested capital, or rate base, generally measured at historical cost. Historical cost information therefore is the most relevant presentation for the financial statements of PHI’s rate regulated utility subsidiary registrants, Pepco, DPL and ACE. As such, Exelon and PHI did not push-down the application of acquisition accounting to PHI's utility registrants, and therefore the financial statements of Pepco, DPL and ACE do not reflect the revaluation of any assets and liabilities. The current impact of PHI, including its unregulated businesses, on Exelon's Consolidated Statements of Operations and Comprehensive Income includes Operating revenues of $4,829 million and Net income of $364 million during the year ended December 31, 2017 , and Operating revenues of $3,785 million and Net loss of $ (66) million for the year ended December 31, 2016 . For the periods ended December 31, 2017 and 2016 , the Registrants have recognized costs to achieve the PHI acquisition as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2017 2016 Exelon $ 16 $ 143 Generation 22 37 ComEd (b) 1 (6 ) PECO 4 5 BGE (b) 4 (1 ) Pepco (b) (6 ) 28 DPL (b) (7 ) 20 ACE (b) (6 ) 19 Successor Predecessor Acquisition, Integration and Financing Costs (a) For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI (b) $ (18 ) $ 69 $ 29 ______________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above. (b) For the year ended December 31, 2017 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million , $8 million , $8 million , and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million , $6 million , $11 million , and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information. Pro-forma Impact of the Merger The following unaudited pro-forma financial information reflects the consolidated results of operations of Exelon as if the merger with PHI had taken place on January 1, 2015 . The unaudited pro forma information was calculated after applying Exelon’s accounting policies and adjusting PHI’s results to reflect purchase accounting adjustments. The unaudited pro-forma financial information has been presented for illustrative purposes only and is not necessarily indicative of results of operations that would have been achieved had the merger events taken place on the dates indicated, or the future consolidated results of operations of the combined company. Year Ended December 31, 2016 (a) 2015 (b) Total operating revenues $ 32,342 $ 33,823 Net income attributable to common shareholders 1,562 2,618 Basic earnings per share $ 1.69 $ 2.85 Diluted earnings per share 1.69 2.84 ______________ (a) The amounts above exclude non-recurring costs directly related to the merger of $680 million and intercompany revenue of $171 million for the year ended December 31, 2016 . (b) The amounts above exclude non-recurring costs directly related to the merger of $92 million and intercompany revenue of $559 million for the year ended December 31, 2015 . Asset Dispositions (Exelon, Generation, PHI, Pepco and DPL) EGTP, a Delaware limited liability company, was formed in 2014 with the purpose of financing a portfolio of assets comprised of two combined-cycle gas turbines (CCGTs) and three peaking/simple cycle facilities consisting of approximately 3.4 GW of generation capacity in ERCOT North and Houston Zones. EGTP is an indirect wholly owned subsidiary of Exelon and Generation. Each of the aforementioned facilities are held through a wholly owned direct subsidiary of EGTP. EGTP also owns two equity method investments in shared facility companies. EGTP, its direct parent and its wholly owned subsidiaries secured a nonrecourse senior secured term loan facility, a revolving loan facility and certain commodity and interest rate swaps. EGTP’s operating cash flows were negatively impacted by certain market conditions and the seasonality of its cash flows. On May 2, 2017, as a result of the negative impacts of certain market conditions and the seasonality of its cash flows, EGTP entered into a consent agreement with its lenders to permit EGTP to draw on its revolving credit facility and initiate an orderly sales process to sell the assets of its wholly owned subsidiaries. As a result, Exelon and Generation classified certain of EGTP assets and liabilities as held for sale at their respective fair values less costs to sell and recorded a $460 million pre-tax impairment loss . See Note 13 - Debt and Credit Agreements for details regarding the nonrecourse debt associated with EGTP and Note 7 - Impairment of Long-Lived Assets and Intangibles for further information. On November 7, 2017, EGTP and all of its wholly owned subsidiaries (collectively with EGTP, the "Debtors") filed voluntary petitions for relief under Chapter 11 of Title 11 of the United States Code in the United States Bankruptcy Court for the District of Delaware. The Debtors sought Bankruptcy Court authorization to jointly administer the Chapter 11 cases. The Debtors are continuing to manage their assets and operate their businesses as "debtors in possession" under the jurisdiction of the Bankruptcy Court and in accordance with the applicable provisions of the Bankruptcy Code and the orders of the Bankruptcy Court. As a result of the bankruptcy filing, Exelon and Generation deconsolidated EGTP's assets and liabilities from their consolidated financial statements, resulting in a pre-tax gain upon deconsolidation of $213 million . Concurrently with the Chapter 11 filings, Generation entered into an asset purchase agreement to acquire one of EGTP’s generating plants, the Handley Generating Station, for approximately $60 million , subject to a potential adjustment for fuel oil and assumption of certain liabilities. In the Chapter 11 Filings, EGTP requested that the proposed acquisition of the Handley Generating Station be consummated through a court-approved and supervised sales process. The acquisition was approved by the Bankruptcy Court in January 2018 and the transaction is expected to be completed in the first half of 2018. In December 2017, Pepco Building Services, Inc. entered into a purchase and sale agreement to sell its interest in an electrical contracting business that primarily installs, maintains and repairs underground and high-voltage cable transmission and distribution systems. The closing of the sale is expected to be completed in the first quarter of 2018. As a result, as of December 31, 2017 , certain assets and liabilities were classified as held for sale at their respective fair values less costs to sell and included in the Other current assets and Other current liabilities balances on Exelon's and Generation's Consolidated Balance Sheet. During the fourth quarter 2016, as part of its continual assessment of growth and development opportunities, Generation reevaluated and in certain instances terminated or renegotiated certain projects and contracts. As a result, a pre-tax loss of $69 million was recorded within Loss on sale of assets and pre-tax impairment charges of $23 million was recorded within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. In July 2016, DPL completed the sale of a 9-acre land parcel located on South Madison Street in Wilmington, DE, resulting in a pre-tax gain of approximately $4 million . In December 2016, DPL completed the sale of a 48-acre land parcel located in Middletown, DE, resulting in a pre-tax gain of approximately $5 million . Due to the fair value adjustments recorded at Exelon and PHI as part of purchase accounting, no gain was recorded in Exelon's and PHI's Consolidated Statements of Operations and Comprehensive Income. On June 16, 2016, Generation initiated the sales process of its Upstream business by executing a forbearance agreement with the lenders of the nonrecourse debt. See Note 13 - Debt and Credit Agreements for more information. In December 2016, Generation sold substantially all of the Upstream assets for $37 million which resulted in a pre-tax loss on sale of $10 million which is included in Gain (loss) on sales of assets on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2016. On May 2, 2016, Pepco completed the sale of the New York Avenue land parcel, located in Washington, D.C., resulting in a pre-tax gain of approximately $8 million at Pepco. Due to the fair value adjustments recorded at Exelon and PHI as part of purchase accounting, no gain was recorded in Exelon's and PHI's Consolidated Statements of Operations and Comprehensive Income. On April 21, 2016, Generation completed the sale of the retired New Boston generating site, located in Boston, Massachusetts, resulting in a pre-tax gain of approximately $32 million . On November 10, 2015, Pepco completed the sale of a 3.5-acre parcel of unimproved land (held as non-utility property) in the Buzzard Point area of southeast Washington, D.C., resulting in a pre-tax gain of $37 million . On December 31, 2015, Pepco completed the sale of a 3.8-acre parcel of unimproved land (held as non-utility property) in the NoMa area of northeast Washington, D.C., resulting in a pre-tax gain of $9 million . The purchase and sale agreement also provided the third party with a 90-day option to purchase the remaining 1.8-acre land parcel.

Accounts Receivable (All Regist

Accounts Receivable (All Registrants)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Accounts Receivable (All Registrants)	Accounts Receivable (All Registrants) Accounts receivable at December 31, 2017 and 2016 included estimated unbilled revenues, representing an estimate for the unbilled amount of energy or services provided to customers, and is net of an allowance for uncollectible accounts as follows: Successor 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer $ 1,858 $ 1,017 (a) $ 242 $ 162 $ 205 $ 232 $ 133 $ 68 $ 31 Allowance for uncollectible (b) (322 ) (114 ) (73 ) (56 ) (c) (24 ) (55 ) (21 ) (16 ) (18 ) Successor 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues $ 1,673 $ 910 (a) $ 219 $ 140 $ 182 $ 222 $ 123 $ 58 $ 41 Allowance for uncollectible (b) (334 ) (91 ) (70 ) (61 ) (c) (32 ) (80 ) (d) (29 ) (d) (24 ) (d) (27 ) (d) __________ (a) Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable. (c) Excludes the non-current allowance for uncollectible accounts of $15 million and $23 million at December 31, 2017 and 2016 , respectively, related to PECO’s current installment plan receivables described below. (d) At December 31, 2016 , as explained in Note 1 — Significant Accounting Policies , PHI, Pepco, DPL and ACE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in an overall increase of $30 million , $14 million , $8 million , and $8 million in the allowance for uncollectible accounts with $20 million , $8 million , $4 million , and $8 million deferred as a regulatory asset on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets at December 31, 2016, respectively. This also resulted in a $10 million , $6 million , and $4 million pre-tax charge to provision for uncollectible accounts expense for the year ended December 31, 2016 , which is included in Operating and maintenance expense on PHI's, Pepco's and DPL's Consolidated Statements of Operations and Comprehensive Income, respectively. PECO Installment Plan Receivables (Exelon and PECO) PECO enters into payment agreements with certain delinquent customers, primarily residential, seeking to restore their service, as required by the PAPUC. Customers with past due balances that meet certain income criteria are provided the option to enter into an installment payment plan, some of which have terms greater than one year, to repay past due balances in addition to paying for their ongoing service on a current basis. The receivable balance for these payment agreement receivables is recorded in accounts receivable for the current portion and other deferred debits and other assets for the noncurrent portion. The net receivable balance for installment plans with terms greater than one year was $11 million and $9 million at December 31, 2017 and 2016 , respectively. The allowance for uncollectible accounts reserve methodology and assessment of the credit quality of the installment plan receivables are consistent with the customer accounts receivable methodology discussed in Note 1 — Significant Accounting Policies . The allowance for uncollectible accounts balance associated with these receivables at December 31, 2017 of $11 million consists of $3 million and $8 million for medium risk and high-risk segments, respectively. The allowance for uncollectible accounts balance associated with these receivables at December 31, 2016 of $13 million consists of $1 million , $3 million and $9 million for low risk, medium risk and high risk-segments, respectively. The balance of the payment agreement is billed to the customer in equal monthly installments over the term of the agreement. Installment receivables outstanding as of December 31, 2017 and 2016 include balances not yet presented on the customer bill, accounts currently billed and an immaterial amount of past due receivables. When a customer defaults on its payment agreement, the terms of which are defined by plan type, the entire balance of the agreement becomes due and the balance is reclassified to current customer accounts receivable and reserved for in accordance with the methodology discussed in Note 1 — Significant Accounting Policies .

Property, Plant and Equipment (

Property, Plant and Equipment (All Registrants)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment (All Registrants)	Property, Plant and Equipment (All Registrants) Exelon The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-90 $ 49,506 $ 45,698 Electric—generation 2-56 29,019 27,193 Gas—transportation and distribution 5-90 5,050 4,642 Common—electric and gas 5-75 1,447 1,312 Nuclear fuel (a) 1-8 6,420 6,546 Construction work in progress N/A 2,825 4,306 Other property, plant and equipment (b) 2-50 999 1,027 Total property, plant and equipment 95,266 90,724 Less: accumulated depreciation (c) 21,064 19,169 Property, plant and equipment, net $ 74,202 $ 71,555 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016 , respectively. The original cost basis of the buildings was $47 million and $52 million , and total accumulated amortization was $40 million and $42 million , as of December 31, 2017 and 2016 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 , of $7 million . The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016 . Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $44 million , $21 million , $26 million , $59 million , $15 million and $27 million , respectively, at December 31, 2017 . Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016 , respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017 . (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $3,159 million and $3,186 million as of December 31, 2017 and 2016 , respectively. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.75 % 2.73 % 2.83 % Electric—generation (a) 4.36 % (a) 5.94 % (a) 3.47 % Gas 2.10 % 2.17 % 2.17 % Common—electric and gas 7.05 % 7.41 % 7.79 % __________ (a) See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI. Generation The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—generation 2-56 $ 29,019 $ 27,193 Nuclear fuel (a) 1-8 6,420 6,546 Construction work in progress N/A 838 2,332 Other property, plant and equipment (b) 2-3 57 76 Total property, plant and equipment 36,334 36,147 Less: accumulated depreciation (c) 11,428 10,562 Property, plant and equipment, net $ 24,906 $ 25,585 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016 , respectively. (b) Includes buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016 , respectively. The original cost basis of the buildings was $47 million and $52 million , and total accumulated amortization was $40 million and $42 million , as of December 31, 2017 and 2016 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016 , respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017 . (c) Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million and $3,186 million as of December 31, 2017 and 2016 , respectively. The annual depreciation provisions as a percentage of average service life for electric generation assets were 4.36% , 5.94% and 3.47% for the years ended December 31, 2017 , 2016 and 2015 , respectively. See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI. License Renewals Generation’s depreciation provisions are based on the estimated useful lives of its generating stations, which reflect the renewal of the licenses for all nuclear generating stations (except for Oyster Creek, Clinton and TMI) and the hydroelectric generating stations. As a result, the receipt of license renewals has no material impact on the Consolidated Statements of Operations and Comprehensive Income. Clinton depreciation provisions are based on 2027 which is the last year of the Illinois ZECs. In 2017, Oyster Creek and TMI depreciation provisions were based on their 2019 expected shutdown dates. Beginning February 2018, Oyster Creek depreciation provisions will be based on its announced shutdown date of 2018. See Note 3 — Regulatory Matters for additional information regarding license renewals and the Illinois ZECs. See Note 8 — Early Nuclear Plant Retirements for additional information on the impacts of expected and potential early plant retirement. ComEd The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-80 $ 24,423 $ 22,636 Construction work in progress N/A 517 569 Other property, plant and equipment (a), (b) 36-50 52 67 Total property, plant and equipment 24,992 23,272 Less: accumulated depreciation 4,269 3,937 Property, plant and equipment, net $ 20,723 $ 19,335 __________ (a) Includes buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 of $7 million . The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016 . (b) Includes land held for future use and non-utility property. The annual depreciation provisions as a percentage of average service life for electric transmission and distribution assets were 2.99% , 3.03% and 3.03% for the years ended December 31, 2017 , 2016 and 2015 , respectively. PECO The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-65 $ 7,975 $ 7,591 Gas—transportation and distribution 5-70 2,504 2,348 Common—electric and gas 5-50 710 670 Construction work in progress N/A 254 188 Other property, plant and equipment (a) 50 21 21 Total property, plant and equipment 11,464 10,818 Less: accumulated depreciation 3,411 3,253 Property, plant and equipment, net $ 8,053 $ 7,565 __________ (a) Represents land held for future use and non-utility property. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.37 % 2.32 % 2.39 % Gas 1.89 % 1.82 % 1.87 % Common—electric and gas 5.47 % 5.11 % 5.16 % BGE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-90 $ 7,464 $ 7,067 Gas—distribution 5-90 2,379 2,170 Common—electric and gas 5-40 771 707 Construction work in progress N/A 367 318 Other property, plant and equipment (a) 20 26 32 Total property, plant and equipment 11,007 10,294 Less: accumulated depreciation 3,405 3,254 Property, plant and equipment, net $ 7,602 $ 7,040 __________ (a) Represents land held for future use and non-utility property. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.58 % 2.56 % 2.62 % Gas 2.33 % 2.45 % 2.50 % Common—electric and gas 8.64 % 9.45 % 10.35 % PHI The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Successor Average 2017 2016 Asset Category Electric—transmission and distribution 5-75 $ 11,517 $ 10,315 Gas—distribution 5-75 449 414 Common—electric and gas 5-75 82 65 Construction work in progress N/A 835 892 Other property, plant and equipment (a) 3-43 102 107 Total property, plant and equipment 12,985 11,793 Less: accumulated depreciation 487 — 195 Property, plant and equipment, net $ 12,498 $ 11,598 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.63 % 2.52 % 2.48 % Gas 2.07 % 2.57 % 2.55 % Common—electric and gas 6.50 % 8.12 % 5.19 % Pepco The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-75 $ 8,646 $ 8,018 Construction work in progress N/A 473 537 Other property, plant and equipment (a) 25-33 59 66 Total property, plant and equipment 9,178 8,621 Less: accumulated depreciation 3,177 — 3,050 Property, plant and equipment, net $ 6,001 $ 5,571 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The annual depreciation provisions as a percentage of average service life for electric transmission and distribution assets were 2.35% , 2.17% and 2.13% for the years ended December 31, 2017 , 2016 and 2015 , respectively. DPL The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-70 $ 3,875 $ 3,574 Gas—distribution 5-75 614 580 Common—electric and gas 5-75 117 115 Construction work in progress N/A 205 163 Other property, plant and equipment (a) 10-43 15 16 Total property, plant and equipment 4,826 4,448 Less: accumulated depreciation 1,247 — 1,175 Property, plant and equipment, net $ 3,579 $ 3,273 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.75 % 2.49 % 2.44 % Gas 2.07 % 2.57 % 2.55 % Common—electric and gas 4.14 % 4.99 % 4.24 % ACE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-60 $ 3,607 $ 3,341 Construction work in progress N/A 138 169 Other property, plant and equipment (a) 13-15 27 27 Total property, plant and equipment 3,772 3,537 Less: accumulated depreciation 1,066 — 1,016 Property, plant and equipment, net $ 2,706 $ 2,521 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The annual depreciation provisions as a percentage of average service life for electric transmission and distribution assets were 2.46% , 2.45% and 2.46% for the years ended December 31, 2017 , 2016 and 2015 , respectively. See Note 1 — Significant Accounting Policies for further information regarding property, plant and equipment policies and accounting for capitalized software costs for the Registrants. See Note 13 — Debt and Credit Agreements for further information regarding Exelon’s, ComEd’s and PECO’s property, plant and equipment subject to mortgage liens.

Impairment of Long-lived Assets

Impairment of Long-lived Assets (Exelon and Generation)	12 Months Ended
	Dec. 31, 2017
Impairment or Disposal of Tangible Assets Disclosure [Abstract]
Impairment Of Long-Lived Assets (Exelon and Generation)	(Exelon, Generation and PHI) Long-Lived Assets (Exelon, Generation and PHI) Registrants evaluate long-lived assets for recoverability whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. At Generation, EGTP’s operating cash flows have been negatively impacted by certain market conditions and the seasonality of its cash flows. On May 2, 2017, EGTP entered into a consent agreement with its lenders to initiate an orderly sales process to sell the assets of its wholly owned subsidiaries. As a result, Exelon and Generation classified certain of EGTP's assets and liabilities as held for sale at their respective fair values less costs to sell and recorded a pre-tax impairment charge of $460 million within Operating and maintenance expense on their Consolidated Statements of Operations and Comprehensive Income during 2017. On November 7, 2017, EGTP and its wholly owned subsidiaries filed voluntary petitions for relief under Chapter 11 of Title 11 of the United States Code in the United States Bankruptcy Court for the District of Delaware and, as a result, Exelon and Generation deconsolidated EGTP's assets and liabilities from their consolidated financial statements. See Note 4 — Mergers, Acquisitions and Dispositions and Note 13 — Debt and Credit Agreements , for further information. In the third quarter of 2015, PHI entered into a sponsorship agreement with the District of Columbia for future sponsorship rights associated with public property within the District of Columbia and paid the District of Columbia $25 million , which Exelon and PHI had recorded as a finite-lived intangible asset as of December 31, 2016. The specific sponsorship rights were to be determined over time through future negotiations. In the fourth quarter of 2017, based upon the lack of currently available sponsorship opportunities, the asset was written off and a pre-tax impairment charge of $25 million was recorded within Operating and maintenance expense in Exelon’s and PHI’s Consolidated Statements of Operations and Comprehensive Income. During the first quarter of 2016, significant changes in Generation’s intended use of the Upstream oil and gas assets, developments with nonrecourse debt held by its Upstream subsidiary CEU Holdings, LLC (as described in Note 13 — Debt and Credit Agreements ) and continued declines in both production volumes and commodity prices suggested that the carrying value may be impaired. Generation concluded that the estimated undiscounted future cash flows and fair value of its Upstream properties were less than their carrying values. As a result, a pre-tax impairment charge of $119 million was recorded in March 2016 within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. On June 16, 2016, Generation initiated the sales process of its Upstream natural gas and oil exploration and production business by executing a forbearance agreement with the lenders of the nonrecourse debt, see Note 13 — Debt and Credit Agreements for additional information. An additional pre-tax impairment charge of $15 million was recorded in September 2016 within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income due to further declines in fair value. In December 2016, Generation sold substantially all of the Upstream Assets. See Note 4 — Mergers, Acquisitions and Dispositions for additional information. In the second quarter of 2016, updates to Exelon's long-term view of energy and capacity prices suggested that the carrying value of a group of merchant wind assets, located in West Texas, may be impaired. Upon review, the estimated undiscounted future cash flows and fair value of the group were less than their carrying value. The fair value analysis was based on the income approach using significant unobservable inputs (Level 3) including revenue and generation forecasts, projected capital and maintenance expenditures and discount rates. As a result of the fair value analysis, long-lived merchant wind assets held and used with a carrying amount of approximately $60 million were written down to their fair value of $24 million and a pre-tax impairment charge of $36 million was recorded during the second quarter of 2016 in Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Also in the second quarter of 2016, updates to Exelon's long-term view, as described above, in conjunction with the retirement announcements of the Quad Cities and Clinton nuclear plants in Illinois suggested that the carrying value of our Midwest asset group may be impaired. Generation completed a comprehensive review of the estimated undiscounted future cash flows of the Midwest asset group and no impairment charge was required. The fair value analysis used in the above impairments was primarily based on the income approach using significant unobservable inputs (Level 3) including revenue, generation and production forecasts, projected capital and maintenance expenditures and discount rates. Changes in the assumptions described above could potentially result in future impairments of Exelon’s long-lived assets, which could be material. Like-Kind Exchange Transaction (Exelon) In June 2000, UII, LLC (formerly Unicom Investments, Inc.) (UII), a wholly owned subsidiary of Exelon Corporation, entered into transactions pursuant to which UII invested in coal-fired generating station leases (Headleases) with the Municipal Electric Authority of Georgia (MEAG). The generating stations were leased back to MEAG as part of the transactions (Leases). Pursuant to the applicable authoritative guidance, Exelon is required to review the estimated residual values of its direct financing lease investments at least annually and record an impairment charge if the review indicates an other-than-temporary decline in the fair value of the residual values below their carrying values. Exelon estimates the fair value of the residual values of its direct financing lease investments based on the income approach, which uses a discounted cash flow analysis, taking into consideration significant unobservable inputs (Level 3) including the expected revenues to be generated and costs to be incurred to operate the plants over their remaining useful lives subsequent to the lease end dates. Significant assumptions used in estimating the fair value include fundamental energy and capacity prices, fixed and variable costs, capital expenditure requirements, discount rates, tax rates and the estimated remaining useful lives of the plants. The estimated fair values also reflect the cash flows associated with the service contract option discussed above given that a market participant would take into consideration all of the terms and conditions contained in the lease agreements. All the Headleases were terminated by the second quarter of 2016, and no events occurred prior to the termination that required Exelon to review the estimated residual values of the direct financing lease investments in 2016. On March 31, 2016, UII and MEAG finalized an agreement to terminate the MEAG Headleases, the MEAG Leases, and other related agreements prior to their expiration dates. As a result of the lease termination, UII received an early termination payment of $360 million from MEAG and wrote-off the $356 million net investment in the MEAG Headleases and the Leases. The transaction resulted in a pre-tax gain of $4 million which is reflected in Operating and maintenance expense in Exelon's Consolidated Statements of Operations and Comprehensive Income. See Note 14 — Income Taxes for additional information.

Early Nuclear Plant Retirements

Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Exelon, Generation)	12 Months Ended
	Dec. 31, 2017
Implications of Potential Early Plant Retirements [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	8 . Early Nuclear Plant Retirements (Exelon and Generation) Exelon and Generation continue to evaluate the current and expected economic value of each of Generation’s nuclear plants. Factors that will continue to affect the economic value of Generation’s nuclear plants include, but are not limited to: market power prices, results of capacity auctions, potential legislative and regulatory solutions to ensure nuclear plants are fairly compensated for their carbon-free emissions, and the impact of final rules from the EPA requiring reduction of carbon and other emissions and the efforts of states to implement those final rules. The precise timing of an early retirement date for any nuclear plant, and the resulting financial statement impacts, may be affected by a number of factors, including the status of potential regulatory or legislative solutions, results of any transmission system reliability study assessments, the nature of any co-owner requirements and stipulations, and decommissioning trust fund requirements, among other factors. However, the earliest retirement date for any plant would usually be the first year in which the unit does not have capacity or other obligations, where applicable, and just prior to its next scheduled nuclear refueling outage. In 2015 and 2016, Generation identified the Quad Cities, Clinton, Ginna, Nine Mile Point and Three Mile Island (TMI) nuclear plants as having the greatest risk of early retirement based on economic valuation and other factors. In 2017, PSEG has made public similar financial challenges facing its New Jersey nuclear plants including Salem, of which Generation owns a 42.59% ownership interest. In Illinois, the Clinton and Quad Cities nuclear plants continued to face significant economic challenges and risk of retirement before the end of each unit’s respective operating license period (2026 for Clinton and 2032 for Quad Cities). In April 2016, Clinton cleared the MISO primary reliability auction as a price taker for the 2016-2017 planning year. The resulting capacity price was insufficient to cover cash operating costs and a risk-adjusted rate of return to shareholders. In May 2016, Quad Cities did not clear in the PJM capacity auction for the 2019-2020 planning year. Based on these capacity auction results, and given the lack of progress on Illinois energy legislation and MISO market reforms, on June 2, 2016 Generation announced it would shut down the Clinton and Quad Cities nuclear plants on June 1, 2017 and June 1, 2018, respectively. On December 7, 2016, Illinois FEJA was signed into law by the Governor of Illinois and included a ZES that provides compensation through the procurement of ZECs targeted at preserving the environmental attributes of zero-emissions nuclear-powered generating facilities that meet specific eligibility criteria, much like the solution implemented with the New York CES. The Illinois ZES will have a 10-year duration extending from June 1, 2017 through May 31, 2027. See Note 3 - Regulatory Matters for additional discussion on the Illinois FEJA and the ZES. With the passage of the Illinois ZES, and subject to prevailing over any related potential administrative or legal challenges , in December 2016 Generation reversed its June 2016 decision to permanently cease generation operations at the Clinton and Quad Cities nuclear generating plants. In New York, the Ginna and Nine Mile Point nuclear plants continue to face significant economic challenges and risk of retirement before the end of each unit’s respective operating license period (2029 for Ginna and Nine Mile Point Unit 1, and 2046 for Nine Mile Point Unit 2). On August 1, 2016, the NYPSC issued an order adopting the CES, which would provide payments to Ginna and Nine Mile Point for the environmental attributes of their production. On November 18, 2016, Ginna and Nine Mile Point executed the necessary contracts with NYSERDA, as required under the CES. Subject to prevailing over any administrative or legal challenges, the New York CES will allow Ginna and Nine Mile Point to continue to operate at least through the life of the program (March 31, 2029). The assumed useful life for depreciation purposes is through the end of their current operating licenses. The approved RSSA required Ginna to operate through the RSSA term expiring on March 31, 2017 and required notification to the NYPSC if Ginna did not plan to retire shortly after the expiration of the RSSA. On September 30, 2016, Ginna filed the required notice with the NYPSC of its intent to continue operating beyond the expiry of the RSSA. Refer to Note 3 - Regulatory Matters for additional discussion on the Ginna RSSA and the New York CES. Assuming the successful implementation of the Illinois ZES and the New York CES and the continued effectiveness of these programs, Generation and CENG, through its ownership of Ginna and Nine Mile Point, no longer consider Clinton, Quad Cities, Ginna or Nine Mile Point to be at heightened risk for early retirement. However, to the extent either the Illinois ZES or the New York CES programs do not operate as expected over their full terms, each of these plants could again be at heightened risk for early retirement, which could have a material impact on Exelon’s and Generation’s future results of operations, cash flows and financial positions. In Pennsylvania, the TMI nuclear plant did not clear in the May 2017 PJM capacity auction for the 2020-2021 planning year, the third consecutive year that TMI failed to clear the PJM base residual capacity auction. The plant is currently committed to operate through May 2019 and is licensed to operate through 2034. On May 30, 2017, based on these capacity auction results, prolonged periods of low wholesale power prices, and the absence of federal or state policies that place a value on nuclear energy for its ability to produce electricity without air pollution, Exelon announced that Generation will permanently cease generation operations at TMI on or about September 30, 2019. Generation has filed the required market and regulatory notifications to shut down the plant. PJM has subsequently notified Generation that it has not identified any reliability issues and has approved the deactivation of TMI as proposed. As a result of these plant retirement decisions, Exelon and Generation recognized one-time charges in Operating and maintenance expense related to materials and supplies inventory reserve adjustments, employee-related costs and CWIP impairments, among other items. In addition to these one-time charges, annual incremental non-cash charges to earnings stemming from shortening the expected economic useful lives primarily related to accelerated depreciation of plant assets (including any ARC), accelerated amortization of nuclear fuel, and additional ARO accretion expense associated with the changes in decommissioning timing and cost assumptions were also recorded. See Note 15 — Asset Retirement Obligations for additional detail on changes to the nuclear decommissioning ARO balances. The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2017 (a) 2016 (b) Depreciation and Amortization Accelerated depreciation (c) $ 250 $ 712 Accelerated nuclear fuel amortization 12 60 Operating and Maintenance One-time charges (d,e) 77 26 Change in ARO accretion, net of any contractual offset (f) — 2 Contractual offset for ARC depreciation (f) — (86 ) Total $ 339 $ 714 _________ (a) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (b) Reflects incremental charges for Clinton and Quad Cities including incremental accelerated depreciation and amortization from June 2, 2016 through December 6, 2016. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation updated the expected economic useful life for both facilities, to 2027 for Clinton, commensurate with the end of the Illinois ZES, and to 2032 for Quad Cities, the end of its current operating license. Depreciation was therefore adjusted beginning December 7, 2016, to reflect these extended useful life estimates. (c) Reflects incremental accelerated depreciation of plant assets, including any ARC. (d) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. (e) In June 2016, as a result of the retirement decision for Clinton and Quad Cities, Exelon and Generation recognized one-time charges of $146 million . In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation reversed approximately $120 million of these one-time charges initially recorded in June 2016. (f) For Quad Cities based on the regulatory agreement with the Illinois Commerce Commission, decommissioning-related activities are offset within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The offset results in an equal adjustment to the noncurrent payables to ComEd at Generation and an adjustment to the regulatory liabilities at ComEd. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability. Although Salem is committed to operate through May 2021, the plant faces continued economic challenges and PSEG, as the operator of the plant, is exploring all options. The following table provides the balance sheet amounts as of December 31, 2017 for Generation’s ownership share of the significant assets and liabilities associated with Salem. (in millions) 12/31/2017 Asset Balances Materials and supplies inventory $ 44 Nuclear fuel inventory, net 113 Completed plant, net 439 Construction work in progress 33 Liability Balances Asset retirement obligation (442 ) NRC License Renewal Term 2036 (unit 1) 2040 (unit 2) On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at Oyster Creek at the end of its current operating cycle in October 2018. See Note 28 — Subsequent Events for additional information regarding the early retirement of Oyster Creek.

Jointly Owned Electric Utility

Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, BGE, PHI, Pepco, DPL and ACE)	12 Months Ended
	Dec. 31, 2017
Public Utilities, Property, Plant and Equipment [Abstract]
Jointly Owned Electric Utility Plant	Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, BGE, PHI, Pepco, DPL and ACE) Exelon's, Generation's, PECO's, BGE's, PHI's and ACE's undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2017 and 2016 were as follows: Nuclear Generation Fossil-Fuel Generation Transmission Other Quad Cities Peach Bottom Salem (a) Nine Mile Point Unit 2 Wyman PA (b) NJ/ DE (c) Other (d) Operator Generation Generation PSEG Generation FP&L First PSEG/ DPL various Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % 5.89 % various various various Exelon’s share at December 31, 2017: Plant (e) $ 1,074 $ 1,417 $ 631 $ 839 $ 3 $ 27 $ 102 $ 15 Accumulated depreciation (e) 550 461 205 97 3 15 52 13 Construction work in progress 35 18 33 55 — — — — Exelon’s share at December 31, 2016: Plant (e) $ 1,054 $ 1,384 $ 596 $ 830 $ 3 $ 27 $ 97 $ 15 Accumulated depreciation (e) 515 407 186 68 3 15 52 13 Construction work in progress — 16 41 37 — — — — __________ (a) Generation also owns a proportionate share in the fossil-fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2017 and 2016 . (b) PECO, BGE, Pepco, DPL and ACE own a 22% , 7% , 27% , 9% and 8% share, respectively, in 127 miles of 500 kV lines located in Pennsylvania as well as a 20.72% , 10.56% , 9.72% , 3.72% and 3.83% share, respectively, of a 500 kV substation immediately outside of the Conemaugh fossil-generating station which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (c) PECO, DPL and ACE own a 42.55% , 1% and 13.9% share, respectively in 151.3 miles of 500 kV lines located in New Jersey and Delaware Station. PECO, DPL and ACE also own a 42.55% , 7.45% and 7.45% share, respectively, in 2.5 miles of 500 kV line located over the Delaware River. ACE also has a 21.78% share in a 500 kV New Freedom Switching (d) Generation, DPL and ACE own a 44.24% , 4.83% and 11.91% share, respectively in assets located at Merrill Creek Reservoir located in New Jersey. Pepco, DPL and ACE own a 11.9% , 7.4% and 6.6% share, respectively, in Valley Forge Corporate Center. (e) Excludes asset retirement costs. Exelon’s, Generation’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's undivided ownership interests are financed with their funds and all operations are accounted for as if such participating interests were wholly owned facilities. Exelon’s, Generation’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's share of direct expenses of the jointly owned plants are included in Purchased power and fuel and Operating and maintenance expenses on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income and in Operating and maintenance expenses on PECO’s, BGE’s, Pepco, DPL's and ACE's Consolidated Statements of Operations and Comprehensive Income.

Intangible Assets (All Registra

Intangible Assets (All Registrants)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets (All Registrants)	Intangible Assets (Exelon, Generation, ComEd, PECO, PHI, Pepco, DPL and ACE) Goodwill Exelon’s, Generation's, ComEd’s, PHI's and DPL's gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2017 and 2016 were as follows: Balance at January 1, 2016 Goodwill from business combination Impairment losses Measurement period adjustments (b) Balance at December 31, 2016 Impairment losses Balance at December 31, 2017 Exelon Gross amount $ 4,655 $ 4,016 $ — $ (11 ) $ 8,660 $ — $ 8,660 Accumulated impairment loss 1,983 — — — 1,983 — 1,983 Carrying amount 2,672 4,016 — (11 ) 6,677 — 6,677 Generation Gross amount 47 — — — 47 — 47 Carrying amount 47 — — — 47 — 47 ComEd (a) Gross amount 4,608 — — — 4,608 — 4,608 Accumulated impairment loss 1,983 — — — 1,983 — 1,983 Carrying amount 2,625 — — — 2,625 — 2,625 DPL Gross amount 8 — — — 8 — 8 Carrying amount 8 — — — 8 — 8 For the Year Ended December 31, 2017 Beginning Balance Goodwill from business combination Impairment losses Measurement period adjustments (b) Ending Balance PHI - Successor Gross amount $ 4,005 $ — $ — $ — $ 4,005 Accumulated impairment loss — — — — — Carrying Amount 4,005 — — — 4,005 March 24, 2016 to December 31, 2016 PHI - Successor Gross amount — 4,016 — (11 ) 4,005 Accumulated impairment loss — — — — — Carrying amount — 4,016 — (11 ) 4,005 January 1, 2016 to March 23, 2016 PHI - Predecessor Gross amount 1,418 — — — 1,418 Accumulated impairment loss 12 — — — 12 Carrying amount 1,406 — — — 1,406 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance. (b) Represents various measurement period adjustments to the valuation of the fair value of the PHI assets acquired and liabilities assumed as a result of the merger. Goodwill is not amortized, but is subject to an assessment for impairment at least annually, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of the Exelon, Generation, ComEd, PHI and DPL reporting unit below its carrying amount. Under the authoritative guidance for goodwill, a reporting unit is an operating segment or one level below an operating segment (known as a component) and is the level at which goodwill is tested for impairment. A component of an operating segment is a reporting unit if the component constitutes a business for which discrete financial information is available and its operating results are regularly reviewed by segment management. Generation's operating segments are Mid-Atlantic, Midwest, New England, New York, ERCOT and all other power regions referred to collectively as “Other Power Regions”, PHI's operating segments are Pepco, DPL and ACE, and ComEd and DPL have a single operating segment. See Note 25 — Segment Information for additional information. There is no level below these operating segments for which operating results are regularly reviewed by segment management. Therefore, the ComEd, Pepco, DPL and ACE operating segments are also considered reporting units for goodwill impairment testing purposes. Exelon's and ComEd's $2.6 billion of goodwill has been assigned entirely to the ComEd reporting unit, while Exelon's and PHI's $4 billion of goodwill has been assigned to the Pepco, DPL and ACE reporting units in the amounts of $1.7 billion , $1.1 billion and $1.2 billion , respectively. DPL's $8 million of goodwill is assigned entirely to the DPL reporting unit. Entities assessing goodwill for impairment have the option of first performing a qualitative assessment to determine whether a quantitative assessment is necessary. In performing a qualitative assessment, entities should assess, among other things, macroeconomic conditions, industry and market considerations, overall financial performance, cost factors and entity-specific events. If an entity determines, on the basis of qualitative factors, that the fair value of the reporting unit is more likely than not greater than the carrying amount, no further testing is required. If an entity bypasses the qualitative assessment or performs the qualitative assessment, but determines that it is more likely than not that its fair value is less than its carrying amount, a quantitative two-step, fair value-based test is performed. Exelon's, Generation's, ComEd's, PHI's and DPL's accounting policy is to perform a quantitative test of goodwill at least once every three years. The first step in the quantitative test compares the fair value of the reporting unit to its carrying amount, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the second step is performed. The second step requires an allocation of fair value to the individual assets and liabilities using purchase price allocation accounting guidance in order to determine the implied fair value of goodwill. If the implied fair value of goodwill is less than the carrying amount, an impairment loss is recorded as a reduction to goodwill and a charge to operating expense. Application of the goodwill impairment test requires management judgment, including the identification of reporting units and determining the fair value of the reporting unit, which management estimates using a weighted combination of a discounted cash flow analysis and a market multiples analysis. Significant assumptions used in these fair value analyses include discount and growth rates, utility sector market performance and transactions, projected operating and capital cash flows for Generation's, ComEd's, Pepco's, DPL's and ACE's businesses and the fair value of debt. In applying the second step (if needed), management must estimate the fair value of specific assets and liabilities of the reporting unit. 2017 and 2016 Goodwill Impairment Assessment. Generation performed a quantitative test as of November 1, 2017, for its 2017 annual goodwill impairment assessment. The first step of the test comparing the estimated fair value of Generation's reporting unit with goodwill to its carrying value, including goodwill, indicated no impairments of goodwill; therefore, the second step was not required. Generation performed a qualitative test as of November 1, 2016, for its 2016 annual goodwill impairment assessment. Based on the qualitative factors assessed, Generation concluded that the fair value of its reporting units is more likely than not greater than the carrying amount, and no further testing was required. As of November 1, 2017, ComEd, PHI and DPL each qualitatively determined that it was more likely than not that the fair value of its reporting units exceeded their carrying values and, therefore, did not perform a quantitative assessment. As part of their qualitative assessments, ComEd, PHI and DPL evaluated, among other things, management’s best estimate of projected operating and capital cash flows for their businesses, outcomes of recent regulatory proceedings, changes in certain market conditions, including the discount rate and regulated utility peer company EBITDA multiples, while also considering, the passing margin from their last quantitative assessments. ComEd, PHI and DPL performed quantitative tests as of November 1, 2016, for their 2016 annual goodwill impairment assessments. The first step of the tests comparing the estimated fair values of the ComEd, Pepco, DPL and ACE reporting units to their carrying values, including goodwill, indicated no impairments of goodwill; therefore, no second steps were required. While the annual assessments indicated no impairments, certain assumptions used to estimate reporting unit fair values are highly sensitive to changes. Adverse regulatory actions or changes in significant assumptions could potentially result in future impairments of ComEd's, PHI’s or DPL’s goodwill, which could be material. Based on the results of the annual goodwill test performed as of November 1, 2016, the estimated fair values of the ComEd, Pepco, DPL and ACE reporting units would have needed to decrease by more than 30% , 10% , 10% and 10% , respectively, for ComEd and PHI to fail the first step of their respective impairment tests. The $8 million of goodwill recorded at DPL is related to DPL’s 1995 acquisition of the Conowingo Power Company and the fair value of the DPL reporting unit would have needed to decrease by more than 50% for DPL to fail the first step of the impairment test. Other Intangible Assets and Liabilities Exelon’s, Generation’s, ComEd’s and PHI's other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Exelon Software License (a) $ 95 $ (25 ) $ 70 $ 95 $ (15 ) $ 80 Generation Unamortized Energy Contracts (b) 1,938 (1,574 ) 364 1,926 (1,543 ) 383 Customer Relationships 305 (133 ) 172 299 (109 ) 190 Trade Name 243 (148 ) 95 243 (125 ) 118 Service Contract Backlog — — — 9 (7 ) 2 ComEd Chicago Settlement Agreements (c) 162 (141 ) 21 162 (133 ) 29 PHI Unamortized Energy Contracts (b) (1,515 ) 766 (749 ) (1,515 ) 430 (1,085 ) Pepco DC Sponsorship Agreement (d) — — — 25 — 25 Total $ 1,228 $ (1,255 ) $ (27 ) $ 1,244 $ (1,502 ) $ (258 ) __________ (a) On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term. (b) Includes unamortized energy contract assets and liabilities on Exelon's, Generations and PHI's Consolidated Balance Sheets. (c) In March 1999 and February 2003, ComEd entered into separate agreements with the City of Chicago and Midwest Generation, LLC. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement. (d) PHI entered into a sponsorship agreement with the District of Columbia for future sponsorship rights associated with public property within the District of Columbia. In December 2017, the asset was written off. See Note 7 - Impairment of Long-Lived Assets and Intangibles for additional information. The following table summarizes the estimated future amortization expense related to intangible assets and liabilities as of December 31, 2017 : For the Years Ending December 31, Exelon Generation ComEd PHI 2018 $ 10 $ 62 $ 7 $ (189 ) 2019 10 57 7 (119 ) 2020 10 68 7 (115 ) 2021 10 77 — (92 ) 2022 10 54 — (89 ) The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2017 , 2016 and 2015 : For the Years Ended December 31, Exelon (a) Generation (a) ComEd 2017 $ 92 $ 83 $ 7 2016 87 79 7 2015 76 69 7 __________ (a) At Exelon, amortization of unamortized energy contracts totaling $35 million , $35 million and $22 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, was recorded in Operating revenues or Purchased power and fuel expense within Exelon’s Consolidated Statements of Operations and Comprehensive Income. At Generation, amortization of unamortized energy contracts totaling $35 million , $35 million and $22 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, was recorded in Operating revenues or Purchased power and fuel expense within Generation’s Consolidated Statements of Operations and Comprehensive Income Acquired Intangible Assets and Liabilities Accounting guidance for business combinations requires the acquirer to separately recognize identifiable intangible assets in the application of purchase accounting. Unamortized Energy Contracts. Unamortized energy contract assets and liabilities represent the remaining unamortized fair value of non-derivative energy contracts that Exelon and Generation have acquired. The valuation of unamortized energy contracts was estimated by applying either the market approach or the income approach depending on the nature of the underlying contract. The market approach was utilized when prices and other relevant information generated by market transactions involving comparable transactions were available. Otherwise, the income approach, which is based upon discounted projected future cash flows associated with the underlying contracts, was utilized. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key estimates and inputs include forecasted power and fuel prices and the discount rate. The Exelon Wind unamortized energy contracts are amortized on a straight-line basis over the period in which the associated contract revenues are recognized as a decrease in Operating revenues within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. In the case of Antelope Valley, Constellation, CENG, Integrys and ConEdison, the fair value amounts are amortized over the life of the contract in relation to the present value of the underlying cash flows as of the acquisition dates through either Operating revenues or Purchased power and fuel expense within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. At PHI, offsetting regulatory assets or liabilities were also recorded. The unamortized energy contract assets and liabilities and any corresponding regulatory assets or liabilities, respectively, are amortized over the life of the contract in relation to the expected realization of the underlying cash flows. Customer Relationships. The customer relationship intangibles were determined based on a “multi-period excess method” of the income approach. Under this method, the intangible asset’s fair value is determined to be the estimated future cash flows that will be earned on the current customer base, taking into account expected contract renewals based on customer attrition rates and costs to retain those customers. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key assumptions include the customer attrition rate and the discount rate. The accounting guidance requires that customer-based intangibles be amortized over the period expected to be benefited using the pattern of economic benefit. The amortization of the customer relationships recorded in Depreciation and amortization expense within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Service Contract Backlog. The service contract backlog intangibles were determined based on a “multi-period excess method” of the income approach. Under this method, the intangible asset’s fair value is determined to be the estimated future cash flows that will be earned on the contracts. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key assumptions include estimated revenues and expenses to complete the contracts as well as the discount rate. The accounting guidance requires that customer-based intangibles be amortized over the period expected to be benefited using the pattern of economic benefit. The amortization of the service contract backlog is recorded in Depreciation and amortization expense within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Trade Name. The Constellation trade name intangible was determined based on the relief from royalty method of income approach whereby fair value is determined to be the present value of the license fees avoided by owning the assets. The fair value is based upon certain unobservable inputs, which are considered Level 3 inputs, pursuant to applicable accounting guidance. Key assumptions include the hypothetical royalty rate and the discount rate. The Constellation trade name intangible is amortized on a straight-line basis over a period of 10 years . The amortization of the trade name is recorded in Depreciation and amortization expense within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Renewable Energy Credits and Alternative Energy Credits (Exelon, Generation, PECO, PHI, DPL and ACE) Exelon’s, Generation’s, ComEd’s, PECO's, PHI's, DPL's and ACE's other intangible assets, included in Other current assets and Other deferred debits and other assets on the Consolidated Balance Sheets, include RECs (Exelon, Generation, ComEd, PHI, DPL and ACE) and AECs (Exelon and PECO). Purchased RECs are recorded at cost on the date they are purchased. The cost of RECs purchased on a stand-alone basis is based on the transaction price, while the cost of RECs acquired through PPAs represents the difference between the total contract price and the market price of energy at contract inception. Generally, revenue for RECs that are part of a bundled power sale is recognized when the power is produced and delivered to the customer, otherwise, the revenue is recognized upon physical transfer of the REC. The following table summarizes the current and noncurrent Renewable and Alternative Energy Credits for the years ended December 31, 2017 and 2016 : As of December 31, 2017 Successor Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Noncurrent AEC's — — — — — — Current REC's 321 312 — 9 8 1 Noncurrent REC's 27 27 — — — — As of December 31, 2016 Successor Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Noncurrent AEC's — — — — — — Current REC's 330 318 — 12 11 1 Noncurrent REC's 29 29 — — — —

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	11 . Fair Value of Financial Assets and Liabilities (All Registrants) Fair Value of Financial Liabilities Recorded at the Carrying Amount The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2017 and 2016 : Exelon December 31, 2017 Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 929 $ — $ 929 $ — $ 929 Long-term debt (including amounts due within one year) (a) 34,264 — 34,735 1,970 36,705 Long-term debt to financing trusts (b) 389 — — 431 431 SNF obligation 1,147 — 936 — 936 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 1,267 $ — $ 1,267 $ — $ 1,267 Long-term debt (including amounts due within one year) (a) 34,005 1,113 31,741 1,959 34,813 Long-term debt to financing trusts (b) 641 — — 667 667 SNF obligation 1,024 — 732 — 732 Generation December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 2 $ — $ 2 $ — $ 2 Long-term debt (including amounts due within one year) (a) 8,990 — 7,839 1,673 9,512 SNF obligation 1,147 — 936 — 936 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 699 $ — $ 699 $ — $ 699 Long-term debt (including amounts due within one year) (a) 9,241 — 7,482 1,670 9,152 SNF obligation 1,024 — 732 — 732 ComEd December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 7,601 $ — $ 8,418 $ — $ 8,418 Long-term debt to financing trusts (b) 205 — — 227 227 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 7,033 $ — $ 7,585 $ — $ 7,585 Long-term debt to financing trusts (b) 205 — — 215 215 PECO December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,903 $ — $ 3,194 $ — $ 3,194 Long-term debt to financing trusts 184 — — 204 204 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,580 $ — $ 2,794 $ — $ 2,794 Long-term debt to financing trusts 184 — — 192 192 BGE December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 77 $ — $ 77 $ — $ 77 Long-term debt (including amounts due within one year) (a) 2,577 — 2,825 — 2,825 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 45 $ — $ 45 $ — $ 45 Long-term debt (including amounts due within one year) (a) 2,322 — 2,467 — 2,467 Long-term debt to financing trusts (b) 252 — — 260 260 PHI (Successor) December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 350 $ — $ 350 $ — $ 350 Long-term debt (including amounts due within one year) (a) 5,874 — 5,722 297 6,019 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 522 $ — $ 522 $ — $ 522 Long-term debt (including amounts due within one year) (a) 5,898 — 5,520 289 5,809 Pepco December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 26 $ — $ 26 $ — $ 26 Long-term debt (including amounts due within one year) (a) 2,540 — 3,114 9 3,123 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 23 $ — $ 23 $ — $ 23 Long-term debt (including amounts due within one year) (a) 2,349 — 2,788 8 2,796 DPL December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (a) 1,300 — 1,393 — 1,393 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,340 $ — $ 1,383 $ — $ 1,383 ACE December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 108 $ — $ 108 $ — $ 108 Long-term debt (including amounts due within one year) (a) 1,121 — 949 288 1,237 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,155 $ — $ 1,007 $ 280 $ 1,287 __________ (a) Includes unamortized debt issuance costs which are not fair valued of $201 million , $60 million , $52 million , $17 million , $17 million , $6 million , $32 million , $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2017 . Includes unamortized debt issuance costs which are not fair valued of $200 million , $64 million , $46 million , $15 million , $15 million , $2 million , $30 million , $11 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2016 . (b) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2017 . Includes unamortized debt issuance costs which are not fair valued of $7 million , $1 million , and $6 million for Exelon, ComEd and BGE, respectively, as of December 31, 2016 . Short-Term Liabilities. The short-term liabilities included in the tables above are comprised of dividends payable (included in Other current liabilities) (Level 1) and short-term borrowings (Level 2). The Registrants’ carrying amounts of the short-term liabilities are representative of fair value because of the short-term nature of these instruments. Long-Term Debt. The fair value amounts of Exelon’s taxable debt securities (Level 2) and private placement taxable debt securities (Level 3) are determined by a valuation model that is based on a conventional discounted cash flow methodology and utilizes assumptions of current market pricing curves. In order to incorporate the credit risk of the Registrants into the discount rates, Exelon obtains pricing (i.e., U.S. Treasury rate plus credit spread) based on trades of existing Exelon debt securities as well as debt securities of other issuers in the utility sector with similar credit ratings in both the primary and secondary market, across the Registrants’ debt maturity spectrum. The credit spreads of various tenors obtained from this information are added to the appropriate benchmark U.S. Treasury rates in order to determine the current market yields for the various tenors. The yields are then converted into discount rates of various tenors that are used for discounting the respective cash flows of the same tenor for each bond or note. Due to low trading volume of private placement debt, qualitative factors such as market conditions, low volume of investors and investor demand, this debt is classified as Level 3. The fair value of Exelon's equity units (Level 1) are valued based on publicly traded securities issued by Exelon. The fair value of Generation’s and Pepco's non-government-backed fixed rate nonrecourse debt (Level 3) is based on market and quoted prices for its own and other nonrecourse debt with similar risk profiles. Given the low trading volume in the nonrecourse debt market, the price quotes used to determine fair value will reflect certain qualitative factors, such as market conditions, investor demand, new developments that might significantly impact the project cash flows or off-taker credit, and other circumstances related to the project (e.g., political and regulatory environment). The fair value of Generation’s government-backed fixed rate project financing debt (Level 3) is largely based on a discounted cash flow methodology that is similar to the taxable debt securities methodology described above. Due to the lack of market trading data on similar debt, the discount rates are derived based on the original loan interest rate spread to the applicable Treasury rate as well as a current market curve derived from government-backed securities. Variable rate financing debt resets on a monthly or quarterly basis and the carrying value approximates fair value (Level 2). When trading data is available on variable rate financing debt, the fair value is based on market and quoted prices for its own and other nonrecourse debt with similar risk profiles (Level 2). Generation, Pepco, DPL and ACE also have tax-exempt debt (Level 2). Due to low trading volume in this market, qualitative factors, such as market conditions, investor demand, and circumstances related to the issuer (e.g., conduit issuer political and regulatory environment), may be incorporated into the credit spreads that are used to obtain the fair value as described above. Variable rate tax-exempt debt (Level 2) resets on a regular basis and the carrying value approximates fair value. SNF Obligation . The carrying amount of Generation’s SNF obligation (Level 2) is derived from a contract with the DOE to provide for disposal of SNF from Generation’s nuclear generating stations. When determining the fair value of the obligation, the future carrying amount of the SNF obligation is calculated by compounding the current book value of the SNF obligation at the 13-week Treasury rate. The compounded obligation amount is discounted back to present value using Generation’s discount rate, which is calculated using the same methodology as described above for the taxable debt securities, and an estimated maturity date of 2030. The carrying amount also includes $114 million as of December 31, 2017 for the one-time fee obligation associated with closing of the FitzPatrick acquisition on March 31, 2017. The fair value was determined using a similar methodology, however the New York Power Authority's (NYPA) discount rate is used in place of Generation's given the contractual right to reimbursement from NYPA for the obligation; see Note 4 - Mergers, Acquisitions and Dispositions for additional information on Generation's acquisition of FitzPatrick. Long-Term Debt to Financing Trusts . Exelon’s long-term debt to financing trusts is valued based on publicly traded securities issued by the financing trusts. Due to low trading volume of these securities, qualitative factors, such as market conditions, investor demand, and circumstances related to each issue, this debt is classified as Level 3. Recurring Fair Value Measurements Exelon records the fair value of assets and liabilities in accordance with the hierarchy established by the authoritative guidance for fair value measurements. The hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels as follows: • Level 1 — quoted prices (unadjusted) in active markets for identical assets or liabilities that the Registrants have the ability to liquidate as of the reporting date. • Level 2 — inputs other than quoted prices included within Level 1 that are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. • Level 3 — unobservable inputs, such as internally developed pricing models or third-party valuations for the asset or liability due to little or no market activity for the asset or liability. Transfers in and out of levels are recognized as of the end of the reporting period when the transfer occurred. Given derivatives categorized within Level 1 are valued using exchange-based quoted prices within observable periods, transfers between Level 2 and Level 1 were not material. Additionally, there were no material transfers between Level 1 and Level 2 during the years ended December 31, 2017 and 2016 for Cash equivalents, Nuclear decommissioning trust fund investments, Pledged assets for Zion Station decommissioning, Rabbi trust investments, and Deferred compensation obligations. For derivative contracts, transfers into Level 2 from Level 3 generally occur when the contract tenor becomes more observable and due to changes in market liquidity or assumptions for certain commodity contracts. Generation and Exelon In accordance with the applicable guidance on fair value measurement, certain investments that are measured at fair value using the NAV per share as a practical expedient are no longer classified within the fair value hierarchy and are included under "Not subject to leveling" in the table below. The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 168 $ — $ — $ — $ 168 $ 656 $ — $ — $ — $ 656 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total NDT fund investments Cash equivalents (b) 135 85 — — 220 135 85 — — 220 Equities 4,163 915 — 2,176 7,254 4,163 915 — 2,176 7,254 Fixed income Corporate debt — 1,614 251 — 1,865 — 1,614 251 — 1,865 U.S. Treasury and agencies 1,917 52 — — 1,969 1,917 52 — — 1,969 Foreign governments — 82 — — 82 — 82 — — 82 State and municipal debt — 263 — — 263 — 263 — — 263 Other (c) — 47 — 510 557 — 47 — 510 557 Fixed income subtotal 1,917 2,058 251 510 4,736 1,917 2,058 251 510 4,736 Middle market lending — — 397 131 528 — — 397 131 528 Private equity — — — 222 222 — — — 222 222 Real estate — — — 471 471 — — — 471 471 NDT fund investments subtotal (d) 6,215 3,058 648 3,510 13,431 6,215 3,058 648 3,510 13,431 Pledged assets for Zion Station decommissioning Cash equivalents 2 — — — 2 2 — — — 2 Equities — 1 — — 1 — 1 — — 1 Middle market lending — — 12 24 36 — — 12 24 36 Pledged assets for Zion Station decommissioning subtotal 2 1 12 24 39 2 1 12 24 39 Rabbi trust investments Cash equivalents 5 — — — 5 77 — — — 77 Mutual funds 23 — — — 23 58 — — — 58 Fixed income — — — — — — 12 — — 12 Life insurance contracts — 22 — — 22 — 71 22 — 93 Rabbi trust investments subtotal 28 22 — — 50 135 83 22 — 240 Commodity derivative assets Economic hedges 557 2,378 1,290 — 4,225 557 2,378 1,290 — 4,225 Proprietary trading 2 31 35 — 68 2 31 35 — 68 Effect of netting and allocation of (e)(f) (585 ) (1,769 ) (635 ) — (2,989 ) (585 ) (1,769 ) (635 ) — (2,989 ) Commodity derivative assets subtotal (26 ) 640 690 — 1,304 (26 ) 640 690 — 1,304 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 3 — — 3 — 6 — — 6 Economic hedges — 10 — — 10 — 10 — — 10 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of (e)(f) 650 2,089 716 — 3,455 651 2,089 716 — 3,456 Commodity derivative liabilities subtotal (64 ) (179 ) (138 ) — (381 ) (64 ) (179 ) (394 ) — (637 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (2 ) — — (2 ) — (2 ) — — (2 ) Economic hedges (1 ) (8 ) — — (9 ) (1 ) (8 ) — — (9 ) Effect of netting and allocation of collateral 2 5 — — 7 2 5 — — 7 Interest rate and foreign currency derivative liabilities subtotal 1 (5 ) — — (4 ) 1 (5 ) — — (4 ) Deferred compensation obligation — (38 ) — — (38 ) — (145 ) — — (145 ) Total liabilities (63 ) (222 ) (138 ) — (423 ) (63 ) (329 ) (394 ) — (786 ) Total net assets $ 6,322 $ 3,507 $ 1,249 $ 3,534 $ 14,612 $ 6,917 $ 3,464 $ 1,015 $ 3,534 $ 14,930 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 39 $ — $ — $ — $ 39 $ 373 $ — $ — $ — $ 373 NDT fund investments Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Cash equivalents (b) 110 19 — — 129 110 19 — — 129 Equities 3,551 452 — 2,011 6,014 3,551 452 — 2,011 6,014 Fixed income Corporate debt — 1,554 250 — 1,804 — 1,554 250 — 1,804 U.S. Treasury and agencies 1,291 29 — — 1,320 1,291 29 — — 1,320 Foreign governments — 37 — — 37 — 37 — — 37 State and municipal debt — 264 — — 264 — 264 — — 264 Other (c) — 59 — 493 552 — 59 — 493 552 Fixed income subtotal 1,291 1,943 250 493 3,977 1,291 1,943 250 493 3,977 Middle market lending — — 427 71 498 — — 427 71 498 Private equity — — — 148 148 — — — 148 148 Real estate — — — 326 326 — — — 326 326 NDT fund investments subtotal (d) 4,952 2,414 677 3,049 11,092 4,952 2,414 677 3,049 11,092 Pledged assets for Zion Station decommissioning Cash equivalents 11 — — — 11 11 — — — 11 Equities — 2 — — 2 — 2 — — 2 Fixed Income - U.S. Treasury and agencies 16 1 — — 17 16 1 — — 17 Middle market lending — — 19 64 83 — — 19 64 83 Pledged assets for Zion Station decommissioning subtotal 27 3 19 64 113 27 3 19 64 113 Rabbi trust investments Cash equivalents 2 — — — 2 74 — — — 74 Mutual funds 19 — — — 19 50 — — — 50 Fixed income — — — — — — 16 — — 16 Life insurance contracts — 18 — — 18 — 64 20 — 84 Rabbi trust investments subtotal 21 18 — — 39 124 80 20 — 224 Commodity derivative assets Economic hedges 1,356 2,505 1,229 — 5,090 1,358 2,505 1,229 — 5,092 Proprietary trading 3 50 23 — 76 3 50 23 — 76 Effect of netting and allocation of (e)(f) (1,162 ) (2,142 ) (481 ) — (3,785 ) (1,164 ) (2,142 ) (481 ) — (3,787 ) Commodity derivative assets subtotal 197 413 771 — 1,381 197 413 771 — 1,381 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — 16 — — 16 Economic hedges — 28 — — 28 — 28 — — 28 Proprietary trading 3 2 — — 5 3 2 — — 5 Effect of netting and allocation of collateral (2 ) (19 ) — — (21 ) (2 ) (19 ) — — (21 ) Interest rate and foreign currency derivative assets subtotal 1 11 — — 12 1 27 — — 28 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,237 2,859 1,509 3,113 12,718 5,674 2,937 1,529 3,113 13,253 Liabilities Commodity derivative liabilities Economic hedges (1,267 ) (2,378 ) (794 ) — (4,439 ) (1,267 ) (2,378 ) (1,052 ) — (4,697 ) Proprietary trading (3 ) (50 ) (26 ) — (79 ) (3 ) (50 ) (26 ) — (79 ) Effect of netting and allocation of (e)(f) 1,233 2,339 542 — 4,114 1,233 2,339 542 — 4,114 Commodity derivative liabilities subtotal (37 ) (89 ) (278 ) — (404 ) (37 ) (89 ) (536 ) — (662 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (10 ) — — (10 ) — (10 ) — — (10 ) Economic hedges — (21 ) — — (21 ) — (21 ) — — (21 ) Proprietary trading (4 ) — — — (4 ) (4 ) — — — (4 ) Effect of netting and allocation of collateral 4 19 — — 23 4 19 — — 23 Interest rate and foreign currency derivative liabilities subtotal — (12 ) — — (12 ) — (12 ) — — (12 ) Deferred compensation obligation — (34 ) — — (34 ) — (136 ) — — (136 ) Total liabilities (37 ) (135 ) (278 ) — (450 ) (37 ) (237 ) (536 ) — (810 ) Total net assets $ 5,200 $ 2,724 $ 1,231 $ 3,113 $ 12,268 $ 5,637 $ 2,700 $ 993 $ 3,113 $ 12,443 __________ (a) Generation excludes cash of $259 million and $252 million at December 31, 2017 and 2016 and restricted cash of $127 million and $157 million at December 31, 2017 and 2016 . Exelon excludes cash of $389 million and $360 million at December 31, 2017 and 2016 and restricted cash of $145 million and $180 million at December 31, 2017 and 2016 and includes long-term restricted cash of $85 million and $25 million at December 31, 2017 and 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $77 million and $29 million of cash received from outstanding repurchase agreements at December 31, 2017 and 2016 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of less than $1 million and $(2) million , which have a total notional amount of $811 million and $933 million at December 31, 2017 and 2016 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss. (d) Excludes net liabilities of $82 million and $31 million at December 31, 2017 and 2016 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less. (e) Collateral posted/(received) from counterparties totaled $65 million , $320 million and $81 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2017 . Collateral posted/(received) from counterparties totaled $71 million , $197 million and $61 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2016 . (f) Of the collateral posted/(received), $(117) million and $(158) million represents variation margin on the exchanges as of December 31, 2017 and 2016 , respectively. ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : ComEd PECO BGE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 98 $ — $ — $ 98 $ 228 $ — $ — $ 228 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 6 — — 6 Total assets 98 — — 98 235 10 — 245 6 — — 6 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (256 ) (256 ) — — — — — — — — Total liabilities — (8 ) (256 ) (264 ) — (11 ) — (11 ) — (5 ) — (5 ) Total net assets (liabilities) $ 98 $ (8 ) $ (256 ) $ (166 ) $ 235 $ (1 ) $ — $ 234 $ 6 $ (5 ) $ — $ 1 ComEd PECO BGE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 20 $ — $ — $ 20 $ 45 $ — $ — $ 45 $ 36 $ — $ — $ 36 Rabbi trust investments Mutual funds — — — — 7 — — 7 4 — — 4 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 4 — — 4 Total assets 20 — — 20 52 10 — 62 40 — — 40 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (b) — — (258 ) (258 ) — — — — — — — — Total liabilities — (8 ) (258 ) (266 ) — (11 ) — (11 ) — (4 ) — (4 ) Total net assets (liabilities) $ 20 $ (8 ) $ (258 ) $ (246 ) $ 52 $ (1 ) $ — $ 51 $ 40 $ (4 ) $ — $ 36 __________ (a) ComEd excludes cash of $45 million and $36 million at December 31, 2017 and 2016 and restricted cash of $2 million at December 31, 2016 and includes long-term restricted cash of $62 million at December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $47 million and $22 million at December 31, 2017 and 2016 . BGE excludes cash of $17 million and $13 million at December 31, 2017 and 2016 and restricted cash of $1 million at December 31, 2017 and includes long-term restricted cash of $2 million at December 31, 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) The Level 3 balance consists of the current and noncurrent liability of $21 million and $235 million , respectively, at December 31, 2017 , and $19 million and $239 million , respectively, at December 31, 2016 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Successor As of December 31, 2017 As of December 31, 2016 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 83 $ — $ — $ 83 $ 217 $ — $ — $ 217 Mark-to-market derivative assets (b) — — — — 2 — — 2 Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) Mark-to-market derivative assets subtotal — — — — — — — — Rabbi trust investments Cash equivalents 72 — — 72 73 — — 73 Fixed income — 12 — 12 — 16 — 16 Life insurance contracts — 23 22 45 — 22 20 42 Rabbi trust investments subtotal 72 35 22 129 73 38 20 131 Total assets 155 35 22 212 290 38 20 348 Liabilities Deferred compensation obligation — (25 ) — (25 ) — (28 ) — (28 ) Mark-to-market derivative liabilities (b) (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (25 ) — (25 ) — (28 ) — (28 ) Total net assets $ 155 $ 10 $ 22 $ 187 $ 290 $ 10 $ 20 $ 320 Pepco DPL ACE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 36 $ — $ — $ 36 $ — $ — $ — $ — $ 29 $ — $ — $ 29 Rabbi trust investments Cash equivalents 44 — — 44 — — — — — — — — Fixed income — 12 — 12 — — — — — — — — Life insurance contracts — 23 22 45 — — — — — — — — Rabbi trust investments subtotal 44 35 22 101 — — — — — — — — Total assets 80 35 22 137 — — — — 29 — — 29 Liabilities Deferred compensation obligation — (4 ) — (4 ) — (1 ) — (1 ) — — — — Mark-to-market derivative liabilities (b) — — — — (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral — — — — 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — — — — — Total liabilities — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 80 $ 31 $ 22 $ 133 $ — $ (1 ) $ — $ (1 ) $ 29 $ — $ — $ 29 Pepco DPL ACE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 33 $ — $ — $ 33 $ 42 $ — $ — $ 42 $ 130 $ — $ — $ 130 Mark-to-market derivative assets (b) — — — — 2 — — 2 — — — — Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) — — — — Mark-to-market derivative assets subtotal — — — — — — — — — — — — Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 16 — 16 — — — — — — — — Life insurance contracts — 22 19 41 — — — — — — — — Rabbi trust investments subtotal 43 38 19 100 — — — — — — — — Total assets 76 38 19 133 42 — — 42 130 — — 130 Liabilities Deferred compensation obligation — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total liabilities — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 76 $ 33 $ 19 $ 128 $ 42 $ (1 ) $ — $ 41 $ 130 $ — $ — $ 130 _______ (a) PHI excludes cash of $12 million and $19 million at December 31, 2017 and 2016 and includes long term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $4 million and $9 million at December 31, 2017 and 2016 . DPL excludes cash of $2 million and $4 million at December 31, 2017 and 2016 . ACE excludes cash of $2 million and $3 million at December 31, 2017 and 2016 and includes long-term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2017 and 2016 : Successor Generation ComEd PHI Exelon For the year ended December 31, 2017 NDT Fund Investments Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Total Balance as of January 1, 2017 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 Total realized / unrealized gains (losses) Included in net income 3 — (90 ) (a) 3 (84 ) — 3 — (81 ) Included in noncurrent payables to affiliates 6 — — — 6 — — (6 ) — Included in payable for Zion Station decommissioning — (8 ) — — (8 ) — — — (8 ) Included in regulatory assets/liabilities — — — — — 2 (b) — 6 8 Change in collateral — — 20 — 20 — — — 20 Purchases, sales, issuances and settlements Purchases 64 1 178 5 248 — — — 248 Sales — — (16 ) — (16 ) — — — (16 ) Issuances — — — — — — (1 ) — (1 ) Settlements (102 ) — (8 ) (c) — (110 ) — — — (110 ) Transfers into Level 3 — — (6 ) — (6 ) — — — (6 ) Transfers out of Level 3 — — (50 ) (11 ) (61 ) — — — (61 ) Other miscellaneous — — 31 (d) (2 ) 29 — — — 29 Balance as of December 31, 2017 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of December 31, 2017 $ 1 $ — $ 254 $ 3 $ 258 $ — $ 3 $ — $ 261 Successor Generation ComEd PHI (f) Exelon For the year ended December 31, 2016 NDT Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Total Balance as of January 1, 2016 $ 670 $ 22 $ 1,051 $ 33 $ 1,776 $ (247 ) $ — $ — $ 1,529 Included due to merger — — — — — — 20 — 20 Total realized / unrealized gains (losses) Included in net income 7 — (568 ) (a) 1 (560 ) — 3 — (557 ) Included in noncurrent payables to affiliates 16 — — — 16 — — (16 ) — Included in regulatory assets/liabilities — — — — — (11 ) (b) — 16 5 Change in collateral — — (141 ) — (141 ) — — — (141 ) Purchases, sales, issuances and settlements Purchases 143 2 342 (e) 7 494 — — — 494 Sales (1 ) (5 ) (9 ) — (15 ) — — — (15 ) Issuances — — — — — — (3 ) — (3 ) Settlements (144 ) — — — (144 ) — — — (144 ) Transfers into Level 3 — — 1 1 2 — — — 2 Transfers out of Level 3 (14 ) — (183 ) — (197 ) — — — (197 ) Balance as of December 31, 2016 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2016 $ 5 $ — $ 109 $ — $ 114 $ — $ 2 $ — $ 116 __________ (a) Includes a reduction for the reclassification of $352 million and $677 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2017 and 2016 , respectively. (b) Includes $18 million of decreases in fair value and an increase for realized losses due to settlements of $20 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2017 . Includes $29 million of decreases in fair value and an increase for realized losses due to settlements of $18 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2016 . (c) Exelon includes the settlement value for any open contracts that were net settled prior to their scheduled maturity within this line item. (d) As a result of the bankruptcy filing for EGTP on November 7, 2017, the net mark-to-market commodity contracts were deconsolidated from Exelon's and Generation's consolidated financial statements. (e) Includes $168 million of fair value from contract

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments (All Registrants)	12 . Derivative Financial Instruments (All Registrants) The Registrants use derivative instruments to manage commodity price risk, interest rate risk and foreign exchange risk related to ongoing business operations. Commodity Price Risk (All Registrants) To the extent the total amount of power Generation produces and purchases differs from the amount of power it has contracted to sell, Exelon and Generation are exposed to market fluctuations in the prices of electricity, fossil fuels and other commodities. Each of the Registrants employ established policies and procedures to manage their risks associated with market fluctuations in commodity prices by entering into physical and financial derivative contracts, including swaps, futures, forwards, options and short-term and long-term commitments to purchase and sell energy and commodity products. The Registrants believe these instruments, which are either determined to be non-derivative or classified as economic hedges, mitigate exposure to fluctuations in commodity prices. Derivative authoritative guidance requires that derivative instruments be recognized as either assets or liabilities at fair value, with changes in fair value of the derivative recognized in earnings immediately. Other accounting treatments are available through special election and designation, provided they meet specific, restrictive criteria both at the time of designation and on an ongoing basis. These alternative permissible accounting treatments include normal purchases and normal sales (NPNS), cash flow hedges and fair value hedges. For Generation, all derivative economic hedges related to commodities are recorded at fair value through earnings for the consolidated company, referred to as economic hedges in the following tables. Additionally, Generation is exposed to certain market risks through its proprietary trading activities. The proprietary trading activities are a complement to Generation’s energy marketing portfolio but represent a small portion of Generation’s overall energy marketing activities. Fair value authoritative guidance and disclosures about offsetting assets and liabilities requires the fair value of derivative instruments to be shown in the Notes to the Consolidated Financial Statements on a gross basis, even when the derivative instruments are subject to legally enforceable master netting agreements and qualify for net presentation in the Consolidated Balance Sheet. A master netting agreement is an agreement between two counterparties that may have derivative and non-derivative contracts with each other providing for the net settlement of all referencing contracts via one payment stream, which takes place as the contracts deliver, when collateral is requested or in the event of default. Generation’s use of cash collateral is generally unrestricted unless Generation is downgraded below investment grade (i.e., to BB+ or Ba1). In the table below, Generation’s energy related economic hedges and proprietary trading derivatives are shown gross. The impact of the netting of fair value balances with the same counterparty that are subject to legally enforceable master netting agreements, as well as netting of cash collateral including initial margin on exchange positions, is aggregated in the collateral and netting column. As of December 31, 2017 and 2016 , $4 million and $8 million of cash collateral held, respectively, was not offset against derivative positions because such collateral was not associated with any energy-related derivatives, were associated with accrual positions, or had no positions to offset as of the balance sheet date. Excluded from the tables below are economic hedges that qualify for the NPNS scope exception and other non-derivative contracts that are accounted for under the accrual method of accounting. ComEd’s use of cash collateral is generally unrestricted unless ComEd is downgraded below investment grade (i.e., to BB+ or Ba1). Cash collateral held by BGE and PECO must be deposited in a non-affiliate major U.S. commercial bank or foreign bank with a U.S. branch office that meet certain qualifications. In the table below, DPL's economic hedges are shown gross. The impact of the netting of fair value balances with the same counterparty that are subject to legally enforceable master netting agreements, as well as netting of cash collateral, including margin on exchange positions, is aggregated in the collateral and netting column. The following table provides a summary of the derivative fair value balances related to commodity contracts recorded by the Registrants as of December 31, 2017 : Successor Generation ComEd DPL PHI Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,061 $ 56 $ (2,144 ) $ 973 $ — $ — $ — $ — $ — $ 973 Mark-to-market derivative assets (noncurrent assets) 1,164 12 (845 ) 331 — — — — — 331 Total mark-to-market derivative assets 4,225 68 (2,989 ) 1,304 — — — — — 1,304 Mark-to-market derivative liabilities (current liabilities) (2,646 ) (43 ) 2,480 (209 ) (21 ) (1 ) 1 — — (230 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,137 ) (10 ) 975 (172 ) (235 ) — — — — (407 ) Total mark-to-market derivative liabilities (3,783 ) (53 ) 3,455 (381 ) (256 ) (1 ) 1 — — (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ (1 ) $ 1 $ — $ — $ 667 __________ (a) Exelon, Generation, PHI and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $169 million and $53 million , respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(117) million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances related to commodity contracts recorded by the Registrants as of December 31, 2016 : Successor Generation ComEd DPL PHI Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,623 $ 55 $ (2,769 ) $ 909 $ — $ 2 $ (2 ) $ — $ — $ 909 Mark-to-market derivative assets (noncurrent assets) 1,467 21 (1,016 ) 472 — — — — — 472 Total mark-to-market derivative assets 5,090 76 (3,785 ) 1,381 — 2 (2 ) — — 1,381 Mark-to-market derivative liabilities (current liabilities) (3,165 ) (54 ) 2,964 (255 ) (19 ) — — — — (274 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,274 ) (25 ) 1,150 (149 ) (239 ) — — — — (388 ) Total mark-to-market derivative liabilities (4,439 ) (79 ) 4,114 (404 ) (258 ) — — — — (662 ) Total mark-to-market derivative net assets (liabilities) $ 651 $ (3 ) $ 329 $ 977 $ (258 ) $ 2 $ (2 ) $ — $ — $ 719 __________ (a) Exelon, Generation, PHI and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, and letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $100 million and $72 million , respectively, and current and noncurrent liabilities are shown net of collateral of $95 million and $62 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $329 million at December 31, 2016 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(158) million represents variation margin on the exchanges. Economic Hedges (Commodity Price Risk) Within Exelon, Generation has the most exposure to commodity price risk. As such, Generation uses a variety of derivative and non-derivative instruments to manage the commodity price risk of its electric generation facilities, including power and gas sales, fuel and power purchases, natural gas transportation and pipeline capacity agreements and other energy-related products marketed and purchased. To manage these risks, Generation may enter into fixed-price derivative or non-derivative contracts to hedge the variability in future cash flows from expected sales of power and gas and purchases of power and fuel. The objectives for executing such hedges include fixing the price for a portion of anticipated future electricity sales at a level that provides an acceptable return. Generation is also exposed to differences between the locational settlement prices of certain economic hedges and the hedged generating units. This price difference is actively managed through other instruments which include derivative congestion products, whose changes in fair value are recognized in earnings each period, and auction revenue rights, which are accounted for on an accrual basis. For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Operating revenues $ (126 ) $ (490 ) $ 196 Purchased power and fuel (43 ) 459 54 Total Exelon and Generation $ (169 ) $ (31 ) $ 250 In general, increases and decreases in forward market prices have a positive and negative impact, respectively, on Generation’s owned and contracted generation positions which have not been hedged. Generation hedges commodity price risk on a ratable basis over three-year periods. As of December 31, 2017 , the percentage of expected generation hedged is 85% - 88% , 55% - 58% and 26% - 29% for 2018 , 2019 and 2020 , respectively. On December 17, 2010, ComEd entered into several 20 -year floating-to-fixed energy swap contracts with unaffiliated suppliers for the procurement of long-term renewable energy and associated RECs. Delivery under the contracts began in June 2012. These contracts are designed to lock in a portion of the long-term commodity price risk resulting from the renewable energy resource procurement requirements in the Illinois Settlement Legislation. ComEd has not elected hedge accounting for these derivative financial instruments. ComEd records the fair value of the swap contracts on its balance sheet. Because ComEd receives full cost recovery for energy procurement and related costs from retail customers, the change in fair value each period is recorded by ComEd as a regulatory asset or liability. See Note 3 — Regulatory Matters for additional information. PECO has contracts to procure electric supply that were executed through the competitive procurement process outlined in its PAPUC-approved DSP Programs, which are further discussed in Note 3 — Regulatory Matters . Based on Pennsylvania legislation and the DSP Programs permitting PECO to recover its electric supply procurement costs from retail customers with no mark-up, PECO’s commodity price risk related to electric supply procurement is limited. PECO locked in fixed prices for a significant portion of its commodity price risk through full requirements contracts. PECO has certain full requirements contracts that are considered derivatives and qualify for the NPNS scope exception under current derivative authoritative guidance. PECO’s natural gas procurement policy is designed to achieve a reasonable balance of long-term and short-term gas purchases under different pricing approaches to achieve system supply reliability at the least cost. PECO’s reliability strategy is two-fold. First, PECO must assure that there is sufficient transportation capacity to satisfy delivery requirements. Second, PECO must ensure that a firm source of supply exists to utilize the capacity resources. All of PECO’s natural gas supply and asset management agreements that are derivatives either qualify for the NPNS scope exception and have been designated as such, or have no mark-to-market balances because the derivatives are index priced. Additionally, in accordance with the 2016 PAPUC PGC settlement and to reduce the exposure of PECO and its customers to natural gas price volatility, PECO has continued its program to purchase natural gas for both winter and summer supplies using a layered approach of locking-in prices ahead of each season with long-term gas purchase agreements (those with primary terms of at least twelve months). Under the terms of the 2016 PGC settlement, PECO is required to lock in (i.e., economically hedge) the price of a minimum volume of its long-term gas commodity purchases. PECO’s gas-hedging program is designed to cover about 20% of planned natural gas purchases in support of projected firm sales. The hedging program for natural gas procurement has no direct impact on PECO’s results of operations and financial position as natural gas costs are fully recovered from customers under the PGC. BGE has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC. The SOS rates charged recover BGE’s wholesale power supply costs and include an administrative fee. BGE’s commodity price risk related to electric supply procurement is limited. BGE locks in fixed prices for all of its SOS requirements through full requirements contracts. Certain of BGE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other BGE full requirements contracts are not derivatives. BGE provides natural gas to its customers under a MBR mechanism approved by the MDPSC. Under this mechanism, BGE’s actual cost of gas is compared to a market index (a measure of the market price of gas in a given period). The difference between BGE’s actual cost and the market index is shared equally between shareholders and customers. BGE must also secure fixed price contracts for at least 10% , but not more than 20% , of forecasted system supply requirements for flowing (i.e., non-storage) gas for the November through March period. These fixed-price contracts are not subject to sharing under the MBR mechanism. BGE also ensures it has sufficient pipeline transportation capacity to meet customer requirements. BGE’s natural gas supply and asset management agreements qualify for the NPNS scope exception and result in physical delivery. Pepco has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and DCPSC. The SOS rates charged recover Pepco's wholesale power supply costs and include an administrative fee. The administrative fee includes an incremental cost component and a shareholder return component for residential and commercial rate classes. Pepco’s commodity price risk related to electric supply procurement is limited. Pepco locks in fixed prices for its SOS requirements through full requirements contracts. Certain of Pepco’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other Pepco full requirements contracts are not derivatives. DPL has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and the DPSC. The SOS rates charged recover DPL's wholesale power supply costs. In Delaware, DPL is also entitled to recover a Reasonable Allowance for Retail Margin (RARM). The RARM includes a fixed annual margin of approximately $2.75 million , plus an incremental cost component and a cash working capital allowance. In Maryland, DPL charges an administrative fee intended to allow it to recover its administrative costs. DPL locks in fixed prices for its SOS requirements through full requirements contracts. DPL’s commodity price risk related to electric supply procurement is limited. Certain of DPL’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. DPL provides natural gas to its customers under an Annual GCR mechanism approved by the DPSC. Under this mechanism, DPL’s Annual GCR Filing establishes a future GCR for firm bundled sales customers by using a forecast of demand and commodity costs. The actual costs are trued up against forecast on a monthly basis and any shortfall or excess is carried forward as a recovery balance in the next GCR filing. The demand portion of the GCR is based upon DPL’s firm transportation and storage contracts. DPL has firm deliverability of swing and seasonal storage; a liquefied natural gas facility and firm transportation capacity to meet customer demand and provide a reserve margin. The commodity portion of the GCR includes a commission approved hedging program which is intended to reduce gas commodity price volatility while limiting the firm natural gas customers’ exposure to adverse changes in the market price of natural gas. The hedge program requires that DPL hedge, on a non-discretionary basis, an amount equal to 50% of estimated purchase requirements for each month, including estimated monthly purchases for storage injections. The 50% hedge monthly target is achieved by hedging 1/12th of the 50% target each month beginning 12-months prior to the month in which the physical gas is to be purchased. Currently, DPL uses only exchange traded futures for its gas hedging program, which are considered derivatives, however, it retains the capability to employ other physical and financial hedges if needed. DPL has not elected hedge accounting for these derivative financial instruments. Because of the DPSC-approved fuel adjustment clause for DPL's derivatives, the change in fair value of the derivatives each period, in addition to all premiums paid and other transaction costs incurred as part of the Gas Hedging Program, are fully recoverable and are recorded by DPL as regulatory assets or liabilities. DPL’s physical gas purchases are currently all daily, monthly or intra-month transactions. From time to time, DPL will enter into seasonal purchase or sale arrangements, however, there are none currently in the portfolio. Certain of DPL's full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. ACE has contracts to procure BGS electric supply that are executed through a competitive procurement process approved by the NJBPU. The BGS rates charged recover ACE's wholesale power supply costs. ACE does not make any profit or incur any loss on the supply component of the BGS it supplies to customers. ACE’s commodity price risk related to electric supply procurement is limited. ACE locks in fixed prices for its BGS requirements through full requirements contracts. Certain of ACE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other ACE full requirements contracts are not derivatives. Proprietary Trading (Commodity Price Risk) Generation also executes commodity derivatives for proprietary trading purposes. Proprietary trading includes all contracts entered into with the intent of benefiting from shifts or changes in market prices as opposed to those executed with the intent of hedging or managing risk. Proprietary trading activities are subject to limits established by Exelon’s RMC. The proprietary trading portfolio is subject to a risk management policy that includes stringent risk management limits to manage exposure to market risk. Additionally, the Exelon risk management group and Exelon's RMC monitor the financial risks of the proprietary trading activities. The proprietary trading activities are a complement to Generation's energy marketing portfolio, but represent a small portion of Generation's overall revenue from energy marketing activities. Gains and losses associated with proprietary trading are reported as Operating revenues in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Operating revenues $ 6 $ 2 $ (6 ) Interest Rate and Foreign Exchange Risk (All Registrants) The Registrants use a combination of fixed-rate and variable-rate debt to manage interest rate exposure. The Registrants utilize fixed-to-floating interest rate swaps, which are typically designated as fair value hedges, to manage their interest rate exposure. In addition, the Registrants may utilize interest rate derivatives to lock in rate levels, which are typically designated as cash flow hedges to manage interest rate risk. To manage foreign exchange rate exposure associated with international commodity purchases in currencies other than U.S. dollars, Generation utilizes foreign currency derivatives, which are treated as economic hedges. Below is a summary of the interest rate and foreign exchange hedge balances as of December 31, 2017 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary Collateral and Netting (a) Subtotal Derivatives Total Mark-to-market derivative assets (current assets) $ — $ 10 $ — $ (7 ) $ 3 $ — $ 3 Mark-to-market derivative assets (noncurrent assets) 3 — — — 3 3 6 Total mark-to-market derivative assets 3 10 — (7 ) 6 3 9 Mark-to-market derivative liabilities (current liabilities) (2 ) (7 ) — 7 (2 ) — (2 ) Mark-to-market derivative liabilities (noncurrent liabilities) — (2 ) — — (2 ) — (2 ) Total mark-to-market derivative liabilities (2 ) (9 ) — 7 (4 ) — (4 ) Total mark-to-market derivative net assets (liabilities) $ 1 $ 1 $ — $ — $ 2 $ 3 $ 5 __________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above. The following table provides a summary of the interest rate and foreign exchange hedge balances recorded by the Registrants as of December 31, 2016 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Total Mark-to-market derivative assets (current assets) $ — $ 17 $ 4 $ (13 ) $ 8 $ — $ 8 Mark-to-market derivative assets (noncurrent assets) — 11 1 (8 ) 4 16 20 Total mark-to-market derivative assets — 28 5 (21 ) 12 16 28 Mark-to-market derivative liabilities (current liabilities) (7 ) (13 ) (2 ) 14 (8 ) — (8 ) Mark-to-market derivative liabilities (noncurrent liabilities) (3 ) (8 ) (2 ) 9 (4 ) — (4 ) Total mark-to-market derivative liabilities (10 ) (21 ) (4 ) 23 (12 ) — (12 ) Total mark-to-market derivative net assets (liabilities) $ (10 ) $ 7 $ 1 $ 2 $ — $ 16 $ 16 __________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above. Fair Value Hedges (Interest Rate Risk) For derivative instruments that qualify and are designated as fair value hedges, the gain or loss on the derivative as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in earnings immediately. Exelon and Generation include the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps as follows: Year Ended December 31, Income Statement Location 2017 2016 2015 2017 2016 2015 Gain (Loss) on Swaps Gain (Loss) on Borrowings Generation Interest expense (a) $ — $ — $ (1 ) $ — $ — $ — Exelon Interest expense (13 ) (9 ) 3 28 23 14 __________ (a) For the year ended December 31, 2015 , the loss on Generation swaps included $(1) million realized in earnings with an immaterial amount excluded from hedge effectiveness testing. The table below provides the notional amounts of fixed-to-floating hedges outstanding held by Exelon at December 31, 2017 and 2016 . For the Years Ended December 31, 2017 2016 Fixed-to-floating hedges $ 800 $ 800 During the years ended December 31, 2017 , 2016 and 2015 , the impact on the results of operations due to ineffectiveness from fair value hedges were gains of $15 million , $14 million and $17 million , respectively. Cash Flow Hedges (Interest Rate Risk) For derivative instruments that qualify and are designated as cash flow hedges, the gain or loss on the effective portion of the derivative will be deferred in AOCI and reclassified into earnings when the underlying transaction occurs. To mitigate interest rate risk, Exelon and Generation enter into floating-to-fixed interest rate swaps to manage a portion of interest rate exposure associated with debt issuances. The table below provides the notional amounts of floating-to-fixed hedges outstanding held by Exelon and Generation at December 31, 2017 and 2016 . For the Years Ended December 31, 2017 2016 Floating-to-fixed hedges $ 636 $ 659 The tables below provide the activity of OCI related to cash flow hedges for the years ended December 31, 2017 and 2016 , containing information about the changes in the fair value of cash flow hedges and the reclassification from AOCI into results of operations. The amounts reclassified from AOCI, when combined with the impacts of the hedged transactions, result in the ultimate recognition of net revenues or expenses at the contractual price. Total Cash Flow Hedge AOCI Activity, Net of Income Tax Generation Exelon For the Year Ended December 31, 2017 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2016 $ (19 ) $ (17 ) Effective portion of changes in fair value (1 ) (1 ) Reclassifications from AOCI to net income Interest expense 4 (a) 4 (a) AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Total Cash Flow Hedge AOCI Activity, Net of Income Tax Generation Exelon For the Year Ended December 31, 2016 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2015 $ (21 ) $ (19 ) Effective portion of changes in fair value (6 ) (6 ) Reclassifications from AOCI to net income Interest expense 8 (b) 8 (b) AOCI derivative loss at December 31, 2016 $ (19 ) $ (17 ) __________ (a) Amount is net of related income tax expense of $1 million for the year ended December 31, 2017 . (b) Amount is net of related income tax expense of $5 million for the year ended December 31, 2016 . During the years ended December 31, 2017 , 2016 and 2015 , the impact on the results of operations due to the ineffectiveness from cash flow hedges that continue to be designated in hedging relationships was immaterial. The estimated amount of existing gains and losses that are reported in AOCI at the reporting date that are expected to be reclassified into earnings within the next twelve months is immaterial. Economic Hedges (Interest Rate and Foreign Exchange Risk) Exelon and Generation executes these instruments to mitigate exposure to fluctuations in interest rates or foreign exchange but for which the fair value or cash flow hedge elections were not made. Generation also enters into interest rate derivative contracts and foreign exchange currency swaps ("treasury") to manage the exposure related to the interest rate component of commodity positions and international purchases of commodities in currencies other than U.S. Dollars. At December 31, 2017 and 2016 , Generation had immaterial notional amounts of interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 and 2016 related to foreign currency exchange rate swaps that are marked-to-market to manage the exposure associated with international purchases of commodities in currencies other than U.S. dollars. For the Years Ended December 31, 2017 2016 Foreign currency exchange rate swaps $ 94 $ 85 For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax mark-to-market gains (losses) in the Consolidated Statements of Operations and Comprehensive Income and are included in “Net fair value changes related to derivatives” in Exelon’s and Generation’s Consolidated Statements of Cash Flows. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Generation Operating Revenues $ (6 ) $ (10 ) $ 7 Generation Interest Expense (3 ) — — Total Generation $ (9 ) $ (10 ) $ 7 For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Exelon Operating Revenues $ (6 ) $ (10 ) $ 7 Exelon Interest Expense (3 ) — 100 Total Exelon $ (9 ) $ (10 ) $ 107 Proprietary Trading (Interest Rate and Foreign Exchange Risk) Generation also executes derivative contracts for proprietary trading purposes to hedge risk associated with the interest rate and foreign exchange components of underlying comm

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt and Credit Agreements (All Registrants)	Debt and Credit Agreements (All Registrants) Short-Term Borrowings Exelon, ComEd and BGE meet their short-term liquidity requirements primarily through the issuance of commercial paper. Generation and PECO meet their short-term liquidity requirements primarily through the issuance of commercial paper and borrowings from the intercompany money pool. PHI meets its short-term liquidity requirements primarily through the issuance of short-term notes and the Exelon intercompany money pool. Pepco, DPL and ACE meet their short-term liquidity requirements primarily through the issuance of commercial paper and short-term notes. The Registrants may use their respective credit facilities for general corporate purposes, including meeting short-term funding requirements and the issuance of letters of credit. Commercial Paper The following table reflects the Registrants' commercial paper programs supported by the revolving credit agreements and bilateral credit agreements at December 31, 2017 and 2016 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2017 (a)(b)(c) 2016 (a)(b)(c) 2017 2016 2017 2016 Exelon Corporate $ 600 $ 600 $ — $ — 1.16 % 0.70 % Generation 5,300 5,300 — 620 1.23 % 0.94 % ComEd 1,000 1,000 — — 1.24 % 0.77 % PECO 600 600 — — 1.13 % N/A BGE 600 600 77 45 1.28 % 0.77 % Pepco 500 500 26 23 1.06 % 0.71 % DPL 500 500 216 — 1.48 % 0.68 % ACE 350 350 108 — 1.43 % 0.65 % Total $ 9,450 $ 9,450 $ 427 $ 688 __________ (a) Excludes $480 million and $500 million in bilateral credit facilities that do not back Generation's commercial paper program at December 31, 2017 and 2016 , respectively. (b) Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $34 million , $34 million , $5 million , $2 million , $2 million and $2 million , respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively. (c) Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility. In order to maintain their respective commercial paper programs in the amounts indicated above, each Registrant must have credit facilities in place, at least equal to the amount of its commercial paper program. While the amount of outstanding commercial paper does not reduce available capacity under a Registrant’s credit facility, a Registrant does not issue commercial paper in an aggregate amount exceeding the then available capacity under its credit facility. At December 31, 2017 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2017 Borrower Facility Type Aggregate Bank (a)(b) Facility Draws Outstanding Letters of Credit (c) Actual To Support Additional Commercial (b)(d) Exelon Corporate Syndicated Revolver $ 600 $ — $ 45 $ 555 $ 555 Generation Syndicated Revolver 5,300 — 868 4,432 4,432 Generation Bilaterals 480 — 231 249 — ComEd Syndicated Revolver 1,000 — 2 998 998 PECO Syndicated Revolver 600 — 1 599 599 BGE Syndicated Revolver 600 — — 600 523 Pepco Syndicated Revolver 300 — — 300 274 DPL Syndicated Revolver 300 — — 300 84 ACE Syndicated Revolver 300 — — 300 192 Total $ 9,480 $ — $ 1,147 $ 8,333 $ 7,657 __________ (a) Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $34 million , $34 million , $5 million , $2 million , $2 million and $2 million , respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively. (b) Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility. (c) Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Wind. (d) Excludes $480 million in bilateral credit facilities that do not back Generation’s commercial paper program. The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2017 , 2016 and 2015 . Exelon 2017 2016 2015 Average borrowings $ 823 $ 1,125 $ 499 Maximum borrowings outstanding 2,147 3,076 739 Average interest rates, computed on a daily basis 1.32 % 0.88 % 0.53 % Average interest rates, at December 31 1.24 % 1.12 % 0.88 % Generation 2017 2016 2015 Average borrowings $ 405 $ 536 $ 1 Maximum borrowings outstanding 1,455 1,735 50 Average interest rates, computed on a daily basis 1.23 % 0.94 % 0.49 % Average interest rates, at December 31 1.23 % 1.14 % N/A ComEd 2017 2016 2015 Average borrowings $ 200 $ 256 $ 461 Maximum borrowings outstanding 470 755 684 Average interest rates, computed on a daily basis 1.24 % 0.77 % 0.53 % Average interest rates, at December 31 1.24 % N/A 0.89 % PECO 2017 2016 2015 Average borrowings $ 2 $ — $ — Maximum borrowings outstanding 60 — — Average interest rates, computed on a daily basis 1.13 % N/A N/A Average interest rates, at December 31 1.13 % N/A N/A BGE 2017 2016 2015 Average borrowings $ 54 $ 143 $ 37 Maximum borrowings outstanding 165 369 210 Average interest rates, computed on a daily basis 1.28 % 0.77 % 0.48 % Average interest rates, computed at December 31 1.28 % 0.95 % 0.87 % PHI Corporate Successor Predecessor 2017 2016 2015 Average borrowings N/A $ 153 $ 444 Maximum borrowings outstanding N/A 559 784 Average interest rates, computed on a daily basis N/A 1.03 % 0.90 % Average interest rates, computed at December 31 N/A N/A 1.22 % Pepco 2017 2016 2015 Average borrowings $ 51 $ 4 $ 34 Maximum borrowings outstanding 197 73 190 Average interest rates, computed on a daily basis 1.06 % 0.71 % 0.44 % Average interest rates, computed at December 31 1.06 % 0.90 % 0.68 % DPL 2017 2016 2015 Average borrowings $ 40 $ 33 $ 81 Maximum borrowings outstanding 216 116 179 Average interest rates, computed on a daily basis 1.48 % 0.68 % 0.47 % Average interest rates, computed at December 31 1.48 % N/A 0.79 % ACE 2017 2016 2015 Average borrowings $ 30 $ — $ 175 Maximum borrowings outstanding 133 5 253 Average interest rates, computed on a daily basis 1.43 % 0.65 % 0.46 % Average interest rates, computed at December 31 1.43 % N/A 0.65 % Short-Term Loan Agreements On July 30, 2015, PHI entered into a $300 million term loan agreement. The net proceeds of the loan were used to repay PHI's outstanding commercial paper and for general corporate purposes. Pursuant to the loan agreement, loans made thereunder bear interest at a variable rate equal to LIBOR plus 0.95% , and all indebtedness thereunder is unsecured. On April 4, 2016, PHI repaid $300 million of its term loan in full. On January 13, 2016, PHI entered into a $500 million term loan agreement, which was amended on March 28, 2016. The net proceeds of the loan were used to repay PHI's outstanding commercial paper, and for general corporate purposes. Pursuant to the loan agreement, as amended, loans made thereunder bear interest at a variable rate equal to LIBOR plus 1% , and all indebtedness thereunder is unsecured. On March 23, 2017, the aggregate principal amount of all loans, together with any accrued but unpaid interest due under the loan agreement was fully repaid and the loan terminated. On March 23, 2017, Exelon Corporate entered into a similar type term loan for $500 million which expires on March 22, 2018. Pursuant to the loan agreement, loans made thereunder bear interest at a variable rate equal to LIBOR plus 1% and all indebtedness thereunder is unsecured. The loan agreement is reflected in Exelon’s Consolidated Balance Sheet within Short-Term borrowings. On February 22, 2016, Generation and EDF entered into separate member revolving promissory notes with CENG to finance short-term working capital needs. The notes are scheduled to mature on January 31, 2017 and bear interest at a variable rate equal to LIBOR plus 1.75% . On July 25, 2016, CENG paid off the outstanding balances under each note. Credit Agreement On January 5, 2016, Generation entered into a credit agreement establishing a $150 million bilateral credit facility, scheduled to mature in January of 2019. This facility will solely be utilized by Generation to issue lines of credit. This facility does not back Generation's commercial paper program. On April 1, 2016, the credit agreement for CENG's $100 million bilateral credit facility was amended to increase the overall facility size to $200 million . This facility is utilized by CENG to fund working capital and capital projects. The facility does not back Generation's commercial paper program. On May 26, 2016, Exelon Corporate, Generation, ComEd, PECO and BGE entered into amendments to each of their respective syndicated revolving credit facilities, which extended the maturity of each of the facilities to May 26, 2021. Exelon Corporate also increased the size of its facility from $500 million to $600 million . On May 26, 2016, PHI, Pepco, DPL and ACE entered into an amendment to their Second Amended and Restated Credit Agreement dated as of August 1, 2011, which (i) extended the maturity date of the facility to May 26, 2021, (ii) removed PHI as a borrower under the facility, (iii) decreased the size of the facility from $1.5 billion to $900 million and (iv) aligned its financial covenant from debt to capitalization leverage ratio to interest coverage ratio. On May 26, 2017, each of the Registrants' respective syndicated revolving credit facilities had their maturity dates extended to May 26, 2022. On January 9, 2017, the credit agreement for Generation's $75 million bilateral credit facility was amended and restated to increase the facility size to $100 million and extend the maturity to January 2019. This facility will solely be used by Generation to issue letters of credit. Borrowings under Exelon Corporate’s, Generation’s, ComEd’s, PECO’s, BGE's, Pepco's, DPL's and ACE's revolving credit agreements bear interest at a rate based upon either the prime rate or a LIBOR-based rate, plus an adder based upon the particular Registrant’s credit rating. The adders for the prime based borrowings and LIBOR-based borrowings are presented in the following table: Exelon Generation ComEd PECO BGE Pepco DPL ACE Prime based borrowings 27.5 27.5 7.5 0.0 0.0 7.5 7.5 7.5 LIBOR-based borrowings 127.5 127.5 107.5 90.0 100.0 107.5 107.5 107.5 The maximum adders for prime rate borrowings and LIBOR-based rate borrowings are 90 basis points and 165 basis points, respectively. The credit agreements also require the borrower to pay a facility fee based upon the aggregate commitments. The fee varies depending upon the respective credit ratings of the borrower. Each revolving credit agreement for Exelon, Generation, ComEd, PECO, BGE, Pepco, DPL and ACE requires the affected borrower to maintain a minimum cash from operations to interest expense ratio for the twelve-month period ended on the last day of any quarter. The following table summarizes the minimum thresholds reflected in the credit agreements for the year ended December 31, 2017 : Exelon Generation ComEd PECO BGE Pepco DPL ACE Credit agreement threshold 2.50 to 1 3.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 At December 31, 2017 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Pepco DPL ACE Interest coverage ratio 6.34 9.02 11.68 7.99 10.50 6.35 8.69 5.57 An event of default under Exelon, Generation, ComEd, PECO or BGE's indebtedness will not constitute an event of default under any of the others’ credit facilities, except that a bankruptcy or other event of default in the payment of principal, premium or indebtedness in principal amount in excess of $100 million in the aggregate by Generation will constitute an event of default under the Exelon Corporate credit facility. An event of default under Pepco, DPL or ACE's indebtedness will not constitute an event of default with respect to the other PHI Utilities under the PHI Utilities' combined credit facility. The absence of a material adverse change in Exelon's or PHI’s business, property, results of operations or financial condition is not a condition to the availability of credit under any of the borrowers' credit agreement. None of the credit agreements include any rating triggers. Variable Rate Demand Bonds DPL has outstanding obligations in respect of Variable Rate Demand Bonds (VRDB). VRDBs are subject to repayment on the demand of the holders and, for this reason, are accounted for as short-term debt in accordance with GAAP. However, bonds submitted for purchase are remarketed by a remarketing agent on a best efforts basis. PHI expects that any bonds submitted for purchase will be remarketed successfully due to the creditworthiness of the issuer and, as applicable, the credit support, and because the remarketing resets the interest rate to the then-current market rate. The bonds may be converted to a fixed-rate, fixed-term option to establish a maturity which corresponds to the date of final maturity of the bonds. On this basis, PHI views VRDBs as a source of long-term financing. As of December 31, 2017 and December 31, 2016 , $79 million and $105 million , respectively, in variable rate demand bonds issued by DPL were outstanding and are included in the Long-term debt due within one year on Exelon's, PHI's and DPL's Consolidated Balance Sheet. Long-Term Debt The following tables present the outstanding long-term debt at the Registrants as of December 31, 2017 and 2016 : Exelon Maturity Date December 31, Rates 2017 2016 Long-term debt Rate stabilization bonds 5.82 % 2017 $ — $ 41 First mortgage bonds (a) 1.70 % - 7.90 % 2018 - 2047 15,197 14,123 Senior unsecured notes 2.45 % - 7.60 % 2019 - 2046 11,285 11,868 Unsecured notes 2.40 % - 6.35 % 2021 - 2047 2,600 2,300 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 82 105 Notes payable and other (b)(c) 2.61 % - 8.88 % 2018 - 2053 405 576 Junior subordinated notes 3.50 % 2022 1,150 1,150 Contract payment - junior subordinated notes 2.50 % 2017 — 19 Long-term software licensing agreement 3.95 % 2024 79 103 Unsecured Tax-Exempt Bonds 5.40 % — 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % — 2018 - 2027 26 40 Transition bonds 5.05 % - 5.55 % — 2020 - 2023 90 124 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,331 1,400 Variable rates 3.18 % - 4.00 % 2019 - 2024 865 915 Total long-term debt 33,657 33,311 Unamortized debt discount and premium, net (57 ) (68 ) Unamortized debt issuance costs (201 ) (200 ) Fair value adjustment 865 962 Long-term debt due within one year (2,088 ) (2,430 ) Long-term debt $ 32,176 $ 31,575 Long-term debt to financing trusts (d) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Subordinated debentures to BGE Capital Trust II 6.20 % 2043 — 258 Total long-term debt to financing trusts 390 648 Unamortized debt issuance costs (1 ) (7 ) Long-term debt to financing trusts $ 389 $ 641 __________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s, Pepco's, DPL's and ACE's assets are subject to the liens of their respective mortgage indentures. (b) Includes capital lease obligations of $53 million and $69 million at December 31, 2017 and 2016 , respectively. Lease payments of $18 million , $20 million , $5 million , $1 million , $1 million and $8 million will be made in 2018 , 2019 , 2020 , 2021 , 2022 and thereafter, respectively. (c) Includes financing related to Albany Green Energy, LLC (AGE). During the third quarter of 2017, Generation retired $228 million of its outstanding debt balance. As of December 31, 2016, $198 million was outstanding. (d) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. Generation Maturity Date December 31, Rates 2017 2016 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2019 - 2042 $ 6,019 $ 5,971 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 82 105 Notes payable and other (a)(b) 2.61 % - 8.88 % 2018 - 2019 223 382 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,331 1,400 Variable rates 3.18 % - 4.00 % 2019 - 2024 865 915 Total long-term debt 8,955 9,208 Unamortized debt discount and premium, net (8 ) (17 ) Unamortized debt issuance costs (60 ) (65 ) Fair value adjustment 103 115 Long-term debt due within one year (346 ) (1,117 ) Long-term debt $ 8,644 $ 8,124 __________ (a) Includes Generation’s capital lease obligations of $18 million and $22 million at December 31, 2017 and 2016 , respectively. Generation will make lease payments of $5 million , $6 million , $5 million , $1 million and $1 million in 2018 , 2019 , 2020 , 2021 and 2022 respectively. The capital lease matures in 2022. (b) Includes financing related to Albany Green Energy, LLC (AGE). During the third quarter of 2017, Generation retired $228 million of its outstanding debt balance. As of December 31, 2016, $198 million was outstanding. ComEd Maturity Date December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 2.15 % - 6.45 % 2018 - 2047 $ 7,529 $ 6,954 Notes payable and other (b) 6.95 % - 7.49 % 2018 - 2053 147 147 Total long-term debt 7,676 7,101 Unamortized debt discount and premium, net (23 ) (22 ) Unamortized debt issuance costs (52 ) (46 ) Long-term debt due within one year (840 ) (425 ) Long-term debt $ 6,761 $ 6,608 Long-term debt to financing trust (c) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 __________ (a) Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture. (b) Includes ComEd’s capital lease obligations of $8 million at both December 31, 2017 and 2016 , respectively. Lease payments of less than $1 million annually will be made from 2018 through expiration at 2053. (c) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. PECO Maturity Date December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2018 - 2047 $ 2,925 $ 2,600 Total long-term debt 2,925 2,600 Unamortized debt discount and premium, net (5 ) (5 ) Unamortized debt issuance costs (17 ) (15 ) Long-term debt due within one year (500 ) — Long-term debt $ 2,403 $ 2,580 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 __________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. BGE Maturity Date December 31, Rates 2017 2016 Long-term debt Rate stabilization bonds 5.82 % 2017 $ — $ 41 Unsecured notes 2.40 % - 6.35 % 2021 - 2047 2,600 2,300 Total long-term debt 2,600 2,341 Unamortized debt discount and premium, net (6 ) (4 ) Unamortized debt issuance costs (17 ) (15 ) Long-term debt due within one year — (41 ) Long-term debt $ 2,577 $ 2,281 Long-term debt to financing trusts (a) Subordinated debentures to BGE Capital Trust II 6.20 % 2043 $ — $ 258 Total long-term debt to financing trusts — 258 Unamortized debt issuance costs — (6 ) Long-term debt to financing trusts $ — $ 252 __________ (a) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within BGE’s Consolidated Balance Sheets. On August 28, 2017, BGE redeemed all of the outstanding shares of BGE Capital Trust II 6.20% Preferred Securities (“Securities”), pursuant to the optional redemption provisions of the Indenture under which the Securities were issued. The redemption price per share was $25.19, which equaled the stated value per share plus accrued and unpaid dividends to, but excluding, the redemption date. No dividends on the Securities redeemed were accrued on or after the redemption date, nor did any interest accrue on amounts held to pay the redemption price. PHI Successor Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2018 - 2045 $ 4,743 $ 4,569 Senior unsecured notes 7.45 % 2017 - 2032 185 266 Unsecured Tax-Exempt Bonds 5.40 % 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % 2018 - 2027 26 40 Transition bonds (b) 5.05 % - 5.55 % 2020 - 2023 90 124 Notes payable and other (c) 6.20 % - 8.88 % 2018 - 2022 33 46 Total long-term debt 5,189 5,157 Unamortized debt discount and premium, net 5 1 Unamortized debt issuance costs (6 ) (2 ) Fair value adjustment 686 742 Long-term debt due within one year (396 ) (253 ) Long-term debt $ 5,478 $ 5,645 __________ (a) Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture. (b) Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets. (c) Includes Pepco's capital lease obligations of $27 million and $39 million at December 31, 2017 and 2016 , respectively. Pepco Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2043 $ 2,535 $ 2,335 Notes payable and other (b) 6.20 % - 8.88 % 2018 - 2022 35 46 Total long-term debt 2,570 2,381 Unamortized debt discount and premium, net 2 (2 ) Unamortized debt issuance costs (32 ) (30 ) Long-term debt due within one year (19 ) (16 ) Long-term debt $ 2,521 $ 2,333 __________ (a) Substantially all of Pepco's assets are subject to the lien of its respective mortgage indenture. (b) Includes capital lease obligations of $27 million and $39 million at December 31, 2017 and 2016 , respectively. Lease payments of $13 million and $14 million will be made in 2018 and 2019 , respectively. DPL Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.50 % - 4.15 % 2023 - 2045 $ 1,171 $ 1,196 Unsecured Tax-Exempt Bonds 5.40 % 2024 - 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % 2018 - 2027 26 40 Total long-term debt 1,309 1,348 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (11 ) (10 ) Long-term debt due within one year (83 ) (119 ) Long-term debt $ 1,217 $ 1,221 __________ (a) Substantially all of DPL's assets are subject to the lien of its respective mortgage indenture. ACE Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.38 % - 7.75 % 2018 - 2036 $ 1,037 $ 1,038 Transition bonds (b) 5.05 % - 5.55 % 2020 - 2023 90 124 Total long-term debt 1,127 1,162 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (5 ) (6 ) Long-term debt due within one year (281 ) (35 ) Long-term debt $ 840 $ 1,120 __________ (a) Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture. (b) Maturities of ACE's Transition Bonds outstanding at December 31, 2017 are $31 million in 2018, $18 million in 2019, $20 million in 2020 and $21 million in 2021. Long-term debt maturities at Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE in the periods 2018 through 2022 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2018 $ 2,075 $ 346 $ 840 $ 500 $ — $ 383 $ 19 $ 83 $ 281 2019 959 615 300 — — 44 14 12 18 2020 3,564 2,144 500 — — 20 — — 20 2021 1,513 1 350 300 300 262 2 — 260 2022 3,084 1,024 — 350 250 310 310 — — Thereafter 22,852 (a) 4,825 5,892 (b) 1,959 (c) 2,050 4,170 2,225 1,214 548 Total $ 34,047 $ 8,955 $ 7,882 $ 3,109 $ 2,600 $ 5,189 $ 2,570 $ 1,309 $ 1,127 __________ (a) Includes $390 million due to ComEd and PECO financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts. Junior Subordinated Notes In June 2014, Exelon issued $1.15 billion of junior subordinated notes in the form of 23 million equity units at a stated amount of $50.00 per unit. Each equity unit represented an undivided beneficial ownership interest in Exelon’s $1.15 billion of 2.50% junior subordinated notes due in 2024 (“2024 notes”) and a forward equity purchase contract. As contemplated in the June 2014 equity unit structure, in April 2017, Exelon completed the remarketing of the 2024 notes into $1.15 billion of 3.497% junior subordinated notes due in 2022 (“Remarketing”). Exelon conducted the Remarketing on behalf of the holders of equity units and did not directly receive any proceeds therefrom. Instead, the former holders of the 2024 notes used debt remarketing proceeds towards settling the forward equity purchase contract with Exelon on June 1, 2017. Exelon issued approximately 33 million shares of common stock from treasury stock and received $1.15 billion upon settlement of the forward equity purchase contract. When reissuing treasury stock Exelon uses the average price paid to repurchase shares to calculate a gain or loss on issuance and records gains or losses directly to retained earnings. A loss on reissuance of treasury shares of $1.05 billion was recorded to retained earnings as of December 31, 2017 . See Note 21 — Earnings Per Share for further information on the issuance of common stock. Nonrecourse Debt Exelon and Generation have issued nonrecourse debt financing, in which approximately $3 billion of generating assets have been pledged as collateral at December 31, 2017 . Borrowings under these agreements are secured by the assets and equity of each respective project. The lenders do not have recourse against Exelon or Generation in the event of a default. If a specific project financing entity does not maintain compliance with its specific nonrecourse debt financing covenants, there could be a requirement to accelerate repayment of the associated debt or other borrowings earlier than the stated maturity dates. In these instances, if such repayment was not satisfied, the lenders or security holders would generally have rights to foreclose against the project-specific assets and related collateral. The potential requirement to satisfy its associated debt or other borrowings earlier than otherwise anticipated could lead to impairments due to a higher likelihood of disposing of the respective project-specific assets significantly before the end of their useful lives. Denver Airport. In June 2011, Generation entered into a 20-year, $7 million solar loan agreement to finance a solar construction project in Denver, Colorado. The agreement is scheduled to mature on June 30, 2031. The agreement bears interest at a fixed rate of 5.50% annually with interest payable annually. As of December 31, 2017 , $ 6 million was outstanding. CEU Upstream. In July 2011, CEU Holdings, LLC, a wholly owned subsidiary of Generation, entered into a 5-year reserve based lending agreement (RBL) associated with certain Upstream oil and gas properties. The lenders do not have recourse against Exelon or Generation in the event of default pursuant to the RBL. Borrowings under this arrangement are secured by the assets and equity of CEU Holdings. In December 2016, substantially all of the Upstream natural gas and oil exploration and production assets were sold for $37 million . The proceeds were used to reduce the debt balance by $31 million . The remaining proceeds of $6 million were being held in escrow. In addition, during 2016, $15 million of the debt was repaid using CEU Holding’s cash, resulting in an outstanding debt balance of $22 million at December 31, 2016. During 2017, additional assets were sold for $1 million and the remaining $6 million in escrow was released and applied to the debt balance resulting in an outstanding amount of $15 million at December 31, 2017. Upon final resolution, CEU Holdings will be released of its obligations regardless of the amount of asset sale proceeds received. The ultimate resolution of this matter has no direct effect on any Exelon or Generation credit facilities or other debt of an Exelon entity. At December 31, 2017, the outstanding debt balance of $15 million was classified within Long term debt due within one year on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 4 — Mergers, Acquisitions and Dispositions and Note 7 — Impairment of Long-Lived Assets and Intangibles for additional information. Holyoke Solar Cooperative. In October 2011, Generation entered into a 20-year, $11 million solar loan agreement related to a solar construction project in Holyoke, Massachusetts. The agreement is scheduled to mature on December 2031. The agreement bears interest at a fixed rate of 5.25% annually with interest payable monthly. As of December 31, 2017 , $9 million was outstanding. Antelope Valley Solar Ranch One. In December 2011, the DOE Loan Programs Office issued a guarantee for up to $646 million for a nonrecourse loan from the Federal Financing Bank to support the financing of the construction of the Antelope Valley facility. The project became fully operational in the first half of 2014. The loan will mature on January 5, 2037. Interest rates on the loan were fixed upon each advance at a spread of 37.5 basis points above U.S. Treasuries of comparable maturity. The advances were completed as of December 31, 2015 and the outstanding loan balance will bear interest at an average blended interest rate of 2.82% . As of December 31, 2017 , $530 million was outstanding. In addition, Generation has issued letters of credit to support its equity investment in the project. As of December 31, 2017 , Generation had $105 million in letters of credit outstanding related to the project. Continental Wind. In September 2013, Continental Wind, LLC (Continental Wind), an indirect subsidiary of Exelon and Generation, completed the issuance and sale of $613 million senior secured notes. Continental Wind owns and operates a portfolio of wind farms in Idaho, Kansas, Michigan, Oregon, New Mexico and Texas with a total net capacity of 667 MW. The net proceeds were distributed to Generation for its general business purposes. The notes are scheduled to mature on February 28, 2033. The notes bear interest at a fixed rate of 6.00% with interest payable semi-annually. As of December 31, 2017 , $512 million was outstanding. In addition, Continental Wind entered into a $131 million letter of credit facility and $10 million working capital revolver facility. Continental Wind has issued letters of credit to satisfy certain of its credit support and security obligations. As of December 31, 2017 , the Continental Wind letter of credit fa

Income Taxes (All Registrants)

Income Taxes (All Registrants)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes (All Registrants)	Income Taxes (All Registrants) Corporate Tax Reform (All Registrants) On December 22, 2017, President Trump signed the TCJA into law. The TCJA makes many significant changes to the Internal Revenue Code, including, but not limited to, (1) reducing the U.S. federal corporate tax rate from 35% to 21% ; (2) creating a 30% limitation on deductible interest expense (not applicable to regulated utilities); (3) allowing 100% expensing for the cost of qualified property (not applicable to regulated utilities); (4) eliminating the domestic production activities deduction; (5) eliminating the corporate alternative minimum tax and changing how existing alternative minimum tax credits can be realized; and (6) changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017. The most significant change that impacts the Registrants is the reduction of the corporate federal income tax rate from 35% to 21% beginning January 1, 2018. Pursuant to the enactment of the TCJA, the Registrants remeasured their existing deferred income tax balances as of December 31, 2017 to reflect the decrease in the corporate income tax rate from 35% to 21% , which resulted in a material decrease to their net deferred income tax liability balances as shown in the table below. Generation recorded a corresponding net decrease to income tax expense, while the Utility Registrants recorded corresponding regulatory liabilities or assets to the extent such amounts are probable of settlement or recovery through customer rates and an adjustment to income tax expense for all other amounts. The amount and timing of potential settlements of the established net regulatory liabilities will be determined by the Utility Registrants’ respective rate regulators, subject to certain IRS “normalization” rules. See Note 3 — Regulatory Matters for further information. The Registrants have completed their assessment of the majority of the applicable provisions in the TCJA and have recorded the associated impacts as of December 31, 2017. As discussed further below, under SAB 118 issued by the SEC in December 2017, the Registrants have recorded provisional income tax amounts as of December 31, 2017 for changes pursuant to the TCJA related to depreciation for which the impacts could not be finalized upon issuance of the Registrants’ financial statements, but for which reasonable estimates could be determined. For property acquired and placed-in-service after September 27, 2017, the TCJA repeals 50% bonus depreciation for all taxpayers and in addition provides for 100% expensing for taxpayers other than regulated utilities. As a result, Generation will be required to evaluate the contractual terms of its fourth quarter 2017 capital additions and determine if they qualify for 100% expensing under the TCJA as compared to 50% bonus depreciation under prior tax law. Similarly, the Utility Registrants will be required to evaluate the contractual terms of their fourth quarter 2017 capital additions to determine whether they still qualify for the prior tax law’s 50% bonus depreciation as compared to no bonus depreciation pursuant to the TCJA. As of December 31, 2017, the Registrants have not completed this analysis but were able to record a reasonable estimate of the effects of these changes based on capital costs incurred at each of the Registrants prior to and after the beginning of the fourth quarter of 2017. At Generation, any required changes to the provisional estimates during the measurement period related to the above item would result in an adjustment to current income tax expense at 35% and a corresponding adjustment to deferred income tax expense at 21% and such changes could be material to Generation’s future results of operations. At the Utility Registrants, any required changes to the provisional estimates would result in the recording of regulatory assets or liabilities to the extent such amounts are probable of settlement or recovery through customer rates and a net change to income tax expense for any other amounts. The Registrants expect any final adjustments to the provisional amounts to be recorded by the third quarter of 2018, which could be material to the Registrants’ future results of operations or financial positions. The accounting for all other applicable provisions of the TCJA is considered complete based on our current interpretation of the provisions of the TCJA as enacted as of December 31, 2017. While the Registrants have recorded the impacts of the TCJA based on their interpretation of the provisions as enacted, it is expected that technical corrections or other forms of guidance will be issued during 2018, which could result in material changes to previously finalized provisions. At this time, most states have not provided guidance regarding TCJA impacts and may issue guidance in 2018 which may impact estimates. The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: Successor Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Decrease to Deferred Income Tax Liability Balances $8,624 $1,895 $2,819 $1,407 $1,120 $1,944 $968 $540 $456 Successor Exelon Generation ComEd PECO (c) BGE PHI Pepco DPL ACE Net Regulatory Liability Recorded (a) $7,315 N/A $2,818 $1,394 $1,124 $1,979 $976 $545 $458 Successor Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Deferred Income Tax Benefit/(Expense) Recorded $1,309 $1,895 $1 $13 $(4) $(35) $(8) $(5) $(2) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information. The net regulatory liabilities above include (1) amounts subject to IRS “normalization” rules that are required to be passed back to customers generally over the remaining useful life of the underlying assets giving rise to the associated deferred income taxes, and (2) amounts for which the timing of settlement with customers is subject to determinations by the rate regulators. The table below sets forth the Registrants’ estimated categorization of their net regulatory liabilities as of December 31, 2017. The amounts in the table below are shown on an after-tax basis reflecting future net cash outflows after taking into consideration the income tax benefits associated with the ultimate settlement with customers. Successor Exelon ComEd PECO (a) BGE PHI PEPCO DPL ACE Subject to IRS Normalization Rules $3,040 $1,400 $533 $459 $648 $299 $195 $153 Subject to Rate Regulator Determination 1,694 573 43 324 754 391 194 170 Net Regulatory Liabilities $4,734 $1,973 $576 $783 $1,402 $690 $389 $ 323 _________ (a) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information. The net regulatory liability amounts subject to the IRS normalization rules generally relate to property, plant and equipment with remaining useful lives ranging from 30 to 40 years across the Utility Registrants. For the other amounts, rate regulators could require the passing back of amounts to customers over shorter time frames. Components of Income Tax Expense or Benefit Income tax expense (benefit) from continuing operations is comprised of the following components: For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 194 $ 584 $ (191 ) $ 71 $ 74 $ (60 ) $ (20 ) $ (24 ) $ (12 ) Deferred (469 ) (2,003 ) 523 28 101 250 114 82 34 Investment tax credit amortization (25 ) (21 ) (2 ) — (1 ) (1 ) — — — State Current 14 65 (49 ) 14 (5 ) (4 ) (2 ) — — Deferred 161 — 136 (9 ) 49 32 13 13 4 Total $ (125 ) $ (1,375 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26 Successor Predecessor For the Year Ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Included in operations: Federal Current $ 60 $ 513 $ (135 ) $ 63 $ 51 $ (118 ) $ (88 ) $ (26 ) $ (281 ) $ — Deferred 607 (247 ) 379 72 88 136 97 22 283 10 Investment tax credit amortization (24 ) (20 ) (2 ) — (1 ) — — — (1 ) — State Current 39 45 (4 ) 9 5 7 1 — (11 ) — Deferred 79 (1 ) 63 5 31 16 12 — 13 7 Total $ 761 $ 290 $ 301 $ 149 $ 174 $ 41 $ 22 $ (4 ) $ 3 $ 17 For the Year Ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 407 $ 546 $ (80 ) $ 64 $ 25 $ 12 $ (54 ) $ (27 ) $ (2 ) Deferred 566 16 310 69 126 103 126 73 27 Investment tax credit amortization (22 ) (19 ) (2 ) — (1 ) (1 ) — — — State Current (86 ) (90 ) 7 (10 ) — 17 6 2 3 Deferred 208 49 45 20 39 32 24 1 5 Total $ 1,073 $ 502 $ 280 $ 143 $ 189 $ 163 $ 102 $ 49 $ 33 Rate Reconciliation The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: For the Year Ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 2.3 3.0 5.7 0.6 5.4 4.8 3.2 5.4 5.6 Qualified nuclear decommissioning trust fund income 3.8 10.0 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.2 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (a) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.8 ) — — — — — — — Noncontrolling interests 0.1 0.3 — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.7 ) (1.3 ) — — — (9.5 ) (6.3 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.7 ) — — — — — — — Tax Cut and Jobs Act of 2017 (b) (33.1 ) (130.1 ) 0.1 (2.3 ) 0.9 6.4 2.7 2.5 1.6 Other 0.1 (0.4 ) 0.2 (0.1 ) 0.2 (0.1 ) (0.2 ) 0.1 (0.4 ) Effective income tax rate (3.3 )% (96.2 )% 42.4 % 19.3 % 41.5 % 37.5 % 33.9 % 37.0 % 25.2 % Successor Predecessor For the Year Ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL (c) ACE (c) PHI (c) PHI U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit (d) 3.3 3.3 5.6 1.3 5.0 15.7 52.7 6.2 5.8 11.9 Qualified nuclear decommissioning trust fund income 3.4 7.8 — — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (2.3 ) (0.3 ) (0.1 ) (0.1 ) (0.2 ) (3.7 ) 0.8 1.4 (0.9 ) Plant basis differences (4.8 ) — (0.6 ) (9.6 ) (2.7 ) (22.8 ) (25.5 ) 10.3 39.0 (13.5 ) Production tax credits and other credits (3.6 ) (8.2 ) — — — — — — — — Noncontrolling interests (0.2 ) (0.3 ) — — — — — — — — Statute of limitations expiration (0.4 ) (1.7 ) — — — — — — — — Penalties 1.9 — 4.5 — — — — — (0.7 ) — Merger Expenses 5.5 1.1 — — — 23.5 112.9 (44.9 ) (89.0 ) 11.1 Other (e) (0.6 ) (1.5 ) 0.1 (1.2 ) — (1.8 ) (2.2 ) 1.3 3.3 3.6 Effective income tax rate 38.3 % 33.2 % 44.3 % 25.4 % 37.2 % 49.4 % 169.2 % 8.7 % (5.2 )% 47.2 % For the Year Ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.7 1.0 4.9 1.0 5.3 6.6 6.7 1.7 5.7 Qualified nuclear decommissioning trust fund loss (0.4 ) (0.8 ) — — — — — — — Domestic production activities deduction (0.7 ) (1.3 ) — — — — — — — Health care reform legislation — — — — 0.1 — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (1.5 ) (0.3 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.4 ) (0.6 ) Plant basis differences (1.5 ) — (0.1 ) (8.7 ) (0.7 ) (4.3 ) (5.8 ) (2.3 ) (1.3 ) Production tax credits and other credits (1.9 ) (3.4 ) — — — — — — — Noncontrolling interests 0.3 0.5 — — — — — — — Statute of limitations expiration (1.4 ) (2.4 ) — — — — — — — Other (f) — — 0.2 0.2 — (3.2 ) (0.5 ) 5.2 6.4 Effective income tax rate 32.2 % 27.1 % 39.7 % 27.4 % 39.6 % 33.9 % 35.3 % 39.2 % 45.2 % __________ (a) Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL, and ACE of $ 35 million , $ 3 million , $ 5 million , $ 27 million , $ 14 million , $ 6 million , and $ 7 million , respectively (See Footnote 3 - Regulatory Matters). (b) Included are impacts for TJCA other than the corporate rate change, including revisions further limiting tax deductions for compensation of certain highest paid executives, the write-off of foreign tax credit carryforwards, and loss of a 2015 domestic production activities deduction due to an NOL carryback. (c) DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016 , and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016 . As a result, positive percentages represent an income tax benefit for the periods presented. (d) Includes a remeasurement of uncertain state income tax positions for Pepco and DPL. (e) At PECO, includes a cumulative adjustment related to an anticipated gas repairs tax return accounting method change. The method change request was filed and accepted in 2017. No change to the results recorded as of December 31, 2016. (f) Includes impacts of the PHI Global Settlement for Pepco, DPL, ACE and PHI. Tax Differences and Carryforwards The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2017 and 2016 are presented below: As of December 31, 2017 (a) Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,490 ) $ (2,819 ) $ (3,825 ) $ (1,762 ) $ (1,368 ) $ (2,521 ) $ (1,152 ) $ (717 ) $ (607 ) Accrual based contracts 150 (66 ) — — — 216 — — — Derivatives and other financial instruments (85 ) (66 ) (2 ) — — 3 — — — Deferred pension and postretirement obligation 1,463 (205 ) (285 ) (15 ) (29 ) (130 ) (78 ) (51 ) (18 ) Nuclear decommissioning activities (553 ) (553 ) — — — — — — — Deferred debt refinancing costs 217 26 (8 ) (1 ) (3 ) 203 (4 ) (2 ) (1 ) Regulatory assets and liabilities (688 ) — 489 (90 ) 136 (184 ) 39 88 86 Tax loss carryforward 344 76 33 9 11 156 40 68 35 Tax credit carryforward 861 868 1 — — 6 — — — Investment in partnerships (434 ) (416 ) — — — — — — — Other, net 746 78 141 71 13 193 94 14 16 Deferred income tax liabilities (net) $ (10,469 ) $ (3,077 ) $ (3,456 ) $ (1,788 ) $ (1,240 ) $ (2,058 ) $ (1,061 ) $ (600 ) $ (489 ) Unamortized investment tax credits (732 ) (705 ) (13 ) (1 ) (4 ) (8 ) (2 ) (3 ) (4 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,201 ) $ (3,782 ) $ (3,469 ) $ (1,789 ) $ (1,244 ) $ (2,066 ) $ (1,063 ) $ (603 ) $ (493 ) __________ (a) Includes remeasurement impacts related to the TCJA. As of December 31, 2016 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (17,966 ) $ (4,192 ) $ (5,034 ) $ (3,095 ) $ (1,977 ) $ (3,586 ) $ (1,678 ) $ (973 ) $ (869 ) Accrual based contracts 434 (115 ) — — — 548 — — — Derivatives and other financial instruments (179 ) (162 ) (3 ) — — (1 ) — — — Deferred pension and postretirement obligation 2,287 (316 ) (453 ) (18 ) (43 ) (111 ) (122 ) (74 ) (21 ) Nuclear decommissioning activities (509 ) (509 ) — — — — — — — Deferred debt refinancing costs 325 44 (13 ) (1 ) (3 ) 293 (7 ) (4 ) (2 ) Regulatory assets and liabilities (3,319 ) — (226 ) 10 (240 ) (1,205 ) (194 ) (75 ) (69 ) Tax loss carryforward 189 61 29 — 22 77 27 39 14 Tax credit carryforward 446 493 — — — — — — — Investment in partnerships (650 ) (650 ) — — — — — — — Other, net 1,485 403 351 99 27 225 66 34 34 Deferred income tax liabilities (net) $ (17,457 ) $ (4,943 ) $ (5,349 ) $ (3,005 ) $ (2,214 ) $ (3,760 ) $ (1,908 ) $ (1,053 ) $ (913 ) Unamortized investment tax credits (658 ) (626 ) (15 ) (1 ) (5 ) (9 ) (2 ) (3 ) (4 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (18,115 ) $ (5,569 ) $ (5,364 ) $ (3,006 ) $ (2,219 ) $ (3,769 ) $ (1,910 ) $ (1,056 ) $ (917 ) The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2017 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Federal Federal net operating loss $ 624 (a) $ — $ 156 $ 7 $ — $ 261 $ 82 $ 81 $ 63 Deferred taxes on Federal net operating loss 131 — 33 1 — 55 17 17 13 Federal general business credits carryforwards 861 (b) 868 1 — 1 5 — — — State State net operating losses 3,555 (c) 1,479 (c) — 98 (e) 177 (d) 1,440 (f) 347 (g) 753 (h) 299 (i) Deferred taxes on state tax attributes (net) 233 97 — 8 12 98 23 51 21 Valuation allowance on state tax attributes 29 23 — — 1 5 — — — __________ (a) Exelon's federal net operating loss will begin expiring in 2034. (b) Exelon’s federal general business credit carryforwards will begin expiring in 2033. (c) Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2018. (d) BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026. (e) PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031. (f) PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036. (g) Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2028. (h) DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2027. (i) ACE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031. Tabular Reconciliation of Unrecognized Tax Benefits The following tables provide a reconciliation of the Registrants’ unrecognized tax benefits as of December 31, 2017 , 2016 and 2015 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2017 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Increases based on tax positions related to 2017 — — — — — — — — — Decreases based on tax positions related to 2017 — — — — — — — — — Change to positions that only affect timing — — — — — — — — — Increases based on tax positions prior to 2017 28 — 14 — — 14 — — 14 Decreases based on tax positions prior to 2017 (196 ) (17 ) — — — (61 ) (21 ) (16 ) (22 ) Decrease from settlements with taxing authorities (5 ) (5 ) — — — — — — — Decreases from expiration of statute of limitations — — — — — — — — — Unrecognized tax benefits at December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Successor Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2016 $ 1,078 $ 534 $ 142 $ — $ 120 $ 22 $ 8 $ 3 $ — Merger balance transfer 22 5 — — — (5 ) — — — Increases based on tax positions related to 2016 108 10 — — — 59 21 16 22 Decreases based on tax positions related to 2016 — — — — — — — — — Change to positions that only affect timing (332 ) (12 ) (154 ) — — — — — — Increases based on tax positions prior to 2016 88 — — — — 96 51 18 — Decreases based on tax positions prior to 2016 (21 ) (20 ) — — — — — — — Decrease from settlements with taxing authorities (27 ) (27 ) — — — — — — — Decreases from expiration of statute of limitations — — — — — — — — — Unrecognized tax benefits at December 31, 2016 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2015 $ 1,829 $ 1,357 $ 149 $ 44 $ — $ 702 $ — $ — $ — Increases based on tax positions related to 2015 108 — — — 106 — — — — Decreases based on tax positions related to 2015 — — — — — — — — — Change to positions that only affect timing (705 ) (659 ) (7 ) (44 ) — (688 ) — — — Increases based on tax positions prior to 2015 79 65 — — 14 11 8 3 — Decreases based on tax positions prior to 2015 (116 ) (112 ) — — — — — — — Decreases from settlements with taxing authorities (31 ) (31 ) — — — — — — — Decreases from expiration of statute of limitations (86 ) (86 ) — — — (3 ) — — — Unrecognized tax benefits at December 31, 2015 $ 1,078 $ 534 $ 142 $ — $ 120 $ 22 $ 8 $ 3 $ — Exelon established a liability for an uncertain tax position associated with the tax deductibility of certain merger commitments incurred by Exelon in connection with the acquisitions of Constellation in 2012 and PHI in 2016. In the first quarter 2017, as a part of its examination of Exelon’s return, the IRS National Office issued guidance concurring with Exelon’s position that the merger commitments were deductible. As a result, Exelon, Generation, PHI, Pepco, DPL, and ACE decreased their liability for unrecognized tax benefits by $146 million , $19 million , $59 million , $21 million , $16 million , and $22 million , respectively, in the first quarter of 2017 resulting in a benefit to Income taxes on Exelon’s, Generation’s, PHI’s, Pepco’s, DPL’s and ACE’s Consolidated Statements of Operations and Comprehensive Income and corresponding decreases in their effective tax rates. Exelon reduced the liability related to the uncertain tax position associated with the like-kind exchange in the second quarter of 2017. Please see the Other Income Tax Matters section below for additional details related to the like-kind exchange adjustments made in the second quarter of 2017. Exelon and Generation have $7 million of unrecognized tax benefits at December 31, 2017 for which the ultimate tax benefit is highly certain, but for which there is uncertainty about the timing of such benefits. Exelon, Generation, and ComEd had $83 million , $7 million , and $(12) million of unrecognized tax benefits at December 31, 2016 for which the ultimate tax benefit is highly certain, but for which there is uncertainty about the timing of such benefits. Exelon, Generation, and ComEd had $415 million , $20 million and $142 million of unrecognized tax benefits at December 31, 2015 for which the ultimate tax benefit is highly certain, but for which there is uncertainty about the timing of such benefits. The disallowance of such positions would not materially affect the annual effective tax rate but would accelerate the payment of cash to, or defer the receipt of the cash tax benefit from, the taxing authority to an earlier or later period respectively. Unrecognized tax benefits that if recognized would affect the effective tax rate Exelon, Generation, ComEd and PHI have $523 million , $461 million , $2 million , and $32 million , respectively, of unrecognized tax benefits at December 31, 2017 that, if recognized, would decrease the effective tax rate. BGE, PHI, Pepco, DPL, and ACE have $120 million , $94 million , $59 million , $21 million , and $14 million of unrecognized tax benefits at December 31, 2017 that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Exelon, Generation, PHI, Pepco, DPL, and ACE had $633 million , $483 million , $93 million , $21 million , $16 million , and $22 million , respectively, of unrecognized tax benefits at December 31, 2016 that, if recognized, would decrease the effective tax rate. BGE, PHI, Pepco and DPL had $120 million , $80 million , $59 million , and $21 million of unrecognized tax benefits at December 31, 2016 that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Exelon, Generation, and PHI had $538 million , $509 million , and $11 million , respectively, of unrecognized tax benefits at December 31, 2015 that, if recognized, would decrease the effective tax rate. BGE, PHI, Pepco and DPL had $120 million , $11 million , $8 million and $3 million of unrecognized tax benefits at December 31, 2015 that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Reasonably possible the total amount of unrecognized tax benefits could significantly increase or decrease within 12 months after the reporting date Like-Kind Exchange As of December 31, 2017 , Exelon and ComEd have approximately $39 million and $ 2 million , respectively, of unrecognized federal and state income tax benefits that could significantly decrease within the 12 months after the reporting date due to a final resolution of the like-kind exchange litigation described below. The recognition of these unrecognized tax benefits would decrease Exelon and ComEd's effective tax rate. Settlement of Income Tax Audits, Refund Claims, and Litigation As of December 31, 2017 , Exelon, Generation, BGE, PHI, Pepco, DPL, and ACE have approximately $683 million , $469 million , $120 million , $94 million , $59 million , $ 21 million , $ 14 million respectively, of unrecognized federal and state tax benefits that could significantly decrease within the 12 months after the reporting date as a result of completing audits, potential settlements, refund claims, and the outcomes of pending court cases. Of the above unrecognized tax benefits, Exelon and Generation have $462 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefit related to BGE, Pepco, DPL and ACE, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Total amounts of interest and penalties recognized The following tables represent the net interest and penalties receivable (payable), including interest and penalties related to tax positions reflected in the Registrants’ Consolidated Balance Sheets. Successor Net interest receivable (payable) as of Exelon (a) Generation ComEd (a) PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 233 $ (3 ) $ 4 $ — $ — $ 2 $ — $ — $ — December 31, 2016 (507 ) 46 (384 ) 8 (1 ) 2 1 — 1 Successor Net penalties receivable (payable) as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ (17 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2016 (106 ) — (86 ) — — — — — — __________ (a) Change in balance attributable to Like-Kind Exchange interest payments, see Other Tax Matters for further discussion. The following tables set forth the net interest and penalty expense, including interest and penalties related to tax positions, recognized in Interest expense, net and Other, net in Other income and deductions in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Net interest expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2017 $ 37 $ (1 ) $ 11 $ — $ — $ — $ — $ — December 31, 2016 165 (13 ) 117 — — 6 — (1 ) December 31, 2015 (13 ) (31 ) 7 — — (4 ) — — Net penalty expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2017 $ (2 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2016 106 — 86 — — — — — December 31, 2015 — — — — — — — — Successor Predecessor PHI December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 December 31, 2015 Net interest expense (income) $ — $ (2 ) $ — $ (34 ) Description of tax years open to assessment by major jurisdiction Taxpayer Open Years Exelon (and predecessors) and subsidiaries consolidated Federal income tax returns 1999, 2001-2016 PHI Holdings and subsidiaries consolidated Federal income tax returns 2013-2016 Exelon and subsidiaries Illinois unitary income tax returns 2013-2016 Constellation Illinois unitary income tax returns 2011-March 2012 Constellation combined New York corporate income tax returns 2010-March 2012 Exelon combined New York corporate income tax returns 2011-2016 Exelon New Jersey corporate income tax returns 2013-2015 Various separate company (excluding PECO) Pennsylvania corporate net income tax returns 2011-2016 PECO Pennsylvania separate company returns 2010-2016 DPL Delaware separate company returns Same as Federal ACE New Jersey separate company returns 2013-2016 Exelon and subsidiaries District of Columbia corporate income tax returns 2014-2016 PHI Holdings and subsidiaries District of Columbia corporate income tax returns 2014-2016 Various separate company Maryland corporate net income tax returns Same as Federal Other Tax Matters Like-Kind Exchange Exelon, through its ComEd subsidiary, took a position on its 1999 income tax return to defer approximately $1.2 billion of tax gain on the sale of ComEd’s fossil generating assets. The gain was deferred by reinvesting a portion of the proceeds from the sale in qualifying replacement property under the like-kind exchange provisions of the IRC. The like-kind exchange replacement property purchased by Exelon included interests in three municipal-owned electric generation facilities which were properly leased back to the municipalities. The IRS disagreed with this position and asserted that the entire gain of approximately $1.2 billion was taxable in 1999. Exelon was unable to reach agreement with the IRS regarding the dispute over the like-kind exchange position. The IRS asserted that the Exelon purchase and leaseback transaction was substantially similar to a leasing transaction, known as a SILO, which the IRS does not respect as the acquisition of an ownership interest in property. A SILO is a “listed transaction” that the IRS has identified as a potentially abusive tax shelter under guidance issued in 2005. Accordingly, the IRS asserted that the sale of the fossil plants followed by the purchase and leaseback of the municipal owned generation facilities did not qualify as a like-kind exchange and the gain on the sale is fully subject to tax. The IRS also asserted a penalty of approximately $90 million for a substantial understatement of tax. On September 30, 2013, the IRS issued a notice of deficiency to Exelon for the like-kind exchange position. Exelon filed a petition on December 13, 2013 to initiate litigation in the United States Tax Court (Tax Court) and the trial took place in August of 2015. Exelon was not required to remit any part of the asserted tax or penalty in order to litigate the issue. On September 19, 2016, the Tax Court rejected Exelon’s position in the case and ruled that Exelon was not entitled to defer gain on the transaction. In addition, contrary to Exelon’s evaluation that the penalty was unwarranted, the Tax Court ruled that Exelon is liable for the penalty and interest due on the asserted penalty. In June of 2017, the IRS finalized its computation of tax, penalties and interest owed by Exelon pursuant to the Tax Court’s decision. In September of 2017, Exelon appealed this decision to the U.S. Court of Appeals for the Seventh Circuit. In the first quarter of 2013, Exelon concluded that it was no longer more likely than not that the like-kind exchange position would be sustained and recorded charges to earnings representing the amount of interest expense (after-tax) and incremental state income tax expense that would be payable in the event Exelon is unsuccessful in litigation. Exelon agreed to hold ComEd harmless from any unfavorable impacts on ComEd’s equity of the after-tax interest and penalty amounts. Prior to the Tax Court’s decision, however, Exelon did not believe it was likely a penalty would be assessed based on applicable case law and the facts of the transaction. As a result, no charge had been recorded

Asset Retirement Obligations (A

Asset Retirement Obligations (All Registrants)	12 Months Ended
	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations (All Registrants)	Asset Retirement Obligations (All Registrants) Nuclear Decommissioning Asset Retirement Obligations Generation has a legal obligation to decommission its nuclear power plants following the expiration of their operating licenses. To estimate its decommissioning obligation related to its nuclear generating stations for financial accounting and reporting purposes, Generation uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimates and assumptions, and are based on decommissioning cost studies, cost escalation rates, probabilistic cash flow models and discount rates. Generation updates its ARO annually unless circumstances warrant more frequent updates, based on its review of updated cost studies and its annual evaluation of cost escalation factors and probabilities assigned to various scenarios. The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2016 to December 31, 2017 : Exelon and Generation Nuclear decommissioning ARO at January 1, 2016 $ 8,246 Accretion expense 436 Net increase for changes in and timing of estimated future cash flows 61 Costs incurred related to decommissioning plants (9 ) Nuclear decommissioning ARO at December 31, 2016 (a) 8,734 Accretion Expense 458 Acquisition of FitzPatrick 444 Net increase for changes in and timing of estimated future cash flows 34 Costs incurred related to decommissioning plants (8 ) Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 __________ (a) Includes $ 13 million and $ 10 million as the current portion of the ARO at December 31, 2017 and 2016 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. During 2017 , Generation’s total nuclear ARO increased by approximately $928 million , primarily reflecting year-to-date accretion of the ARO liability due to the passage of time, the recording of the fair value of the ARO, including subsequent purchase accounting adjustments, for the acquisition of FitzPatrick (see Note 4 — Mergers, Acquisitions and Dispositions ), the announced early retirement of TMI, and impacts of ARO updates completed during 2017 to reflect changes in amounts and timing of estimated decommissioning cash flows. The net $34 million increase in the ARO during 2017 for changes in the amounts and timing of estimated decommissioning cash flows was driven by multiple adjustments throughout the year, some with offsetting impacts. These adjustments include a $ 178 million increase due to higher assumed probabilities of early retirement of Salem and a $ 138 million increase in TMI’s ARO liability associated with the May 30, 2017 announcement to early retire the unit on September 30, 2019. The increase in the ARO liability for TMI incorporates the early shutdown date, increases the probabilities of longer term decommissioning scenarios, and reflects an increase in the estimated costs to decommission based on an updated decommissioning cost study. See Note 8 — Early Nuclear Plant Retirements for additional information regarding Salem and TMI. These increases in the ARO were partially offset by a $ 180 million decrease for refinements in estimated fleet wide labor costs expected to be incurred for certain on-site personnel during decommissioning as well as net decreases resulting from updates to the cost studies of Clinton, Quad Cities and Dresden. During 2016 , Generation’s ARO increased by approximately $488 million , primarily reflecting year-to-date accretion of the ARO liability of approximately $436 million due to the passage of time and impacts of ARO updates completed during 2016 to reflect changes in amounts and timing of estimated decommissioning cash flows. The $61 million increase in the ARO during 2016 for changes in the amounts and timing of estimated decommissioning cash flows was driven by multiple adjustments throughout the year, some with offsetting impacts. These adjustments include increases of $288 million resulting from the change in the assumed DOE spent fuel acceptance date for disposal from 2025 to 2030 as well as increases resulting from updates to the cost studies of Oyster Creek, Zion, Calvert Cliffs, Ginna and Nine Mile Point. These increases were partially offset by a decrease of $165 million resulting from changes to the decommissioning scenarios and their probabilities as well as reductions in estimated cost escalation rates, primarily for labor, energy and waste burial costs. Most of the increase to the ARO resulting from the June 2, 2016, announcement to early retire Clinton and Quad Cities was reversed pursuant to the December 7, 2016, enactment of the Illinois FEJA. See Note 8 — Early Nuclear Plant Retirements for additional information. Nuclear Decommissioning Trust Fund Investments NDT funds have been established for each generation station unit to satisfy Generation’s nuclear decommissioning obligations. Generally, NDT funds established for a particular unit may not be used to fund the decommissioning obligations of any other unit. The NDT funds associated with Generation's nuclear units have been funded with amounts collected from the previous owners and their respective utility customers. PECO is authorized to collect funds, in revenues, for decommissioning the former PECO nuclear plants through regulated rates, and these collections are scheduled through the operating lives of the former PECO plants. The amounts collected from PECO customers are remitted to Generation and deposited into the NDT funds for the unit for which funds are collected. Every five years, PECO files a rate adjustment with the PAPUC that reflects PECO’s calculations of the estimated amount needed to decommission each of the former PECO units based on updated fund balances and estimated decommissioning costs. The rate adjustment is used to determine the amount collectible from PECO customers. On March 31, 2017, PECO filed its Nuclear Decommissioning Cost Adjustment (NDCA) with the PAPUC proposing an annual recovery from customers of approximately $4 million . This amount reflects a decrease from the current approved annual collection of approximately $ 24 million primarily due to the removal of the collections for Limerick Units 1 and 2 as a result of the NRC approving the extension of the operating licenses for an additional 20 years. On August 8, 2017, the PAPUC approved the filing and the new rates became effective January 1, 2018. Any shortfall of funds necessary for decommissioning, determined for each generating station unit, is ultimately required to be funded by Generation, with the exception of a shortfall for the current decommissioning activities at Zion Station, where certain decommissioning activities have been transferred to a third-party (see Zion Station Decommissioning below) and the CENG units, where any shortfall is required to be funded by both Generation and EDF. Generation, through PECO, has recourse to collect additional amounts from PECO customers related to a shortfall of NDT funds for the former PECO units, subject to certain limitations and thresholds, as prescribed by an order from the PAPUC. Generally, PECO, and likewise Generation will not be allowed to collect amounts associated with the first $ 50 million of any shortfall of trust funds compared to decommissioning costs, as well as 5% of any additional shortfalls, on an aggregate basis for all former PECO units. The initial $ 50 million and up to 5% of any additional shortfalls would be borne by Generation. No recourse exists to collect additional amounts from utility customers for any of Generation's other nuclear units. With respect to the former ComEd and PECO units, any funds remaining in the NDTs after all decommissioning has been completed are required to be refunded to ComEd’s or PECO’s customers, subject to certain limitations that allow sharing of excess funds with Generation related to the former PECO units. With respect to Generation's other nuclear units, Generation retains any funds remaining after decommissioning. However, in connection with CENG's acquisition of the Nine Mile Point and Ginna plants and settlements with certain regulatory agencies, CENG is subject to certain conditions pertaining to nuclear decommissioning trust funds that, if met, could possibly result in obligations to make payments to certain third parties (clawbacks). For Nine Mile Point and Ginna, the clawback provisions are triggered only in the event that the required decommissioning activities are discontinued or not started or completed in a timely manner. In the event that the clawback provisions are triggered for Nine Mile Point, then, depending upon the triggering event, an amount equal to 50% of the total amount withdrawn from the funds for non-decommissioning activities or 50% of any excess funds in the trust funds above the amounts required for decommissioning (including spent fuel management and decommissioning) is to be paid to the Nine Mile Point sellers. In the event that the clawback provisions are triggered for Ginna, then an amount equal to any estimated cost savings realized by not completing any of the required decommissioning activities is to be paid to the Ginna sellers. Generation expects to comply with applicable regulations and timely commence and complete all required decommissioning activities. At December 31, 2017 and 2016 , Exelon and Generation had NDT fund investments totaling $ 13,349 million and $11,061 million , respectively. The increase is primarily driven by improved market performance and the acquisition of FitzPatrick. For additional information related to the NDT fund investments, refer to Note 11 — Fair Value of Financial Assets and Liabilities . The following table provides unrealized gains on NDT funds for 2017 , 2016 and 2015 : Exelon and Generation For the Years Ended December 31, 2017 2016 2015 Net unrealized gains (losses) on decommissioning trust funds—Regulatory Agreement Units (a) $ 455 $ 216 $ (282 ) Net unrealized gains (losses) on decommissioning trust funds—Non-Regulatory Agreement Units (b)(c) 521 194 (197 ) __________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $ (10) million , $(1) million and $ 7 million of net unrealized gains (losses) related to the Zion Station pledged assets in 2017 , 2016 and 2015 , respectively. Net unrealized gains related to Zion Station pledged assets are included in the Other current liabilities and Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets in 2017 and 2016, respectively. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends on NDT fund investments are recognized when earned and are included in Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends earned on the NDT fund investments for the Regulatory Agreement Units are eliminated within Other, net in Exelon’s and Generation’s Consolidated Statement of Operations and Comprehensive Income. Accounting Implications of the Regulatory Agreements with ComEd and PECO Based on the regulatory agreement with the ICC that dictates Generation’s obligations related to the shortfall or excess of NDT funds necessary for decommissioning the former ComEd units on a unit-by-unit basis, as long as funds held in the NDT funds are expected to exceed the total estimated decommissioning obligation, decommissioning-related activities, including realized and unrealized gains and losses on the NDT funds and accretion of the decommissioning obligation, are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. The offset of decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income results in an equal adjustment to the noncurrent payables to affiliates at Generation and an adjustment to the regulatory liabilities at Exelon. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability. Should the expected value of the NDT fund for any former ComEd unit fall below the amount of the expected decommissioning obligation for that unit, the accounting to offset decommissioning-related activities in the Consolidated Statement of Operations and Comprehensive Income for that unit would be discontinued, the decommissioning-related activities would be recognized in the Consolidated Statements of Operations and Comprehensive Income and the adverse impact to Exelon’s and Generation’s results of operations and financial positions could be material. As of December 31, 2017 , the NDT funds of each of the former ComEd units, except for Zion (see Zion Station Decommissioning below), are expected to exceed the related decommissioning obligation for each of the units. For the purposes of making this determination, the decommissioning obligation referred to is different, as described below, from the calculation used in the NRC minimum funding obligation filings based on NRC guidelines. Based on the regulatory agreement supported by the PAPUC that dictates Generation’s rights and obligations related to the shortfall or excess of trust funds necessary for decommissioning the former PECO units, regardless of whether the funds held in the NDT funds are expected to exceed or fall short of the total estimated decommissioning obligation, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. The offset of decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income results in an equal adjustment to the noncurrent payables to affiliates at Generation and an adjustment to the regulatory liabilities at Exelon. Likewise, PECO has recorded an equal noncurrent affiliate receivable from Generation and a corresponding regulatory liability. Any changes to the PECO regulatory agreements could impact Exelon’s and Generation’s ability to offset decommissioning-related activities within the Consolidated Statement of Operations and Comprehensive Income, and the impact to Exelon’s and Generation’s results of operations and financial positions could be material. The decommissioning-related activities related to the Non-Regulatory Agreement Units are reflected in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Refer to Note 3 — Regulatory Matters and Note 26 — Related Party Transactions for information regarding regulatory liabilities at ComEd and PECO and intercompany balances between Generation, ComEd and PECO reflecting the obligation to refund to customers any decommissioning-related assets in excess of the related decommissioning obligations. Zion Station Decommissioning On September 1, 2010, Generation completed an Asset Sale Agreement (ASA) with EnergySolutions Inc. and its wholly owned subsidiaries, EnergySolutions, LLC (EnergySolutions) and ZionSolutions, under which ZionSolutions has assumed responsibility for decommissioning Zion Station, which is located in Zion, Illinois and ceased operation in 1998. Specifically, Generation transferred to ZionSolutions substantially all of the assets (other than land) associated with Zion Station, including assets held in related NDT funds. In consideration for Generation’s transfer of those assets, ZionSolutions assumed decommissioning and other liabilities, excluding the obligation to dispose of SNF and decommission the SNF dry storage facility, associated with Zion Station. Pursuant to the ASA, ZionSolutions will periodically request reimbursement from the Zion Station-related NDT funds for costs incurred related to its decommissioning efforts at Zion Station. During 2013, EnergySolutions entered a definitive acquisition agreement and was acquired by another company. Generation reviewed the acquisition as it relates to the ASA to decommission Zion Station. Based on that review, Generation determined that the acquisition will not adversely impact decommissioning activities under the ASA. ZionSolutions is subject to certain restrictions on its ability to request reimbursements from the Zion Station NDT funds as defined within the ASA. Therefore, the transfer of the Zion Station assets did not qualify for asset sale accounting treatment and, as a result, the related NDT funds were reclassified to Pledged assets for Zion Station decommissioning within Generation’s and Exelon’s Consolidated Balance Sheets and will continue to be measured in the same manner as prior to the completion of the transaction. Additionally, the transferred ARO for decommissioning was replaced with a Payable for Zion Station decommissioning in Generation’s and Exelon’s Consolidated Balance Sheets. Changes in the value of the Zion Station NDT assets, net of applicable taxes, will be recorded as a change in the Payable to ZionSolutions. At no point will the payable to ZionSolutions exceed the project budget of the costs remaining to decommission Zion Station. Generation has retained its obligation for the SNF. Following ZionSolutions' completion of its contractual obligations and transfer of the NRC license to Generation, Generation will store the SNF at Zion Station until it is transferred to the DOE for ultimate disposal, and will complete all remaining decommissioning activities associated with the SNF dry storage facility. Generation has a liability of approximately $ 114 million , which is included within the nuclear decommissioning ARO at December 31, 2017 . Generation also has retained NDT assets to fund its obligation to maintain the SNF at Zion Station until transfer to the DOE and to complete all remaining decommissioning activities for the SNF storage facility. Any shortage of funds necessary to maintain the SNF and decommission the SNF storage facility is ultimately required to be funded by Generation. Any Zion Station NDT funds remaining after the completion of all decommissioning activities will be returned to ComEd customers in accordance with the applicable orders. The following table provides the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2017 and 2016 : Exelon and Generation 2017 2016 Carrying value of Zion Station pledged assets (a) $ 39 $ 113 Payable to Zion Solutions (b) 37 104 Current portion of payable to Zion Solutions (c) 37 90 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 942 878 __________ (a) Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017. (b) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized. (c) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (d) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings. ZionSolutions leased the land associated with Zion Station from Generation pursuant to a Lease Agreement. Under the Lease Agreement, ZionSolutions has committed to complete the required decommissioning work according to an established schedule and constructed a dry cask storage facility on the land and has loaded the SNF from the SNF pools onto the dry cask storage facility at Zion Station. Rent payable under the Lease Agreement is $ 1.00 per year, although the Lease Agreement requires ZionSolutions to pay property taxes associated with Zion Station and penalty rents may accrue if there are unexcused delays in the progress of decommissioning work at Zion Station or the construction of the dry cask SNF storage facility. To reduce the risk of default by ZionSolutions, EnergySolutions provided a $ 200 million letter of credit to be used to fund decommissioning costs in the event the NDT assets are insufficient. In accordance with the terms of the ASA, the letter of credit was reduced to $98 million in August 2017 due to the completion of key decommissioning milestones. EnergySolutions and its parent company have also provided a performance guarantee and EnergySolutions has entered into other agreements that will provide rights and remedies for Generation and the NRC in the case of other specified events of default, including a special purpose easement for disposal capacity at the EnergySolutions site in Clive, Utah, for all LLRW volume of Zion Station. NRC Minimum Funding Requirements NRC regulations require that licensees of nuclear generating facilities demonstrate reasonable assurance that funds will be available in specified minimum amounts to decommission the facility at the end of its life. The estimated decommissioning obligations as calculated using the NRC methodology differ from the ARO recorded on Generation’s and Exelon’s Consolidated Balance Sheets primarily due to differences in the type of costs included in the estimates, the basis for estimating such costs, and assumptions regarding the decommissioning alternatives to be used, potential license renewals, decommissioning cost escalation, and the growth rate in the NDT funds. Under NRC regulations, if the minimum funding requirements calculated under the NRC methodology are less than the future value of the NDT funds, also calculated under the NRC methodology, then the NRC requires either further funding or other financial guarantees. Key assumptions used in the minimum funding calculation using the NRC methodology at December 31, 2017 include: (1) consideration of costs only for the removal of radiological contamination at each unit; (2) the option on a unit-by-unit basis to use generic, non-site specific cost estimates; (3) consideration of only one decommissioning scenario for each unit; (4) the plants cease operation at the end of their current license lives (with no assumed license renewals for those units that have not already received renewals and with an assumed end-of-operations date of 2018 for Oyster Creek and 2019 for TMI); (5) the assumption of current nominal dollar cost estimates that are neither escalated through the anticipated period of decommissioning, nor discounted using the CARFR; and (6) assumed annual after-tax returns on the NDT funds of 2% ( 3% for the former PECO units, as specified by the PAPUC). In contrast, the key criteria and assumptions used by Generation to determine the ARO and to forecast the target growth in the NDT funds at December 31, 2017 include: (1) the use of site specific cost estimates that are updated at least once every five years; (2) the inclusion in the ARO estimate of all legally unavoidable costs required to decommission the unit (e.g., radiological decommissioning and full site restoration for certain units, on-site spent fuel maintenance and storage subsequent to ceasing operations and until DOE acceptance, and disposal of certain low-level radioactive waste); (3) the consideration of multiple scenarios where decommissioning and site restoration activities, as applicable, are completed under four possible scenarios ranging from 10 to 70 years after the cessation of plant operations; (4) the consideration of multiple end of life scenarios; (5) the measurement of the obligation at the present value of the future estimated costs and an annual average accretion of the ARO of approximately 5% through a period of approximately 30 years after the end of the extended lives of the units; and (6) an estimated targeted annual pre-tax return on the NDT funds of 4.8% to 6.4% (as compared to a historical 5-year annual average pre-tax return of approximately 8% ). Generation is required to provide to the NRC a biennial report by unit (annually for units that have been retired or are within five years of the current approved license life), based on values as of December 31, addressing Generation’s ability to meet the NRC minimum funding levels. Depending on the value of the trust funds, Generation may be required to take steps, such as providing financial guarantees through letters of credit or parent company guarantees or making additional contributions to the trusts, which could be significant, to ensure that the trusts are adequately funded and that NRC minimum funding requirements are met. As a result, Exelon’s and Generation’s cash flows and financial positions may be significantly adversely affected. Generation filed its biennial decommissioning funding status report with the NRC on March 31, 2017 for all units except for Zion Station which is included in a separate report to the NRC submitted by ZionSolutions (see Zion Station Decommissioning above) and FitzPatrick which is still owned by Entergy as of the NRC reporting period. This status report demonstrated adequate decommissioning funding assurance for all units except for Peach Bottom Unit 1. As a former PECO plant, financial assurance for decommissioning Peach Bottom Unit 1 is provided by the NDT fund in addition to collections from PECO ratepayers. As discussed under Nuclear Decommissioning Trust Fund Investments above, the amount collected from PECO ratepayers has been adjusted in the March 31, 2017 filing to the PAPUC which was approved on August 8, 2017 and effective on January 1, 2018. Generation will file its next decommissioning funding status report with the NRC by March 31, 2018 for shutdown reactors and reactors within five years of shutdown. This report will reflect the status of decommissioning funding assurance as of December 31, 2017 and will include the early retirement of TMI announced on May 30, 2017, in addition to an adjustment for the February 2, 2018 announced retirement date for Oyster Creek. A shortfall at any unit could necessitate that Exelon post a parental guarantee for Generation's share of the funding assurance. However, the amount of any required guarantee will ultimately depend on the decommissioning approach adopted, the associated level of costs, and the decommissioning trust fund investment performance going forward. As the future values of trust funds change due to market conditions, the NRC minimum funding status of Generation’s units will change. In addition, if changes occur to the regulatory agreement with the PAPUC that currently allows amounts to be collected from PECO customers for decommissioning the former PECO units, the NRC minimum funding status of those plants could change at subsequent NRC filing dates. Non-Nuclear Asset Retirement Obligations (All Registrants) Generation has AROs for plant closure costs associated with its fossil and renewable generating facilities, including asbestos abatement, removal of certain storage tanks, restoring leased land to the condition it was in prior to construction of renewable generating stations and other decommissioning-related activities. PHI and the Utility Registrants have AROs primarily associated with the abatement and disposal of equipment and buildings contaminated with asbestos and PCBs. See Note 1 — Significant Accounting Policies for additional information on the Registrants’ accounting policy for AROs. The following table provides a rollforward of the non-nuclear AROs reflected on the Registrants’ Consolidated Balance Sheets from January 1, 2016 to December 31, 2017 : Successor Exelon Generation ComEd PECO BGE PHI (g) Pepco DPL ACE Non-nuclear AROs at January 1, 2016 $ 355 $ 197 $ 113 $ 27 $ 18 $ — $ — $ — $ — Merger with PHI (a) 8 1 — — — — — — — Net increase due to changes in, and timing of, estimated future cash flows (b) 34 8 4 1 7 14 2 9 3 Development projects (c) 11 11 — — — — — — — Accretion expense (d) 18 10 7 1 — — — — — Sale of generating assets (e) (22 ) (22 ) — — — — — — — Payments (11 ) (6 ) (3 ) (1 ) (1 ) — — — — Non-nuclear AROs at December 31, 2016 (f) 393 199 121 28 24 14 2 9 3 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (b) (11 ) (1 ) (13 ) (1 ) 2 2 1 1 — Development projects (c) 1 1 — — — — — — — Accretion expense (d) 18 10 7 1 — — — — — Deconsolidation of EGTP (h) (7 ) (7 ) — — — — — — — Payments (10 ) (5 ) (2 ) (1 ) (2 ) — — — — Non-nuclear AROs at December 31, 2017 (f) $ 384 $ 197 $ 113 $ 27 $ 24 $ 16 $ 3 $ 10 $ 3 Predecessor PHI (g) 2016 Non-nuclear AROs at January 1, 2016 $ 8 Accretion expense — Non-nuclear AROs at March 23, 2016 $ 8 __________ (a) Following the completion of the PHI merger on March 23, 2016, PHI's AROs related to its unregulated business interests were transferred to Exelon and Generation. (b) During the year ended December 31, 2017 , ComEd recorded a decrease of $1 million in Operating and maintenance expense. Generation, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2017 . During the year ended December 31, 2016 , Generation recorded a increase of $1 million in Operating and maintenance expense. ComEd, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016 . (c) Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites. (d) For ComEd, PECO and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (e) Reflects a reduction to the ARO resulting primarily from the sales of the New Boston generating site and Upstream business in 2016. See Note 4 — Mergers, Acquisitions and Dispositions for further information. (f) Excludes the current portion of the ARO at December 31, 2017 for Generation, ComEd and BGE of $1 million , $2 million and $2 million , respectively. Excludes the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE of $1 million , $2 million and $3 million , respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets. (g) For PHI, the successor period includes activity for the year ended December 31, 2017 and the period of March 24, 2016 through December 31, 2016 . The PHI predecessor periods include activity for the period of January 1, 2016 through March 23, 2016. (h) See Note 4 — Mergers, Acquisitions and Dispositions for additional information.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Retirement Benefits (All Registrants)	(All Registrants) Exelon sponsors defined benefit pension plans and other postretirement benefit plans for essentially all current employees. Substantially all non-union employees and electing union employees hired on or after January 1, 2001 participate in cash balance pension plans. Effective January 1, 2009, substantially all newly-hired union-represented employees participate in cash balance pension plans. Effective February 1, 2018, most newly-hired Generation and BSC non-represented employees are not eligible for pension benefits, and will instead be eligible to receive an enhanced non-discretionary employer contribution in an Exelon defined contribution savings plan. Effective January 1, 2018, most newly-hired non-represented employees are not eligible for OPEB benefits and employees represented by Local 614 are not eligible for retiree health care benefits. Effective March 23, 2016 , Exelon became the sponsor of all of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. As a result, PHI's benefit plan net obligation and related regulatory assets were transferred to Exelon. The table below shows the pension and other postretirement benefit plans in which employees of each operating company participated at December 31, 2017 : Operating Company (e) Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACE Qualified Pension Plans: Exelon Corporation Retirement Program (a) X X X X X Exelon Corporation Cash Balance Pension Plan (a) X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees (a) X X X Exelon New England Union Employees Pension Plan (a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek (a) X X X X Pension Plan of Constellation Energy Group, Inc. (b) X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X X X X Nine Mile Point Pension Plan (c) X X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B (b) X Pepco Holdings LLC Retirement Plan (d) X X X X X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan (b) X X X Constellation Energy Group, Inc. Supplemental Pension Plan (b) X X X Constellation Energy Group, Inc. Benefits Restoration Plan (b) X X X X Constellation Energy Nuclear Plan, LLC Executive Retirement Plan (c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan (c) X X Baltimore Gas & Electric Company Executive Benefit Plan (b) X X X Baltimore Gas & Electric Company Manager Benefit Plan (b) X X X X Pepco Holdings LLC 2011 Supplemental Executive Retirement Plan (d) X X X X X Conectiv Supplemental Executive Retirement Plan (d) X X X X Pepco Holdings LLC Combined Executive Retirement Plan (d) X X X Atlantic City Electric Director Retirement Plan (d) X Operating Company (e) Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACE Other Postretirement Benefit Plans: PECO Energy Company Retiree Medical Plan (a) X X X X X Exelon Corporation Health Care Program (a) X X X X X Exelon Corporation Employees’ Life Insurance Plan (a) X X X X X Exelon Corporation Health Reimbursement Arrangement Plan (a) X X X X X Constellation Energy Group, Inc. Retiree Medical Plan (b) X X X X X Constellation Energy Group, Inc. Retiree Dental Plan (b) X X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan (b) X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan (b) X Exelon New England Union Post-Employment Medical Savings Account Plan (a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC (c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC (c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees (c) X X Pepco Holdings LLC Welfare Plan for Retirees (d) X X X X X ______________________ (a) These plans are collectively referred to as the legacy Exelon plans. (b) These plans are collectively referred to as the legacy Constellation Energy Group (CEG) Plans. (c) These plans are collectively referred to as the legacy CENG plans. (d) These plans are collectively referred to as the legacy PHI plans. (e) Employees generally remain in their legacy benefit plans when transferring between operating companies. Exelon’s traditional and cash balance pension plans are intended to be tax-qualified defined benefit plans. Exelon has elected that the trusts underlying these plans be treated as qualified trusts under the IRC. If certain conditions are met, Exelon can deduct payments made to the qualified trusts, subject to certain IRC limitations. Benefit Obligations, Plan Assets and Funded Status Exelon recognizes the overfunded or underfunded status of defined benefit pension and OPEB plans as an asset or liability on its balance sheet, with offsetting entries to AOCI and regulatory assets (liabilities), in accordance with the applicable authoritative guidance. The measurement date for the plans is December 31. During the first quarter of 2017, Exelon received an updated valuation of its pension and other postretirement benefit obligations to reflect actual census data as of January 1, 2017. This valuation resulted in an increase to the pension obligation of $92 million and an increase to the other postretirement benefit obligation of $57 million . Additionally, accumulated other comprehensive loss increased by approximately $59 million (after tax), regulatory assets increased by approximately $57 million and regulatory liabilities increased by approximately $4 million . In connection with the acquisition of FitzPatrick in the first quarter of 2017 , Exelon recorded pension and OPEB obligations for FitzPatrick employees of $16 million and $17 million , respectively. Refer to Note 4 — Mergers, Acquisitions and Dispositions for additional discussion of the acquisition of FitzPatrick. The following tables provide a rollforward of the changes in the benefit obligations and plan assets for the most recent two years for all plans combined: Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Change in benefit obligation: Net benefit obligation at beginning of year $ 21,060 $ 17,753 $ 4,457 $ 3,938 Service cost 387 354 106 107 Interest cost 842 830 182 185 Plan participants’ contributions — — 53 54 Actuarial loss (gain) 1,182 567 350 (136 ) Plan amendments 9 (60 ) — — Acquisitions/divestitures (b) 16 2,667 17 589 Settlements (34 ) — — — Gross benefits paid (1,125 ) (1,051 ) (309 ) (280 ) Net benefit obligation at end of year $ 22,337 $ 21,060 $ 4,856 $ 4,457 Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Change in plan assets: Fair value of net plan assets at beginning of year $ 16,791 $ 14,347 $ 2,578 $ 2,293 Actual return on plan assets 2,600 1,061 346 128 Employer contributions 341 347 64 50 Plan participants’ contributions — — 53 54 Gross benefits paid (1,125 ) (1,051 ) (309 ) (280 ) Acquisitions/divestitures (b) — 2,087 — 333 Settlements (34 ) — — — Fair value of net plan assets at end of year $ 18,573 $ 16,791 $ 2,732 $ 2,578 Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Change in benefit obligation: Net benefit obligation at beginning of the period $ 2,490 $ 563 Service cost 12 1 Interest cost 26 6 Actuarial (gain) loss (30 ) (5 ) Gross benefits paid (2 ) (1 ) Net benefit obligation at end of the period $ 2,496 $ 564 Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Change in plan assets: Fair value of net plan assets at beginning of the period $ 2,018 $ 348 Employer and plan participant contributions 4 1 Gross benefits paid by plan (2 ) (1 ) Fair value of net plan assets at end of the period $ 2,020 $ 348 __________ (a) 2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016. (b) Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017. Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans. Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Other current liabilities $ 28 $ 21 $ 31 $ 31 Pension obligations 3,736 4,248 — — Non-pension postretirement benefit obligations — — 2,093 1,848 Unfunded status (net benefit obligation less plan assets) $ 3,764 $ 4,269 $ 2,124 $ 1,879 __________ (a) Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. The funded status of the pension and other postretirement benefit obligations refers to the difference between plan assets and estimated obligations of the plan. The funded status changes over time due to several factors, including contribution levels, assumed discount rates and actual returns on plan assets. The following tables provide the projected benefit obligations (PBO), accumulated benefit obligation (ABO), and fair value of plan assets for all pension plans with a PBO or ABO in excess of plan assets. PBO in excess of plan assets Exelon 2017 2016 Projected benefit obligation $ 22,337 $ 21,060 Fair value of net plan assets 18,573 16,791 ABO in excess of plan assets Exelon 2017 2016 Projected benefit obligation $ 22,337 $ 21,060 Accumulated benefit obligation 21,153 19,930 Fair value of net plan assets 18,573 16,791 On a PBO basis, the Exelon plans were funded at 83% and 80% at December 31, 2017 and 2016 , respectively. On an ABO basis, the Exelon plans were funded at 88% and 84% at December 31, 2017 and 2016 , respectively. The ABO differs from the PBO in that the ABO includes no assumption about future compensation levels. Components of Net Periodic Benefit Costs The majority of the 2017 pension benefit cost for the Exelon-sponsored plans is calculated using an expected long-term rate of return on plan assets of 7.00% and a discount rate of 4.04% . The majority of the 2017 other postretirement benefit cost is calculated using an expected long-term rate of return on plan assets of 6.58% for funded plans and a discount rate of 4.04% . A portion of the net periodic benefit cost for all plans is capitalized within the Consolidated Balance Sheets. The following tables present the components of Exelon’s net periodic benefit costs, prior to capitalization, for the years ended December 31, 2017 , 2016 and 2015 and PHI's net periodic benefit costs, prior to capitalization, for the predecessor period of January 1, 2016 to March 23, 2016 . Pension Benefits Other Postretirement Benefits Exelon 2017 (a) 2016 (b) 2015 2017 (a) 2016 (b) 2015 Components of net periodic benefit cost: Service cost $ 387 $ 354 $ 326 $ 106 $ 107 $ 119 Interest cost 842 830 710 182 185 167 Expected return on assets (1,196 ) (1,141 ) (1,026 ) (162 ) (162 ) (151 ) Amortization of: Prior service cost (credit) 1 14 13 (188 ) (185 ) (174 ) Actuarial loss 607 554 571 61 63 80 Settlement and other charges (c) 3 2 2 — — — Net periodic benefit cost $ 644 $ 613 $ 596 $ (1 ) $ 8 $ 41 __________ (a) FitzPatrick net benefit costs are included for the period after acquisition. (b) PHI net periodic benefit costs for the period prior to the merger are not included in the table above. (c) 2016 amount includes an additional termination benefit for PHI. Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Components of net periodic benefit cost: Service cost $ 12 $ 57 $ 1 $ 7 Interest cost 26 109 6 24 Expected return on assets (30 ) (140 ) (5 ) (22 ) Amortization of: Prior service cost (credit) — 2 (3 ) (13 ) Actuarial loss 14 65 2 8 Net periodic benefit cost $ 22 $ 93 $ 1 $ 4 Components of AOCI and Regulatory Assets Under the authoritative guidance for regulatory accounting, a portion of current year actuarial gains and losses and prior service costs (credits) is capitalized within Exelon’s Consolidated Balance Sheets to reflect the expected regulatory recovery of these amounts, which would otherwise be recorded to AOCI. The following tables provide the components of AOCI and regulatory assets (liabilities) for the years ended December 31, 2017 , 2016 and 2015 for all plans combined and the components of PHI's predecessor AOCI and regulatory assets (liabilities) for the period January 1, 2016 to March 23, 2016 . Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2015 2017 2016 (a) 2015 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ (222 ) $ 644 $ 476 $ 166 $ (101 ) $ (194 ) Amortization of actuarial loss (607 ) (554 ) (571 ) (61 ) (63 ) (80 ) Current year prior service cost (credit) 9 (60 ) — — — (23 ) Amortization of prior service (cost) credit (1 ) (14 ) (13 ) 188 185 174 Settlements (3 ) — (2 ) — — — Acquisitions — 994 — — 94 — Total recognized in AOCI and regulatory assets (liabilities) $ (824 ) $ 1,010 $ (110 ) $ 293 $ 115 $ (123 ) Total recognized in AOCI $ (401 ) $ 51 $ (64 ) $ 168 $ 20 $ (63 ) Total recognized in regulatory assets (liabilities) $ (423 ) $ 959 $ (46 ) $ 125 $ 95 $ (60 ) Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Changes in plan assets and benefit Current year actuarial loss (gain) $ — $ 50 $ — $ (39 ) Amortization of actuarial loss (14 ) (65 ) (2 ) (8 ) Amortization of prior service (cost) credit — (2 ) 3 13 Total recognized in AOCI and regulatory assets (liabilities) $ (14 ) $ (17 ) $ 1 $ (34 ) Total recognized in AOCI $ (1 ) $ (11 ) $ — $ — Total recognized in regulatory assets (liabilities) $ (13 ) $ (6 ) $ 1 $ (34 ) __________ (a) 2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016. The following table provides the components of gross accumulated other comprehensive loss and regulatory assets (liabilities) that have not been recognized as components of periodic benefit cost at December 31, 2017 and 2016 , respectively, for all plans combined: Exelon Exelon Pension Benefits Other Postretirement Benefits 2017 2016 (a) 2017 2016 (a) Prior service (credit) cost $ (24 ) $ (31 ) $ (522 ) $ (710 ) Actuarial loss 7,556 8,387 829 724 Total (a) $ 7,532 $ 8,356 $ 307 $ 14 Total included in AOCI $ 3,896 $ 4,297 $ 125 $ (42 ) Total included in regulatory assets (liabilities) $ 3,636 $ 4,059 $ 182 $ 56 __________ (a) Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. The following table provides the impact to Exelon’s AOCI and regulatory assets (liabilities) at December 31, 2017 as a result of the components of periodic benefit costs that are expected to be amortized in 2018 . These estimates are subject to the completion of an actuarial valuation of Exelon’s pension and other postretirement benefit obligations, which will reflect actual census data as of January 1, 2018 and actual claims activity as of December 31, 2017 . The valuation is expected to be completed in the first quarter of 2018 for the majority of the benefit plans. Pension Benefits Other Postretirement Benefits Prior service cost (credit) $ 2 $ (186 ) Actuarial loss 640 66 Total (a) $ 642 $ (120 ) __________ (a) Of the $642 million related to pension benefits at December 31, 2017 , $317 million and $325 million are expected to be amortized from AOCI and regulatory assets in 2018 , respectively. Of the $(120) million related to other postretirement benefits at December 31, 2017 , $(65) million and $(55) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2018 , respectively. Average Remaining Service Period For pension benefits, Exelon amortizes its unrecognized prior service costs and certain actuarial gains and losses, as applicable, based on participants’ average remaining service periods. The average remaining service period of Exelon's defined benefit pension plan participants was 11.8 years, 11.9 years and 11.9 years for the years ended December 31, 2017 , 2016 and 2015 , respectively. For the predecessor period, the average remaining service period of PHI's defined benefit plans was approximately 11 years for the year ended December 31, 2015 . For other postretirement benefits, Exelon amortizes its unrecognized prior service costs over participants’ average remaining service period to benefit eligibility age and amortizes certain actuarial gains and losses over participants’ average remaining service period to expected retirement. The average remaining service period of postretirement benefit plan participants related to benefit eligibility age was 8.2 years, 9.0 years and 10.8 years for the years ended December 31, 2017 , 2016 and 2015 , respectively. The average remaining service period of postretirement benefit plan participants related to expected retirement was 9.6 years, 9.7 years and 9.7 years for the years ended December 31, 2017 , 2016 and 2015 , respectively. For the predecessor period, the average remaining service period of PHI's other postretirement benefit plans was approximately 11 years for the year ended December 31, 2015 . Assumptions The measurement of the plan obligations and costs of providing benefits under Exelon’s defined benefit and other postretirement plans involves various factors, including the development of valuation assumptions and inputs and accounting policy elections. The measurement of benefit obligations and costs is impacted by several assumptions and inputs, including the discount rate applied to benefit obligations, the long-term EROA, Exelon’s expected level of contributions to the plans, the long-term expected investment rate credited to employees participating in cash balance plans and the anticipated rate of increase of health care costs. Additionally, assumptions related to plan participants include the incidence of mortality, the expected remaining service period, the level of compensation and rate of compensation increases, employee age and length of service, among other factors. When developing the required assumptions, Exelon considers historical information as well as future expectations. Expected Rate of Return. In selecting the EROA, Exelon considers historical economic indicators (including inflation and GDP growth) that impact asset returns, as well as expectations regarding future long-term capital market performance, weighted by Exelon’s target asset class allocations. Mortality. For the December 31, 2014 actuarial valuation, Exelon changed its assumption of mortality to reflect more recent expectations of future improvements in life expectancy. The change was supported through completion of an experience study and supplemental analyses performed by Exelon's actuaries. There were no changes to the mortality assumption in 2015 , 2016 or 2017 . The following assumptions were used to determine the benefit obligations for the plans at December 31, 2017 , 2016 and 2015 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits Other Postretirement Benefits Exelon 2017 2016 2015 2017 2016 2015 Discount rate 3.62 % (a) 4.04 % (b) 4.29 % (c) 3.61 % (a) 4.04 % (b) 4.29 % (c) Rate of compensation increase (d) (e) (e) (d) (e) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% with ultimate trend of 5.00% in 2017 5.00% with 5.50% Predecessor Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 (f) 2015 January 1, 2016 to March 23, 2016 (e) 2015 Discount rate 4.65%/4.55% (g) 4.55 % Rate of compensation 5.00 % 5.00 % Mortality table RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2015 Health care cost trend on covered charges N/A 6.33% pre-65 and 5.40% post-65 __________ (a) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2017. Certain benefit plans used individual rates ranging from 3.49% - 3.65% and 3.57% - 3.68% for pension and other postretirement plans, respectively. (b) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2016. Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively. (c) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2015. Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (d) 3.25% through 2019 and 3.75% thereafter. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and other postretirement plans used a weighted-average rate of compensation increase of 5% for all periods. (f) Obligation was not remeasured during this period. (g) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively. The following assumptions were used to determine the net periodic benefit costs for the plans for the years ended December 31, 2017 , 2016 and 2015 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Pension Benefits Other Postretirement Benefits Exelon 2017 2016 2015 2017 2016 2015 Discount rate 4.04 % (a) 4.29 % (b) 3.94 % (c) 4.04 % (a) 4.29 % (b) 3.92 % (c) Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.00 % (d) 6.58 % (d) 6.71 % (d) 6.50 % (d) Rate of compensation increase (e) (e) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% decreasing to ultimate trend of 5.00% in 2017 5.50% 6.00% decreasing to ultimate trend of 5.00% in 2017 Predecessor Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 2015 January 1, 2016 to March 23, 2016 2015 Discount rate 4.65%/4.55% (f) 4.20 % 4.55 % 4.15 % Expected return on plan assets (g) 6.50 % 6.50 % 6.75 % 6.75 % Rate of compensation 5.00 % 5.00 % 5.00 % 5.00 % Mortality table RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2014 RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2014 Health care cost trend on covered charges N/A N/A 6.33% pre-65 and 5.40% post-65 6.67% pre-65 and 5.50% post-65 __________ (a) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2017 . Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively. (b) The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2016 . Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (c) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015 . Certain benefit plans used the individual rates ranging from 3.29% - 3.82% and 3.99% - 4.06% for pension and other postretirement plans, respectively. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and other postretirement plans used a weighted-average rate of compensation increase of 5% for all periods. (f) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively. (g) Expected return on other postretirement benefit plan assets is pre-tax. Assumed health care cost trend rates impact the other postretirement benefit plan costs reported for Exelon's participant populations with plan designs that do not have a cap on cost growth. A one percentage point change in assumed health care cost trend rates would have the following effects: Effect of a one percentage point increase in assumed health care cost trend: on 2017 total service and interest cost components $ 9 on postretirement benefit obligation at December 31, 2017 125 Effect of a one percentage point decrease in assumed health care cost trend: on 2017 total service and interest cost components (8 ) on postretirement benefit obligation at December 31, 2017 (113 ) Contributions The following tables provide contributions to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2017 (a) 2016 (a) 2015 (a) 2017 2016 2015 Exelon $ 341 $ 347 $ 462 $ 64 $ 50 $ 40 Generation 137 140 231 11 12 14 ComEd 36 33 143 5 5 7 PECO 24 30 40 — — — BGE 39 31 1 14 18 16 BSC (b) 38 39 47 2 3 3 Pepco 62 24 — 10 8 2 DPL — 22 — 2 — — ACE — 15 — 20 2 3 PHISCO (c) 5 17 — — 2 — Pension Benefits Other Postretirement Benefits Successor Predecessor Successor Predecessor 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 PHI $ 67 $ 74 $ 4 $ — $ 32 $ 12 $ — $ 5 __________ (a) Exelon's and Generation's pension contributions include $21 million , $25 million and $36 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2017 , 2016 and 2015 , respectively. (b) Includes $4 million , $6 million , and $5 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (c) PHISCO’s pension contributions for the year ended December 31, 2016 include $4 million of contributions made prior to the closing of Exelon’s merger with PHI on March 23, 2016 . Management considers various factors when making pension funding decisions, including actuarially determined minimum contribution requirements under ERISA, contributions required to avoid benefit restrictions and at-risk status as defined by the Pension Protection Act of 2006 (the Act), management of the pension obligation and regulatory implications. The Act requires the attainment of certain funding levels to avoid benefit restrictions (such as an inability to pay lump sums or to accrue benefits prospectively), and at-risk status (which triggers higher minimum contribution requirements and participant notification). The projected contributions below reflect a funding strategy of contributing the greater of (1) $300 million (which has been updated for the inclusion of PHI) until the qualified plans are fully funded on an ABO basis, and (2) the minimum amounts under ERISA to avoid benefit restrictions and at-risk status. This level funding strategy helps minimize volatility of future period required pension contributions. Unlike the qualified pension plans, Exelon’s non-qualified pension plans are not funded, given that they are not subject to statutory minimum contribution requirements. While other postretirement plans are also not subject to statutory minimum contribution requirements, Exelon does fund certain of its plans. For Exelon's funded OPEB plans, contributions generally equal accounting costs, however, Exelon’s management has historically considered several factors in determining the level of contributions to its other postretirement benefit plans, including liabilities management, levels of benefit claims paid and regulatory implications (amounts deemed prudent to meet regulatory expectations and best assure continued rate recovery). The amounts below include benefit payments related to unfunded plans. The following table provides all registrants' planned contributions to the qualified pension plans, planned benefit payments to non-qualified pension plans, and planned contributions to other postretirement plans in 2018: Qualified Pension Plans Non-Qualified Pension Plans Other Exelon $ 301 $ 30 $ 42 Generation 119 11 13 ComEd 38 2 3 PECO 17 1 — BGE 41 1 16 BSC 36 7 1 PHI 50 8 9 Pepco 4 2 8 DPL — 1 — ACE 6 — — PHISCO 40 5 1 Estimated Future Benefit Payments Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2017 were: Pension Benefits Other Postretirement Benefits 2018 $ 1,166 $ 256 2019 1,165 262 2020 1,210 270 2021 1,236 276 2022 1,265 284 2023 through 2027 6,671 1,509 Total estimated future benefit payments through 2027 $ 12,713 $ 2,857 Allocation to Exelon Subsidiaries All registrants account for their participation in Exelon’s pension and other postretirement benefit plans by applying multi-employer accounting. Employee-related assets and liabilities, including both pension and postretirement liabilities, for the legacy Exelon plans were allocated by Exelon to its subsidiaries based on the number of active employees as of January 1, 2001 as part of Exelon’s corporate restructuring. The obligation for Generation, ComEd and PECO reflects the initial allocation and the cumulative costs incurred and contributions made since January 1, 2001. Historically, Exelon has allocated the components of pension and other postretirement costs to the subsidiaries in the legacy Exelon plans based upon several factors, including the measures of active employee participation in each plan. Pension and other postretirement benefit contributions were allocated to legacy Exelon subsidiaries in proportion to active service costs recognized and total costs recognized, respectively. Beginning in 2015, Exelon began allocating costs related to its legacy Exelon pension and other postretirement benefit plans to its subsidiaries based on both active and retired employee participation and contributions are allocated based on accounting cost. The impact of this allocation methodology change was not material to any Registrant. For legacy CEG, legacy CENG, FitzPatrick, and legacy PHI plans, components of pension and other postretirement benefit costs and contributions have been, and will continue to be, allocated to the subsidiaries based on employee participation (both active and retired). The amounts below were included in

Severance (All Registrants)

Severance (All Registrants)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Severance (All Registrants)	Severance (All Registrants) The Registrants have an ongoing severance plan under which, in general, the longer an employee worked prior to termination the greater the amount of severance benefits. The Registrants record a liability and expense or regulatory asset for severance once terminations are probable of occurrence and the related severance benefits can be reasonably estimated. For severance benefits that are incremental to its ongoing severance plan (“one-time termination benefits”), the Registrants measure the obligation and record the expense at fair value at the communication date if there are no future service requirements, or, if future service is required to receive the termination benefit, ratably over the required service period. Ongoing Severance Plans The Registrants provide severance and health and welfare benefits under Exelon’s ongoing severance benefit plans to terminated employees in the normal course of business. These benefits are accrued for when the benefits are considered probable and can be reasonably estimated. For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs associated with ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Successor Exelon Generation (a) ComEd (a) PECO (a) BGE (a) PHI (a) Pepco (a) DPL (a) ACE (a) Year ended December 31, 2017 $ 14 $ 6 $ 3 $ 1 $ — $ 4 $ 2 $ 1 $ 1 2016 19 13 3 1 1 1 — — — __________ (a) The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016 . Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017 . Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016 . Cost Management Program-Related Severance In August 2015, Exelon announced a cost management program focused on cost savings of approximately $400 million at BSC and Generation. Additionally, in November 2017, Exelon announced a new commitment for an additional $250 million of cost savings, primarily at Generation, to be achieved by 2020. These actions are in response to the continuing economic challenges confronting all parts of Exelon’s business and industry, necessitating continued focus on cost management through enhanced efficiency and productivity. In connection with the program, certain positions have been identified for elimination and severance costs were recognized as both probable and estimable. While there may be additional position eliminations identified leading to potential severance or other termination benefit changes, Exelon, Generation and BSC intend to manage any staff reductions through natural attrition to the extent possible to minimize impacts on employees. Any additional severance or other termination benefit charges related to this commitment will be recognized when such amounts are considered probable and can be reasonably estimated. For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs related to the cost management program within Operating and maintenance expense in their Consolidated Statements of Operations: Exelon Generation ComEd PECO BGE 2017 (a) $ 6 $ 9 $ (1 ) $ (1 ) $ (1 ) 2016 (b) 23 18 3 1 1 __________ (a) The amounts for Generation, ComEd, PECO, and BGE include $(4) million , $(2) million , $(1) million , and $(1) million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017 . (b) The amounts above for Generation, ComEd, PECO and BGE include $7 million , $3 million , $1 million , and $1 million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2016 . Early Plant Retirement-Related Severance (Exelon and Generation) As a result of the Three Mile Island plant retirement decision, Exelon and Generation will incur certain employee-related costs, including severance benefit costs. Severance costs will be provided to management employees that are eligible under the Company's severance policy, to the extent that those employees are not redeployed to other locations. In June 2017, Exelon and Generation recognized severance costs of $17 million related to expected management employee severances resulting from the plant retirements within Operating and maintenance expense in their Consolidated Statements of Operation and Comprehensive Income. Approximately half of the employees at this location fall under a collective bargaining union agreement and are not eligible for severance benefits under an existing plan. The union and Exelon will negotiate terms of any severance benefits. If severance benefits are successfully negotiated, the amounts will be accrued as a one-time employee termination benefit once the established plan is communicated to employees. The final amount of the severance cost will ultimately depend on the specific employees severed. See Note 8 - Early Nuclear Plant Retirements for additional information regarding the announced early retirement of TMI. See Note 28 - Subsequent Events for additional information regarding the early retirement of Oyster Creek. Severance Costs Related to the PHI Merger Upon closing the PHI Merger, Exelon recorded a severance accrual for the anticipated employee position reductions as a result of the post-merger integration. Cash payments under the plan began in May 2016 and will continue through 2020. For the year ended December 31, 2017 , the PHI Merger severance costs were immaterial. For the year ended December 31, 2016 , the Registrants recorded the following severance costs associated with the identified job reductions within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income, pursuant to the authoritative guidance for ongoing severance plans: Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Severance Benefits Severance costs (a) $ 57 $ 9 $ 2 $ 1 $ 1 $ 44 $ 21 $ 13 $ 10 __________ (a) The amounts above for Generation, ComEd, PECO, BGE, Pepco, DPL, and ACE include $8 million , $2 million , $1 million , $1 million , $20 million , $12 million and $10 million , respectively, for amounts billed by BSC and/or PHISCO through intercompany allocations for the year ended December 31, 2016 . PHI, Pepco, DPL and ACE record regulatory assets for merger related integration costs which include a portion of the severance costs in the table above related to the PHI Merger. These regulatory assets are either currently being recovered in rates or are deemed probable of recovery in future rates. See Note 3 — Regulatory Matters for further information. Severance Liability Amounts included in the table below represent the severance liability recorded for employees of each Registrant and exclude amounts included at Exelon and billed through intercompany allocations: Successor Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2015 $ 35 $ 23 $ 3 $ — $ 1 $ — $ — $ — $ — Severance charges (a) 99 22 2 — — 56 1 1 — Payments (46 ) (9 ) (2 ) — (1 ) (27 ) (1 ) (1 ) — Balance at December 31, 2016 $ 88 $ 36 $ 3 $ — $ — $ 29 $ — $ — $ — Severance charges (a) 35 31 2 — — 3 — — — Payments (29 ) (9 ) (2 ) — — (12 ) — — — Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits.

Shareholder Equity (All Registr

Shareholder Equity (All Registrants)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	19 . Shareholders' Equity (Exelon, ComEd, PECO, BGE, Pepco, DPL and ACE) The following table presents common stock authorized and outstanding as of December 31, 2017 and 2016 : December 31, 2017 2016 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 963,335,888 924,035,059 ComEd $ 12.50 250,000,000 127,021,246 127,017,157 PECO no par value 500,000,000 170,478,507 170,478,507 BGE no par value 1,500 1,000 1,000 Pepco $ 0.01 200,000,000 100 100 DPL $ 2.25 1,000 1,000 1,000 ACE $ 3.00 25,000,000 8,546,017 8,546,017 ComEd had 60,584 and 72,859 warrants outstanding to purchase ComEd common stock at December 31, 2017 and 2016 , respectively. The warrants entitle the holders to convert such warrants into common stock of ComEd at a conversion rate of one share of common stock for three warrants. At December 31, 2017 and 2016 , 20,195 and 24,286 shares of common stock, respectively, were reserved for the conversion of warrants. Equity Securities Offering In June 2014, Exelon marketed an equity offering of 57.5 million shares of its common stock at a public offering price of $35 per share. In connection with such offering, Exelon entered into forward sale agreements with two counterparties. In July 2015, Exelon settled the forward sale agreement by the issuance of 57.5 million shares of Exelon common stock. Exelon received net cash proceeds of $1.87 billion , which was calculated based on a forward price of $32.48 per share as specified in the forward sale agreements. The net proceeds were used to fund the merger with PHI and related costs and expenses, and for general corporate purposes. The forward sale agreements are classified as equity transactions. As a result, no amounts were recorded in the consolidated financial statements until the July 2015 settlement of the forward sale agreements. However, prior to the July 2015 settlement, incremental shares, if any, were included within the calculation of diluted EPS using the treasury stock method. Concurrent with the forward equity transaction, Exelon also issued $1.15 billion of junior subordinated notes in the form of 23 million equity units. On June 1, 2017, Exelon settled the forward purchase contract, which was a component of the June 2014 equity units, through the issuance of Exelon common stock from treasury stock. See Note 13 — Debt and Credit Agreements for further information on the equity units. Share Repurchases Share Repurchase Programs There currently is no Exelon Board of Director authority to repurchase shares. Any previous shares repurchased are held as treasury shares, at cost, unless cancelled or reissued at the discretion of Exelon’s management. Under the previous share repurchase programs, 2 million and 35 million shares of common stock were held as treasury stock with a historical cost of $123 million and $2.3 billion at December 31, 2017 and 2016 , respectively. During 2017 , Exelon issued approximately 33 million shares of Exelon common stock from treasury stock in order to settle the forward purchase contract, which was a component of the June 2014 equity units discussed above. During 2016 and 2015 , Exelon had no common stock repurchases. Preferred and Preference Securities of Subsidiaries At December 31, 2017 and 2016 , Exelon was authorized to issue up to 100,000,000 shares of preferred securities, none of which were outstanding. At December 31, 2017 and 2016 , ComEd prior preferred securities and ComEd cumulative preference securities consisted of 850,000 shares and 6,810,451 shares authorized, respectively, none of which were outstanding. BGE had $190 million of cumulative preference stock that was redeemable at its option at any time after October 1, 2015 for the redemption price of $100 per share, plus accrued and unpaid dividends. On July 3, 2016, BGE redeemed all 400,000 shares of its outstanding 7.125% Cumulative Preference Stock, 1993 Series and all 600,000 shares of its outstanding 6.990% Cumulative Preference Stock, 1995 Series for $100 million , plus accrued and unpaid dividends. On September 18, 2016, BGE redeemed the remaining 500,000 shares of its outstanding 6.970% Cumulative Preference Stock, 1993 Series and the remaining 400,000 shares of its outstanding 6.700% Cumulative Preference Stock, 1993 Series for $90 million , plus accrued and unpaid dividends.

Stock-Based Compensation Plans

Stock-Based Compensation Plans (All Registrants)	12 Months Ended
	Dec. 31, 2017
Common Stock [Abstract]
Stock-Based Compensation Plans	Stock-Based Compensation Plans (All Registrants) Stock-Based Compensation Plans Exelon grants stock-based awards through its LTIP, which primarily includes stock options, restricted stock units and performance share awards. At December 31, 2017 , there were approximately 13 million shares authorized for issuance under the LTIP. For the years ended December 31, 2017 , 2016 and 2015 , exercised and distributed stock-based awards were primarily issued from authorized but unissued common stock shares. ComEd, PECO, BGE and PHI grant cash awards. The following tables do not include expense related to these plans as they are not considered stock-based compensation plans under the applicable authoritative guidance . In connection with the acquisition of PHI in March 2016, PHI’s unvested time-based restricted stock units and performance-based restricted stock units issued prior to April 29, 2014 were immediately vested and paid in cash upon the close of the merger. PHI’s remaining unvested time-based restricted stock units as of the close of the merger were cancelled. There were no remaining unvested performance-based restricted stock units as of the close of the merger. For the years ended December 31, 2017 , 2016 and 2015 , there were no significant modifications to the granted stock based awards. The following tables present the stock-based compensation expense included in Exelon's and PHI’s Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2017 , 2016 and 2015 and PHI's predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2017 2016 (a) 2015 Performance share awards $ 107 $ 93 $ 41 Restricted stock units 77 75 71 Stock options — — 1 Other stock-based awards 7 7 6 Total stock-based compensation expense included in operating and maintenance expense 191 175 119 Income tax benefit (74 ) (68 ) (46 ) Total after-tax stock-based compensation expense $ 117 $ 107 $ 73 __________ (a) 2016 amounts include expense related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016 . PHI Predecessor January 1 to March 23, Year Ended Components of Stock-Based Compensation Expense 2016 2015 Time-based restricted stock units $ 2 $ 7 Performance-based restricted stock units 1 5 Time-based restricted stock awards — 1 Total stock-based compensation expense included in operating and maintenance expense 3 13 Income tax benefit (1 ) (5 ) Total after-tax stock-based compensation expense $ 2 $ 8 The following tables present the Registrants' stock-based compensation expense (pre-tax) for the years ended December 31, 2017 , 2016 and 2015 , as well as for the PHI predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Year Ended December 31, Subsidiaries 2017 2016 2015 Exelon $ 191 $ 175 $ 119 Generation 88 78 64 ComEd 7 8 6 PECO 3 3 3 BGE 1 1 3 BSC (a) 88 81 43 PHI Successor (b)(c) 4 4 — Predecessor January 1 to For the Year Ended December 31, 2016 2015 PHI $ 3 $ 13 __________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE or PHI amounts above. (b) Pepco's, DPL's and ACE's stock-based compensation expense for the years ended December 31, 2017 and 2016 was not material. (c) These amounts primarily represent amounts billed to PHI’s subsidiaries through PHISCO intercompany allocations. There were no significant stock-based compensation costs capitalized during the years ended December 31, 2017 , 2016 and 2015 for Exelon or PHI, or for PHI during the predecessor period January 1, 2016 to March 23, 2016 . Exelon and PHI receive a tax deduction based on the intrinsic value of the award on the exercise date for stock options and the distribution date for performance share awards and restricted stock units. For each award, throughout the requisite service period, Exelon and PHI recognize the tax benefit related to compensation costs. The following tables present information regarding Exelon’s and PHI's tax benefits for the years ended December 31, 2017 , 2016 and 2015 and PHI's predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Exelon Year Ended December 31, 2017 2016 2015 Realized tax benefit when exercised/distributed: Restricted stock units 35 27 30 Performance share awards 29 18 18 PHI Predecessor January 1 to For the Year Ended December 31, 2016 2015 Realized tax benefit when exercised/distributed: Time-based restricted stock units $ — $ 2 Performance-based restricted stock units — 5 Stock Options Non-qualified stock options to purchase shares of Exelon’s common stock were granted under the LTIP through 2012. Due to changes in the LTIP, there were no stock options granted in 2017, 2016 or 2015. For all stock options granted through 2012, the exercise price of the stock options is equal to the fair market value of the underlying stock on the date of option grant. The vesting period of stock options is generally four years and all stock options will expire no later than ten years from the date of grant. The value of stock options at the date of grant is expensed over the requisite service period using the straight-line method. The requisite service period for stock options is generally four years . However, certain stock options become fully vested upon the employee reaching retirement-eligibility. The value of the stock options granted to retirement-eligible employees is either recognized immediately upon the date of grant or through the date at which the employee reaches retirement eligibility. The following table presents information with respect to stock option activity for the year ended December 31, 2017 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2016 12,531,591 $ 46.23 3.50 $ 13 Options exercised (3,093,156 ) 34.69 Options forfeited — — Options expired (2,714,824 ) 55.78 Balance of shares outstanding at December 31, 2017 6,723,611 $ 47.69 2.65 $ 7 Exercisable at December 31, 2017 (a) 6,723,611 $ 47.69 2.65 $ 7 __________ (a) Includes stock options issued to retirement eligible employees. The following table summarizes additional information regarding stock options exercised for the years ended December 31, 2017 , 2016 and 2015 : Year Ended 2017 2016 2015 Intrinsic value (a) $ 15 $ 11 $ — Cash received for exercise price 107 19 — __________ (a) The difference between the market value on the date of exercise and the option exercise price. At December 31, 2016 , all stock options were vested and at December 31, 2017 there were no unrecognized compensation costs related to nonvested stock options. Restricted Stock Units Restricted stock units are granted under the LTIP with the majority being settled in a specific number of shares of common stock after the service condition has been met. The corresponding cost of services is measured based on the grant date fair value of the restricted stock unit issued. The value of the restricted stock units is expensed over the requisite service period using the straight-line method. The requisite service period for restricted stock units is generally three to five years . However, certain restricted stock unit awards become fully vested upon the employee reaching retirement-eligibility. The value of the restricted stock units granted to retirement-eligible employees is either recognized immediately upon the date of grant or through the date at which the employee reaches retirement eligibility. Exelon processes forfeitures as they occur for employees who do not complete the requisite service period. The following table summarizes Exelon’s nonvested restricted stock unit activity for the year ended December 31, 2017 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2016 (a)(c) 3,824,416 $ 30.49 Granted 2,266,199 34.98 Vested (1,736,965 ) 30.98 Forfeited (92,938 ) 33.12 Undistributed vested awards (b) (871,209 ) 34.09 Nonvested at December 31, 2017 (a) 3,389,503 $ 32.24 __________ (a) Excludes 1,488,383 and 1,319,372 of restricted stock units issued to retirement-eligible employees as of December 31, 2017 and 2016 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2017 . (c) 2016 amounts include activity related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016 . For Exelon, the weighted average grant date fair value (per share) of restricted stock units granted for the years ended December 31, 2017 , 2016 and 2015 was $34.98 , $28.14 and $36.55 , respectively. At December 31, 2017 and 2016 , Exelon had obligations related to outstanding restricted stock units not yet settled of $108 million and $101 million , respectively, which are included in common stock in Exelon’s Consolidated Balance Sheets. For the years ended December 31, 2017 , 2016 and 2015 , Exelon settled restricted stock units with fair value totaling $88 million , $68 million and $75 million , respectively. At December 31, 2017 , $51 million of total unrecognized compensation costs related to nonvested restricted stock units are expected to be recognized over the remaining weighted-average period of 1.7 years. For PHI, the weighted average grant date fair value (per share) of time-based restricted stock units granted for the year ended December 31, 2015 was $27.40 and for performance-based restricted stock units was $26.08 for the same period. For the year ended December 31, 2015 , PHI settled time-based restricted stock units with fair value totaling $6 million and settled performance-based restricted stock units with fair value totaling $15 million , for the same period. There were no settled restricted stock units for the predecessor period January 1, 2016 to March 23, 2016 . Performance Share Awards Performance share awards are granted under the LTIP. The performance share awards are settled 50% in common stock and 50% in cash at the end of the three-year performance period, except for awards granted to vice presidents and higher officers that are settled 100% in cash if certain ownership requirements are satisfied. The common stock portion of the performance share awards is considered an equity award and is valued based on Exelon's stock price on the grant date. The cash portion of the performance share awards is considered a liability award which is remeasured each reporting period based on Exelon’s current stock price. As the value of the common stock and cash portions of the awards are based on Exelon’s stock price during the performance period, coupled with changes in the total shareholder return modifier and expected payout of the award, the compensation costs are subject to volatility until payout is established. Effective January 2017 for nonretirement-eligible employees, stock-based compensation costs are recognized over the vesting period of three years using the straight-line method. For performance share awards granted to retirement-eligible employees, the value of the performance shares is recognized ratably over the vesting period, which is the year of grant. In 2016 and prior, for nonretirement-eligible employees, stock-based compensation costs are recognized over the vesting period of three years using the graded-vesting method. For performance share awards granted to retirement-eligible employees, the value of the performance shares is recognized ratably over the vesting period, which is the year of grant. Exelon processes forfeitures as they occur for employees who do not complete the requisite service period. The following table summarizes Exelon’s nonvested performance share awards activity for the year ended December 31, 2017 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2016 (a)(c) 3,116,261 $ 30.77 Granted 1,632,186 35.00 Change in performance 545,793 30.97 Vested (1,111,751 ) 29.11 Forfeited (18,034 ) 33.74 Undistributed vested awards (b) (1,207,489 ) 33.46 Nonvested at December 31, 2017 (a) 2,956,966 $ 32.65 __________ (a) Excludes 2,723,440 and 2,443,409 of performance share awards issued to retirement-eligible employees as of December 31, 2017 and 2016 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2017 . (c) 2016 amounts include activity related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016. The following table summarizes the weighted average grant date fair value and the fair value of performance share awards granted and settled for the years ended December 31, 2017 , 2016 and 2015 : Year Ended 2017 (a) 2016 2015 Weighted average grant date fair value (per share) $ 35.00 $ 28.85 $ 35.88 Fair value of performance shares settled 72 45 46 Fair value of performance shares settled in cash 56 28 29 __________ (a) As of December 31, 2017 , $41 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.5 years. For PHI, the weighted average grant date fair value (per share) of performance-based restricted stock awards was $26.10 for the year ended December 31, 2015 . There were no time-based restricted stock awards granted for the year ended December 31, 2015 . There were no time-based share settlements or performance-based share settlements for the year-ended December 31, 2015 or the predecessor period January 1, 2016 to March 23, 2016 . The following table presents the balance sheet classification of obligations related to outstanding performance share awards not yet settled: December 31, 2017 2016 Current liabilities (a) $ 57 $ 49 Deferred credits and other liabilities (b) 100 52 Common stock 26 40 Total $ 183 $ 141 __________ (a) Represents the current liability related to performance share awards expected to be settled in cash. (b) Represents the long-term liability related to performance share awards expected to be settled in cash.

Earnings Per Share (Exelon)

Earnings Per Share (Exelon)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share (Exelon)	21 . Earnings Per Share (Exelon) Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to common shareholders by the weighted average number of common shares outstanding, including the effect of issuing common stock assuming (i) stock options are exercised, and (ii) performance share awards and restricted stock awards are fully vested under the treasury stock method. The following table sets forth the components of basic and diluted earnings per share and shows the effect of these stock options, performance share awards and restricted stock awards on the weighted average number of shares outstanding used in calculating diluted earnings per share: Year Ended December 31, 2017 2016 2015 Net income attributable to common shareholders $ 3,770 $ 1,134 $ 2,269 Weighted average common shares outstanding — basic 947 924 890 Assumed exercise and/or distributions of stock-based awards 2 3 3 Weighted average common shares outstanding — diluted 949 927 893 The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 8 million in 2017 , 12 million in 2016 , and 16 million in 2015 . There were no equity units related to the PHI merger not included in the calculation of diluted common shares outstanding due to their antidilutive effect for the years ended December 31, 2017 and 2016 . The number of equity units related to the PHI merger not included in the calculation of diluted common shares outstanding due to their antidilutive effect was 3 million for the year ended 2015 . Refer to Note 19 — Shareholders' Equity for further information regarding the equity units and equity forward units. On June 1, 2017, Exelon settled the forward purchase contract, which was a component of the June 2014 equity units, through the issuance of approximately 33 million shares of Exelon common stock from treasury stock. The issuance of shares on June 1, 2017 triggered full dilution in the EPS calculation, which prior to settlement were included in the calculation of diluted EPS using the treasury stock method. Refer to Note 19 — Shareholders' Equity for further information regarding share repurchases.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon, Generation, PECO and PHI)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Exelon, Generation, PECO and PHI)	Changes in Accumulated Other Comprehensive Income (Exelon, Generation, PECO and PHI) The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications (1 ) 6 11 7 6 29 Amounts reclassified from AOCI (b) 4 — 140 — — 144 Net current-period OCI 3 6 151 7 6 173 Ending balance $ (14 ) $ 10 $ (2,459 ) $ (23 ) $ (1 ) $ (2,487 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications (1 ) 1 — 7 6 13 Amounts reclassified from AOCI (b) 4 — — — — 4 Net current-period OCI 3 1 — 7 6 17 Ending balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 For the Year Ended December 31, 2016 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ (19 ) $ 3 $ (2,565 ) $ (40 ) $ (3 ) $ (2,624 ) OCI before reclassifications (6 ) 1 (182 ) 5 (4 ) (186 ) Amounts reclassified from AOCI (b) 8 — 137 5 — 150 Net current-period OCI 2 1 (45 ) 10 (4 ) (36 ) Ending balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) Generation (a) Beginning balance $ (21 ) $ 1 $ — $ (40 ) $ (3 ) $ (63 ) OCI before reclassifications (6 ) 1 — 5 (4 ) (4 ) Amounts reclassified from AOCI (b) 8 — — 5 — 13 Net current-period OCI 2 1 — 10 (4 ) 9 Ending balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 PHI Predecessor (a) Beginning balance January 1, 2016 $ (8 ) $ — $ (28 ) $ — $ — $ (36 ) OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — 1 — — 1 Net current-period OCI — — 1 — — 1 Ending balance March 23, 2016 (c) $ (8 ) $ — $ (27 ) $ — $ — $ (35 ) __________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) As a result of the PHI Merger, the PHI predecessor balances at March 23, 2016 were reduced to zero on March 24, 2016 due to purchase accounting adjustments applied to PHI. ComEd, PECO, BGE, Pepco, DPL and ACE did not have any reclassifications out of AOCI to Net income during the years ended December 31, 2017 and 2016 . The following tables present amounts reclassified out of AOCI to Net income for Exelon, Generation and PHI during the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense Total before tax (5 ) (5 ) Tax benefit 1 1 Net of tax $ (4 ) $ (4 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 92 $ — Actuarial losses (b) (324 ) — Total before tax (232 ) — Tax benefit 92 — Net of tax $ (140 ) $ — Comprehensive Income Total Reclassifications $ (144 ) $ (4 ) Comprehensive income For the Year Ended December 31, 2016 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Predecessor January 1, 2016 to March 23, 2016 Exelon Generation PHI Loss on cash flow hedges Other cash flow hedges $ (13 ) $ (13 ) $ — Interest expense Total before tax (13 ) (13 ) — Tax benefit 5 5 — Net of tax $ (8 ) $ (8 ) $ — Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 78 $ — $ — Actuarial losses (b) (302 ) — (1 ) Total before tax (224 ) — (1 ) Tax benefit 87 — — Net of tax $ (137 ) $ — $ (1 ) Comprehensive Income Losses on foreign currency translation Loss $ (5 ) $ (5 ) $ — Other income and (deductions) Total before tax (5 ) (5 ) — Tax benefit — — — Net of tax $ (5 ) $ (5 ) $ — Total Reclassifications $ (150 ) $ (13 ) $ (1 ) Comprehensive income __________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 16 — Retirement Benefits for additional details). The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 2016 2015 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 36 $ 30 $ 30 Actuarial loss reclassified to periodic benefit cost (128 ) (118 ) (140 ) Pension and non-pension postretirement benefit plans valuation adjustment 13 115 62 Change in unrealized loss on cash flow hedges (7 ) — (6 ) Change in unrealized (loss)/gain on equity investments (3 ) 3 1 Change in unrealized loss on marketable securities (1 ) — — Total $ (90 ) $ 30 $ (53 ) Generation Change in unrealized (loss)/gain on cash flow hedges $ (6 ) $ (2 ) $ 2 Change in unrealized (loss)/gain on equity investments (3 ) 3 1 Change in unrealized loss marketable securities (1 ) — — Total $ (10 ) $ 1 $ 3 Predecessor January 1 to For the Year Ended December 31, PHI 2016 2015 Pension and non-pension postretirement benefit plans: Actuarial loss reclassified to periodic cost $ — $ 6

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (All Registrants)	23 . Commitments and Contingencies (All Registrants) Commitments Constellation Merger Commitments In February 2012, the MDPSC issued an Order approving the Exelon and Constellation merger. As part of the MDPSC Order, Exelon agreed to provide a package of benefits to BGE customers, the City of Baltimore and the State of Maryland, resulting in an estimated direct investment in the State of Maryland of approximately $1 billion . The direct investment includes the construction of a new 21-story headquarters building in Baltimore for Generation’s competitive energy business that was substantially complete in November 2016 and is now occupied by approximately 1,500 Exelon employees. Generation’s investment includes leasehold improvements that are not expected to exceed $110 million . In addition, Generation entered into a 20 -year operating lease as the primary lessee of the building. The direct investment commitment also includes $450 million to $500 million relating to Exelon and Generation’s development or assistance in the development of 285 - 300 MWs of new generation in Maryland, which is expected to be completed within a period of 10 years. The MDPSC order contemplates various options for complying with the new generation development commitments, including building or acquiring generating assets, making subsidy or compliance payments, or in circumstances in which the generation build is delayed or certain specified provisions are elected, making liquidated damages payments. Exelon and Generation have incurred $457 million towards satisfying the commitment for new generation development in the state of Maryland, with approximately 220 MW of the new generation commencing with commercial operations to date and an additional 10 MW commitment satisfied through a liquidated damages payment made in the fourth quarter of 2016. Additionally, during the fourth quarter of 2016, given continued declines in projected energy and capacity prices, Generation terminated rights to certain development projects originally intended to meet its remaining 55 MW commitment amount. The commitment will now most likely be satisfied via payment of liquidated damages or execution of a third party PPA, rather than by Generation constructing renewable generating assets. As a result, Exelon and Generation recorded a pre-tax $50 million loss contingency in Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2016. Commercial Commitments Exelon’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 1,226 $ 1,056 $ 154 $ 16 $ — $ — $ — Surety bonds (b) 1,381 1,293 66 16 6 — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (c) 21 — — — — — 21 Total commercial commitments $ 3,006 $ 2,349 $ 220 $ 32 $ 6 $ — $ 399 __________ (a) Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million , $16 million of which is a guarantee by Pepco, $23 million by DPL and $15 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Generation’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 1,177 $ 1,007 $ 154 $ 16 $ — $ — $ — Surety bonds 1,209 1,164 45 — — — — Total commercial commitments $ 2,386 $ 2,171 $ 199 $ 16 $ — $ — $ — __________ (a) Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties. ComEd’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 10 8 2 — — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 212 $ 10 $ 2 $ — $ — $ — $ 200 __________ (a) Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PECO’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 9 $ 8 $ 1 $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 8 $ 1 $ — $ — $ — $ 178 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. BGE’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 11 10 1 — — — — Total commercial commitments $ 13 $ 12 $ 1 $ — $ — $ — $ — __________ (a) Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PHI commercial commitments (Successor) as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds $ 63 $ 48 $ 15 $ — $ — $ — $ — Guaranteed lease residual values (a) 21 — — — — — 21 Total commercial commitments $ 84 $ 48 $ 15 $ — $ — $ — $ 21 __________ (a) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Pepco commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 54 $ 41 $ 13 $ — $ — $ — $ — Guaranteed lease residual values (b) 6 — — — — — 6 Total commercial commitments $ 60 $ 41 $ 13 $ — $ — $ — $ 6 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $16 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. DPL commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 4 $ 3 $ 1 $ — $ — $ — $ — Guaranteed lease residual values (b) 8 — — — — — 8 Total commercial commitments $ 12 $ 3 $ 1 $ — $ — $ — $ 8 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $23 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. ACE commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds $ 4 $ 3 $ 1 $ — $ — $ — $ — Guaranteed lease residual values (a) 6 — — — — — 6 Total commercial commitments $ 10 $ 3 $ 1 $ — $ — $ — $ 6 __________ (a) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $15 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Leases Minimum future operating lease payments, including lease payments for contracted generation, vehicles, real estate, computers, rail cars, operating equipment and office equipment, as of December 31, 2017 were: Successor Exelon (a) Generation (a) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2018 $ 188 $ 74 $ 7 $ 5 $ 34 $ 56 $ 8 $ 20 $ 9 2019 129 29 6 5 34 42 7 10 8 2020 147 47 4 5 34 44 6 13 8 2021 142 48 4 5 32 40 5 12 7 2022 119 46 2 5 17 39 4 12 6 Remaining years 787 573 — — 19 194 8 54 19 Total minimum future lease payments $ 1,512 $ 817 $ 23 $ 25 $ 170 $ 415 $ 38 $ 121 $ 57 __________ (a) Includes amounts related to shared use land arrangements. (b) Excludes Generation’s contingent operating lease payments associated with contracted generation agreements. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd’s, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2018—2022, was $2 million , $5 million , $1 million and $2 million , respectively. Also includes amounts related to shared use land arrangements. (d) Includes all future lease payments on a 99 -year real estate lease that expires in 2106 . (e) The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $25 million , $26 million , $28 million , $28 million and $14 million related to years 2018, 2019, 2020, 2021and 2022, respectively. The following table presents the Registrants’ rental expense under operating leases for the years ended December 31, 2017, 2016 and 2015: For the Year Ended December 31, Exelon Generation (a) ComEd PECO BGE Pepco DPL ACE 2017 $ 709 $ 578 $ 9 $ 9 $ 32 $ 11 $ 16 $ 14 2016 777 667 15 7 22 8 15 13 2015 922 851 12 9 32 7 14 13 Successor Predecessor For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 PHI Rental expense under operating leases $ 63 $ 49 $ 12 $ 60 __________ (a) Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $508 million , $604 million and $798 million during 2017 , 2016 and 2015 , respectively. Excludes contract amortization associated with purchase accounting and contract acquisitions. For information regarding capital lease obligations, see Note 13 —Debt and Credit Agreements. Nuclear Insurance Generation is subject to liability, property damage and other risks associated with major incidents at any of its nuclear stations. Generation has mitigated its financial exposure to these risks through insurance and other industry risk-sharing provisions. The Price-Anderson Act was enacted to ensure the availability of funds for public liability claims arising from an incident at any of the U.S. licensed nuclear facilities and to limit the liability of nuclear reactor owners for such claims from any single incident. As of December 31, 2017 , the current liability limit per incident is $13.4 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors at least once every five years with the last adjustment effective September 10, 2013. In accordance with the Price-Anderson Act, Generation maintains financial protection at levels equal to the amount of liability insurance available from private sources through the purchase of private nuclear energy liability insurance for public liability claims that could arise in the event of an incident. Effective January 1, 2017, the required amount of nuclear energy liability insurance purchased is $450 million for each operating site. Claims exceeding that amount are covered through mandatory participation in a financial protection pool, as required by the Price Anderson-Act, which provides the additional $13.0 billion per incident in funds available for public liability claims. Participation in this secondary financial protection pool requires the operator of each reactor to fund its proportionate share of costs for any single incident that exceeds the primary layer of financial protection. Exelon’s share of this secondary layer would be approximately $2.8 billion , however any amounts payable under this secondary layer would be capped at $420 million per year. In addition, the U.S. Congress could impose revenue-raising measures on the nuclear industry to pay public liability claims exceeding the $13.4 billion limit for a single incident. As part of the execution of the NOSA on April 1, 2014, Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF and its affiliates against third-party claims that may arise from any future nuclear incident (as defined in the Price-Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this indemnity. See Note 2 — Variable Interest Entities for additional information on Generation’s operations relating to CENG. Generation is required each year to report to the NRC the current levels and sources of property insurance that demonstrates Generation possesses sufficient financial resources to stabilize and decontaminate a reactor and reactor station site in the event of an accident. The property insurance maintained for each facility is currently provided through insurance policies purchased from NEIL, an industry mutual insurance company of which Generation is a member. NEIL may declare distributions to its members as a result of favorable operating experience. In recent years NEIL has made distributions to its members, but Generation cannot predict the level of future distributions or if they will continue at all. Generation's portion of the distribution declared by NEIL is estimated to be $60 million for 2017, and was $21 million for 2016 and 2015. The distributions were recorded as a reduction to Operating and maintenance expense within Exelon and Generation’s Consolidated Statements of Operations and Comprehensive Income. Premiums paid to NEIL by its members are also subject to a potential assessment for adverse loss experience in the form of a retrospective premium obligation. NEIL has never assessed this retrospective premium since its formation in 1973, and Generation cannot predict the level of future assessments if any. The current maximum aggregate annual retrospective premium obligation for Generation is approximately $360 million . NEIL requires its members to maintain an investment grade credit rating or to ensure collectability of their annual retrospective premium obligation by providing a financial guarantee, letter of credit, deposit premium, or some other means of assurance. NEIL provides “all risk” property damage, decontamination and premature decommissioning insurance for each station for losses resulting from damage to its nuclear plants, either due to accidents or acts of terrorism. If the decision is made to decommission the facility, a portion of the insurance proceeds will be allocated to a fund, which Generation is required by the NRC to maintain, to provide for decommissioning the facility. In the event of an insured loss, Generation is unable to predict the timing of the availability of insurance proceeds to Generation and the amount of such proceeds that would be available. In the event that one or more acts of terrorism cause accidental property damage within a twelve-month period from the first accidental property damage under one or more policies for all insured plants, the maximum recovery by Exelon will be an aggregate of $ 3.2 billion plus such additional amounts as the insurer may recover for all such losses from reinsurance, indemnity and any other source, applicable to such losses. For its insured losses, Generation is self-insured to the extent that losses are within the policy deductible or exceed the amount of insurance maintained. Uninsured losses and other expenses, to the extent not recoverable from insurers or the nuclear industry, could also be borne by Generation. Any such losses could have a material adverse effect on Exelon’s and Generation’s financial conditions, results of operations and cash flows. Spent Nuclear Fuel Obligation Under the NWPA, the DOE is responsible for the development of a geologic repository for and the disposal of SNF and high-level radioactive waste. As required by the NWPA, Generation is a party to contracts with the DOE (Standard Contracts) to provide for disposal of SNF from Generation’s nuclear generating stations. In accordance with the NWPA and the Standard Contracts, Generation historically had paid the DOE one mill ( $0.001 ) per kWh of net nuclear generation for the cost of SNF disposal. On November 19, 2013, the D.C. Circuit Court ordered the DOE to submit to Congress a proposal to reduce the current SNF disposal fee to zero, unless and until there is a viable disposal program. On May 9, 2014, the DOE notified Generation that the SNF disposal fee remained in effect through May 15, 2014, after which time the fee was set to zero. As a result, for the year ended December 31, 2017 , 2016 and 2015 , Generation did not incur any expense in SNF disposal fees. Until a new fee structure is in effect, Exelon and Generation will not accrue any further costs related to SNF disposal fees. This fee may be adjusted prospectively to ensure full cost recovery. The NWPA and the Standard Contracts required the DOE to begin taking possession of SNF generated by nuclear generating units by no later than January 31, 1998. The DOE, however, failed to meet that deadline and its performance has been, and is expected to be, delayed significantly. The 2010 Federal budget (which became effective October 1, 2009) eliminated almost all funding for the creation of the Yucca Mountain repository while the Obama Administration devised a new strategy for long-term SNF management. The Blue Ribbon Commission (BRC) on America’s Nuclear Future, appointed by the U.S. Energy Secretary, released a report on January 26, 2012, detailing comprehensive recommendations for creating a safe, long-term solution for managing and disposing of the nation’s SNF and high-level radioactive waste. In early 2013, the DOE issued an updated “Strategy for the Management and Disposal of Used Nuclear Fuel and High-Level Radioactive Waste” in response to the BRC recommendations. This strategy included a consolidated interim storage facility that was planned to be operational in 2025. However, due to continued delays on the part of the DOE, Generation currently assumes the DOE will begin accepting SNF in 2030 and uses that date for purposes of estimating the nuclear decommissioning asset retirement obligations. The SNF acceptance date assumption is based on management’s estimates of the amount of time required for DOE to select a site location and develop the necessary infrastructure for long-term SNF storage. In August 2004, Generation and the DOJ, in close consultation with the DOE, reached a settlement under which the government agreed to reimburse Generation, subject to certain damage limitations based on the extent of the government’s breach, for costs associated with storage of SNF at Generation’s nuclear stations pending the DOE’s fulfillment of its obligations. Generation’s settlement agreement does not include FitzPatrick and FitzPatrick does not currently have a settlement agreement in place. Calvert Cliffs, Ginna and Nine Mile Point each have separate settlement agreements in place with the DOE which were extended during 2017 to provide for the reimbursement of SNF storage costs through December 31, 2019. Generation submits annual reimbursement requests to the DOE for costs associated with the storage of SNF. In all cases, reimbursement requests are made only after costs are incurred and only for costs resulting from DOE delays in accepting the SNF. Under the settlement agreements, Generation has received cumulative cash reimbursements for costs incurred as follows: Total Net (a) Cumulative cash reimbursements (b) $ 1,167 $ 1,006 __________ (a) Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek. (b) Includes $53 and $49 , respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG. As of December 31, 2017 and 2016, the amount of SNF storage costs for which reimbursement has been or will be requested from the DOE under the DOE settlement agreements is as follows: December 31, 2017 December 31, 2016 DOE receivable - current (a) $ 94 $ 109 DOE receivable - noncurrent (b) 15 15 Amounts owed to co-owners (a)(c) (11 ) (13 ) __________ (a) Recorded in Accounts receivable, other. (b) Recorded in Deferred debits and other assets, other (c) Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities. The Standard Contracts with the DOE also required the payment to the DOE of a one-time fee applicable to nuclear generation through April 6, 1983. The fee related to the former PECO units has been paid. Pursuant to the Standard Contracts, ComEd previously elected to defer payment of the one-time fee of $277 million for its units (which are now part of Generation), with interest to the date of payment, until just prior to the first delivery of SNF to the DOE. The unfunded liabilities for SNF disposal costs, including the one-time fee, were transferred to Generation as part of Exelon’s 2001 corporate restructuring. A prior owner of FitzPatrick also elected to defer payment of the one-time fee of $34 million for the FitzPatrick unit. As part of the FitzPatrick acquisition on March 31, 2017, Generation assumed a SNF liability for the DOE one-time fee obligation with interest related to FitzPatrick along with an offsetting asset for the contractual right to reimbursement from NYPA, a prior owner of FitzPatrick, for amounts paid for the FitzPatrick DOE one-time fee obligation. The amounts were recorded at fair value. See Note 4 - Mergers, Acquisitions and Dispositions for additional information on the FitzPatrick acquisition. As of December 31, 2017 and 2016 , the SNF liability for the one-time fee with interest was $1,147 million and $1,024 million , respectively, which is included in Exelon's and Generation's Consolidated Balance Sheets. Interest for Exelon's and Generation's SNF liabilities accrues at the 13-week Treasury Rate. The 13-week Treasury Rate in effect, for calculation of the interest accrual at December 31, 2017, was 1.149% . The outstanding one-time fee obligations for the Nine Mile Point, Ginna, Oyster Creek and TMI units remain with the former owners. The Clinton and Calvert Cliffs units have no outstanding obligation. See Note 11 — Fair Value of Financial Assets and Liabilities for additional information. Environmental Remediation Matters General. The Registrants’ operations have in the past, and may in the future, require substantial expenditures to comply with environmental laws. Additionally, under Federal and state environmental laws, the Registrants are generally liable for the costs of remediating environmental contamination of property now or formerly owned by them and of property contaminated by hazardous substances generated by them. The Registrants own or lease a number of real estate parcels, including parcels on which their operations or the operations of others may have resulted in contamination by substances that are considered hazardous under environmental laws. In addition, the Registrants are currently involved in a number of proceedings relating to sites where hazardous substances have been deposited and may be subject to additional proceedings in the future. Unless otherwise disclosed, the Registrants cannot reasonably estimate whether they will incur significant liabilities for additional investigation and remediation costs at these or additional sites identified by the Registrants, environmental agencies or others, or whether such costs will be recoverable from third parties, including customers. Additional costs could have a material, unfavorable impact on the Registrants' financial conditions, results of operations and cash flows. MGP Sites ComEd, PECO, BGE and DPL have identified sites where former MGP activities have or may have resulted in actual site contamination. For almost all of these sites, there are additional PRPs that may share responsibility for the ultimate remediation of each location. • ComEd has identified 42 sites, 19 of which have been remediated and approved by the Illinois EPA or the U.S. EPA and 23 that are currently under some degree of active study and/or remediation. ComEd expects the majority of the remediation at these sites to continue through at least 2022. • PECO has identified 26 sites, 17 of which have been remediated in accordance with applicable PA DEP regulatory requirements and 9 that are currently under some degree of active study and/or remediation. PECO expects the majority of the remediation at these sites to continue through at least 2022. • BGE has identified 13 former gas manufacturing or purification sites, 11 of which the remediation has been completed and approved by the MDE and 2 that require some level of remediation and/or ongoing monitoring. BGE has determined that a loss associated with these sites is probable and has recorded an estimated liability, which is included in the table below. However, it is reasonably possible that BGE’s cost of remediation for one of its sites could be up to $13 million . • DPL has identified 3 sites, 2 of which remediation has been completed and approved by the MDE or the Delaware Department of Natural Resources and Environmental Control. The remaining site is under study and the required cost at the site is not expected to be material. The historical nature of the MGP sites and the fact that many of the sites have been buried and built over, impacts the ability to determine a precise estimate of the ultimate costs prior to initial sampling and determination of the exact scope and method of remedial activity. Management determines its best estimate of remediation costs using all available information at the time of each study, including probabilistic and deterministic modeling for ComEd and PECO, and the remediation standards currently required by the applicable state environmental agency. Prior to completion of any significant clean up, each site remediation plan is approved by the appropriate state environmental agency. ComEd, pursuant to an ICC order, and PECO, pursuant to settlements of natural gas distribution rate cases with the PAPUC, are currently recovering environmental remediation costs of former MGP facility sites through customer rates. See Note 3 — Regulatory Matters for additional information regarding the associated regulatory assets. While BGE and DPL do not have riders for MGP clean-up costs, they have historically received recovery of actual clean-up costs in distribution rates. As of December 31, 2017 and 2016 , the Registrants had accrued the following undiscounted amounts for environmental liabilities in Other current liabilities and Other deferred credits and other liabilities within their respective Consolidated Balance Sheets: December 31, 2017 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 466 $ 315 Generation 117 — ComEd 285 283 PECO 30 28 BGE 5 4 PHI 29 — Pepco 27 — DPL 1 — ACE 1 — December 31, 2016 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 429 $ 325 Generation 72 — ComEd 292 291 PECO 33 31 BGE 2 2 PHI 30 1 Pepco 27 — DPL 2 1 ACE 1 — During the third quarter of 2017, ComEd, PECO, BGE and DPL completed an annual study of their future estimated MGP remediation requirements. The study resulted in a $13 million and $2 million increase to environmental liabilities and related regulatory assets for ComEd and PECO, respectively, and no change at BGE and DPL. Solid and Hazardous Waste Cotter Corporation. The EPA has advised Cotter Corporation (Cotter), a former ComEd subsidiary, that it is potentially liable in connection with radiological contamination at a site known as the West Lake Landfill in Missouri. In 2000, ComEd sold Cotter to an unaffiliated third-party. As part of the sale, ComEd agreed to indemnify Cotter for any liability arising in connection with the West Lake Landfill. In connection with Exelon’s 2001 corporate restructuring, this responsibility to indemnify Cotter was transferred to Generation. On May 29, 2008, the EPA issued a Record of Decision (ROD) approving a landfill cover remediation approach. By letter dated January 11, 2010, the EPA requested that the PRPs perform a supplemental feasibility study for a remediation alternative that would involve complete excavation of the radiological contamination. On September 30, 2011, the PRPs submitted the supplemental feasibility study to the EPA for review. Since June 2012, the EPA has requested that the PRPs perform a series of additional analyses and groundwater and soil sampling as part of the supplemental feasibility study. This further analysis was focused on a partial excavation remedial option. The PRPs provided the draft final Remedial Investigation and Feasibility Study (RI/FS) to the EPA in January 2018, which formed the basis for EPA’s proposed remedy selection, as further discussed below. There are currently three PRPs participating in the West Lake Landfill remediation proceeding. Investigation by Generation has identified a number of other parties who also may be PRPs and c

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	12 Months Ended
	Dec. 31, 2017
Supplemental Financial Information [Abstract]
Supplemental Financial Information (All Registrants)	Supplemental Financial Information (All Registrants) Supplemental Statement of Operations Information The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2017 , 2016 and 2015 . For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 898 $ 126 $ 240 $ 125 $ 89 $ 318 $ 300 $ 18 $ — Property 545 269 28 14 132 101 62 32 3 Payroll 230 121 26 15 15 26 6 4 2 Other 58 39 2 — 4 7 3 3 1 Total taxes other than income $ 1,731 $ 555 $ 296 $ 154 $ 240 $ 452 $ 371 $ 57 $ 6 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Taxes other than income Utility (a) $ 753 $ 122 $ 242 $ 136 $ 85 $ 312 $ 18 $ — $ 253 $ 78 Property 483 246 27 13 123 53 31 3 73 18 Payroll 226 117 28 15 17 8 5 3 23 8 Other 114 21 (4 ) — 4 4 1 1 5 1 Total taxes other than income $ 1,576 $ 506 $ 293 $ 164 $ 229 $ 377 $ 55 $ 7 $ 354 $ 105 For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 474 $ 105 $ 236 $ 133 $ 85 $ 326 $ 308 $ 18 $ — Property 407 250 27 11 119 94 57 28 3 Payroll 201 118 28 14 16 27 6 4 2 Other 118 16 5 2 4 8 5 1 2 Total taxes other than income $ 1,200 $ 489 $ 296 $ 160 $ 224 $ 455 $ 376 $ 51 $ 7 __________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 455 455 — — — — — — — Non-regulatory agreement units 521 521 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (10 ) (10 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (724 ) (724 ) — — — — — — — Total decommissioning-related activities 939 939 — — — — — — — Investment income 8 6 — — — 2 1 — — Interest income (expense) related to uncertain income tax positions 3 (1 ) — — — — — — — Penalty related to uncertain income tax positions (c) 2 — — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Other 31 4 10 — — 16 8 7 1 Other, net $ 1,056 $ 948 $ 22 $ 9 $ 16 $ 54 $ 32 $ 14 $ 7 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 237 $ 237 $ — $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 126 126 — — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 216 216 — — — — — — — — Non-regulatory agreement units 194 194 — — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (1 ) (1 ) — — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (372 ) (372 ) — — — — — — — — Total decommissioning-related activities 400 400 — — — — — — — — Investment income (loss) 17 8 — (1 ) 2 1 — 1 1 — Long-term lease income 4 — — — — — — — — — Interest income (expense) related to uncertain income tax positions 13 — — — — 1 — — (1 ) — Penalty related to uncertain income tax positions (c) (106 ) — (86 ) — — — — — — — AFUDC—Equity 64 — 14 8 19 19 5 6 23 7 Loss on debt extinguishment (3 ) (2 ) — — — — — — — — Other 24 (5 ) 7 1 — 15 8 2 21 (11 ) Other, net $ 413 $ 401 $ (65 ) $ 8 $ 21 $ 36 $ 13 $ 9 $ 44 $ (4 ) For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 232 $ 232 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 156 156 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (282 ) (282 ) — — — — — — — Non-regulatory agreement units (197 ) (197 ) — — — — — — — Net unrealized gains on pledged assets Zion Station decommissioning 7 7 — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) 21 21 — — — — — — — Total decommissioning-related activities (63 ) (63 ) — — — — — — — Investment income (loss) 8 3 — (2 ) 4 — — — — Long-term lease income 15 — — — — — — — — Interest income related to uncertain income tax positions 1 1 — — — 34 5 — — AFUDC—Equity 24 — 5 5 14 14 12 1 1 Terminated interest rate swaps (d) (26 ) — — — — — — — — PHI merger related debt exchange (e) (22 ) — — — — — — — — Other 17 (1 ) 16 2 — 40 11 9 2 Other, net $ (46 ) $ (60 ) $ 21 $ 5 $ 18 $ 88 $ 28 $ 10 $ 3 __________ (a) Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (c) See Note 14 — Income Taxes for discussion of the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position. (d) In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten-year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from AOCI to Other, net in Exelon's Consolidated Statements of Operations and Comprehensive Income. (e) See Note 13 — Debt and Credit Agreements and Note 4 — Mergers, Acquisitions and Dispositions for additional information on the PHI merger related debt exchange. Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2017 , 2016 and 2015 . For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment $ 3,293 $ 1,409 $ 777 $ 261 $ 312 $ 457 $ 203 $ 124 $ 89 Regulatory assets 478 — 73 25 161 218 118 43 57 Amortization of intangible assets, net 57 48 — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — Nuclear fuel (b) 1,096 1,096 — — — — — — — ARO accretion (c) 468 468 — — — — — — — Total depreciation, amortization and accretion $ 5,427 $ 3,056 $ 850 $ 286 $ 473 $ 675 $ 321 $ 167 $ 146 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Depreciation, amortization and accretion Property, plant and equipment $ 3,477 $ 1,835 $ 708 $ 244 $ 299 $ 175 $ 110 $ 82 $ 325 $ 94 Regulatory assets 407 — 67 26 124 120 47 83 190 58 Amortization of intangible assets, net 52 44 — — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — — Nuclear fuel (b) 1,159 1,159 — — — — — — — — ARO accretion (c) 446 446 — — — — — — — — Total depreciation, amortization and accretion $ 5,576 $ 3,519 $ 775 $ 270 $ 423 $ 295 $ 157 $ 165 $ 515 $ 152 For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI Depreciation, amortization and accretion Property, plant and equipment $ 2,227 $ 1,007 $ 635 $ 240 $ 289 $ 164 $ 103 $ 76 $ 392 Regulatory assets 170 — 72 20 77 92 45 99 232 Amortization of intangible assets, net 54 47 — — — — — — — Amortization of energy contract assets and liabilities (a) 22 22 — — — — — — — Nuclear fuel (b) 1,116 1,116 — — — — — — — ARO accretion (c) 398 397 — — — — — — — Total depreciation, amortization and accretion $ 3,987 $ 2,589 $ 707 $ 260 $ 366 $ 256 $ 148 $ 175 $ 624 __________ (a) Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 2,430 $ 391 $ 307 $ 103 $ 96 $ 236 $ 114 $ 49 $ 59 Income taxes (net of refunds) 540 337 83 47 (2 ) (144 ) (104 ) (49 ) (2 ) Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 643 $ 227 $ 176 $ 29 $ 62 $ 94 $ 25 $ 13 $ 13 Loss (Gain) from equity method investments 32 33 — — — (1 ) — — — Provision for uncollectible accounts 125 38 34 26 8 19 8 3 8 Provision for excess and obsolete inventory 56 51 3 — — 2 1 1 — Stock-based compensation costs 88 — — — — — — — — Other decommissioning-related activity (a) (313 ) (313 ) — — — — — — — Energy-related options (b) 7 7 — — — — — — — Amortization of regulatory asset related to debt costs 9 — 4 1 — 4 2 1 1 Amortization of rate stabilization deferral (10 ) — — — 7 (17 ) (17 ) — — Amortization of debt fair value adjustment (18 ) (12 ) — — — (6 ) — — — Merger-related commitments (c) — — — — — (8 ) (6 ) (2 ) — Severance costs 35 31 — — — 3 — — — Amortization of debt costs 64 37 5 2 2 4 2 — 1 Discrete impacts from EIMA and FEJA (d) (52 ) — (52 ) — — — — — — Vacation accrual adjustment (e) (68 ) (35 ) (12 ) — — (8 ) (8 ) — — Long-term incentive plan 109 — — — — — — — — Change in environmental liabilities 44 44 — — — — — — — Other (30 ) 4 6 (4 ) (14 ) (27 ) (12 ) (7 ) (6 ) Total other non-cash operating activities $ 721 $ 112 $ 164 $ 54 $ 65 $ 59 $ (5 ) $ 9 $ 17 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ 42 $ 73 $ (61 ) $ 22 $ 23 $ (12 ) $ 5 $ 4 $ (13 ) Change in PPE related to ARO update 29 29 — — — — — — — Non-cash financing of capital projects 16 16 — — — — — — — Indemnification of like-kind exchange position (f) — — 21 — — — — — — Dividends on stock compensation 7 — — — — — — — — Dissolution of financing trust due to long-term debt retirement 8 — — — 8 — — — — Fair value adjustment of long-term debt due to retirement (5 ) — — — — — — — — Fair value of pension and OPEB obligation transferred in connection with FitzPatrick — 33 — — — — — — — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 4 - Mergers, Acquisitions and Dispositions for more information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 3 — Regulatory Matters for more information. (e) On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that will now be accrued ratably over the year in 2018. (f) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 1,340 $ 339 $ 298 $ 104 $ 92 $ 118 $ 47 $ 62 $ 209 $ 43 Income taxes (net of refunds) (441 ) 435 (444 ) 64 31 216 115 200 258 11 Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 619 $ 218 $ 166 $ 33 $ 67 $ 31 $ 18 $ 15 $ 86 $ 23 Loss from equity method investments 24 25 — — — — — — — — Provision for uncollectible accounts 155 19 41 30 1 29 23 32 65 16 Stock-based compensation costs 111 — — — — — — — — 3 Other decommissioning-related activity (a) (384 ) (384 ) — — — — — — — — Energy-related options (b) (11 ) (11 ) — — — — — — — — Amortization of regulatory asset related to debt costs 9 — 4 1 — 2 1 1 3 1 Amortization of rate stabilization deferral 76 — — — 81 (12 ) 2 — (5 ) 5 Amortization of debt fair value adjustment (11 ) (11 ) — — — — — — — — Merger-related commitments (c)(d) 558 53 — — — 125 82 110 317 — Severance costs 99 22 — — — — — — 56 — Discrete impacts from EIMA (e) 8 — 8 — — — — — — — Amortization of debt costs 35 17 4 3 1 — — — 1 — Provision for excess and obsolete inventory 12 6 4 — — 3 1 1 1 1 Lower of cost or market inventory adjustment 37 36 — 1 — — — — — — Baltimore City Conduit Lease Settlement (28 ) — — — (28 ) — — — — — Cash Working Capital Order (13 ) — — — (13 ) — — — — — Asset Retirement Costs 2 — — — — — 1 2 2 — Long-term incentive plan 70 — — — — — — — — — Other (35 ) 25 (12 ) (3 ) (21 ) 5 (14 ) (6 ) (12 ) (3 ) Total other non-cash operating activities $ 1,333 $ 15 $ 215 $ 65 $ 88 $ 183 $ 114 $ 155 $ 514 $ 46 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (128 ) $ 50 $ (91 ) $ (11 ) $ (86 ) $ 27 $ (12 ) $ 11 $ 21 $ 11 Change in PPE related to ARO update 191 191 — — — — — — — — Indemnification of like-kind exchange position (g) — — 158 — — — — — — — Dividends on stock compensation 6 — — — — — — — — — Non-cash financing of capital projects 95 95 — — — — — — — — Sale of Upstream assets (c) 37 37 — — — — — — — — Pending FitzPatrick Acquisition (h) (54 ) (54 ) — — — — — — — — Fair value of net assets contributed to Generation in connection with the PHI merger, net of cash — 119 — — — — — — — — Fair value of net assets distributed to Exelon in connection with the PHI Merger, net of cash (c)(f) — — — — — — — — 127 — Fair value of pension obligation transferred in connection with the PHI Merger (c)(f) — — — — — — — — 53 — Assumption of member purchase liability — — — — — — — — 29 — Assumption of merger commitment liability — — — — — 33 — — 33 — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 4 - Mergers, Acquisitions and Dispositions for more information. (d) Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts. (e) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information. (f) Immediately following closing of the PHI Merger, the net assets associated with PHI’s unregulated business interests were distributed by PHI to Exelon. Exelon contributed a portion of such net assets to Generation. (g) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. (h) Reflects the transfer of nuclear fuel to Entergy under the cost reimbursement provisions of the FitzPatrick acquisition agreements. See Note 4 - Mergers, Acquisitions and Dispositions for more information. For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 930 $ 348 $ 308 $ 94 $ 120 $ 268 $ 116 $ 47 $ 63 Income taxes (net of refunds) 342 476 (265 ) 64 73 (13 ) (6 ) (5 ) — Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 637 $ 269 $ 206 $ 39 $ 65 $ 97 $ 30 $ 15 $ 15 Loss from equity method investments 7 8 — — — — — — — Provision for uncollectible accounts 120 22 53 30 15 61 21 20 20 Provision for excess and obsolete inventory 10 9 1 — — 1 — — — Stock-based compensation costs 97 — — — — 13 — — — Other decommissioning-related activity (a) (82 ) (82 ) — — — — — — — Energy-related options (b) 21 21 — — — — — — — Amortization of regulatory asset related to debt costs 7 — 5 2 — 5 2 1 1 Amortization of rate stabilization deferral 73 — — — 73 (2 ) 1 (3 ) — Amortization of debt fair value adjustment (17 ) (17 ) — — — — — — — Discrete impacts from EIMA (c) 144 — 144 — — — — — — Amortization of debt costs 58 15 4 2 2 2 — — — Lower of cost or market inventory adjustment 23 23 — — — — — — — Long-term incentive plan 24 — — — — — — — — Other (13 ) — 3 (3 ) (18 ) (10 ) — — 1 Total other non-cash operating activities $ 1,109 $ 268 $ 416 $ 70 $ 137 $ 167 $ 54 $ 33 $ 37 Non-cash investing and financing activities: Change in PPE related to ARO update $ 885 $ 885 $ — $ — $ — $ — $ — $ — $ — Increase (decrease) in capital expenditures not paid 96 82 34 (13 ) (9 ) 6 (1 ) 3 3 Nuclear fuel procurement (d) 57 57 — — — — — — — Indemnification of like-kind exchange position (e) — — 7 — — — — — — Dividends on stock compensation 6 — — — — — — — — Non-cash financing of capital projects 77 77 — — — — — — — Long-term software licensing agreement (f) 95 — — — — — — — — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information. (d) Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 30, 2018, with the final payment being due no later than September 30, 2020. (e) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. (f) Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 13 - Debt and Credit Agreements . Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2017 and 2016 . Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 14 $ — $ 6 $ 8 $ — $ — $ — $ — $ — Bloom 206 206 — — — — — — — Net Power 76 76 — — — — — — — Other equity method investments 1 1 — — — — — — — Total equity method investments 297 283 6 8 — — — — — Other investments: Employee benefit trusts and investments (b) 244 51 — 17 5 132 102 — — Other cost method investments 62 62 — — — — — — — Other available for sale investments 37 37 — — — — — — — Total investments $ 640 $ 433 $ 6 $ 25 $ 5 $ 132 $ 102 $ — $ — Successor December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 $ — $ — $ — $ — Bloom 216 216 — — — — — — — Net Power 57 57 — — — — — — — Other equity method investments 16 15 — — — — — — — Total equity method investments 311 288 6 8 8 — — — — Other investments: Employee benefit trusts and investments (b) 232 44 — 17 4 133 102 — — Other cost method investments 52 52 — — — — — — — Other available for sale investments 34 34 — — — — — — — Total investments $ 629 $ 418 $ 6 $ 25 $ 12 $ 133 $ 102 $ — $ — __________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) The Registrants’ investments in these marketable securities are recorded at fair market value. The following tables provide additional information about liabilities of the Registrants at December 31, 2017 and 2016 . Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 978 $ 407 $ 158 $ 64 $ 58 $ 106 $ 29 $ 17 $ 11 Taxes accrued 373 444 60 15 71 61 68 4 5 Interest accrued 328 78 102 33 34 48 23 8 12 Severance accrued 58 30 2 — — 17 — — — Other accrued expenses 98 61 5 2 1 29 17 6 5 Total accrued expenses $ 1,835 $ 1,020 $ 327 $ 114 $ 164 $ 261 $ 137 $ 35 $ 33 Successor December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 1,199 $ 557 $ 199 $ 67 $ 64 $ 112 $ 30 $ 17 $ 11 Taxes accrued 723 239 330 4 78 65 48 4 9 Interest accrued 1,234 82 609 30 31 49 21 8 12 Severance accrued 44 15 2 — — 19 — — — Other accrued expenses 260 96 110 3 2 27 14 7 6 Total accrued expenses $ 3,460 $ 989 $ 1,250 $ 104 $ 175 $ 272 $ 113 $ 36 $ 38 __________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

Segment Information (All Regist

Segment Information (All Registrants)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information (All Registrants)	Segment Information (All Registrants) Operating segments for each of the Registrants are determined based on information used by the chief operating decision maker(s) (CODM) in deciding how to evaluate performance and allocate resources at each of the Registrants. In the first quarter of 2016, following the consummation of the PHI Merger, three new reportable segments were added: Pepco, DPL and ACE. As a result, Exelon has twelve reportable segments, which include ComEd, PECO, BGE, PHI's three reportable segments consisting of Pepco, DPL, and ACE, and Generation’s six reportable segments consisting of the Mid-Atlantic, Midwest, New England, New York, ERCOT and all other power regions referred to collectively as “Other Power Regions”, which includes activities in the South, West and Canada. ComEd, PECO, BGE, Pepco, DPL and ACE each represent a single reportable segment, and as such, no separate segment information is provided for these Registrants. Exelon, ComEd, PECO, BGE, Pepco, DPL and ACE's CODMs evaluate the performance of and allocate resources to ComEd, PECO, BGE, Pepco, DPL and ACE based on net income and return on equity. Effective with the consummation of the PHI Merger, PHI's reportable segments have changed based on the information used by the CODM to evaluate performance and allocate resources. PHI's reportable segments consist of Pepco, DPL and ACE. PHI's Predecessor periods' segment information was recast in 2016 to conform to the current Exelon presentation. The reclassification of the segment information did not impact PHI's reported consolidated revenues or net income. PHI's CODM evaluates the performance of and allocates resources to Pepco, DPL and ACE based on net income and return on equity. The basis for Generation's reportable segments is the integrated management of its electricity business that is located in different geographic regions, and largely representative of the footprints of ISO/RTO and/or NERC regions, which utilize multiple supply sources to provide electricity through various distribution channels (wholesale and retail). Generation's hedging strategies and risk metrics are also aligned to these same geographic regions. Descriptions of each of Generation’s six reportable segments are as follows: • Mid-Atlantic represents operations in the eastern half of PJM, which includes New Jersey, Maryland, Virginia, West Virginia, Delaware, the District of Columbia and parts of Pennsylvania and North Carolina. • Midwest represents operations in the western half of PJM, which includes portions of Illinois, Pennsylvania, Indiana, Ohio, Michigan, Kentucky and Tennessee, and the United States footprint of MISO, excluding MISO’s Southern Region, which covers all or most of North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, the remaining parts of Illinois, Indiana, Michigan and Ohio not covered by PJM, and parts of Montana, Missouri and Kentucky. • New England represents the operations within ISO-NE covering the states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont. • New York represents operations within ISO-NY, which covers the state of New York in its entirety. • ERCOT represents operations within Electric Reliability Council of Texas, covering most of the state of Texas. • Other Power Regions : • South represents operations in the FRCC, MISO’s Southern Region, and the remaining portions of the SERC not included within MISO or PJM, which includes all or most of Florida, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Tennessee, North Carolina, South Carolina and parts of Missouri, Kentucky and Texas. Generation’s South region also includes operations in the SPP, covering Kansas, Oklahoma, most of Nebraska and parts of New Mexico, Texas, Louisiana, Missouri, Mississippi and Arkansas. • West represents operations in the WECC, which includes California ISO, and covers the states of California, Oregon, Washington, Arizona, Nevada, Utah, Idaho, Colorado and parts of New Mexico, Wyoming and South Dakota. • Canada represents operations across the entire country of Canada and includes AESO, OIESO and the Canadian portion of MISO. The CODMs for Exelon and Generation evaluate the performance of Generation’s electric business activities and allocate resources based on revenues net of purchased power and fuel expense (RNF). Generation believes that RNF is a useful measurement of operational performance. RNF is not a presentation defined under GAAP and may not be comparable to other companies’ presentations or deemed more useful than the GAAP information provided elsewhere in this report. Generation’s operating revenues include all sales to third parties and affiliated sales to the Utility Registrants. Purchased power costs include all costs associated with the procurement and supply of electricity including capacity, energy and ancillary services. Fuel expense includes the fuel costs for Generation’s owned generation and fuel costs associated with tolling agreements. The results of Generation's other business activities are not regularly reviewed by the CODM and are therefore not classified as operating segments or included in the regional reportable segment amounts. These activities include natural gas, as well as other miscellaneous business activities that are not significant to Generation's overall operating revenues or results of operations. Further, Generation’s unrealized mark-to-market gains and losses on economic hedging activities and its amortization of certain intangible assets and liabilities relating to commodity contracts recorded at fair value from mergers and acquisitions are also excluded from the regional reportable segment amounts. Exelon and Generation do not use a measure of total assets in making decisions regarding allocating resources to or assessing the performance of these reportable segments. An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the years ended December 31, 2017 , 2016 , and 2015 is as follows: Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Operating revenues (c) : 2017 Competitive businesses electric revenues $ 15,300 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,195 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 591 — — — — — (1 ) 590 Rate-regulated electric revenues — 5,536 2,375 2,489 4,469 — (29 ) 14,840 Rate-regulated natural gas revenues — — 495 687 161 — (10 ) 1,333 Shared service and other revenues — — — — 49 1,831 (1,880 ) — 2016 Competitive businesses electric revenues $ 15,390 $ — $ — $ — $ — $ — $ (1,430 ) $ 13,960 Competitive businesses natural gas revenues 2,146 — — — — — — 2,146 Competitive businesses other revenues 215 — — — — — (4 ) 211 Rate-regulated electric revenues — 5,254 2,531 2,609 3,506 — (31 ) 13,869 Rate-regulated natural gas revenues — — 463 624 92 — (13 ) 1,166 Shared service and other revenues — — — — 45 1,648 (1,686 ) 7 2015 Competitive businesses electric revenues $ 15,944 $ — $ — $ — $ — $ — $ (744 ) $ 15,200 Competitive businesses natural gas revenues 2,433 — — — — — — 2,433 Competitive businesses other revenues 758 — — — — — (1 ) 757 Rate-regulated electric revenues — 4,905 2,486 2,490 — — (5 ) 9,876 Rate-regulated natural gas revenues — — 546 645 — — (15 ) 1,176 Shared service and other revenues — — — — — 1,372 (1,367 ) 5 Intersegment revenues (d) : 2017 $ 1,110 $ 15 $ 7 $ 16 $ 50 $ 1,824 $ (3,020 ) $ 2 2016 1,428 15 8 21 45 1,647 (3,159 ) 5 2015 745 4 2 14 — 1,367 (2,127 ) 5 Depreciation and amortization: 2017 $ 1,457 $ 850 $ 286 $ 473 $ 675 $ 87 $ — $ 3,828 2016 1,879 775 270 423 515 74 — 3,936 2015 1,054 707 260 366 — 63 — 2,450 Operating expenses (c) : 2017 $ 17,993 $ 4,214 $ 2,215 $ 2,562 $ 3,911 $ 1,851 $ (3,026 ) $ 29,720 2016 16,856 4,056 2,292 2,683 3,549 1,928 (3,164 ) 28,200 2015 16,872 3,889 2,404 2,578 — 1,444 (2,131 ) 25,056 Equity in earnings (losses) of unconsolidated affiliates: 2017 $ (33 ) $ — $ — $ — $ — $ 1 $ — $ (32 ) 2016 (25 ) — — — — 1 — (24 ) 2015 (8 ) — — — — 1 — (7 ) Interest expense, net: 2017 $ 440 $ 361 $ 126 $ 105 $ 245 $ 283 $ — $ 1,560 2016 364 461 123 103 195 290 — 1,536 2015 365 332 114 99 — 123 — 1,033 Income (loss) before income taxes: 2017 $ 1,429 $ 984 $ 538 $ 525 $ 578 $ (296 ) $ (2 ) $ 3,756 2016 873 679 587 468 (58 ) (555 ) (5 ) 1,989 2015 1,850 706 521 477 — (219 ) (5 ) 3,330 Income taxes: 2017 $ (1,375 ) $ 417 $ 104 $ 218 $ 217 $ 294 $ — $ (125 ) 2016 290 301 149 174 3 (156 ) — 761 2015 502 280 143 189 — (41 ) — 1,073 Net income (loss): 2017 $ 2,771 $ 567 $ 434 $ 307 $ 362 $ (590 ) $ (2 ) $ 3,849 2016 558 378 438 294 (61 ) (398 ) (5 ) 1,204 2015 1,340 426 378 288 — (177 ) (5 ) 2,250 Capital expenditures: 2017 $ 2,259 $ 2,250 $ 732 $ 882 $ 1,396 $ 65 $ — $ 7,584 2016 3,078 2,734 686 934 1,008 113 — 8,553 2015 3,841 2,398 601 719 — 65 — 7,624 Total assets: 2017 $ 48,387 $ 29,726 $ 10,170 $ 9,104 $ 21,247 $ 8,618 $ (10,552 ) $ 116,700 2016 46,974 28,335 10,831 8,704 21,025 10,369 (11,334 ) 114,904 __________ (a) Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $138 million , sales to BGE of $388 million , sales to Pepco of $255 million , sales to DPL of $179 million and sales to ACE of $29 million in the Mid-Atlantic region, and sales to ComEd of $121 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2016 , intersegment revenues for Generation include revenue from sales to PECO of $ 290 million and sales to BGE of $ 608 million in the Mid-Atlantic region, and sales to ComEd of $ 47 million in the Midwest region, which eliminate upon consolidation. For the Successor period of March 24, 2016 to December 31, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $295 million , sales to DPL of $154 million and sales to ACE of $37 million in the Mid-Atlantic region, which eliminate upon consolidation. For the year ended December 31, 2015 , intersegment revenues for Generation include revenue from sales to PECO of $224 million and sales to BGE of $502 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017 , 2016 and 2015 . (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income. (e) Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2017 . PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor periods, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016 and for the year ended December 31, 2015 . Successor and Predecessor PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : December 31, 2017 - Successor Rate-regulated electric revenues $ 2,158 $ 1,139 $ 1,186 $ — $ (14 ) $ 4,469 Rate-regulated natural gas revenues — 161 — — — 161 Shared service and other revenues — — — 52 (3 ) 49 March 24, 2016 to December 31, 2016 - Successor Rate-regulated electric revenues $ 1,675 $ 850 $ 989 $ 5 $ (13 ) $ 3,506 Rate-regulated natural gas revenues — 92 — — — 92 Shared service and other revenues — — — 45 — 45 January 1, 2016 to March 23, 2016 - Predecessor Rate-regulated electric revenues $ 511 $ 279 $ 268 $ 42 $ (4 ) $ 1,096 Rate-regulated natural gas revenues — 56 — 1 — 57 Shared service and other revenues — — — — — — December 31, 2015 - Predecessor Rate-regulated electric revenues $ 2,129 $ 1,138 $ 1,295 $ 210 $ (2 ) $ 4,770 Rate-regulated natural gas revenues — 164 — 1 — 165 Shared service and other revenues — — — — — — Intersegment revenues: December 31, 2017 - Successor $ 6 $ 8 $ 2 $ 53 $ (19 ) $ 50 March 24, 2016 to December 31, 2016 - Successor 4 5 2 47 (13 ) 45 January 1, 2016 to March 23, 2016 - Predecessor 1 2 1 — (4 ) — December 31, 2015 - Predecessor 5 6 4 — (15 ) — Depreciation and amortization: December 31, 2017 - Successor $ 321 $ 167 $ 146 $ 42 $ (1 ) $ 675 March 24, 2016 to December 31, 2016 - Successor 224 120 128 43 — $ 515 January 1, 2016 to March 23, 2016 - Predecessor 71 37 37 11 (4 ) $ 152 December 31, 2015 - Predecessor 256 148 175 45 — $ 624 Operating expenses: December 31, 2017 - Successor $ 1,760 $ 1,071 $ 1,029 $ 68 $ (17 ) $ 3,911 March 24, 2016 to December 31, 2016 - Successor 1,577 952 1,000 33 (13 ) $ 3,549 January 1, 2016 to March 23, 2016 - Predecessor 443 284 251 73 (3 ) $ 1,048 December 31, 2015 - Predecessor 1,790 1,137 1,161 220 — $ 4,308 Interest expense, net: December 31, 2017 - Successor $ 121 $ 51 $ 61 $ 13 $ (1 ) $ 245 March 24, 2016 to December 31, 2016 - Successor 98 38 47 12 — $ 195 January 1, 2016 to March 23, 2016 - Predecessor 29 12 15 11 (2 ) $ 65 December 31, 2015 - Predecessor 124 50 64 43 (1 ) $ 280 Income (loss) before income taxes: December 31, 2017 - Successor $ 310 $ 192 $ 103 $ 377 $ (404 ) $ 578 March 24, 2016 to December 31, 2016 - Successor 36 (30 ) (51 ) (84 ) 71 $ (58 ) January 1, 2016 to March 23, 2016 - Predecessor 47 43 5 59 (118 ) $ 36 December 31, 2015 - Predecessor 289 125 73 23 (29 ) $ 481 Income taxes: December 31, 2017 - Successor $ 105 $ 71 $ 26 $ 15 $ — $ 217 March 24, 2016 to December 31, 2016 - Successor 26 5 (5 ) (23 ) — $ 3 January 1, 2016 to March 23, 2016 - Predecessor 15 17 1 (16 ) — $ 17 December 31, 2015 - Predecessor 102 49 33 (48 ) 27 $ 163 Net income (loss): December 31, 2017 - Successor $ 205 $ 121 $ 77 $ (91 ) $ 50 $ 362 March 24, 2016 to December 31, 2016 - Successor 10 (35 ) (47 ) (34 ) 45 $ (61 ) January 1, 2016 to March 23, 2016 - Predecessor 32 26 5 (44 ) — $ 19 December 31, 2015 - Predecessor 187 76 40 25 (1 ) $ 327 Capital expenditures: December 31, 2017 - Successor $ 628 $ 428 $ 312 $ 28 $ — $ 1,396 March 24, 2016 to December 31, 2016 - Successor 489 277 218 24 — $ 1,008 January 1, 2016 to March 23, 2016 - Predecessor 97 72 93 11 — 273 December 31, 2015 - Predecessor 544 352 300 34 — 1,230 Total assets: December 31, 2017 - Successor $ 7,832 $ 4,357 $ 3,445 $ 10,600 $ (4,987 ) $ 21,247 December 31, 2016 - Successor 7,335 4,153 3,457 10,804 (4,724 ) 21,025 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017 , 2016 and 2015 . (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. For the predecessor periods presented, Other includes the activity of PHI’s unregulated businesses which were distributed to Exelon and Generation as a result of the PHI Merger. Generation total revenues: 2017 2016 2015 Revenues from external customers (a) Intersegment revenues Total revenues Revenues from external customers (a) Intersegment revenues Total revenues Revenues from external customers (a) Intersegment revenues Total revenues Mid-Atlantic $ 5,515 $ 25 $ 5,540 $ 6,212 $ (33 ) $ 6,179 $ 5,974 $ (74 ) $ 5,900 Midwest 4,206 (25 ) 4,181 4,402 10 4,412 4,712 (2 ) 4,710 New England 2,010 (8 ) 2,002 1,778 (9 ) 1,769 2,217 (5 ) 2,212 New York 1,535 (17 ) 1,518 1,198 (42 ) 1,156 996 (11 ) 985 ERCOT 958 4 962 831 6 837 863 (6 ) 857 Other Power Regions 1,076 (27 ) 1,049 969 (62 ) 907 1,182 (80 ) 1,102 Total Revenues for Reportable Segments $ 15,300 $ (48 ) $ 15,252 $ 15,390 $ (130 ) $ 15,260 $ 15,944 $ (178 ) $ 15,766 Other (b) 3,166 48 3,214 2,361 130 2,491 3,191 178 3,369 Total Generation Consolidated Operating Revenues $ 18,466 $ — $ 18,466 $ 17,751 $ — $ 17,751 $ 19,135 $ — $ 19,135 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $38 million decrease to revenues, a $ 52 million decrease to revenues, and a $ 7 million increase to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2017 , 2016 , and 2015 , respectively, unrealized mark-to-market losses of $131 million , losses of $500 million , and gains of $203 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively, and elimination of intersegment revenues. Generation total revenues net of purchased power and fuel expense: 2017 2016 2015 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 3,105 $ 109 $ 3,214 $ 3,282 $ 35 $ 3,317 $ 3,556 $ 15 $ 3,571 Midwest 2,810 10 2,820 2,969 2 2,971 2,912 (20 ) 2,892 New England 538 (24 ) 514 467 (29 ) 438 519 (58 ) 461 New York 975 1 976 761 (19 ) 742 584 50 634 ERCOT 575 (243 ) 332 412 (131 ) 281 425 (132 ) 293 Other Power Regions 476 (171 ) 305 483 (147 ) 336 440 (190 ) 250 Total Revenues net of purchased power and fuel expense for Reportable Segments $ 8,479 $ (318 ) $ 8,161 $ 8,374 $ (289 ) $ 8,085 $ 8,436 $ (335 ) $ 8,101 Other (b) 297 318 615 547 289 836 678 335 1,013 Total Generation Revenues net of purchased power and fuel expense $ 8,776 $ — $ 8,776 $ 8,921 $ — $ 8,921 $ 9,114 $ — $ 9,114 __________ (a) Includes purchases and sales from third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million decrease in RNF, a $57 million decrease in RNF, and a $8 million increase in RNF for the amortization of intangible assets and liabilities related to commodity contracts for the years ended December 31, 2017 , 2016 , and 2015 , respectively, unrealized mark-to-market losses of $175 million , losses of $41 million , and gains of $257 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively, accelerated nuclear fuel amortization associated with the announced early retirement decision for Clinton and Quad Cities as discussed in Note 8 - Early Nuclear Plant Retirements of $12 million and $60 million for the year ended December 31, 2017 and 2016 , and the elimination of intersegment revenues net of purchased power and fuel expense.

Related Party Transactions (All

Related Party Transactions (All Registrants)	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions (All Registrants)	(All Registrants) Exelon The financial statements of Exelon include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PECO (a) $ 1 $ 1 $ 1 BGE (a) 4 4 4 Other 2 5 4 Total operating revenues from affiliates $ 7 $ 10 $ 9 Interest expense to affiliates, net: ComEd Financing III $ 14 $ 13 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II 10 16 16 Total interest expense to affiliates, net $ 36 $ 41 $ 41 Earnings (losses) in equity method investments: Qualifying facilities and domestic power projects $ (33 ) $ (25 ) $ (8 ) Other 1 1 1 Total losses in equity method investments $ (32 ) $ (24 ) $ (7 ) December 31, 2017 2016 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 BGE Capital Trust II — 3 Total payables to affiliates (current) $ 5 $ 8 Long-term debt due to financing trusts: ComEd Financing III $ 205 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 BGE Capital Trust II — 252 Total long-term debt due to financing trusts $ 389 $ 641 __________ (a) The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 3 — Regulatory Matters for additional information. Transactions involving Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE are further described in the tables below. Generation The financial statements of Generation include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: ComEd (a) $ 121 $ 47 $ 18 PECO (b) 138 290 224 BGE (c) 388 608 502 Pepco (d) 255 295 — DPL (e) 179 154 — ACE (f) 29 37 — BSC 1 2 1 Other 4 6 4 Total operating revenues from affiliates $ 1,115 $ 1,439 $ 749 Purchased power and fuel from affiliates: ComEd $ 13 $ — $ — BGE 9 12 14 Other (3 ) — — Total purchased power and fuel from affiliates $ 19 $ 12 $ 14 Operating and maintenance from affiliates: ComEd (g) $ 7 $ 7 $ 4 PECO (g) 1 3 2 BGE (g) 1 1 — Pepco — 1 — PHISCO 1 1 — BSC (h) 689 650 614 Other $ (2 ) $ — $ — Total operating and maintenance from affiliates $ 697 $ 663 $ 620 Interest expense to affiliates, net: Exelon Corporate (i) $ 37 $ 39 $ 43 PCI 1 — — PECO 1 — — Total interest expense to affiliates, net: 39 39 43 Earnings (losses) in equity method investments Qualifying facilities and domestic power projects $ (33 ) $ (25 ) $ (8 ) Capitalized costs BSC (h) $ 98 $ 98 $ 76 Cash distribution paid to member $ 659 $ 922 $ 2,474 Contribution from member $ 102 $ 142 $ 47 December 31, 2017 2016 Receivables from affiliates (current): ComEd (a) $ 28 $ 14 PECO (b) 26 33 BGE (c) 24 26 Pepco (d) 36 44 DPL (e) 12 16 ACE (f) 6 9 PHISCO (h) 1 5 PCI — 8 Other 7 1 Total receivables from affiliates (current) $ 140 $ 156 Intercompany money pool (current): PCI $ 54 $ 55 Payables to affiliates (current): Exelon Corporate (i) $ 21 $ 22 BSC (h) 74 99 ComEd 12 9 PECO (b) 4 — Other 12 7 Total payables to affiliates (current) $ 123 $ 137 Long-term debt due to affiliates (noncurrent): Exelon Corporate (k) $ 910 $ 922 Payables to affiliates (noncurrent): BSC (h) $ — $ 1 ComEd (j) 2,528 2,169 PECO (j) 537 438 Total payables to affiliates (noncurrent) $ 3,065 $ 2,608 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3 — Regulatory Matters for additional information. (b) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3 — Regulatory Matters for additional information. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (d) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3 — Regulatory Matters for additional information. (e) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (f) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3 — Regulatory Matters for additional information. (g) Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and BGE and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations. (h) Generation receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (i) The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation. (j) Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 15 — Asset Retirement Obligations . (k) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets. ComEd The financial statements of ComEd include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates Generation $ 9 $ 7 $ 4 BSC 6 6 — PECO — 1 — BGE — 1 — Total operating revenues from affiliates $ 15 $ 15 $ 4 Purchased power from affiliate Generation (a) $ 108 $ 47 $ 18 Operating and maintenance from affiliates BSC (b) $ 270 $ 225 $ 195 PECO — 1 — BGE — 1 — Total operating and maintenance from affiliates $ 270 $ 227 $ 195 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 118 $ 112 $ 103 Cash dividends paid to parent $ 422 $ 369 $ 299 Contribution from parent $ 651 $ 315 $ 202 December 31, 2017 2016 Prepaid voluntary employee beneficiary association trust (c) $ 2 $ 5 Receivable from affiliates (current): Voluntary employee beneficiary association trust $ 1 $ 2 Generation 12 9 Exelon Corporate (d) — 345 Total receivable from affiliates (current) $ 13 $ 356 Receivable from affiliates (noncurrent): Generation (e) $ 2,528 $ 2,169 Other — 1 Total receivable from affiliates (noncurrent) $ 2,528 $ 2,170 Payables to affiliates (current): Generation (a) $ 28 $ 14 BSC (b) 39 42 ComEd Financing III 4 4 PECO — 2 Exelon Corporate 3 3 Total payables to affiliates (current) $ 74 $ 65 Long-term debt to ComEd financing trust ComEd Financing III $ 205 $ 205 __________ (a) ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information. (b) ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (c) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets. (d) Represents indemnification from Exelon Corporate related to the like-kind exchange. (e) ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers. PECO The financial statements of PECO include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ 1 $ 3 $ 2 BSC 5 3 — ComEd — 1 — BGE 1 1 — Total operating revenues from affiliates $ 7 $ 8 $ 2 Purchased power from affiliate Generation (b) $ 135 $ 287 $ 220 Operating and maintenance from affiliates: BSC (c) $ 146 $ 142 $ 107 Generation 2 2 3 ComEd — 1 — BGE 1 1 — Total operating and maintenance from affiliates $ 149 $ 146 $ 110 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Generation (1 ) — — Total interest expense to affiliates, net: $ 11 $ 12 $ 12 Capitalized costs BSC (c) $ 59 $ 57 $ 40 Cash dividends paid to parent $ 288 $ 277 $ 279 Contribution from parent $ 16 $ 18 $ 16 December 31, 2017 2016 Prepaid voluntary employee beneficiary association trust (d) $ — $ 1 Receivable from affiliate (current): ComEd $ — $ 2 BGE — 2 Total receivable from affiliates (current) $ — $ 4 Receivable from affiliate (noncurrent): Generation (e) $ 537 $ 438 Payables to affiliates (current): Generation (b) $ 22 $ 33 BSC (c) 29 28 Exelon Corporate 1 1 PECO Trust III 1 1 Total payables to affiliates (current) $ 53 $ 63 Long-term debt to financing trusts: PECO Trust III $ 81 $ 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 184 $ 184 __________ (a) PECO provides energy to Generation for Generation’s own use. (b) PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information on AECs. (c) PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. (e) PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers. BGE The financial statements of BGE include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ 10 $ 13 $ 14 BSC 5 6 — ComEd — 1 — PECO 1 1 — Total operating revenues from affiliates $ 16 $ 21 $ 14 Purchased power from affiliate Generation (b) $ 384 $ 604 $ 498 Operating and maintenance from affiliates: BSC (c) $ 152 $ 130 $ 118 ComEd — 1 — PECO 1 1 — Total operating and maintenance from affiliates $ 153 $ 132 $ 118 Interest expense to affiliates, net: BGE Capital Trust II $ 10 $ 16 $ 16 Capitalized costs BSC (c) $ 54 $ 36 $ 28 Cash dividends paid to parent $ 198 $ 179 $ 158 Contribution from parent $ 184 $ 61 $ 7 December 31, 2017 2016 Receivable from affiliates (current): Other $ 1 $ — Payables to affiliates (current): Generation (b) $ 24 $ 26 BSC (c) 25 22 Exelon Corporate 1 1 PECO — 2 BGE Capital Trust II — 3 Other 2 1 Total payables to affiliates (current) $ 52 $ 55 Long-term debt to BGE financing trust BGE Capital Trust II $ — $ 252 __________ (a) BGE provides energy to Generation for Generation’s own use. (b) BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (c) BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. PHI The financial statements of PHI include related party transactions as presented in the tables below: Successor For the Year Ended December 31, March 24, 2016 to December 31, 2017 2016 Operating revenues from affiliates: BSC $ 48 $ 44 PHISCO 2 — Generation — 1 Total operating revenues from affiliates $ 50 $ 45 Purchased power from affiliate Generation $ 463 $ 486 Operating and maintenance from affiliates: BSC (a) $ 145 $ 86 Other 5 3 Total operating and maintenance from affiliates $ 150 $ 89 Cash dividends paid to parent $ 311 $ 273 Contribution from member $ 758 $ 1,251 Successor December 31, 2017 2016 Payables to affiliates (current): Generation $ 54 $ 74 BGE 1 — BSC (a) 24 10 Exelon Corporate 6 6 Other 5 4 Total payables to affiliates (current) $ 90 $ 94 __________ (a) PHI receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. Pepco The financial statements of Pepco include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ — $ 1 $ — PHISCO 6 4 5 Total operating revenues from affiliates $ 6 $ 5 $ 5 Purchased power from affiliate Generation (b) $ 255 $ 295 $ — Operating and maintenance: PHISCO (c) $ 219 $ 263 $ 240 PES (d) 29 39 26 Total operating and maintenance $ 248 $ 302 $ 266 Operating and maintenance from affiliates: BSC (c) $ 53 $ 31 $ — PHISCO (c) 5 4 4 Total operating and maintenance from affiliates $ 58 $ 35 $ 4 Cash dividends paid to parent $ 133 $ 136 $ 146 Contribution from parent $ 161 $ 187 $ 112 December 31, 2017 2016 Payables to affiliates (current): Generation (b) $ 36 $ 44 BSC (c) 11 4 DPL — 1 PHISCO (c) 27 25 Total payables to affiliates (current) $ 74 $ 74 __________ (a) Pepco provides energy to Generation for Generation’s own use. (b) Pepco procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (c) Pepco receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) PES performs underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco. DPL The financial statements of DPL include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PHISCO $ 6 $ 5 $ 5 Other 2 2 1 Total operating revenues from affiliates $ 8 $ 7 $ 6 Purchased power from affiliate Generation (a) $ 179 $ 154 $ — Operating and maintenance: PHISCO (b) $ 165 $ 194 $ 179 PES (c) 9 8 3 Total operating and maintenance $ 174 $ 202 $ 182 Operating and maintenance from affiliates: BSC (b) $ 31 $ 18 $ — Other 1 1 1 Total operating and maintenance from affiliates $ 32 $ 19 $ 1 Cash dividends paid to parent $ 112 $ 54 $ 92 Contribution from parent $ — $ 152 $ 75 December 31, 2017 2016 Receivables from affiliates (current): Pepco $ — $ 1 ACE — 2 Total receivable from affiliates (current) $ — $ 3 Payables to affiliates (current): Generation (a) $ 12 $ 16 BSC (b) 7 3 PHISCO (b) 27 19 Total payables to affiliates (current) $ 46 $ 38 __________ (a) DPL procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (b) DPL receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (c) PES performs underground transmission construction services, including services that are treated as capital costs, for DPL. ACE The financial statements of ACE include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PHISCO $ 1 $ 2 $ 2 Other 1 1 2 Total operating revenues from affiliates $ 2 $ 3 $ 4 Purchased power from affiliate Generation (a) $ 29 $ 37 $ — Operating and maintenance: PHISCO (b) $ 135 $ 155 $ 143 Operating and maintenance from affiliates: BSC (b) $ 25 $ 15 $ — Other 3 3 3 Total operating and maintenance from affiliates $ 28 $ 18 $ 3 Cash dividends paid to parent $ 68 $ 63 $ 12 Contribution from parent $ — $ 139 $ 95 December 31, 2017 2016 Payables to affiliates (current): Generation (a) $ 6 $ 9 BSC (b) 5 2 DPL — 2 PHISCO (b) 18 16 Total payables to affiliates (current) $ 29 $ 29 __________ (a) ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. See Note 3 — Regulatory Matters for additional information. (b) ACE receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

Quarterly Data (Unaudited) (All

Quarterly Data (Unaudited) (All Registrants)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Data (Unaudited) (All Registrants)	(Unaudited) (All Registrants) Exelon The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 8,757 $ 7,573 $ 1,296 $ 483 $ 995 $ 173 June 30 7,623 6,910 232 647 80 267 September 30 8,769 9,002 1,475 1,267 824 490 December 31 8,381 7,875 1,258 714 1,871 204 Average Basic Shares Net Income 2017 2016 2017 2016 Quarter ended: March 31 928 923 $ 1.07 $ 0.19 June 30 934 924 0.09 0.29 September 30 962 925 0.86 0.53 December 31 964 925 1.94 0.22 Net Income 2017 2016 2017 2016 Quarter ended: March 31 930 925 $ 1.07 $ 0.19 June 30 936 926 0.09 0.29 September 30 965 927 0.85 0.53 December 31 967 928 1.93 0.22 The following table presents the New York Stock Exchange—Composite Common Stock Prices and dividends by quarter on a per share basis: 2017 2016 Fourth Quarter Third Quarter Second Quarter First Quarter Fourth Quarter Third Quarter Second Quarter First Quarter High price $ 42.67 $ 38.78 $ 37.44 $ 37.19 $ 36.36 $ 37.70 $ 36.37 $ 35.95 Low price 37.55 35.37 33.30 34.47 29.82 32.86 33.18 26.26 Close 39.41 37.67 36.07 35.98 35.49 33.29 36.36 35.86 Dividends 0.328 0.328 0.328 0.328 0.318 0.318 0.318 0.310 Generation The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating (Loss) Income Net (Loss) Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 4,888 $ 4,739 $ 387 $ 415 $ 423 $ 310 June 30 4,174 3,589 (467 ) (13 ) (250 ) (8 ) September 30 4,751 5,035 500 342 305 236 December 31 4,654 4,388 501 94 2,215 (41 ) ComEd The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 1,298 $ 1,249 $ 314 $ 274 $ 141 $ 115 June 30 1,357 1,286 319 324 118 145 September 30 1,571 1,497 404 389 189 37 December 31 1,309 1,223 286 217 120 80 PECO The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 796 $ 841 $ 192 $ 196 $ 127 $ 124 June 30 630 664 137 152 88 100 September 30 715 788 169 204 112 122 December 31 729 701 157 150 107 92 BGE The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 951 $ 929 $ 228 $ 187 $ 125 $ 98 June 30 674 680 98 59 45 31 September 30 738 812 124 115 62 54 December 31 813 812 163 190 76 103 PHI The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Successor Operating Revenues Operating Income (Loss) Net Income (Loss) Membership Interest 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 1,175 $ 105 (a) $ 180 $ (411 ) (a) $ 140 $ (309 ) (a) June 30 1,074 1,066 148 136 66 52 September 30 1,310 1,394 285 279 153 166 December 31 1,121 1,078 159 90 4 30 Predecessor Operating Revenues Operating Income Net Income Attributable to Membership Interest January 1, 2016 - March 23, 2016 1,153 105 19 __________ (a) Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016. Pepco The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 530 $ 551 $ 79 $ (105 ) $ 58 $ (108 ) June 30 514 509 84 97 43 49 September 30 604 635 149 132 87 79 December 31 510 491 87 51 17 23 DPL The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 362 $ 362 $ 78 $ (72 ) $ 57 $ (72 ) June 30 282 281 41 30 19 12 September 30 327 331 59 72 31 44 December 31 330 303 52 20 14 7 ACE The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 275 $ 291 $ 25 $ (121 ) $ 28 $ (100 ) June 30 270 270 25 19 8 3 September 30 370 421 79 83 41 47 December 31 271 275 28 26 — 8

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Event [Line Items]
Subsequent Events [Text Block]	Subsequent Events (Exelon, Generation and ComEd) Illinois ZEC Procurement On January 25, 2018, the ICC announced that Generation’s Clinton Unit 1, Quad Cities Unit 1 and Quad Cities Unit 2 nuclear plants were selected as the winning bidders through the IPA's ZEC procurement event. Generation executed the ZEC procurement contracts with Illinois utilities, including ComEd, effective January 26, 2018 and will begin recognizing revenue. Winning bidders will be entitled to compensation for the sale of ZECs retroactive to the June 1, 2017 effective date of FEJA. In the first quarter of 2018, Generation will recognize approximately $150 million of revenue and ComEd will record an obligation to Generation and corresponding reduction to its regulatory liability of approximately $100 million related to ZECs generated from June 1, 2017 through December 31, 2017. Early Retirement of Oyster Creek Generating Station On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at Oyster Creek at the end of its current operating cycle in October 2018. In 2010, Generation announced that Oyster Creek would retire by the end of 2019 as part of an agreement with the State of New Jersey to avoid significant costs associated with the construction of cooling towers to meet the State’s then new environmental regulations. Since then, like other nuclear sites, Oyster Creek has continued to face rising operating costs amid a historically low wholesale power price environment. The decision to retire Oyster Creek in 2018 at the end of its current operating cycle involved consideration of several factors, including economic and operating efficiencies, and avoids a refueling outage scheduled for the fall of 2018 that would have required advanced purchasing of fuel fabrication and materials beginning in late February 2018. Because of the decision to retire Oyster Creek in 2018, Exelon and Generation will recognize certain one-time charges in the first quarter of 2018 ranging from an estimated $25 million to $35 million (pre-tax) related to a materials and supplies inventory reserve adjustment, employee-related costs, and construction work-in-progress impairment, among other items. Estimated cash expenditures related to the one-time charges primarily for employee-related costs are expected to range from $5 million to $10 million. In addition to these one-time charges, there will be financial impacts stemming from shortening the expected economic useful life of Oyster Creek primarily related to accelerated depreciation of plant assets (including any ARC), accelerated amortization of nuclear fuel, and additional ARO accretion expense associated with the changes in decommissioning timing and cost assumptions to reflect an earlier retirement date. The following table summarizes the estimated amount of expected incremental non-cash expense items expected to be incurred in 2018 because of the early retirement decision. Projected (b) Income statement expense (pre-tax) 2018 Depreciation and Amortization Accelerated depreciation (a) $110 to $140 Accelerated nuclear fuel amortization $40 Operating and Maintenance Increased ARO accretion Up to $5 __________ (a) Includes the accelerated depreciation of plant assets including any ARC. (b) Actual results may differ based on incremental future capital additions, actual units of production for nuclear fuel amortization, future revised ARO assumptions, etc.

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Operations and Other Comprehensive Income For the Years Ended December 31, (In millions) 2017 2016 2015 Operating expenses Operating and maintenance $ 10 $ 221 $ — Operating and maintenance from affiliates 25 51 43 Other 4 4 4 Total operating expenses 39 276 47 Operating loss (39 ) (276 ) (47 ) Other income and (deductions) Interest expense, net (315 ) (312 ) (168 ) Equity in earnings of investments 4,398 1,521 2,461 Interest income from affiliates, net 40 39 43 Other, net 1 7 (43 ) Total other income 4,124 1,255 2,293 Income before income taxes 4,085 979 2,246 Income taxes 315 (155 ) (23 ) Net income $ 3,770 $ 1,134 $ 2,269 Other comprehensive income (loss) Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic costs $ (56 ) $ (48 ) $ (46 ) Actuarial loss reclassified to periodic cost 197 184 220 Pension and non-pension postretirement benefit plan valuation adjustment 10 (181 ) (99 ) Unrealized gain on cash flow hedges 3 2 9 Unrealized gain on marketable securities 6 1 — Unrealized gain (loss) on equity investments 6 (4 ) (3 ) Unrealized gain (loss) on foreign currency translation 7 10 (21 ) Other comprehensive income (loss) 173 (36 ) 60 Comprehensive income $ 3,943 $ 1,098 $ 2,329 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Statements of Cash Flows For the Years Ended December 31, (In millions) 2017 2016 2015 Net cash flows provided by operating activities $ 1,921 $ 1,029 $ 3,071 Cash flows from investing activities Changes in Exelon intercompany money pool (129 ) 1,390 (1,217 ) Notes receivable from affiliates — — 550 Investment in affiliates (1,717 ) (1,757 ) (212 ) Acquisition of business — (6,962 ) — Other investing activities (5 ) 5 (55 ) Net cash flows used in investing activities (1,851 ) (7,324 ) (934 ) Cash flows from financing activities Issuance of long-term debt — 1,800 4,200 Proceeds from short-term borrowings with maturities greater than 90 days 500 — — Retirement of long-term debt (569 ) (46 ) (2,263 ) Issuance of common stock — — 1,868 Common stock issued from treasury stock 1,150 — — Dividends paid on common stock (1,236 ) (1,166 ) (1,105 ) Proceeds from employee stock plans 150 55 32 Other financing activities (9 ) (20 ) (58 ) Net cash flows (used in) provided by financing activities (14 ) 623 2,674 Increase (Decrease) in cash and cash equivalents 56 (5,672 ) 4,811 Cash and cash equivalents at beginning of period 18 5,690 879 Cash and cash equivalents at end of period $ 74 $ 18 $ 5,690 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2017 2016 ASSETS Current assets Cash and cash equivalents $ 74 $ 18 Deposit with IRS — 1,250 Accounts receivable, net Other accounts receivable 431 73 Accounts receivable from affiliates 33 48 Notes receivable from affiliates 217 88 Regulatory assets 284 263 Other 4 — Total current assets 1,043 1,740 Property, plant and equipment, net 50 51 Deferred debits and other assets Regulatory assets 3,697 4,033 Investments in affiliates 39,272 34,869 Deferred income taxes 1,431 2,107 Notes receivable from affiliates 910 922 Other 234 256 Total deferred debits and other assets 45,544 42,187 Total assets $ 46,637 $ 43,978 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2017 2016 LIABILITIES AND SHAREHOLDERS’ EQUITY Current liabilities Short-term borrowings $ 500 $ — Long-term debt due within one year — 570 Accounts payable 2 2 Accrued expenses 99 489 Payables to affiliates 360 706 Regulatory liabilities 16 16 Pension obligations 65 58 Other 46 50 Total current liabilities 1,088 1,891 Long-term debt 7,161 7,193 Deferred credits and other liabilities Regulatory liabilities 15 31 Pension obligations 7,792 8,608 Non-pension postretirement benefit obligations 322 7 Deferred income taxes 220 226 Other 180 182 Total deferred credits and other liabilities 8,529 9,054 Total liabilities 16,778 18,138 Commitments and contingencies Shareholders’ equity Common stock (No par value, 2000 shares authorized, 963 shares and 924 shares outstanding at December 31, 2017 and 2016, respectively) 18,966 18,797 Treasury stock, at cost (2 shares and 35 shares at December 31, 2017 and 2016, respectively) (123 ) (2,327 ) Retained earnings 13,503 12,030 Accumulated other comprehensive loss, net (2,487 ) (2,660 ) Total shareholders’ equity 29,859 25,840 Total liabilities and shareholders’ equity $ 46,637 $ 43,978 Basis of Presentation Exelon Corporate is a holding company that conducts substantially all of its business operations through its subsidiaries. These condensed financial statements and related footnotes have been prepared in accordance with Rule 12-04, Schedule I of Regulation S-X. These statements should be read in conjunction with the consolidated financial statements and notes thereto of Exelon Corporation. Exelon Corporate owns 100% of all of its significant subsidiaries, either directly or indirectly, except for Commonwealth Edison Company (ComEd), of which Exelon Corporate owns more than 99% , and BGE, of which Exelon owns 100% of the common stock but none of BGE’s preferred stock. BGE redeemed all of its outstanding preferred stock in 2016. Mergers On March 23, 2016, Exelon completed the merger contemplated by the Merger Agreement among Exelon, Purple Acquisition Corp., a wholly owned subsidiary of Exelon (Merger Sub) and Pepco Holdings, Inc. (PHI). As a result of that merger, Merger Sub was merged into PHI (the PHI Merger) with PHI surviving as a wholly owned subsidiary of Exelon and Exelon Energy Delivery Company, LLC (EEDC), a wholly owned subsidiary of Exelon which also owns Exelon's interests in ComEd, PECO and BGE (through a special purpose subsidiary in the case of BGE). See Note 4 — Mergers, Acquisitions and Dispositions of the Combined Notes to Consolidated Financial Statements for additional information on the PHI Merger. Debt and Credit Agreements Short-Term Borrowings Exelon Corporate meets its short-term liquidity requirements primarily through the issuance of commercial paper. Exelon Corporate had no commercial paper borrowings at both December 31, 2017 and December 31, 2016 . Short-Term Loan Agreements On March 23, 2017, Exelon Corporate entered into a $500 million term loan agreement which expires on March 22, 2018. Pursuant to the loan agreement, loans made thereunder bear interest at a variable rate equal to LIBOR plus 1% and all indebtedness thereunder is unsecured. The loan agreement is reflected in Exelon’s Consolidated Balance Sheet within Short-Term borrowings. Credit Agreements On May 26, 2016, Exelon Corporate amended and extended its syndicated revolving credit facility with aggregate bank commitments of $600 million through May 26, 2021. As of December 31, 2017 , Exelon Corporation had available capacity under those commitments of $555 million . See Note 13 — Debt and Credit Agreements of the Combined Notes to Consolidated Financial Statements for further information regarding Exelon Corporation’s credit agreement. Long-Term Debt The following tables present the outstanding long-term debt for Exelon Corporate as of December 31, 2017 and December 31, 2016 : Maturity Date December 31, Rates 2017 2016 Long-term debt Junior subordinated notes 3.50 % 2022 $ 1,150 $ 1,150 Contract payment - junior subordinated notes 2.50 % 2017 — 19 Senior unsecured notes (a) 2.45 % 7.60 % 2020 - 2046 5,889 6,439 Total long-term debt 7,039 7,608 Unamortized debt discount and premium, net (8 ) (8 ) Unamortized debt issuance costs (49 ) (57 ) Fair value adjustment of consolidated subsidiary 179 220 Long-term debt due within one year — (570 ) Long-term debt $ 7,161 $ 7,193 __________ (a) Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets. The debt maturities for Exelon Corporate for the periods 2018 , 2019 , 2020 , 2021 , 2022 and thereafter are as follows: 2018 $ — 2019 — 2020 1,450 2021 300 2022 1,150 Remaining years 4,139 Total long-term debt $ 7,039 Commitments and Contingencies See Note 23 — Commitments and Contingencies of the Combined Notes to Consolidated Financial Statements for Exelon Corporate’s commitments and contingencies related to environmental matters and fund transfer restrictions. Related Party Transactions The financial statements of Exelon Corporate include related party transactions as presented in the tables below: For the Years Ended December 31, (In millions) 2017 2016 2015 Operating and maintenance from affiliates: BSC (a) $ 23 $ 51 $ 43 Other 2 — — Total operating and maintenance from affiliates: $ 25 $ 51 $ 43 Interest income from affiliates, net: Generation $ 37 $ 39 $ 43 BSC 3 — — Total interest income from affiliates, net: $ 40 $ 39 $ 43 Equity in earnings (losses) of investments: Exelon Energy Delivery Company, LLC (b) $ 1,670 $ 1,041 $ 1,079 PCI 1 6 — BSC 1 1 — UII, LLC 41 (9 ) 20 Exelon Transmission Company, LLC (10 ) (13 ) (8 ) Exelon Enterprise 1 (1 ) (1 ) Generation 2,694 496 1,371 Total equity in earnings of investments $ 4,398 $ 1,521 $ 2,461 Cash contributions received from affiliates $ 1,879 $ 1,912 $ 3,209 December 31, (in millions) 2017 2016 Accounts receivable from affiliates (current): BSC (a) $ 1 $ 15 Generation 21 22 ComEd 3 3 PECO 1 1 BGE 1 1 PHISCO 6 6 Total accounts receivable from affiliates (current) $ 33 $ 48 Notes receivable from affiliates (current): BSC (a) $ 217 $ 88 Investments in affiliates: BSC (a) $ 196 $ 194 Exelon Energy Delivery Company, LLC (b) 25,082 23,003 PCI 78 77 UII, LLC 268 92 Exelon Transmission Company, LLC 1 5 Voluntary Employee Beneficiary Association trust (4 ) (5 ) Exelon Enterprises 22 21 Generation 13,635 11,488 Other (6 ) (6 ) Total investments in affiliates $ 39,272 $ 34,869 Notes receivable from affiliates (non-current): Generation (c) $ 910 $ 922 Accounts payable to affiliates (current): ComEd $ — $ 345 UII, LLC 360 361 Total accounts payable to affiliates (current) $ 360 $ 706 __________ (a) Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. (b) Exelon Energy Delivery Company, LLC consists of ComEd, PECO, BGE, PHI, Pepco, DPL and ACE. (c) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-Term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	Exelon Corporation and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts (a) $ 334 $ 126 $ 27 (c) $ 165 (d) $ 322 Deferred tax valuation allowance 20 — 17 — 37 Reserve for obsolete materials 113 56 10 5 174 For the year ended December 31, 2016 Allowance for uncollectible accounts (a) $ 284 $ 162 $ 99 (b)(c) $ 211 (d) $ 334 Deferred tax valuation allowance 13 — 10 (b) 3 20 Reserve for obsolete materials 105 12 1 (b) 5 113 For the year ended December 31, 2015 Allowance for uncollectible accounts (a) $ 311 $ 113 $ 27 (c) $ 167 (d) $ 284 Deferred tax valuation allowance 50 — (27 ) 10 13 Reserve for obsolete materials 95 10 2 2 105 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million , $23 million , and $8 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (b) Primarily represents the addition of PHI's results as of March 23, 2016 , the date of the merger (c) Includes charges for late payments and non-service receivables. (d) Write-off of individual accounts receivable. Exelon Generation Company, LLC and Subsidiary Companies Generation 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Exelon Generation Company, LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 91 $ 34 $ — $ 11 $ 114 Deferred tax valuation allowance 9 — 14 — 23 Reserve for obsolete materials 106 51 9 — 166 For the year ended December 31, 2016 Allowance for uncollectible accounts $ 77 $ 19 $ 3 $ 8 $ 91 Deferred tax valuation allowance 11 — — 2 9 Reserve for obsolete materials 102 6 — 2 106 For the year ended December 31, 2015 Allowance for uncollectible accounts $ 60 $ 22 $ — $ 5 $ 77 Deferred tax valuation allowance 48 — (27 ) 10 11 Reserve for obsolete materials 93 9 — — 102 Commonwealth Edison Company and Subsidiary Companies ComEd 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Commonwealth Edison Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 70 $ 39 $ 20 (a) $ 56 (b) $ 73 Reserve for obsolete materials 4 3 1 3 5 For the year ended December 31, 2016 Allowance for uncollectible accounts $ 75 $ 45 $ 23 (a) $ 73 (b) $ 70 Reserve for obsolete materials 3 4 1 4 4 For the year ended December 31, 2015 Allowance for uncollectible accounts $ 84 $ 39 $ 18 (a) $ 66 (b) $ 75 Reserve for obsolete materials 2 1 2 2 3 __________ (a) Primarily charges for late payments and non-service receivables. (b) Write-off of individual accounts receivable. PECO Energy Company and Subsidiary Companies PECO 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto PECO Energy Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts (a) $ 61 $ 26 $ 4 (b) $ 35 (c) $ 56 Reserve for obsolete materials 2 — — — 2 For the year ended December 31, 2016 Allowance for uncollectible accounts (a) $ 83 $ 32 $ 7 (b) $ 61 (c) $ 61 Reserve for obsolete materials 1 1 — — 2 For the year ended December 31, 2015 Allowance for uncollectible accounts (a) $ 100 $ 37 $ 9 (b) $ 63 (c) $ 83 Reserve for obsolete materials 1 — — — 1 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million , $23 million , and $8 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (b) Primarily charges for late payments. (c) Write-off of individual accounts receivable. Baltimore Gas and Electric Company and Subsidiary Companies BGE 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Baltimore Gas and Electric Company and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Beginning of Period Charged to Costs and Expenses Charged to Other Accounts Deductions Balance at End of Period (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 32 $ 8 $ (3 ) $ 13 (a) $ 24 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — — — — — For the year ended December 31, 2016 Allowance for uncollectible accounts $ 49 $ 1 $ 9 $ 27 (a) $ 32 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — — — — — For the year ended December 31, 2015 Allowance for uncollectible accounts $ 67 $ 15 $ — $ 33 (a) $ 49 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — — — — — __________ (a) Write-off of individual accounts receivable. Pepco Holdings LLC and Subsidiary Companies PHI 1. Successor Company Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income (Loss) for the Year Ended December 31, 2017 and for the Period March 24, 2016 to December 31, 2016 Consolidated Statements of Cash Flows for the Year Ended December 31, 2017 and for the Period March 24, 2016 to December 31, 2016 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Equity for the Year Ended December 31, 2017 and for the Period March 24, 2016 to December 31, 2016 Notes to Consolidated Financial Statements Predecessor Company Financial Statements: Report of Independent Registered Public Accounting Firm dated February 13, 2017 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income (Loss) for the Period January 1, 2016 to March 23, 2016 and the Year Ended December 31, 2015 Consolidated Statements of Cash Flows for the Period January 1, 2016 to March 23, 2016 and for the Year Ended December 31, 2015 Consolidated Statements of Changes in Equity for the Period January 1, 2016 to March 23, 2016 and for the Year Ended December 31, 2015 Notes to Consolidated Financial Statements 2. Successor Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts - For the Year Ended December 31, 2017 and the Period March 24, 2016 to December 31, 2016 Predecessor Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts - For the Period January 1, 2016 to March 23, 2016 and For the Year Ended December 31, 2015 Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Pepco Holdings LLC and Subsidiary Companies Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the Year Ended December 31, 2017 (Successor) Allowance for uncollectible accounts $ 80 $ 19 $ 6 (a) $ 50 (b) $ 55 Deferred tax valuation allowance 10 — 3 — 13 Reserve for obsolete materials 2 2 — 2 2 March 24, 2016 to December 31, 2016 (Successor) Allowance for uncollectible accounts $ 52 $ 65 $ 5 (a) $ 42 (b) $ 80 Deferred tax valuation allowance 63 — (53 ) — 10 Reserve for obsolete materials — 1 — (1 ) 2 January 1, 2016 to March 23, 2016 (Predecessor) Allowance for uncollectible accounts $ 56 $ 16 $ 2 (a) $ 22 (b) $ 52 Deferred tax valuation allowance 63 — — — 63 Reserve for obsolete materials — — — — — For the Year Ended December 31, 2015 (Predecessor) Allowance for uncollectible accounts $ 40 $ 59 $ 5 (a) $ 48 (b) $ 56 Deferred tax valuation allowance 61 — 2 — 63 Reserve for obsolete materials — — — — — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Potomac Electric Power Company Pepco 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income for the Years Ended December 31, 2017, 2016 and 2015 Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Balance Sheets at December 31, 2017 and 2016 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Potomac Electric Power Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 29 $ 8 $ 2 (a) $ 18 (b) $ 21 Deferred tax valuation allowance — — — — — Reserve for obsolete materials 1 1 — 1 1 For the year ended December 31, 2016 Allowance for uncollectible accounts $ 17 $ 29 $ 3 (a) $ 20 (b) $ 29 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — 3 — 2 1 For the year ended December 31, 2015 Allowance for uncollectible accounts $ 16 $ 20 $ 1 (a) $ 20 (b) $ 17 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — — — — — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Delmarva Power & Light Company DPL 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income (Loss) for the Years Ended December 31, 2017, 2016 and 2015 Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Balance Sheets at December 31, 2017 and 2016 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Delmarva Power & Light Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 24 $ 3 $ 2 (a) $ 13 (b) $ 16 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — 1 — 1 — For the year ended December 31, 2016 Allowance for uncollectible accounts $ 17 $ 23 $ 2 (a) $ 18 (b) $ 24 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — 1 — 1 — For the year ended December 31, 2015 Allowance for uncollectible accounts $ 11 $ 20 $ 2 (a) $ 16 (b) $ 17 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — — — — — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Atlantic City Electric Company and Subsidiary Company ACE 1. Financial Statements: Report of Independent Registered Public Accounting Firm dated February 9, 2018 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income (Loss) for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Statements of Cash Flows for the Years Ended December 31, 2017, 2016 and 2015 Consolidated Balance Sheets at December 31, 2017 and 2016 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2017, 2016 and 2015 Notes to Consolidated Financial Statements 2. Financial Statement Schedules: Schedule II – Valuation and Qualifying Accounts Schedules not included are omitted because of the absence of conditions under which they are required or because the required information is provided in the consolidated financial statements, including the notes thereto Atlantic City Electric Company and Subsidiary Company Schedule II – Valuation and Qualifying Accounts Column A Column B Column C Column D Column E Additions and adjustments Description Balance at Charged to Charged Deductions Balance at (in millions) For the year ended December 31, 2017 Allowance for uncollectible accounts $ 27 $ 8 $ 2 (a) $ 19 (b) $ 18 Deferred tax valuation allowance — — — — — Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2016 Allowance for uncollectible accounts $ 17 $ 32 $ 2 (a) $ 24 (b) $ 27 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — 1 — — 1 For the year ended December 31, 2015 Allowance for uncollectible accounts $ 9 $ 18 $ 2 (a) $ 12 (b) $ 17 Deferred tax valuation allowance — — — — — Reserve for obsolete materials — — — — — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable.

Significant Accounting Polici37

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Description of Business (All Registrants)	Description of Business (All Registrants) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy distribution and transmission businesses. Prior to March 23, 2016 , Exelon's principal, wholly owned subsidiaries included Generation, ComEd, PECO and BGE. On March 23, 2016 , in conjunction with the Amended and Restated Agreement and Plan of Merger (the PHI Merger Agreement), Purple Acquisition Corp, a wholly owned subsidiary of Exelon, merged with and into PHI, with PHI continuing as the surviving entity as a wholly owned subsidiary of Exelon. PHI is a utility services holding company engaged through its principal wholly owned subsidiaries, Pepco, DPL and ACE, in the energy distribution and transmission businesses. Refer to Note 4 — Mergers, Acquisitions and Dispositions for further information regarding the merger transaction. Name of Registrant Business Service Territories Exelon Generation Generation, physical delivery and marketing of power across multiple geographical regions through its customer-facing business, Constellation, which sells electricity to both wholesale and retail customers. Generation also sells natural gas, renewable energy and other energy-related products and services. Six reportable segments: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions Commonwealth Edison Company Purchase and regulated retail sale of electricity Northern Illinois, including the City of Chicago Transmission and distribution of electricity to retail customers PECO Energy Company Purchase and regulated retail sale of electricity and natural gas Southeastern Pennsylvania, including the City of Philadelphia (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Pennsylvania counties surrounding the City of Philadelphia (natural gas) Baltimore Gas and Electric Company Purchase and regulated retail sale of electricity and natural gas Central Maryland, including the City of Baltimore (electricity and natural gas) Transmission and distribution of electricity and distribution of natural gas to retail customers Pepco Holdings LLC Utility services holding company engaged, through its reportable segments Pepco, DPL and ACE Service Territories of Pepco, DPL and ACE Potomac Electric Purchase and regulated retail sale of electricity District of Columbia, and major portions of Montgomery and Prince George’s Counties, Maryland. Transmission and distribution of electricity to retail customers Delmarva Power & Light Company Purchase and regulated retail sale of electricity and natural gas Portions of Delaware and Maryland (electricity) Transmission and distribution of electricity and distribution of natural gas to retail customers Portions of New Castle County, Delaware (natural gas) Atlantic City Electric Company Purchase and regulated retail sale of electricity Portions of Southern New Jersey Transmission and distribution of electricity to retail customers Basis of Presentation (All Registrants) This is a combined annual report of all Registrants. The Notes to the Consolidated Financial Statements apply to the Registrants as indicated above in the Index to Combined Notes to Consolidated Financial Statements and parenthetically next to each corresponding disclosure. When appropriate, the Registrants are named specifically for their related activities and disclosures. Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. As a result of the acquisition of PHI, Exelon’s financial reporting reflects PHI’s consolidated financial results subsequent to the March 23, 2016 , acquisition date. Exelon has accounted for the merger transaction applying the acquisition method of accounting, which requires the assets acquired and liabilities assumed by Exelon to be reported in Exelon’s financial statements at fair value, with any excess of the purchase price over the fair value of net assets acquired reported as goodwill. Exelon has pushed-down the application of the acquisition method of accounting to the consolidated financial statements of PHI such that the assets and liabilities of PHI are similarly recorded at their respective fair values, and goodwill has been established as of the acquisition date. Accordingly, the consolidated financial statements of PHI for periods before and after the March 23, 2016 , acquisition date reflect different bases of accounting, and the results of operations and the financial positions of the predecessor and successor periods are not comparable. The acquisition method of accounting has not been pushed down to PHI’s wholly owned subsidiary utility registrants, Pepco, DPL and ACE. For financial statement purposes, beginning on March 24, 2016 , disclosures related to Exelon now also apply to PHI, Pepco, DPL and ACE, unless otherwise noted. Through its business services subsidiary, BSC, Exelon provides its subsidiaries with a variety of support services at cost, including legal, human resources, financial, information technology and supply management services. The costs of BSC, including support services, are directly charged or allocated to the applicable subsidiaries using a cost-causative allocation method. Corporate governance-type costs that cannot be directly assigned are allocated based on a Modified Massachusetts Formula, which is a method that utilizes a combination of gross revenues, total assets and direct labor costs for the allocation base. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. PHISCO, a wholly owned subsidiary of PHI, provides a variety of support services at cost, including legal, accounting, engineering, distribution and transmission planning, asset management, system operations, and power procurement, to PHI and its operating subsidiaries. These services are directly charged or allocated pursuant to service agreements among PHISCO and the participating operating subsidiaries. Exelon owns 100% of its significant consolidated subsidiaries, including PHI, either directly or indirectly, except for ComEd, of which Exelon owns more than 99% . As of December 31, 2017 , Exelon owned none of BGE's preferred securities, which BGE redeemed in 2016. Exelon has reflected the third-party interests in ComEd, which totaled less than $1 million at December 31, 2017 and December 31, 2016 , as equity, in its consolidated financial statements. BGE is subject to certain ring-fencing measures established by order of the MDPSC. As part of this arrangement, BGE common stock is held directly by RF Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (BGE Utility), an unrelated party, holds a nominal non-economic interest in RF Holdco LLC with limited voting rights on specified matters. PHI is subject to some ring-fencing measures established by orders of the DCPSC, DPSC, MDPSC and NJBPU, pursuant to which all of the membership interest in PHI is held directly by PH Holdco LLC, which is an indirect subsidiary of Exelon. GSS Holdings (PH Utility), Inc., an unrelated party, holds a nominal non-economic interest in PH Holdco LLC with limited voting rights on specified matters. PHI owns 100% of its subsidiaries including Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and ExGen Renewables Partners, LLC, of which Generation holds a 50.01% and 51% interest, respectively. The remaining interests in these consolidated VIEs are included in noncontrolling interests on Exelon’s and Generation’s Consolidated Balance Sheets. See Note 2 — Variable Interest Entities for further discussion of Exelon’s and Generation’s consolidated VIEs. The Registrants consolidate the accounts of entities in which a Registrant has a controlling financial interest, after the elimination of intercompany transactions. A controlling financial interest is evidenced by either a voting interest greater than 50% in which the Registrant can exercise control over the operations and policies of the investee, or the results of a model that identifies the Registrant or one of its subsidiaries as the primary beneficiary of a VIE. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or cost method accounting is applied. The Registrants apply proportionate consolidation when they have an undivided interest in an asset and are proportionately liable for their share of each liability associated with the asset. The Registrants proportionately consolidate their undivided ownership interests in jointly owned electric plants and transmission facilities. Under proportionate consolidation, the Registrants separately record their proportionate share of the assets, liabilities, revenues and expenses related to the undivided interest in the asset. The Registrants apply equity method accounting when they have significant influence over an investee through an ownership in common stock, which generally approximates a 20% to 50% voting interest. The Registrants apply equity method accounting to certain investments and joint ventures, including certain financing trusts of ComEd, PECO and BGE. Under equity method accounting, the Registrants report their interest in the entity as an investment and the Registrants’ percentage share of the earnings from the entity as single line items in their financial statements. The Registrants use cost method accounting if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under cost method accounting, the Registrants report their investments at cost and recognize income only to the extent dividends or distributions are received. The accompanying consolidated financial statements have been prepared in accordance with GAAP for annual financial statements and in accordance with the instructions to Form 10-K and Regulation S-X promulgated by the SEC.
Use Of Estimates (All Registrants)	Use of Estimates (All Registrants) The preparation of financial statements of each of the Registrants in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Areas in which significant estimates have been made include, but are not limited to, the accounting for nuclear decommissioning costs and other AROs, pension and other postretirement benefits, the application of purchase accounting, inventory reserves, allowance for uncollectible accounts, goodwill and asset impairments, derivative instruments, unamortized energy contracts, fixed asset depreciation, environmental costs and other loss contingencies, taxes and unbilled energy revenues. Actual results could differ from those estimates.
Reclassifications (Exelon, ComEd, and BGE)	Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been reclassified between line items for comparative purposes. The reclassifications did not affect any of the Registrants’ net income, cash flows from operating activities or financial positions.
Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE)	Accounting for the Effects of Regulation (Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) The Registrants apply the authoritative guidance for accounting for certain types of regulation, which requires them to record in their consolidated financial statements the effects of cost-based rate regulation for entities with regulated operations that meet the following criteria: 1) rates are established or approved by a third-party regulator; (2) rates are designed to recover the entities’ cost of providing services or products; and (3) there is a reasonable expectation that rates designed to recover costs can be charged to and collected from customers. Exelon and the Utility Registrants account for their regulated operations in accordance with regulatory and legislative guidance from the regulatory authorities having jurisdiction, principally the ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU, under state public utility laws and the FERC under various Federal laws. Regulatory assets and liabilities are amortized and the related expense or revenue is recognized in the Consolidated Statements of Operations consistent with the recovery or refund included in customer rates. Exelon believes that it is probable that its currently recorded regulatory assets and liabilities will be recovered and settled, respectively, in future rates. Exelon and the Utility Registrants continue to evaluate their respective abilities to continue to apply the authoritative guidance for accounting for certain types of regulation, including consideration of current events in their respective regulatory and political environments. If a separable portion of the Registrants' business was no longer able to meet the criteria discussed above, the affected entities would be required to eliminate from their consolidated financial statements the effects of regulation for that portion, which could have a material impact on their results of operations and financial positions. See Note 3 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, the Registrants classify regulatory assets and liabilities with a recovery or settlement period greater than one year as both current and non-current in their Consolidated Balance Sheets, with the current portion representing the amount expected to be recovered from or settled to customers over the next twelve-month period as of the balance sheet date. Income tax-related regulatory assets and liabilities are classified entirely as non-current on the Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. The Registrants treat the impacts of a final rate order received after the balance sheet date but prior to the issuance of the financial statements as a non-recognized subsequent event, as the receipt of a final rate order is a separate and distinct event that has future impacts on the parties affected by the order.
Revenues (All Registrants)	Revenues (All Registrants) Operating Revenues Operating revenues are recorded as service is rendered or energy is delivered to customers. At the end of each month, the Registrants accrue an estimate for the unbilled amount of energy delivered or services provided to customers. ComEd records its best estimate of its electric distribution, energy efficiency and transmission revenue impacts resulting from changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. PECO, BGE, Pepco, DPL and ACE record their best estimate of the transmission revenue impacts resulting from changes in rates that they each believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 3 — Regulatory Matters and Note 5 — Accounts Receivable for further information. RTOs and ISOs In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly activity. In addition, capacity revenue and expense classification is based on the net sale or purchase position of Exelon in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 3 — Regulatory Matters and Note 12 — Derivative Financial Instruments for further information.
Income Taxes (All Registrants)	Income Taxes (All Registrants) Deferred Federal and state income taxes are recorded on significant temporary differences between the book and tax basis of assets and liabilities and for tax benefits carried forward. Investment tax credits have been deferred on the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. In accordance with applicable authoritative guidance, the Registrants account for uncertain income tax positions using a benefit recognition model with a two-step approach; a more-likely-than-not recognition criterion; and a measurement approach that measures the position as the largest amount of tax benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more-likely-than-not that the benefit of the tax position will be sustained on its technical merits, no benefit is recorded. Uncertain tax positions that relate only to timing of when an item is included on a tax return are considered to have met the recognition threshold. The Registrants recognize accrued interest related to unrecognized tax benefits in Interest expense or Other income and deductions (interest income) and recognize penalties related to unrecognized tax benefits in Other, net on their Consolidated Statements of Operations and Comprehensive Income. In the first quarter of 2016, PHI, Pepco, DPL and ACE changed their accounting for classification of interest on uncertain tax positions. PHI, Pepco, DPL and ACE have reclassified interest on uncertain tax positions as Interest expense from Income tax expense in the Consolidated Statements of Operations and Comprehensive Income. GAAP does not address the preferability of one acceptable method of accounting over the other for the classification of interest on uncertain tax positions. However, PHI, Pepco, DPL and ACE believe this change is preferable for comparability of their financial statements with the financial statements of the other Registrants in the combined filing, for consistency with FERC classification and for a more appropriate representation of the effective tax rate as they manage the settlement of uncertain tax positions and interest expense separately. PHI, Pepco, DPL and ACE applied the change retrospectively. The reclassification in the Consolidated Statements of Operations and Comprehensive Income for the year ended December 31, 2015 was $34 million and $4 million for PHI and Pepco, respectively. The impact on all other PHI Registrants for the year ended December 31, 2015 was less than $1 million . Pursuant to the IRC and relevant state taxing authorities, Exelon and its subsidiaries file consolidated or combined income tax returns for Federal and certain state jurisdictions where allowed or required. See Note 14 — Income Taxes for further information. Taxes Directly Imposed on Revenue-Producing Transactions (All Registrants) The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees that are levied by state or local governments on the sale or distribution of gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed on the Registrants. Where these taxes are imposed on the customer, such as sales taxes, they are reported on a net basis with no impact to the Consolidated Statements of Operations and Comprehensive Income. However, where these taxes are imposed on the Registrants, such as gross receipts taxes or other surcharges or fees, they are reported on a gross basis. Accordingly, revenues are recognized for the taxes collected from customers along with an offsetting expense. See Note 24 — Supplemental Financial Information for Generation’s, ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes that are presented on a gross basis.
Cash and Cash Equivalents (All Registrants)	Cash and Cash Equivalents (All Registrants) The Registrants consider investments purchased with an original maturity of three months or less to be cash equivalents. Restricted Cash and Cash Equivalents (All Registrants) Restricted cash and cash equivalents represent funds that are restricted to satisfy designated current liabilities. As of December 31, 2017 and 2016 , Exelon Corporate’s restricted cash and cash equivalents primarily represented restricted funds for payment of medical, dental, vision and long-term disability benefits. Generation’s restricted cash and cash equivalents primarily included cash at various project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities, see Note 13 — Debt and Credit Agreements for additional information on Generation’s project- specific financing structures. ComEd’s restricted cash primarily represented cash collateral held from suppliers associated with ComEd’s energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and certain funds set aside for the remediation of one of ComEd's MGP sites. PECO’s restricted cash primarily represented funds from the sales of assets that were subject to PECO’s mortgage indenture. BGE’s restricted cash primarily represented funds restricted for certain energy conservation incentive programs. PHI Corporate's restricted cash and cash equivalents primarily represented funds restricted for the payment of merger commitments and cash collateral held from its utility suppliers. Pepco's restricted cash and cash equivalents primarily represented funds restricted for the payment of merger commitments and collateral held from its utility suppliers. DPL's restricted cash and cash equivalents primarily represented cash collateral held from suppliers associated with procurement contracts. ACE's restricted cash and cash equivalents primarily represented funds restricted at its consolidated variable interest entity for repayment of transition bonds and cash collateral held from suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets.
Allowance for Uncollectible Accounts (All Registrants)	Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. Allowance for Uncollectible Accounts (All Registrants) The allowance for uncollectible accounts reflects the Registrants’ best estimates of losses on the customers' accounts receivable balances. For Generation, the allowance is based on accounts receivable aging historical experience and other currently available information. ComEd, PECO, BGE, Pepco, DPL and ACE estimate the allowance for uncollectible accounts on customer receivables by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Risk segments represent a group of customers with similar credit quality indicators that are comprised based on various attributes, including delinquency of their balances and payment history. Loss rates applied to the accounts receivable balances are based on a historical average of charge-offs as a percentage of accounts receivable in each risk segment. Utility Registrants' customer accounts are generally considered delinquent if the amount billed is not received by the time the next bill is issued, which normally occurs on a monthly basis. Utility Registrants' customer accounts are written off consistent with approved regulatory requirements. Utility Registrants' allowances for uncollectible accounts will continue to be affected by changes in volume, prices and economic conditions as well as changes in ICC, PAPUC, MDPSC, DCPSC, DPSC and NJBPU regulations. See Note 3
Variable Interest Entities (All Registrants)	Variable Interest Entities (All Registrants) Exelon accounts for its investments in and arrangements with VIEs based on the authoritative guidance which includes the following specific requirements: • requires an entity to qualitatively assess whether it should consolidate a VIE based on whether the entity has a controlling financial interest, meaning (1) has the power to direct the activities that most significantly impact the VIE's economic performance, and (2) has the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE, • requires an ongoing reconsideration of this assessment instead of only upon certain triggering events, and • requires the entity that consolidates a VIE (the primary beneficiary) to disclose (1) the assets of the consolidated VIE, if they can be used to only settle specific obligations of the consolidated VIE, and (2) the liabilities of a consolidated VIE for which creditors do not have recourse to the general credit of the primary beneficiary. See Note 2 — Variable Interest Entities for additional information.
Inventories (All Registrants)	Inventories (All Registrants) Inventory is recorded at the lower of weighted average cost or net realizable value. Provisions are recorded for excess and obsolete inventory. Fossil Fuel Fossil fuel inventory includes natural gas held in storage, propane and oil. The costs of natural gas, propane and oil are generally included in inventory when purchased and charged to purchased power and fuel expense at weighted average cost when used or sold. Materials and Supplies Materials and supplies inventory generally includes transmission, distribution and generating plant materials. Materials are generally charged to inventory when purchased and expensed or capitalized to property, plant and equipment, as appropriate, at weighted average cost when installed or used. Emission Allowances Emission allowances are included in inventory (for emission allowances exercisable in the current year) and other deferred debits (for emission allowances that are exercisable beyond one year) and charged to purchased power and fuel expense at weighted average cost as they are used in operations.
Marketable Securities (All Registrants)	Marketable Securities (All Registrants) All marketable securities are reported at fair value. Marketable securities held in the NDT funds are classified as trading securities, and all other securities are classified as available-for-sale securities. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Regulatory Agreement Units are included in regulatory liabilities at Exelon, ComEd and PECO and in Noncurrent payables to affiliates at Generation and in Noncurrent receivables from affiliates at ComEd and PECO. Realized and unrealized gains and losses, net of tax, on Generation’s NDT funds associated with the Non-Regulatory Agreement Units are included in earnings at Exelon and Generation. Unrealized gains and losses, net of tax, for Exelon's available-for-sale securities are reported in OCI. Exelon’s and Generation’s NDT funds, which are designated to satisfy future decommissioning obligations, are classified as either noncurrent or current assets, depending on the timing of the decommissioning activities and income taxes on trust earnings. Beginning January 1, 2018, the authoritative guidance eliminates the available-for-sale classification for equity securities and requires that all equity investments (other than those accounted for using the equity method of accounting) be measured and recorded at fair value with any changes in fair value recorded through earnings. The new authoritative guidance does not impact the classification or measurement of investments in debt securities. See Note 3 — Regulatory Matters for additional information regarding ComEd’s and PECO’s regulatory assets and liabilities and Note 11 — Fair Value of Financial Assets and Liabilities and Note 15 — Asset Retirement Obligations for information regarding marketable securities held by NDT funds.
Property Plant And Equipment (All Registrants)	Property, Plant and Equipment (All Registrants) Property, plant and equipment is recorded at original cost. Original cost includes construction-related direct labor and material costs. The Utility Registrants also include indirect construction costs including labor and related costs of departments associated with supporting construction activities. When appropriate, original cost also includes capitalized interest for Generation, Exelon Corporate and PHI and AFUDC for regulated property at ComEd, PECO, BGE, Pepco, DPL and ACE. The cost of repairs and maintenance, including planned major maintenance activities and minor replacements of property, is charged to Operating and maintenance expense as incurred. Third parties reimburse the Utility Registrants for all or a portion of expenditures for certain capital projects. Such contributions in aid of construction costs (CIAC) are recorded as a reduction to Property, plant and equipment. DOE SGIG and other funds reimbursed to the Utility Registrants have been accounted for as CIAC. For Generation, upon retirement, the cost of property is generally charged to accumulated depreciation in accordance with the composite and group methods of depreciation. Upon replacement of an asset, the costs to remove the asset, net of salvage, are capitalized to gross plant when incurred as part of the cost of the newly-installed asset and recorded to depreciation expense over the life of the new asset. Removal costs, net of salvage, incurred for property that will not be replaced is charged to Operating and maintenance expense as incurred. For the Utility Registrants, upon retirement, the cost of property, net of salvage, is charged to accumulated depreciation consistent with the composite and group methods of depreciation. Depreciation expense at ComEd, BGE, Pepco, DPL and ACE includes the estimated cost of dismantling and removing plant from service upon retirement. Actual incurred removal costs are applied against a related regulatory liability or recorded to a regulatory asset if in excess of previously collected removal costs. PECO’s removal costs are capitalized to accumulated depreciation when incurred, and recorded to depreciation expense over the life of the new asset constructed consistent with PECO’s regulatory recovery method. See Note 6 — Property, Plant and Equipment , Note 9 — Jointly Owned Electric Utility Plant and Note 24 — Supplemental Financial Information for additional information regarding property, plant and equipment.
Nuclear Fuel (Exelon and Generation)	Nuclear Fuel (Exelon and Generation) The cost of nuclear fuel is capitalized within Property, plant and equipment and charged to fuel expense using the unit-of-production method. Prior to May 16, 2014, the estimated disposal cost of SNF was established per the Standard Waste Contract with the DOE and was expensed through fuel expense at one mill ($0.001) per kWh of net nuclear generation. Effective May 16, 2014, the SNF disposal fee was set to zero by the DOE and Exelon and Generation are not accruing any further costs related to SNF disposal fees until a new fee structure goes into effect. Certain on-site SNF storage costs are being reimbursed by the DOE since a DOE (or government-owned) long-term storage facility has not been completed. See Note 23 — Commitments and Contingencies for additional information regarding the SNF disposal fee.
Nuclear Outage Costs (Exelon and Generation)	Nuclear Outage Costs (Exelon and Generation) Costs associated with nuclear outages, including planned major maintenance activities, are expensed to Operating and maintenance expense or capitalized to Property, plant and equipment (based on the nature of the activities) in the period incurred.
New Site Development Costs (Exelon and Generation)	New Site Development Costs (Exelon and Generation) New site development costs represent the costs incurred in the assessment and design of new power generating facilities. Such costs are capitalized when management considers project completion to be probable, primarily based on management’s determination that the project is economically and operationally feasible, management and/or the Exelon Board of Directors has approved the project and has committed to a plan to develop it, and Exelon and Generation have received the required regulatory approvals or management believes the receipt of required regulatory approvals is probable. As of December 31, 2017 and 2016 , Generation has capitalized $228 million and $1.7 billion , respectively, to Property, plant and equipment, net on its Consolidated Balance Sheets. Capitalized development costs are charged to Operating and maintenance expense when project completion is no longer probable. New site development costs incurred prior to a project’s completion being deemed probable are expensed as incurred. Approximately $4 million , $30 million and $22 million of costs were expensed by Exelon and Generation for the years ended December 31, 2017 , 2016 and 2015 , respectively. These costs are primarily related to the possible development of new power generating facilities with the exception of approximately $13 million of costs expensed in 2016 which relate to projects for which completion is no longer probable.
Capitalized Software Costs (Exelon, Generation, ComEd, PECO and BGE)	Capitalized Software Costs (All Registrants) Costs incurred during the application development stage of software projects that are internally developed or purchased for operational use are capitalized within Property, plant and equipment. Such capitalized amounts are amortized ratably over the expected lives of the projects when they become operational, generally not to exceed five years. Certain other capitalized software costs are being amortized over longer lives based on the expected life or pursuant to prescribed regulatory requirements. The following table presents net unamortized capitalized software costs and amortization of capitalized software costs by year:
Depreciation, Depletion, and Amortization (All Registrants)	Depreciation and Amortization (All Registrants) Except for the amortization of nuclear fuel, depreciation is generally recorded over the estimated service lives of property, plant and equipment on a straight-line basis using the group, composite or unitary methods of depreciation. The group approach is typically for groups of similar assets that have approximately the same useful lives and the composite approach is used for dissimilar assets that have different lives. Under both methods, a reporting entity depreciates the assets over the average life of the assets in the group. The Utility Registrants' depreciation expense includes the estimated cost of dismantling and removing plant from service upon retirement, which is consistent with each utility's regulatory recovery method. The estimated service lives for the Utility Registrants are primarily based on each company's most recent depreciation studies of historical asset retirement and removal cost experience. At Generation, along with depreciation study results, management considers expected future energy market conditions and generation plant operating costs and capital investment requirements in determining the estimated service lives of its generating facilities. For its nuclear generating facilities, except for Oyster Creek, Clinton and TMI, Generation estimates each unit will operate through the full term of its initial 20-year operating license renewal period. See Note 8 — Early Nuclear Plant Retirements for additional information on the impacts of expected and potential early plant retirements . The estimated service lives of Generation's hydroelectric generating facilities are based on the remaining useful lives of the stations, which assume a license renewal extension of 40 years. See Note 6 — Property, Plant and Equipment for further information regarding depreciation. Amortization of regulatory assets and liabilities are recorded over the recovery or refund period specified in the related legislation or regulatory order or agreement. When the recovery or refund period is less than one year, amortization is recorded to the line item in which the deferred cost or income would have originally been recorded in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Amortization of ComEd’s electric distribution and energy efficiency formula rate regulatory assets and ComEd’s, PECO's, BGE’s, Pepco's, DPL's and ACE's transmission formula rate regulatory assets is recorded to Operating revenues. Amortization of income tax related regulatory assets and liabilities are generally recorded to Income tax expense. With the exception of the regulatory assets and liabilities discussed above, when the recovery period is more than one year, the amortization is generally recorded to Depreciation and amortization in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 3 — Regulatory Matters and Note 24 — Supplemental Financial Information for additional information regarding Generation’s nuclear fuel, Generation’s ARC and the amortization of the Utility Registrants' regulatory assets.
Asset Retirement Obligations (All Registrants)	Asset Retirement Obligations (All Registrants) The authoritative guidance for accounting for AROs requires the recognition of a liability for a legal obligation to perform an asset retirement activity even though the timing and/or method of settlement may be conditional on a future event. To estimate its decommissioning obligation related to its nuclear generating stations, Generation uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimates and assumptions, and are based on decommissioning cost studies, cost escalation rates, probabilistic future cash flow models and discount rates. Generation generally updates its ARO annually, unless circumstances warrant more frequent updates, based on its review of updated cost studies and its annual evaluation of cost escalation factors and probabilities assigned to various decommissioning scenarios. Decommissioning cost studies are updated, on a rotational basis, for each of Generation’s nuclear units at least every five years unless circumstances warrant more frequent updates (such as a change in assumed operating life for a nuclear plant). As part of the annual cost study update process, Generation evaluates newly assumed costs or substantive changes in previously assumed costs to determine if the cost estimate impacts are sufficiently material to warrant application of the updated estimates to the AROs across the nuclear fleet outside of the normal five-year rotating cost study update cycle. The liabilities associated with Exelon’s non-nuclear AROs are adjusted on an ongoing rotational basis, at least once every five years unless circumstances warrant more frequent updates. Changes to the recorded value of an ARO result from the passage of new laws and regulations, revisions to either the timing or amount of estimated undiscounted cash flows, and estimates of cost escalation factors. AROs are accreted throughout each year to reflect the time value of money for these present value obligations through a charge to Operating and maintenance expense in the Consolidated Statements of Operations and Comprehensive Income or, in the case of the Utility Registrants' accretion, through an increase to regulatory assets. See Note 15 — Asset Retirement Obligations for additional information.
Capitalized Interest (All Registrants)	Capitalized Interest and AFUDC (All Registrants) During construction, Exelon and Generation capitalize the costs of debt funds used to finance non-regulated construction projects. Capitalization of debt funds is recorded as a charge to construction work in progress and as a non-cash credit to interest expense. Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE apply the authoritative guidance for accounting for certain types of regulation to calculate AFUDC, which is the cost, during the period of construction, of debt and equity funds used to finance construction projects for regulated operations. AFUDC is recorded to construction work in progress and as a non-cash credit to AFUDC that is included in interest expense for debt-related funds and other income and deductions for equity-related funds. The rates used for capitalizing AFUDC are computed under a method prescribed by regulatory authorities.
Allowance For Funds Used During Construction (Exelon, Generation, ComEd, PECO and BGE)	Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE apply the authoritative guidance for accounting for certain types of regulation to calculate AFUDC, which is the cost, during the period of construction, of debt and equity funds used to finance construction projects for regulated operations. AFUDC is recorded to construction work in progress and as a non-cash credit to AFUDC that is included in interest expense for debt-related funds and other income and deductions for equity-related funds. The rates used for capitalizing AFUDC are computed under a method prescribed by regulatory authorities.
Guarantees (All Registrants)	Guarantees (All Registrants) The Registrants recognize, at the inception of a guarantee, a liability for the fair market value of the obligations they have undertaken by issuing the guarantee, including the ongoing obligation to perform over the term of the guarantee in the event that the specified triggering events or conditions occur. The liability that is initially recognized at the inception of the guarantee is reduced as the Registrants are released from risk under the guarantee. Depending on the nature of the guarantee, the release from risk of the Registrant may be recognized only upon the expiration or settlement of the guarantee or by a systematic and rational amortization method over the term of the guarantee. See Note 23 — Commitments and Contingencies for additional information.
Long-lived Assets (All Registrants)	Long-Lived Assets The Registrants evaluate the carrying value of their long-lived assets or asset groups, excluding goodwill, when circumstances indicate the carrying value of those assets may not be recoverable. Indicators of impairment may include a deteriorating business climate, including, but not limited to, declines in energy prices, condition of the asset, specific regulatory disallowance, or plans to dispose of a long-lived asset significantly before the end of its useful life. The Registrants determine if long-lived assets and asset groups are impaired by comparing the undiscounted expected future cash flows to the carrying value. When the undiscounted cash flow analysis indicates a long-lived asset or asset group is not recoverable, the amount of the impairment loss is determined by measuring the excess of the carrying amount of the long-lived asset or asset group over its fair value. Cash flows for long-lived assets and asset groups are determined at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. The cash flows from the generating units are generally evaluated at a regional portfolio level along with cash flows generated from the customer supply and risk management activities, including cash flows from related intangible assets and liabilities on the balance sheet. In certain cases, generating assets may be evaluated on an individual basis where those assets are contracted on a long-term basis with a third party and operations are independent of other generation assets (typically contracted renewables). See Note 7 — Impairment of Long-Lived Assets and Intangibles for additional information.
Goodwill (All Registrants)	Goodwill Goodwill represents the excess of the purchase price paid over the estimated fair value of the net assets acquired and liabilities assumed in the acquisition of a business. Goodwill is not amortized, but is tested for impairment at least annually or in an interim basis if an event occurs or circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying value. See Note 10 — Intangible Assets for additional information regarding Exelon’s, Generation's, ComEd’s, PHI's and DPL's goodwill.
Equity Method Investments (All Registrants)	Equity Method Investments Exelon and Generation regularly monitor and evaluate equity method investments to determine whether they are impaired. An impairment is recorded when the investment has experienced a decline in value that is other-than-temporary in nature. Additionally, if the entity in which Generation holds an investment recognizes an impairment loss, Exelon and Generation would record their proportionate share of that impairment loss and evaluate the investment for an other-than-temporary decline in value. Equity Investment Earnings (Losses) of Unconsolidated Affiliates (Exelon and Generation) Exelon and Generation include equity in earnings from equity method investments in qualifying facilities and power projects in Equity in earnings (losses) of unconsolidated affiliates within their Consolidated Statements of Operations and Comprehensive Income.
Direct Financing Lease Investments (Exelon, Generation, ComEd, PECO and BGE)
Derivatives Financial Instruments (All Registrants)	Derivative Financial Instruments (All Registrants) All derivatives are recognized on the balance sheet at their fair value unless they qualify for certain exceptions, including the normal purchases and normal sales exception. Additionally, derivatives that qualify and are designated for hedge accounting are classified as either hedges of the fair value of a recognized asset or liability or of an unrecognized firm commitment (fair value hedge) or hedges of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge). For fair value hedges, changes in fair values for both the derivative and the underlying hedged exposure are recognized in earnings each period. For cash flow hedges, the portion of the derivative gain or loss that is effective in offsetting the change in the cost or value of the underlying exposure is deferred in AOCI and later reclassified into earnings when the underlying transaction occurs. Gains and losses from the ineffective portion of any hedge are recognized in earnings immediately. For derivative contracts intended to serve as economic hedges and that are not designated or do not qualify for hedge accounting or the normal purchases and normal sales exception, changes in the fair value of the derivatives are recognized in earnings each period, except for the Utility Registrants where changes in fair value may be recorded as a regulatory asset or liability if there is an ability to recover or return the associated costs. See Note 3 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information. Amounts classified in earnings are included in revenue, purchased power and fuel, interest expense or other, net on the Consolidated Statements of Operations and Comprehensive Income based on the activity the transaction is economically hedging. For energy-related derivatives entered into for proprietary trading purposes, which are subject to Exelon’s Risk Management Policy, changes in the fair value of the derivatives are recognized in earnings each period. All amounts classified in earnings related to proprietary trading are included in revenue on the Consolidated Statements of Operations and Comprehensive Income. Cash inflows and outflows related to derivative instruments are included as a component of operating, investing or financing cash flows in the Consolidated Statements of Cash Flows, depending on the nature of each transaction. As part of Generation’s energy marketing business, Generation enters into contracts to buy and sell energy to meet the requirements of its customers. These contracts include short-term and long-term commitments to purchase and sell energy and energy-related products in the energy markets with the intent and ability to deliver or take delivery of the underlying physical commodity. Normal purchases and normal sales are contracts where physical delivery is probable, quantities are expected to be used or sold in the normal course of business over a reasonable period of time and will not be financially settled. Revenues and expenses on derivative contracts that qualify, and are designated, as normal purchases and normal sales are recognized when the underlying physical transaction is completed. While these contracts are considered derivative financial instruments, they are not required to be recorded at fair value, but rather are recorded on an accrual basis of accounting. See Note 12 — Derivative Financial Instruments for additional information.
Retirement Benefits (All Registrants)	Retirement Benefits (All Registrants) Exelon sponsors defined benefit pension plans and other postretirement benefit plans for essentially all employees. The measurement of the plan obligations and costs of providing benefits under these plans involve various factors, including numerous assumptions and inputs and accounting elections. The assumptions are reviewed annually and at any interim remeasurement of the plan obligations. The impact of assumption changes or experience different from that assumed on pension and other postretirement benefit obligations is recognized over time rather than immediately recognized in the Consolidated Statements of Operations and Comprehensive Income. Gains or losses in excess of the greater of ten percent of the projected benefit obligation or the MRV of plan assets are amortized over the expected average remaining service period of plan participants. See Note 16 — Retirement Benefits for additional information.
Investment, Policy [Policy Text Block]	Equity Investment Earnings (Losses) of Unconsolidated Affiliates (Exelon and Generation) Exelon and Generation include equity in earnings from equity method investments in qualifying facilities and power projects in Equity in earnings (losses) of unconsolidated affiliates within their Consolidated Statements of Operations and Comprehensive Income. Debt and Equity Security Investments Declines in the fair value of Exelon's debt and equity investments below the cost basis are reviewed to determine if such decline is other-than-temporary. For available-for-sale securities and cost investments, if the decline is determined to be other-than-temporary, the cost basis is written down to fair value as a new cost basis. For equity securities and cost investments, the amount of the impairment loss is included in earnings. For debt securities, the amount of the impairment loss is included in earnings or separated between earnings and OCI depending on whether Exelon intends to sell the debt securities before recovery of its cost basis. Beginning January 1, 2018, the authoritative guidance eliminates the available-for-sale and cost method classifications for equity securities and requires that all equity investments (other than those accounted for using the equity method of accounting) be measured and recorded at fair value with any changes in fair value recorded through earnings. Investments in equity securities without readily determinable fair values must be qualitatively assessed for impairment each reporting period and fair value determined if any significant impairment indicators exist. If fair value is less than carrying value, the impairment is recorded through earnings immediately in the period in which it is identified without regard to whether the decline in value is temporary in nature. The new authoritative guidance does not impact the classification or measurement of investments in debt securities.

Earnings Per Share Earnings Per

Earnings Per Share Earnings Per Share (Policies)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share, Policy [Policy Text Block]	Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to common shareholders by the weighted average number of common shares outstanding, including the effect of issuing common stock assuming (i) stock options are exercised, and (ii) performance share awards and restricted stock awards are fully vested under the treasury stock method.

Significant Accounting Polici39

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule Of Capitalized Software	The following table presents net unamortized capitalized software costs and amortization of capitalized software costs by year: Net unamortized software costs Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 834 $ 173 $ 227 $ 111 $ 179 $ 133 $ 2 $ 1 $ 1 December 31, 2016 808 173 213 91 164 153 1 1 1 Amortization of capitalized software costs Exelon Generation ComEd PECO BGE Pepco DPL ACE 2017 $ 270 $ 73 $ 73 $ 39 $ 46 $ — $ — $ — 2016 255 72 62 33 44 — — — 2015 208 73 47 33 46 (2 ) — — Successor Predecessor PHI For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Amortization of capitalized software costs $ 34 $ 29 $ 8 $ 36
Schedule Of Capitalized Interest And AFUDC	The following table summarizes total incurred interest, capitalized interest and credits to AFUDC by year: Exelon Generation ComEd PECO BGE Pepco DPL ACE 2017 Total incurred interest (a) $ 1,658 $ 502 $ 369 $ 130 $ 111 $ 133 $ 54 $ 64 Capitalized interest 63 63 — — — — — — Credits to AFUDC debt and equity 108 — 20 12 22 34 10 9 2016 Total incurred interest (a) $ 1,678 $ 472 $ 469 $ 127 $ 114 $ 137 $ 52 $ 65 Capitalized interest 108 107 — — — — — — Credits to AFUDC debt and equity 98 — 22 11 30 29 7 9 2015 Total incurred interest (a) $ 1,170 $ 445 $ 336 $ 116 $ 113 $ 131 $ 51 $ 65 Capitalized interest 79 79 — — — — — — Credits to AFUDC debt and equity 44 — 9 7 28 19 2 2 Successor Predecessor PHI For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Total incurred interest (a) $ 263 $ 207 $ 68 $ 289 Credits to AFUDC debt and equity 54 35 10 23

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2017
Variable Interest Entity [Abstract]
Schedule of Variable Interest Entities	As of December 31, 2017 and 2016 , these assets and liabilities primarily consisted of the following: December 31, 2017 Successor Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 126 $ 126 $ — $ — Restricted cash 64 58 6 6 Accounts receivable, net Customer 138 138 — — Other 25 25 — — Inventory Materials and supplies 205 205 — — Other current assets 45 41 4 — Total current assets 603 593 10 6 Property, plant and equipment, net 6,186 6,186 — — Nuclear decommissioning trust funds 2,502 2,502 — — Other noncurrent assets 274 243 31 23 Total noncurrent assets 8,962 8,931 31 23 Total assets $ 9,565 $ 9,524 $ 41 $ 29 Long-term debt due within one year $ 102 $ 67 $ 35 $ 31 Accounts payable 114 114 — — Accrued expenses 65 64 1 1 Unamortized energy contract liabilities 18 18 — — Other current liabilities 7 7 — — Total current liabilities 306 270 36 32 Long-term debt 1,154 1,088 66 58 Asset retirement obligations 2,035 2,035 — — Unamortized energy contract liabilities 5 5 — — Other noncurrent liabilities 112 112 — — Noncurrent liabilities 3,306 3,240 66 58 Total liabilities $ 3,612 $ 3,510 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. December 31, 2016 Successor Exelon (a)(b) Generation BGE PHI (a) ACE Cash and cash equivalents $ 150 $ 150 $ — $ — $ — Restricted cash 59 27 23 9 9 Accounts receivable, net Customer 371 371 — — — Other 48 48 — — — Mark-to-market derivative assets 31 31 — — — Inventory Materials and supplies 199 199 — — — Other current assets 50 44 — 5 — Total current assets 908 870 23 14 9 Property, plant and equipment, net 5,415 5,415 — — — Nuclear decommissioning trust funds 2,185 2,185 — — — Goodwill 47 47 — — — Mark-to-market derivative assets 23 23 — — — Other noncurrent assets 315 277 3 35 23 Total noncurrent assets 7,985 7,947 3 35 23 Total assets $ 8,893 $ 8,817 $ 26 $ 49 $ 32 Long-term debt due within one year $ 181 $ 99 $ 41 $ 40 $ 35 Accounts payable 269 269 — — — Accrued expenses 119 116 1 2 2 Mark-to-market derivative liabilities 60 60 — — — Unamortized energy contract liabilities 15 15 — — — Other current liabilities 30 30 — — — Total current liabilities 674 589 42 42 37 Long-term debt 641 540 — 101 89 Asset retirement obligations 1,904 1,904 — — — Pension obligation (c) 9 9 — — — Unamortized energy contract liabilities 22 22 — — — Other noncurrent liabilities 106 106 — — — Noncurrent liabilities 2,682 2,581 — 101 89 Total liabilities $ 3,356 $ 3,170 $ 42 $ 143 $ 126 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity. (c) Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 16 - Retirement Benefits for additional details. The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at December 31, 2017 and 2016 are as follows: December 31, 2017 Successor Exelon (a) Generation PHI (a) ACE Current assets $ 630 $ 620 $ 10 6 Noncurrent assets 9,317 9,286 31 23 Total assets $ 9,947 $ 9,906 $ 41 $ 29 Current liabilities $ 306 $ 270 $ 36 32 Noncurrent liabilities 3,312 3,246 66 58 Total liabilities $ 3,618 $ 3,516 $ 102 $ 90 December 31, 2016 Successor Exelon (a)(b) Generation BGE PHI (a) ACE Current assets $ 954 $ 916 $ 23 $ 14 $ 9 Noncurrent assets 8,563 8,525 3 35 23 Total assets $ 9,517 $ 9,441 $ 26 $ 49 $ 32 Current liabilities $ 885 $ 802 $ 42 $ 42 $ 37 Noncurrent liabilities 2,713 2,612 — 101 89 Total liabilities $ 3,598 $ 3,414 $ 42 $ 143 $ 126 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. (b) Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity. December 31, 2017 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 625 $ 509 $ 1,134 Total liabilities (a) 37 228 265 Exelon's ownership interest in VIE (a) — 251 251 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 251 251 Contract intangible asset 8 — 8 Debt and payment guarantees — — — Net assets pledged for Zion Station decommissioning (b) 2 — 2 December 31, 2016 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 638 $ 567 $ 1,205 Total liabilities (a) 215 287 502 Exelon's ownership interest in VIE (a) — 248 248 Other ownership interests in VIE (a) 423 32 455 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 264 264 Contract intangible asset 9 — 9 Debt and payment guarantees — 3 3 Net assets pledged for Zion Station decommissioning (b) 9 — 9 __________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $39 million and $113 million as of December 31, 2017 and December 31, 2016 , respectively; offset by payables to ZionSolutions LLC of $37 million and $104 million as of December 31, 2017 and December 31, 2016 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's electric distributions formula rate filings: Annual Electric Distribution Filings 2017 2016 2015 ComEd's requested total revenue requirement increase (decrease) $ 96 $ 138 $ (50 ) Final ICC Order Initial revenue requirement increase $ 78 $ 134 $ 85 Annual reconciliation increase (decrease) 18 (7 ) (152 ) Total revenue requirement increase (decrease) $ 96 $ 127 (a) $ (67 ) Allowed Return on Rate Base: Initial revenue requirement 6.47 % 6.71 % 7.05 % Annual reconciliation 6.45 % 6.69 % 7.02 % Allowed ROE: Initial revenue requirement 8.40 % 8.64 % 9.14 % Annual reconciliation 8.34 % (b) 8.59 % (b) 9.09 % (b) Effective date of rates January 2018 January 2017 January 2016 __________ (a) On March 22, 2017, the ICC issued an order approving ComEd's proposal to reduce the 2016 revenue requirement by $18 million , which was reflected in customer rates beginning in April 2017. This reduction is not reflected in the 2016 revenue requirement amounts above. (b) Includes a reduction of 6 basis points in 2017 and 5 basis points in 2016 and 2015 for a reliability performance metric penalty. For each of the following years, the following total increases/(decreases) were included in ComEd’s, BGE’s, Pepco's, DPL's and ACE's electric transmission formula rate filings: ComEd BGE Annual Transmission Filings (a) 2017 2016 2015 2017 2016 2015 Initial revenue requirement increase $ 44 $ 90 $ 68 $ 31 $ 12 $ — Annual reconciliation increase (decrease) (33 ) 4 18 3 3 (3 ) Dedicated facilities (decrease) increase (b) — — — (8 ) 13 13 Total revenue requirement increase $ 11 $ 94 $ 86 $ 26 $ 28 $ 10 Allowed return on rate base (d) 8.43 % 8.47 % 8.61 % 7.47 % 8.09 % 8.46 % Allowed ROE (e) 11.50 % 11.50 % 11.50 % 10.50 % 10.50 % 11.30 % Pepco DPL ACE Annual Transmission Filings (a) 2017 2016 2015 2017 2016 2015 2017 2016 2015 Initial revenue requirement increase (decrease) $ 5 $ 2 $ 10 $ 6 $ 8 $ 15 $ 20 $ 8 $ 10 Annual reconciliation (decrease) increase 15 (10 ) (3 ) 8 (10 ) (1 ) 22 (14 ) 2 MAPP abandonment recovery (decrease) increase (c) — (15 ) (2 ) — (12 ) (2 ) — — — Total revenue requirement (decrease) increase $ 20 $ (23 ) $ 5 $ 14 $ (14 ) $ 12 $ 42 $ (6 ) $ 12 Allowed return on rate base (d) 7.92 % 7.88 % 8.36 % 7.16 % 7.21 % 7.80 % 8.02 % 7.83 % 8.51 % Allowed ROE (e) 10.50 % 10.50 % 11.30 % 10.50 % 10.50 % 11.30 % 10.50 % 10.50 % 11.30 % __________ (a) The time period for any challenges to the annual transmission formula rate update flings expired with no challenges submitted. (b) BGE's transmission revenues include a FERC approved dedicated facilities charge to recover the costs of providing transmission service to specifically designated load by BGE. (c) In 2012, PJM terminated the MAPP transmission line construction project planned for the Pepco and DPL service territories. Pursuant to a FERC approved settlement agreement, the abandonment costs associated with MAPP were being recovered in transmission rates over a three-year period that ended in May 2016. (d) Represents to the weighted average debt and equity return on transmission rate bases. (e) As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% , inclusive of a 50-basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55% . As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50% , inclusive of a 50-basis-point incentive adder for being a member of a RTO. The following table illustrates our authorized amounts capitalized for ratemaking purposes related to earnings on shareholders’ investment that are not recognized for financial reporting purposes on our Consolidated Balance Sheets. These amounts will be recognized as revenues in our Consolidated Statements of Operations and Comprehensive Income in the periods they are billable to our customers. Successor Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE December 31, 2017 $ 69 $ 6 $ — $ 53 $ 10 $ 6 $ 4 $ — December 31, 2016 $ 72 $ 5 $ — $ 57 $ 10 $ 6 $ 4 $ — __________ (a) Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its under-recovered distribution services costs regulatory assets. (b) BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs (c) Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only.
Schedule of Revenue Requirement Increases (Decreases) [Table Text Block]	For each of the following years, the ICC approved the following total increases/(decreases) in ComEd's requested energy efficiency revenue requirement: Annual Energy Efficiency Filings Initial 2017 ComEd's requested total revenue requirement (decrease) increase $ (7 ) (a) $ 12 Allowed Return on Rate Base: Initial revenue requirement 6.47 % 6.47 % Allowed ROE: Initial revenue requirement 8.40 % 8.40 % Effective date of rates (b) October 2017 January 2018 __________ (a) Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs. (b) An ICC order on the annual reconciliation of any differences between the revenue requirement in effect and the revenue requirement based on actual costs for 2017 and 2018 is expected in December 2018 and December 2019, respectively.
Schedule of Regulatory Asset Impairments [Table Text Block]	As a result, Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE recorded the following charges to Income tax expense within their Consolidated Statements of Operations and Comprehensive Income in the fourth quarter 2017, reducing their associated transmission-related income tax regulatory assets. For the year ended December 31, 2017 Exelon (a) $ 35 ComEd 3 BGE 5 PHI (a) 27 Pepco 14 DPL 6 ACE 7 __________ (a) Exelon reflects the consolidated regulatory asset impairments of ComEd, BGE, Pepco, DPL and ACE, and PHI reflects the consolidated regulatory asset impairments of Pepco, DPL and ACE.
Regulatory Construction Commitment	The Utility Registrants will work with PJM to continue to evaluate the scope and timing of any required construction projects. The Utility Registrants' estimated commitments are as follows: Total 2018 2019 2020 2021 2022 ComEd $ 164 $ 36 $ 60 $ 44 $ 24 $ — PECO 53 16 19 10 5 3 BGE 118 35 35 35 13 — Pepco 86 5 11 27 33 10 DPL 27 19 2 1 2 3 ACE 121 68 20 6 21 6
Schedule of Regulatory Assets	Successor December 31, 2016 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 4,162 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 2,016 75 1,583 98 260 171 38 51 AMI programs 701 164 49 230 258 174 84 — Electric distribution formula rate 188 188 — — — — — — Debt costs 124 42 1 7 81 17 9 6 Fair value of long-term debt 812 — — — 671 — — — Fair value of PHI's unamortized energy contracts 1,085 — — — 1,085 — — — Asset retirement obligations 111 76 23 12 — — — — MGP remediation costs 305 278 26 1 — — — — Under-recovered uncollectible accounts 56 56 — — — — — — Renewable energy 260 258 — — 2 — — 2 Energy and transmission programs 89 23 — 38 28 6 5 17 Deferred storm costs 36 — — 1 35 12 5 18 Electric generation-related regulatory asset 10 — — 10 — — — — Rate stabilization deferral 7 — — 7 — — — — Energy efficiency and demand response programs 621 — 1 285 335 250 85 — Merger integration costs 25 — — 10 15 11 4 — Under-recovered revenue decoupling 27 — — 3 24 21 3 — COPCO acquisition adjustment 8 — — — 8 — 8 — Workers compensation and long-term disability costs 34 — — — 34 34 — — Vacation accrual 31 — 7 — 24 — 14 10 Securitized stranded costs 138 — — — 138 — — 138 CAP arrearage 11 — 11 — — — — — Removal costs 477 — — — 477 134 88 255 Other 54 7 9 10 29 22 5 4 Total regulatory assets 11,388 1,167 1,710 712 3,504 852 348 501 Less: current portion 1,342 190 29 208 653 162 59 96 Total noncurrent regulatory assets $ 10,046 $ 977 $ 1,681 $ 504 $ 2,851 $ 690 $ 289 $ 405 Successor December 31, 2016 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 47 $ — $ — $ — $ — $ — $ — $ — Nuclear decommissioning 2,607 2,169 438 — — — — — Removal costs 1,601 1,324 — 141 136 18 118 — Deferred rent 39 — — — 39 — — — Energy efficiency and demand response programs 185 141 41 — 3 3 — — DLC program costs 8 — 8 — — — — — Electric distribution tax repairs 76 — 76 — — — — — Gas distribution tax repairs 20 — 20 — — — — — Energy and transmission programs 134 60 56 — 18 8 5 5 Other 72 4 5 19 41 2 17 20 Total regulatory liabilities 4,789 3,698 644 160 237 31 140 25 Less: current portion 602 329 127 50 79 11 43 25 Total noncurrent regulatory liabilities $ 4,187 $ 3,369 $ 517 $ 110 $ 158 $ 20 $ 97 $ — The following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE as of December 31, 2017 and December 31, 2016 : Successor December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 3,848 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 306 — 297 — 9 9 — — AMI programs 640 155 36 214 235 158 77 — Electric distribution formula rate 244 244 — — — — — — Energy efficiency costs 166 166 — — — — — — Debt costs 116 37 1 11 73 15 8 5 Fair value of long-term debt 758 — — — 619 — — — Fair value of PHI's unamortized energy contracts 750 — — — 750 — — — Asset retirement obligations 109 73 22 14 — — — — MGP remediation costs 295 273 22 — — — — — Under-recovered uncollectible accounts 61 61 — — — — — — Renewable energy 258 256 — — 2 — 1 1 Energy and transmission programs 82 6 1 23 52 11 15 26 Deferred storm costs 27 — — — 27 7 5 15 Energy efficiency and demand response programs 596 — 1 285 310 229 81 — Merger integration costs 45 — — 6 39 20 10 9 Under-recovered revenue decoupling 55 — — 14 41 38 3 — COPCO acquisition adjustment 5 — — — 5 — 5 — Workers compensation and long-term disability costs 35 — — — 35 35 — — Vacation accrual 19 — 6 — 13 — 8 5 Securitized stranded costs 79 — — — 79 — — 79 CAP arrearage 8 — 8 — — — — — Removal costs 529 — — — 529 150 93 286 DC PLUG charge 190 — — — 190 190 — — Other 67 8 16 4 39 29 8 4 Total regulatory assets 9,288 1,279 410 571 3,047 891 314 430 Less: current portion 1,267 225 29 174 554 213 69 71 Total noncurrent regulatory assets $ 8,021 $ 1,054 $ 381 $ 397 $ 2,493 $ 678 $ 245 $ 359
Schedule of Regulatory Liabilities	Successor December 31, 2016 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 47 $ — $ — $ — $ — $ — $ — $ — Nuclear decommissioning 2,607 2,169 438 — — — — — Removal costs 1,601 1,324 — 141 136 18 118 — Deferred rent 39 — — — 39 — — — Energy efficiency and demand response programs 185 141 41 — 3 3 — — DLC program costs 8 — 8 — — — — — Electric distribution tax repairs 76 — 76 — — — — — Gas distribution tax repairs 20 — 20 — — — — — Energy and transmission programs 134 60 56 — 18 8 5 5 Other 72 4 5 19 41 2 17 20 Total regulatory liabilities 4,789 3,698 644 160 237 31 140 25 Less: current portion 602 329 127 50 79 11 43 25 Total noncurrent regulatory liabilities $ 4,187 $ 3,369 $ 517 $ 110 $ 158 $ 20 $ 97 $ — Successor December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 30 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 5,241 2,479 — 1,032 $ 1,730 809 510 411 Nuclear decommissioning 3,064 2,528 536 — — — — — Removal costs 1,573 1,338 — 105 130 20 110 — Deferred rent 36 — — — 36 — — — Energy efficiency and demand response programs 23 4 19 — — — — — DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 35 — 35 — — — — — Gas distribution tax repairs 9 — 9 — — — — — Energy and transmission programs 111 47 60 — 4 — 1 3 Renewable portfolio standards costs 63 63 — — — — — — Zero emission credit costs 112 112 — — — — — — Over-recovered uncollectible accounts 2 — — — 2 — — 2 Other 82 6 24 26 26 3 14 6 Total regulatory liabilities 10,388 6,577 690 1,163 1,928 832 635 422 Less: current portion 523 249 141 62 56 3 42 11 Total noncurrent regulatory liabilities $ 9,865 $ 6,328 $ 549 $ 1,101 $ 1,872 $ 829 $ 593 $ 411
Purchase Of Receivables	The following tables provide information about the purchased receivables of those companies as of December 31, 2017 and December 31, 2016 . Successor As of December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 298 $ 87 $ 70 $ 58 $ 83 $ 56 $ 9 $ 18 Allowance for uncollectible accounts (a) (31 ) (14 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 267 $ 73 $ 65 $ 55 $ 74 $ 51 $ 8 $ 15 Successor As of December 31, 2016 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 313 $ 87 $ 72 $ 59 $ 95 $ 63 $ 10 $ 22 Allowance for uncollectible accounts (a) (37 ) (14 ) (6 ) (4 ) (13 ) (7 ) (2 ) (4 ) Purchased receivables, net $ 276 $ 73 $ 66 $ 55 $ 82 $ 56 $ 8 $ 18 __________ (a) For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing tariff.

Mergers, Acquisitions and Dis42

Mergers, Acquisitions and Dispositions (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Combinations [Abstract]
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The following table summarizes the final acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the FitzPatrick acquisition by Generation as of December 31, 2017 : Cash paid for purchase price $ 110 Cash paid for net cost reimbursement 125 Nuclear fuel transfer 54 Total consideration transferred $ 289 Identifiable assets acquired and liabilities assumed Current assets $ 60 Property, plant and equipment 298 Nuclear decommissioning trust funds 807 Other assets (a) 114 Total assets $ 1,279 Current liabilities $ 6 Nuclear decommissioning ARO 444 Pension and OPEB obligations 33 Deferred income taxes 149 Spent nuclear fuel obligation 110 Other liabilities 15 Total liabilities $ 757 Total net identifiable assets, at fair value $ 522 Bargain purchase gain (after-tax) $ 233 _________ (a) Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23 - Commitments and Contingencies for additional background regarding SNF obligations to the DOE. Exelon applied push-down accounting to PHI, and accordingly, the PHI assets acquired and liabilities assumed were recorded at their estimated fair values on Exelon’s and PHI's Consolidated Balance Sheets as follows: Purchase Price Allocation (a) Current assets $ 1,441 Property, plant and equipment 11,088 Regulatory assets 5,015 Other assets 248 Goodwill 4,005 Total assets $ 21,797 Current liabilities $ 2,752 Unamortized energy contracts 1,515 Regulatory liabilities 297 Long-term debt, including current maturities 5,636 Deferred income taxes 3,447 Pension and OPEB obligations 821 Other liabilities 187 Total liabilities $ 14,655 Total purchase price $ 7,142 __________ (a) Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.	The following table summarizes the final acquisition-date fair value of the consideration transferred and the assets and liabilities assumed for the ConEdison Solutions acquisition by Generation: Total consideration transferred $ 257 Identifiable assets acquired and liabilities assumed Working capital assets $ 204 Property, plant and equipment 2 Mark-to-market derivative assets 6 Unamortized energy contract assets 100 Customer relationships 9 Other assets 1 Total assets $ 322 Mark-to-market derivative liabilities $ 65 Total liabilities $ 65 Total net identifiable assets, at fair value $ 257
Business Combination, Separately Recognized Transactions [Table Text Block]	The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date: Expected Payment Period Successor Description Pepco DPL ACE PHI Exelon Rate credits 2016 - 2017 $ 91 $ 67 $ 101 $ 259 $ 259 Energy efficiency 2016 - 2021 — — — — 122 Charitable contributions 2016 - 2026 28 12 10 50 50 Delivery system modernization Q2 2017 — — — — 22 Green sustainability fund Q2 2017 — — — — 14 Workforce development 2016 - 2020 — — — — 17 Other 1 5 — 6 29 Total $ 120 $ 84 $ 111 $ 315 $ 513 The total purchase price consideration of approximately $7.1 billion for the PHI Merger consisted of cash paid to PHI shareholders, cash paid for PHI preferred securities and cash paid for PHI stock-based compensation equity awards as follows: (In millions of dollars, except per share data) Total Consideration Cash paid to PHI shareholders at $27.25 per share (254 million shares outstanding at March 23, 2016) $ 6,933 Cash paid for PHI preferred stock 180 Cash paid for PHI stock-based compensation equity awards (a) 29 Total purchase price $ 7,142 __________ (a) PHI’s unvested time-based restricted stock units and performance-based restricted stock units issued prior to April 29, 2014 were immediately vested and paid in cash upon the close of the merger. PHI’s remaining unvested time-based restricted stock units as of the close of the merger were cancelled. There were no remaining unvested performance-based restricted stock units as of the close of the merger.
Business Acquisition, Pro Forma Information, Nonrecurring Adjustments [Table Text Block]	The unaudited pro-forma financial information has been presented for illustrative purposes only and is not necessarily indicative of results of operations that would have been achieved had the merger events taken place on the dates indicated, or the future consolidated results of operations of the combined company. Year Ended December 31, 2016 (a) 2015 (b) Total operating revenues $ 32,342 $ 33,823 Net income attributable to common shareholders 1,562 2,618 Basic earnings per share $ 1.69 $ 2.85 Diluted earnings per share 1.69 2.84 ______________ (a) The amounts above exclude non-recurring costs directly related to the merger of $680 million and intercompany revenue of $171 million for the year ended December 31, 2016 . (b) The amounts above exclude non-recurring costs directly related to the merger of $92 million and intercompany revenue of $559 million for the year ended December 31, 2015 .
Restructuring and Related Costs [Table Text Block]	For the periods ended December 31, 2017 and 2016 , the Registrants have recognized costs to achieve the PHI acquisition as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2017 2016 Exelon $ 16 $ 143 Generation 22 37 ComEd (b) 1 (6 ) PECO 4 5 BGE (b) 4 (1 ) Pepco (b) (6 ) 28 DPL (b) (7 ) 20 ACE (b) (6 ) 19 Successor Predecessor Acquisition, Integration and Financing Costs (a) For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI (b) $ (18 ) $ 69 $ 29 ______________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above. (b) For the year ended December 31, 2017 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million , $8 million , $8 million , and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million , $6 million , $11 million , and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information. For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs related to the cost management program within Operating and maintenance expense in their Consolidated Statements of Operations: Exelon Generation ComEd PECO BGE 2017 (a) $ 6 $ 9 $ (1 ) $ (1 ) $ (1 ) 2016 (b) 23 18 3 1 1 __________ (a) The amounts for Generation, ComEd, PECO, and BGE include $(4) million , $(2) million , $(1) million , and $(1) million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017 . (b) The amounts above for Generation, ComEd, PECO and BGE include $7 million , $3 million , $1 million , and $1 million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2016 . For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs associated with ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Successor Exelon Generation (a) ComEd (a) PECO (a) BGE (a) PHI (a) Pepco (a) DPL (a) ACE (a) Year ended December 31, 2017 $ 14 $ 6 $ 3 $ 1 $ — $ 4 $ 2 $ 1 $ 1 2016 19 13 3 1 1 1 — — — __________ (a) The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016 . Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017 . Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016	For the year ended December 31, 2016 , the Registrants recorded the following severance costs associated with the identified job reductions within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income, pursuant to the authoritative guidance for ongoing severance plans: Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Severance Benefits Severance costs (a) $ 57 $ 9 $ 2 $ 1 $ 1 $ 44 $ 21 $ 13 $ 10 __________ (a) The amounts above for Generation, ComEd, PECO, BGE, Pepco, DPL, and ACE include $8 million , $2 million , $1 million , $1 million , $20 million , $12 million and $10 million , respectively, for amounts billed by BSC and/or PHISCO through intercompany allocations for the year ended December 31, 2016 .

Accounts Receivable (Tables)

Accounts Receivable (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Schedule Of Accounts Notes Loans And Financing Receivable	Accounts receivable at December 31, 2017 and 2016 included estimated unbilled revenues, representing an estimate for the unbilled amount of energy or services provided to customers, and is net of an allowance for uncollectible accounts as follows: Successor 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer $ 1,858 $ 1,017 (a) $ 242 $ 162 $ 205 $ 232 $ 133 $ 68 $ 31 Allowance for uncollectible (b) (322 ) (114 ) (73 ) (56 ) (c) (24 ) (55 ) (21 ) (16 ) (18 ) Successor 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues $ 1,673 $ 910 (a) $ 219 $ 140 $ 182 $ 222 $ 123 $ 58 $ 41 Allowance for uncollectible (b) (334 ) (91 ) (70 ) (61 ) (c) (32 ) (80 ) (d) (29 ) (d) (24 ) (d) (27 ) (d) __________ (a) Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable. (c) Excludes the non-current allowance for uncollectible accounts of $15 million and $23 million at December 31, 2017 and 2016 , respectively, related to PECO’s current installment plan receivables described below. (d) At December 31, 2016 , as explained in Note 1 — Significant Accounting Policies , PHI, Pepco, DPL and ACE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in an overall increase of $30 million , $14 million , $8 million , and $8 million in the allowance for uncollectible accounts with $20 million , $8 million , $4 million , and $8 million deferred as a regulatory asset on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets at December 31, 2016, respectively. This also resulted in a $10 million , $6 million , and $4 million pre-tax charge to provision for uncollectible accounts expense for the year ended December 31, 2016 , which is included in Operating and maintenance expense on PHI's, Pepco's and DPL's Consolidated Statements of Operations and Comprehensive Income, respectively.

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—generation 2-56 $ 29,019 $ 27,193 Nuclear fuel (a) 1-8 6,420 6,546 Construction work in progress N/A 838 2,332 Other property, plant and equipment (b) 2-3 57 76 Total property, plant and equipment 36,334 36,147 Less: accumulated depreciation (c) 11,428 10,562 Property, plant and equipment, net $ 24,906 $ 25,585 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016 , respectively. (b) Includes buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016 , respectively. The original cost basis of the buildings was $47 million and $52 million , and total accumulated amortization was $40 million and $42 million , as of December 31, 2017 and 2016 , respectively. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016 , respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017 . (c) Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million and $3,186 million as of December 31, 2017 and 2016 , respectively The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-90 $ 7,464 $ 7,067 Gas—distribution 5-90 2,379 2,170 Common—electric and gas 5-40 771 707 Construction work in progress N/A 367 318 Other property, plant and equipment (a) 20 26 32 Total property, plant and equipment 11,007 10,294 Less: accumulated depreciation 3,405 3,254 Property, plant and equipment, net $ 7,602 $ 7,040 __________ (a) Represents land held for future use and non-utility property The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-75 $ 8,646 $ 8,018 Construction work in progress N/A 473 537 Other property, plant and equipment (a) 25-33 59 66 Total property, plant and equipment 9,178 8,621 Less: accumulated depreciation 3,177 — 3,050 Property, plant and equipment, net $ 6,001 $ 5,571 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-60 $ 3,607 $ 3,341 Construction work in progress N/A 138 169 Other property, plant and equipment (a) 13-15 27 27 Total property, plant and equipment 3,772 3,537 Less: accumulated depreciation 1,066 — 1,016 Property, plant and equipment, net $ 2,706 $ 2,521 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-80 $ 24,423 $ 22,636 Construction work in progress N/A 517 569 Other property, plant and equipment (a), (b) 36-50 52 67 Total property, plant and equipment 24,992 23,272 Less: accumulated depreciation 4,269 3,937 Property, plant and equipment, net $ 20,723 $ 19,335 __________ (a) Includes buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 of $7 million . The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016 . (b) Includes land held for future use and non-utility property. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-70 $ 3,875 $ 3,574 Gas—distribution 5-75 614 580 Common—electric and gas 5-75 117 115 Construction work in progress N/A 205 163 Other property, plant and equipment (a) 10-43 15 16 Total property, plant and equipment 4,826 4,448 Less: accumulated depreciation 1,247 — 1,175 Property, plant and equipment, net $ 3,579 $ 3,273 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Successor Average 2017 2016 Asset Category Electric—transmission and distribution 5-75 $ 11,517 $ 10,315 Gas—distribution 5-75 449 414 Common—electric and gas 5-75 82 65 Construction work in progress N/A 835 892 Other property, plant and equipment (a) 3-43 102 107 Total property, plant and equipment 12,985 11,793 Less: accumulated depreciation 487 — 195 Property, plant and equipment, net $ 12,498 $ 11,598 __________ (a) Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien. The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-90 $ 49,506 $ 45,698 Electric—generation 2-56 29,019 27,193 Gas—transportation and distribution 5-90 5,050 4,642 Common—electric and gas 5-75 1,447 1,312 Nuclear fuel (a) 1-8 6,420 6,546 Construction work in progress N/A 2,825 4,306 Other property, plant and equipment (b) 2-50 999 1,027 Total property, plant and equipment 95,266 90,724 Less: accumulated depreciation (c) 21,064 19,169 Property, plant and equipment, net $ 74,202 $ 71,555 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016 , respectively. The original cost basis of the buildings was $47 million and $52 million , and total accumulated amortization was $40 million and $42 million , as of December 31, 2017 and 2016 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 , of $7 million . The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016 . Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $44 million , $21 million , $26 million , $59 million , $15 million and $27 million , respectively, at December 31, 2017 . Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016 , respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017 . (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $3,159 million and $3,186 million as of December 31, 2017 and 2016 , respectively The following table presents a summary of property, plant and equipment by asset category as of December 31, 2017 and 2016 : Average Service Life (years) 2017 2016 Asset Category Electric—transmission and distribution 5-65 $ 7,975 $ 7,591 Gas—transportation and distribution 5-70 2,504 2,348 Common—electric and gas 5-50 710 670 Construction work in progress N/A 254 188 Other property, plant and equipment (a) 50 21 21 Total property, plant and equipment 11,464 10,818 Less: accumulated depreciation 3,411 3,253 Property, plant and equipment, net $ 8,053 $ 7,565 __________ (a) Represents land held for future use and non-utility property
Property Plant And Equipment Average Service Life Percentage By Asset Category Table	The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.75 % 2.49 % 2.44 % Gas 2.07 % 2.57 % 2.55 % Common—electric and gas 4.14 % 4.99 % 4.24 % The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.58 % 2.56 % 2.62 % Gas 2.33 % 2.45 % 2.50 % Common—electric and gas 8.64 % 9.45 % 10.35 % The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.37 % 2.32 % 2.39 % Gas 1.89 % 1.82 % 1.87 % Common—electric and gas 5.47 % 5.11 % 5.16 % The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.63 % 2.52 % 2.48 % Gas 2.07 % 2.57 % 2.55 % Common—electric and gas 6.50 % 8.12 % 5.19 % The following table presents the annual depreciation provisions as a percentage of average service life for each asset category. Average Service Life Percentage by Asset Category 2017 2016 2015 Electric—transmission and distribution 2.75 % 2.73 % 2.83 % Electric—generation (a) 4.36 % (a) 5.94 % (a) 3.47 % Gas 2.10 % 2.17 % 2.17 % Common—electric and gas 7.05 % 7.41 % 7.79 % __________ (a) See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI.

Early Nuclear Plant Retiremen45

Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Tables)	12 Months Ended
	Dec. 31, 2017
Implications of Potential Early Plant Retirements [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2017 (a) 2016 (b) Depreciation and Amortization Accelerated depreciation (c) $ 250 $ 712 Accelerated nuclear fuel amortization 12 60 Operating and Maintenance One-time charges (d,e) 77 26 Change in ARO accretion, net of any contractual offset (f) — 2 Contractual offset for ARC depreciation (f) — (86 ) Total $ 339 $ 714 _________ (a) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (b) Reflects incremental charges for Clinton and Quad Cities including incremental accelerated depreciation and amortization from June 2, 2016 through December 6, 2016. In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation updated the expected economic useful life for both facilities, to 2027 for Clinton, commensurate with the end of the Illinois ZES, and to 2032 for Quad Cities, the end of its current operating license. Depreciation was therefore adjusted beginning December 7, 2016, to reflect these extended useful life estimates. (c) Reflects incremental accelerated depreciation of plant assets, including any ARC. (d) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. (e) In June 2016, as a result of the retirement decision for Clinton and Quad Cities, Exelon and Generation recognized one-time charges of $146 million . In December 2016, as a result of reversing its retirement decision for Clinton and Quad Cities, Exelon and Generation reversed approximately $120 million of these one-time charges initially recorded in June 2016. (f) For Quad Cities based on the regulatory agreement with the Illinois Commerce Commission, decommissioning-related activities are offset within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. The offset results in an equal adjustment to the noncurrent payables to ComEd at Generation and an adjustment to the regulatory liabilities at ComEd. Likewise, ComEd has recorded an equal noncurrent affiliate receivable from Generation and corresponding regulatory liability.
ScheduleOfOtherOperatingCostAndExpenseByComponent2 [Table Text Block]	The following table provides the balance sheet amounts as of December 31, 2017 for Generation’s ownership share of the significant assets and liabilities associated with Salem. (in millions) 12/31/2017 Asset Balances Materials and supplies inventory $ 44 Nuclear fuel inventory, net 113 Completed plant, net 439 Construction work in progress 33 Liability Balances Asset retirement obligation (442 ) NRC License Renewal Term 2036 (unit 1) 2040 (unit 2) On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at Oyster Creek at the end of its current operating cycle in October 2018. See Note 28 — Subsequent Events for additional information regarding the early retirement of Oyster Creek.

Jointly Owned Electric Utilit46

Jointly Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2017
Public Utilities, Property, Plant and Equipment [Abstract]
Schedule of Jointly Owned Utility Plants	Exelon's, Generation's, PECO's, BGE's, PHI's and ACE's undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2017 and 2016 were as follows: Nuclear Generation Fossil-Fuel Generation Transmission Other Quad Cities Peach Bottom Salem (a) Nine Mile Point Unit 2 Wyman PA (b) NJ/ DE (c) Other (d) Operator Generation Generation PSEG Generation FP&L First PSEG/ DPL various Ownership interest 75.00 % 50.00 % 42.59 % 82.00 % 5.89 % various various various Exelon’s share at December 31, 2017: Plant (e) $ 1,074 $ 1,417 $ 631 $ 839 $ 3 $ 27 $ 102 $ 15 Accumulated depreciation (e) 550 461 205 97 3 15 52 13 Construction work in progress 35 18 33 55 — — — — Exelon’s share at December 31, 2016: Plant (e) $ 1,054 $ 1,384 $ 596 $ 830 $ 3 $ 27 $ 97 $ 15 Accumulated depreciation (e) 515 407 186 68 3 15 52 13 Construction work in progress — 16 41 37 — — — — __________ (a) Generation also owns a proportionate share in the fossil-fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2017 and 2016 . (b) PECO, BGE, Pepco, DPL and ACE own a 22% , 7% , 27% , 9% and 8% share, respectively, in 127 miles of 500 kV lines located in Pennsylvania as well as a 20.72% , 10.56% , 9.72% , 3.72% and 3.83% share, respectively, of a 500 kV substation immediately outside of the Conemaugh fossil-generating station which supplies power to the 500 kV lines including, but not limited to, the lines noted above. (c) PECO, DPL and ACE own a 42.55% , 1% and 13.9% share, respectively in 151.3 miles of 500 kV lines located in New Jersey and Delaware Station. PECO, DPL and ACE also own a 42.55% , 7.45% and 7.45% share, respectively, in 2.5 miles of 500 kV line located over the Delaware River. ACE also has a 21.78% share in a 500 kV New Freedom Switching (d) Generation, DPL and ACE own a 44.24% , 4.83% and 11.91% share, respectively in assets located at Merrill Creek Reservoir located in New Jersey. Pepco, DPL and ACE own a 11.9% , 7.4% and 6.6% share, respectively, in Valley Forge Corporate Center. (e) Excludes asset retirement costs.

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Schedule Of Goodwill	Exelon’s, Generation's, ComEd’s, PHI's and DPL's gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2017 and 2016 were as follows: Balance at January 1, 2016 Goodwill from business combination Impairment losses Measurement period adjustments (b) Balance at December 31, 2016 Impairment losses Balance at December 31, 2017 Exelon Gross amount $ 4,655 $ 4,016 $ — $ (11 ) $ 8,660 $ — $ 8,660 Accumulated impairment loss 1,983 — — — 1,983 — 1,983 Carrying amount 2,672 4,016 — (11 ) 6,677 — 6,677 Generation Gross amount 47 — — — 47 — 47 Carrying amount 47 — — — 47 — 47 ComEd (a) Gross amount 4,608 — — — 4,608 — 4,608 Accumulated impairment loss 1,983 — — — 1,983 — 1,983 Carrying amount 2,625 — — — 2,625 — 2,625 DPL Gross amount 8 — — — 8 — 8 Carrying amount 8 — — — 8 — 8 For the Year Ended December 31, 2017 Beginning Balance Goodwill from business combination Impairment losses Measurement period adjustments (b) Ending Balance PHI - Successor Gross amount $ 4,005 $ — $ — $ — $ 4,005 Accumulated impairment loss — — — — — Carrying Amount 4,005 — — — 4,005 March 24, 2016 to December 31, 2016 PHI - Successor Gross amount — 4,016 — (11 ) 4,005 Accumulated impairment loss — — — — — Carrying amount — 4,016 — (11 ) 4,005 January 1, 2016 to March 23, 2016 PHI - Predecessor Gross amount 1,418 — — — 1,418 Accumulated impairment loss 12 — — — 12 Carrying amount 1,406 — — — 1,406 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom (predecessor parent company of ComEd) merger net of amortization, resolution of tax matters and other non-impairment-related changes as allowed under previous authoritative guidance. (b) Represents various measurement period adjustments to the valuation of the fair value of the PHI assets acquired and liabilities assumed as a result of the merger.
Schedule of Finite-Lived Intangible Assets	Exelon’s, Generation’s, ComEd’s and PHI's other intangible assets and liabilities, included in Unamortized energy contract assets and liabilities and Other deferred debits and other assets in their Consolidated Balance Sheets, consisted of the following as of December 31, 2017 and 2016 : December 31, 2017 December 31, 2016 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Exelon Software License (a) $ 95 $ (25 ) $ 70 $ 95 $ (15 ) $ 80 Generation Unamortized Energy Contracts (b) 1,938 (1,574 ) 364 1,926 (1,543 ) 383 Customer Relationships 305 (133 ) 172 299 (109 ) 190 Trade Name 243 (148 ) 95 243 (125 ) 118 Service Contract Backlog — — — 9 (7 ) 2 ComEd Chicago Settlement Agreements (c) 162 (141 ) 21 162 (133 ) 29 PHI Unamortized Energy Contracts (b) (1,515 ) 766 (749 ) (1,515 ) 430 (1,085 ) Pepco DC Sponsorship Agreement (d) — — — 25 — 25 Total $ 1,228 $ (1,255 ) $ (27 ) $ 1,244 $ (1,502 ) $ (258 ) __________ (a) On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term. (b) Includes unamortized energy contract assets and liabilities on Exelon's, Generations and PHI's Consolidated Balance Sheets. (c) In March 1999 and February 2003, ComEd entered into separate agreements with the City of Chicago and Midwest Generation, LLC. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement. (d) PHI entered into a sponsorship agreement with the District of Columbia for future sponsorship rights associated with public property within the District of Columbia. In December 2017, the asset was written off. See Note 7 - Impairment of Long-Lived Assets and Intangibles for additional information.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table summarizes the estimated future amortization expense related to intangible assets and liabilities as of December 31, 2017 : For the Years Ending December 31, Exelon Generation ComEd PHI 2018 $ 10 $ 62 $ 7 $ (189 ) 2019 10 57 7 (119 ) 2020 10 68 7 (115 ) 2021 10 77 — (92 ) 2022 10 54 — (89 )
Schedule Of Finite-Lived Intangible Assets Amortization Expense	The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2017 , 2016 and 2015 : For the Years Ended December 31, Exelon (a) Generation (a) ComEd 2017 $ 92 $ 83 $ 7 2016 87 79 7 2015 76 69 7 __________ (a) At Exelon, amortization of unamortized energy contracts totaling $35 million , $35 million and $22 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, was recorded in Operating revenues or Purchased power and fuel expense within Exelon’s Consolidated Statements of Operations and Comprehensive Income. At Generation, amortization of unamortized energy contracts totaling $35 million , $35 million and $22 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, was recorded in Operating revenues or Purchased power and fuel expense within Generation’s Consolidated Statements of Operations and Comprehensive Inco
Schedule of Alternative or Renewable Energy Credits [Table Text Block]	The following table summarizes the current and noncurrent Renewable and Alternative Energy Credits for the years ended December 31, 2017 and 2016 : As of December 31, 2017 Successor Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Noncurrent AEC's — — — — — — Current REC's 321 312 — 9 8 1 Noncurrent REC's 27 27 — — — — As of December 31, 2016 Successor Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Noncurrent AEC's — — — — — — Current REC's 330 318 — 12 11 1 Noncurrent REC's 29 29 — — — —

Fair Value of Financial Asset48

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value of financial liabilities recorded at the carrying amount	The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation, and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of December 31, 2017 and 2016 : Exelon December 31, 2017 Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 929 $ — $ 929 $ — $ 929 Long-term debt (including amounts due within one year) (a) 34,264 — 34,735 1,970 36,705 Long-term debt to financing trusts (b) 389 — — 431 431 SNF obligation 1,147 — 936 — 936 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 1,267 $ — $ 1,267 $ — $ 1,267 Long-term debt (including amounts due within one year) (a) 34,005 1,113 31,741 1,959 34,813 Long-term debt to financing trusts (b) 641 — — 667 667 SNF obligation 1,024 — 732 — 732 Generation December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 2 $ — $ 2 $ — $ 2 Long-term debt (including amounts due within one year) (a) 8,990 — 7,839 1,673 9,512 SNF obligation 1,147 — 936 — 936 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 699 $ — $ 699 $ — $ 699 Long-term debt (including amounts due within one year) (a) 9,241 — 7,482 1,670 9,152 SNF obligation 1,024 — 732 — 732 ComEd December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 7,601 $ — $ 8,418 $ — $ 8,418 Long-term debt to financing trusts (b) 205 — — 227 227 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 7,033 $ — $ 7,585 $ — $ 7,585 Long-term debt to financing trusts (b) 205 — — 215 215 PECO December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,903 $ — $ 3,194 $ — $ 3,194 Long-term debt to financing trusts 184 — — 204 204 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 2,580 $ — $ 2,794 $ — $ 2,794 Long-term debt to financing trusts 184 — — 192 192 BGE December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 77 $ — $ 77 $ — $ 77 Long-term debt (including amounts due within one year) (a) 2,577 — 2,825 — 2,825 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 45 $ — $ 45 $ — $ 45 Long-term debt (including amounts due within one year) (a) 2,322 — 2,467 — 2,467 Long-term debt to financing trusts (b) 252 — — 260 260 PHI (Successor) December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 350 $ — $ 350 $ — $ 350 Long-term debt (including amounts due within one year) (a) 5,874 — 5,722 297 6,019 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 522 $ — $ 522 $ — $ 522 Long-term debt (including amounts due within one year) (a) 5,898 — 5,520 289 5,809 Pepco December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 26 $ — $ 26 $ — $ 26 Long-term debt (including amounts due within one year) (a) 2,540 — 3,114 9 3,123 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 23 $ — $ 23 $ — $ 23 Long-term debt (including amounts due within one year) (a) 2,349 — 2,788 8 2,796 DPL December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (a) 1,300 — 1,393 — 1,393 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,340 $ — $ 1,383 $ — $ 1,383 ACE December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 108 $ — $ 108 $ — $ 108 Long-term debt (including amounts due within one year) (a) 1,121 — 949 288 1,237 December 31, 2016 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,155 $ — $ 1,007 $ 280 $ 1,287 __________ (a) Includes unamortized debt issuance costs which are not fair valued of $201 million , $60 million , $52 million , $17 million , $17 million , $6 million , $32 million , $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2017 . Includes unamortized debt issuance costs which are not fair valued of $200 million , $64 million , $46 million , $15 million , $15 million , $2 million , $30 million , $11 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2016 . (b) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2017 . Includes unamortized debt issuance costs which are not fair valued of $7 million , $1 million , and $6 million for Exelon, ComEd and BGE, respectively, as of December 31, 2016 .
Assets and liabilities measured and recorded at fair value on recurring basis	PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Successor As of December 31, 2017 As of December 31, 2016 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 83 $ — $ — $ 83 $ 217 $ — $ — $ 217 Mark-to-market derivative assets (b) — — — — 2 — — 2 Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) Mark-to-market derivative assets subtotal — — — — — — — — Rabbi trust investments Cash equivalents 72 — — 72 73 — — 73 Fixed income — 12 — 12 — 16 — 16 Life insurance contracts — 23 22 45 — 22 20 42 Rabbi trust investments subtotal 72 35 22 129 73 38 20 131 Total assets 155 35 22 212 290 38 20 348 Liabilities Deferred compensation obligation — (25 ) — (25 ) — (28 ) — (28 ) Mark-to-market derivative liabilities (b) (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (25 ) — (25 ) — (28 ) — (28 ) Total net assets $ 155 $ 10 $ 22 $ 187 $ 290 $ 10 $ 20 $ 320 Pepco DPL ACE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 36 $ — $ — $ 36 $ — $ — $ — $ — $ 29 $ — $ — $ 29 Rabbi trust investments Cash equivalents 44 — — 44 — — — — — — — — Fixed income — 12 — 12 — — — — — — — — Life insurance contracts — 23 22 45 — — — — — — — — Rabbi trust investments subtotal 44 35 22 101 — — — — — — — — Total assets 80 35 22 137 — — — — 29 — — 29 Liabilities Deferred compensation obligation — (4 ) — (4 ) — (1 ) — (1 ) — — — — Mark-to-market derivative liabilities (b) — — — — (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral — — — — 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — — — — — Total liabilities — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 80 $ 31 $ 22 $ 133 $ — $ (1 ) $ — $ (1 ) $ 29 $ — $ — $ 29 Pepco DPL ACE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 33 $ — $ — $ 33 $ 42 $ — $ — $ 42 $ 130 $ — $ — $ 130 Mark-to-market derivative assets (b) — — — — 2 — — 2 — — — — Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) — — — — Mark-to-market derivative assets subtotal — — — — — — — — — — — — Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 16 — 16 — — — — — — — — Life insurance contracts — 22 19 41 — — — — — — — — Rabbi trust investments subtotal 43 38 19 100 — — — — — — — — Total assets 76 38 19 133 42 — — 42 130 — — 130 Liabilities Deferred compensation obligation — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total liabilities — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 76 $ 33 $ 19 $ 128 $ 42 $ (1 ) $ — $ 41 $ 130 $ — $ — $ 130 _______ (a) PHI excludes cash of $12 million and $19 million at December 31, 2017 and 2016 and includes long term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $4 million and $9 million at December 31, 2017 and 2016 . DPL excludes cash of $2 million and $4 million at December 31, 2017 and 2016 . ACE excludes cash of $2 million and $3 million at December 31, 2017 and 2016 and includes long-term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : ComEd PECO BGE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 98 $ — $ — $ 98 $ 228 $ — $ — $ 228 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 6 — — 6 Total assets 98 — — 98 235 10 — 245 6 — — 6 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (256 ) (256 ) — — — — — — — — Total liabilities — (8 ) (256 ) (264 ) — (11 ) — (11 ) — (5 ) — (5 ) Total net assets (liabilities) $ 98 $ (8 ) $ (256 ) $ (166 ) $ 235 $ (1 ) $ — $ 234 $ 6 $ (5 ) $ — $ 1 ComEd PECO BGE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 20 $ — $ — $ 20 $ 45 $ — $ — $ 45 $ 36 $ — $ — $ 36 Rabbi trust investments Mutual funds — — — — 7 — — 7 4 — — 4 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 4 — — 4 Total assets 20 — — 20 52 10 — 62 40 — — 40 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (b) — — (258 ) (258 ) — — — — — — — — Total liabilities — (8 ) (258 ) (266 ) — (11 ) — (11 ) — (4 ) — (4 ) Total net assets (liabilities) $ 20 $ (8 ) $ (258 ) $ (246 ) $ 52 $ (1 ) $ — $ 51 $ 40 $ (4 ) $ — $ 36 __________ (a) ComEd excludes cash of $45 million and $36 million at December 31, 2017 and 2016 and restricted cash of $2 million at December 31, 2016 and includes long-term restricted cash of $62 million at December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $47 million and $22 million at December 31, 2017 and 2016 . BGE excludes cash of $17 million and $13 million at December 31, 2017 and 2016 and restricted cash of $1 million at December 31, 2017 and includes long-term restricted cash of $2 million at December 31, 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) The Level 3 balance consists of the current and noncurrent liability of $21 million and $235 million , respectively, at December 31, 2017 , and $19 million and $239 million , respectively, at December 31, 2016 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 168 $ — $ — $ — $ 168 $ 656 $ — $ — $ — $ 656 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total NDT fund investments Cash equivalents (b) 135 85 — — 220 135 85 — — 220 Equities 4,163 915 — 2,176 7,254 4,163 915 — 2,176 7,254 Fixed income Corporate debt — 1,614 251 — 1,865 — 1,614 251 — 1,865 U.S. Treasury and agencies 1,917 52 — — 1,969 1,917 52 — — 1,969 Foreign governments — 82 — — 82 — 82 — — 82 State and municipal debt — 263 — — 263 — 263 — — 263 Other (c) — 47 — 510 557 — 47 — 510 557 Fixed income subtotal 1,917 2,058 251 510 4,736 1,917 2,058 251 510 4,736 Middle market lending — — 397 131 528 — — 397 131 528 Private equity — — — 222 222 — — — 222 222 Real estate — — — 471 471 — — — 471 471 NDT fund investments subtotal (d) 6,215 3,058 648 3,510 13,431 6,215 3,058 648 3,510 13,431 Pledged assets for Zion Station decommissioning Cash equivalents 2 — — — 2 2 — — — 2 Equities — 1 — — 1 — 1 — — 1 Middle market lending — — 12 24 36 — — 12 24 36 Pledged assets for Zion Station decommissioning subtotal 2 1 12 24 39 2 1 12 24 39 Rabbi trust investments Cash equivalents 5 — — — 5 77 — — — 77 Mutual funds 23 — — — 23 58 — — — 58 Fixed income — — — — — — 12 — — 12 Life insurance contracts — 22 — — 22 — 71 22 — 93 Rabbi trust investments subtotal 28 22 — — 50 135 83 22 — 240 Commodity derivative assets Economic hedges 557 2,378 1,290 — 4,225 557 2,378 1,290 — 4,225 Proprietary trading 2 31 35 — 68 2 31 35 — 68 Effect of netting and allocation of (e)(f) (585 ) (1,769 ) (635 ) — (2,989 ) (585 ) (1,769 ) (635 ) — (2,989 ) Commodity derivative assets subtotal (26 ) 640 690 — 1,304 (26 ) 640 690 — 1,304 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 3 — — 3 — 6 — — 6 Economic hedges — 10 — — 10 — 10 — — 10 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of (e)(f) 650 2,089 716 — 3,455 651 2,089 716 — 3,456 Commodity derivative liabilities subtotal (64 ) (179 ) (138 ) — (381 ) (64 ) (179 ) (394 ) — (637 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (2 ) — — (2 ) — (2 ) — — (2 ) Economic hedges (1 ) (8 ) — — (9 ) (1 ) (8 ) — — (9 ) Effect of netting and allocation of collateral 2 5 — — 7 2 5 — — 7 Interest rate and foreign currency derivative liabilities subtotal 1 (5 ) — — (4 ) 1 (5 ) — — (4 ) Deferred compensation obligation — (38 ) — — (38 ) — (145 ) — — (145 ) Total liabilities (63 ) (222 ) (138 ) — (423 ) (63 ) (329 ) (394 ) — (786 ) Total net assets $ 6,322 $ 3,507 $ 1,249 $ 3,534 $ 14,612 $ 6,917 $ 3,464 $ 1,015 $ 3,534 $ 14,930 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 39 $ — $ — $ — $ 39 $ 373 $ — $ — $ — $ 373 NDT fund investments Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Cash equivalents (b) 110 19 — — 129 110 19 — — 129 Equities 3,551 452 — 2,011 6,014 3,551 452 — 2,011 6,014 Fixed income Corporate debt — 1,554 250 — 1,804 — 1,554 250 — 1,804 U.S. Treasury and agencies 1,291 29 — — 1,320 1,291 29 — — 1,320 Foreign governments — 37 — — 37 — 37 — — 37 State and municipal debt — 264 — — 264 — 264 — — 264 Other (c) — 59 — 493 552 — 59 — 493 552 Fixed income subtotal 1,291 1,943 250 493 3,977 1,291 1,943 250 493 3,977 Middle market lending — — 427 71 498 — — 427 71 498 Private equity — — — 148 148 — — — 148 148 Real estate — — — 326 326 — — — 326 326 NDT fund investments subtotal (d) 4,952 2,414 677 3,049 11,092 4,952 2,414 677 3,049 11,092 Pledged assets for Zion Station decommissioning Cash equivalents 11 — — — 11 11 — — — 11 Equities — 2 — — 2 — 2 — — 2 Fixed Income - U.S. Treasury and agencies 16 1 — — 17 16 1 — — 17 Middle market lending — — 19 64 83 — — 19 64 83 Pledged assets for Zion Station decommissioning subtotal 27 3 19 64 113 27 3 19 64 113 Rabbi trust investments Cash equivalents 2 — — — 2 74 — — — 74 Mutual funds 19 — — — 19 50 — — — 50 Fixed income — — — — — — 16 — — 16 Life insurance contracts — 18 — — 18 — 64 20 — 84 Rabbi trust investments subtotal 21 18 — — 39 124 80 20 — 224 Commodity derivative assets Economic hedges 1,356 2,505 1,229 — 5,090 1,358 2,505 1,229 — 5,092 Proprietary trading 3 50 23 — 76 3 50 23 — 76 Effect of netting and allocation of (e)(f) (1,162 ) (2,142 ) (481 ) — (3,785 ) (1,164 ) (2,142 ) (481 ) — (3,787 ) Commodity derivative assets subtotal 197 413 771 — 1,381 197 413 771 — 1,381 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — 16 — — 16 Economic hedges — 28 — — 28 — 28 — — 28 Proprietary trading 3 2 — — 5 3 2 — — 5 Effect of netting and allocation of collateral (2 ) (19 ) — — (21 ) (2 ) (19 ) — — (21 ) Interest rate and foreign currency derivative assets subtotal 1 11 — — 12 1 27 — — 28 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,237 2,859 1,509 3,113 12,718 5,674 2,937 1,529 3,113 13,253 Liabilities Commodity derivative liabilities Economic hedges (1,267 ) (2,378 ) (794 ) — (4,439 ) (1,267 ) (2,378 ) (1,052 ) — (4,697 ) Proprietary trading (3 ) (50 ) (26 ) — (79 ) (3 ) (50 ) (26 ) — (79 ) Effect of netting and allocation of (e)(f) 1,233 2,339 542 — 4,114 1,233 2,339 542 — 4,114 Commodity derivative liabilities subtotal (37 ) (89 ) (278 ) — (404 ) (37 ) (89 ) (536 ) — (662 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (10 ) — — (10 ) — (10 ) — — (10 ) Economic hedges — (21 ) — — (21 ) — (21 ) — — (21 ) Proprietary trading (4 ) — — — (4 ) (4 ) — — — (4 ) Effect of netting and allocation of collateral 4 19 — — 23 4 19 — — 23 Interest rate and foreign currency derivative liabilities subtotal — (12 ) — — (12 ) — (12 ) — — (12 ) Deferred compensation obligation — (34 ) — — (34 ) — (136 ) — — (136 ) Total liabilities (37 ) (135 ) (278 ) — (450 ) (37 ) (237 ) (536 ) — (810 ) Total net assets $ 5,200 $ 2,724 $ 1,231 $ 3,113 $ 12,268 $ 5,637 $ 2,700 $ 993 $ 3,113 $ 12,443 __________ (a) Generation excludes cash of $259 million and $252 million at December 31, 2017 and 2016 and restricted cash of $127 million and $157 million at December 31, 2017 and 2016 . Exelon excludes cash of $389 million and $360 million at December 31, 2017 and 2016 and restricted cash of $145 million and $180 million at December 31, 2017 and 2016 and includes long-term restricted cash of $85 million and $25 million at December 31, 2017 and 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $77 million and $29 million of cash received from outstanding repurchase agreements at December 31, 2017 and 2016 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of less than $1 million and $(2) million , which have a total notional amount of $811 million and $933 million at December 31, 2017 and 2016 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss. (d) Excludes net liabilities of $82 million and $31 million at December 31, 2017 and 2016 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less. (e) Collateral posted/(received) from counterparties totaled $65 million , $320 million and $81 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2017 . Collateral posted/(received) from counterparties totaled $71 million , $197 million and $61 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2016 .
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Successor As of December 31, 2017 As of December 31, 2016 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 83 $ — $ — $ 83 $ 217 $ — $ — $ 217 Mark-to-market derivative assets (b) — — — — 2 — — 2 Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) Mark-to-market derivative assets subtotal — — — — — — — — Rabbi trust investments Cash equivalents 72 — — 72 73 — — 73 Fixed income — 12 — 12 — 16 — 16 Life insurance contracts — 23 22 45 — 22 20 42 Rabbi trust investments subtotal 72 35 22 129 73 38 20 131 Total assets 155 35 22 212 290 38 20 348 Liabilities Deferred compensation obligation — (25 ) — (25 ) — (28 ) — (28 ) Mark-to-market derivative liabilities (b) (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (25 ) — (25 ) — (28 ) — (28 ) Total net assets $ 155 $ 10 $ 22 $ 187 $ 290 $ 10 $ 20 $ 320 Pepco DPL ACE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 36 $ — $ — $ 36 $ — $ — $ — $ — $ 29 $ — $ — $ 29 Rabbi trust investments Cash equivalents 44 — — 44 — — — — — — — — Fixed income — 12 — 12 — — — — — — — — Life insurance contracts — 23 22 45 — — — — — — — — Rabbi trust investments subtotal 44 35 22 101 — — — — — — — — Total assets 80 35 22 137 — — — — 29 — — 29 Liabilities Deferred compensation obligation — (4 ) — (4 ) — (1 ) — (1 ) — — — — Mark-to-market derivative liabilities (b) — — — — (1 ) — — (1 ) — — — — Effect of netting and allocation of collateral — — — — 1 — — 1 — — — — Mark-to-market derivative liabilities subtotal — — — — — — — — — — — — Total liabilities — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 80 $ 31 $ 22 $ 133 $ — $ (1 ) $ — $ (1 ) $ 29 $ — $ — $ 29 Pepco DPL ACE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 33 $ — $ — $ 33 $ 42 $ — $ — $ 42 $ 130 $ — $ — $ 130 Mark-to-market derivative assets (b) — — — — 2 — — 2 — — — — Effect of netting and allocation of collateral — — — — (2 ) — — (2 ) — — — — Mark-to-market derivative assets subtotal — — — — — — — — — — — — Rabbi trust investments Cash equivalents 43 — — 43 — — — — — — — — Fixed income — 16 — 16 — — — — — — — — Life insurance contracts — 22 19 41 — — — — — — — — Rabbi trust investments subtotal 43 38 19 100 — — — — — — — — Total assets 76 38 19 133 42 — — 42 130 — — 130 Liabilities Deferred compensation obligation — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total liabilities — (5 ) — (5 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 76 $ 33 $ 19 $ 128 $ 42 $ (1 ) $ — $ 41 $ 130 $ — $ — $ 130 _______ (a) PHI excludes cash of $12 million and $19 million at December 31, 2017 and 2016 and includes long term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $4 million and $9 million at December 31, 2017 and 2016 . DPL excludes cash of $2 million and $4 million at December 31, 2017 and 2016 . ACE excludes cash of $2 million and $3 million at December 31, 2017 and 2016 and includes long-term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : ComEd PECO BGE As of December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 98 $ — $ — $ 98 $ 228 $ — $ — $ 228 $ — $ — $ — $ — Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 6 — — 6 Total assets 98 — — 98 235 10 — 245 6 — — 6 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (b) — — (256 ) (256 ) — — — — — — — — Total liabilities — (8 ) (256 ) (264 ) — (11 ) — (11 ) — (5 ) — (5 ) Total net assets (liabilities) $ 98 $ (8 ) $ (256 ) $ (166 ) $ 235 $ (1 ) $ — $ 234 $ 6 $ (5 ) $ — $ 1 ComEd PECO BGE As of December 31, 2016 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 20 $ — $ — $ 20 $ 45 $ — $ — $ 45 $ 36 $ — $ — $ 36 Rabbi trust investments Mutual funds — — — — 7 — — 7 4 — — 4 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal — — — — 7 10 — 17 4 — — 4 Total assets 20 — — 20 52 10 — 62 40 — — 40 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (b) — — (258 ) (258 ) — — — — — — — — Total liabilities — (8 ) (258 ) (266 ) — (11 ) — (11 ) — (4 ) — (4 ) Total net assets (liabilities) $ 20 $ (8 ) $ (258 ) $ (246 ) $ 52 $ (1 ) $ — $ 51 $ 40 $ (4 ) $ — $ 36 __________ (a) ComEd excludes cash of $45 million and $36 million at December 31, 2017 and 2016 and restricted cash of $2 million at December 31, 2016 and includes long-term restricted cash of $62 million at December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $47 million and $22 million at December 31, 2017 and 2016 . BGE excludes cash of $17 million and $13 million at December 31, 2017 and 2016 and restricted cash of $1 million at December 31, 2017 and includes long-term restricted cash of $2 million at December 31, 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) The Level 3 balance consists of the current and noncurrent liability of $21 million and $235 million , respectively, at December 31, 2017 , and $19 million and $239 million , respectively, at December 31, 2016 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers. The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2017 and 2016 : Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 168 $ — $ — $ — $ 168 $ 656 $ — $ — $ — $ 656 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total NDT fund investments Cash equivalents (b) 135 85 — — 220 135 85 — — 220 Equities 4,163 915 — 2,176 7,254 4,163 915 — 2,176 7,254 Fixed income Corporate debt — 1,614 251 — 1,865 — 1,614 251 — 1,865 U.S. Treasury and agencies 1,917 52 — — 1,969 1,917 52 — — 1,969 Foreign governments — 82 — — 82 — 82 — — 82 State and municipal debt — 263 — — 263 — 263 — — 263 Other (c) — 47 — 510 557 — 47 — 510 557 Fixed income subtotal 1,917 2,058 251 510 4,736 1,917 2,058 251 510 4,736 Middle market lending — — 397 131 528 — — 397 131 528 Private equity — — — 222 222 — — — 222 222 Real estate — — — 471 471 — — — 471 471 NDT fund investments subtotal (d) 6,215 3,058 648 3,510 13,431 6,215 3,058 648 3,510 13,431 Pledged assets for Zion Station decommissioning Cash equivalents 2 — — — 2 2 — — — 2 Equities — 1 — — 1 — 1 — — 1 Middle market lending — — 12 24 36 — — 12 24 36 Pledged assets for Zion Station decommissioning subtotal 2 1 12 24 39 2 1 12 24 39 Rabbi trust investments Cash equivalents 5 — — — 5 77 — — — 77 Mutual funds 23 — — — 23 58 — — — 58 Fixed income — — — — — — 12 — — 12 Life insurance contracts — 22 — — 22 — 71 22 — 93 Rabbi trust investments subtotal 28 22 — — 50 135 83 22 — 240 Commodity derivative assets Economic hedges 557 2,378 1,290 — 4,225 557 2,378 1,290 — 4,225 Proprietary trading 2 31 35 — 68 2 31 35 — 68 Effect of netting and allocation of (e)(f) (585 ) (1,769 ) (635 ) — (2,989 ) (585 ) (1,769 ) (635 ) — (2,989 ) Commodity derivative assets subtotal (26 ) 640 690 — 1,304 (26 ) 640 690 — 1,304 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 3 — — 3 — 6 — — 6 Economic hedges — 10 — — 10 — 10 — — 10 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of (e)(f) 650 2,089 716 — 3,455 651 2,089 716 — 3,456 Commodity derivative liabilities subtotal (64 ) (179 ) (138 ) — (381 ) (64 ) (179 ) (394 ) — (637 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (2 ) — — (2 ) — (2 ) — — (2 ) Economic hedges (1 ) (8 ) — — (9 ) (1 ) (8 ) — — (9 ) Effect of netting and allocation of collateral 2 5 — — 7 2 5 — — 7 Interest rate and foreign currency derivative liabilities subtotal 1 (5 ) — — (4 ) 1 (5 ) — — (4 ) Deferred compensation obligation — (38 ) — — (38 ) — (145 ) — — (145 ) Total liabilities (63 ) (222 ) (138 ) — (423 ) (63 ) (329 ) (394 ) — (786 ) Total net assets $ 6,322 $ 3,507 $ 1,249 $ 3,534 $ 14,612 $ 6,917 $ 3,464 $ 1,015 $ 3,534 $ 14,930 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Assets Cash equivalents (a) $ 39 $ — $ — $ — $ 39 $ 373 $ — $ — $ — $ 373 NDT fund investments Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Cash equivalents (b) 110 19 — — 129 110 19 — — 129 Equities 3,551 452 — 2,011 6,014 3,551 452 — 2,011 6,014 Fixed income Corporate debt — 1,554 250 — 1,804 — 1,554 250 — 1,804 U.S. Treasury and agencies 1,291 29 — — 1,320 1,291 29 — — 1,320 Foreign governments — 37 — — 37 — 37 — — 37 State and municipal debt — 264 — — 264 — 264 — — 264 Other (c) — 59 — 493 552 — 59 — 493 552 Fixed income subtotal 1,291 1,943 250 493 3,977 1,291 1,943 250 493 3,977 Middle market lending — — 427 71 498 — — 427 71 498 Private equity — — — 148 148 — — — 148 148 Real estate — — — 326 326 — — — 326 326 NDT fund investments subtotal (d) 4,952 2,414 677 3,049 11,092 4,952 2,414 677 3,049 11,092 Pledged assets for Zion Station decommissioning Cash equivalents 11 — — — 11 11 — — — 11 Equities — 2 — — 2 — 2 — — 2 Fixed Income - U.S. Treasury and agencies 16 1 — — 17 16 1 — — 17 Middle market lending — — 19 64 83 — — 19 64 83 Pledged assets for Zion Station decommissioning subtotal 27 3 19 64 113 27 3 19 64 113 Rabbi trust investments Cash equivalents 2 — — — 2 74 — — — 74 Mutual funds 19 — — — 19 50 — — — 50 Fixed income — — — — — — 16 — — 16 Life insurance contracts — 18 — — 18 — 64 20 — 84 Rabbi trust investments subtotal 21 18 — — 39 124 80 20 — 224 Commodity derivative assets Economic hedges 1,356 2,505 1,229 — 5,090 1,358 2,505 1,229 — 5,092 Proprietary trading 3 50 23 — 76 3 50 23 — 76 Effect of netting and allocation of (e)(f) (1,162 ) (2,142 ) (481 ) — (3,785 ) (1,164 ) (2,142 ) (481 ) — (3,787 ) Commodity derivative assets subtotal 197 413 771 — 1,381 197 413 771 — 1,381 Generation Exelon As of December 31, 2016 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — 16 — — 16 Economic hedges — 28 — — 28 — 28 — — 28 Proprietary trading 3 2 — — 5 3 2 — — 5 Effect of netting and allocation of collateral (2 ) (19 ) — — (21 ) (2 ) (19 ) — — (21 ) Interest rate and foreign currency derivative assets subtotal 1 11 — — 12 1 27 — — 28 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,237 2,859 1,509 3,113 12,718 5,674 2,937 1,529 3,113 13,253 Liabilities Commodity derivative liabilities Economic hedges (1,267 ) (2,378 ) (794 ) — (4,439 ) (1,267 ) (2,378 ) (1,052 ) — (4,697 ) Proprietary trading (3 ) (50 ) (26 ) — (79 ) (3 ) (50 ) (26 ) — (79 ) Effect of netting and allocation of (e)(f) 1,233 2,339 542 — 4,114 1,233 2,339 542 — 4,114 Commodity derivative liabilities subtotal (37 ) (89 ) (278 ) — (404 ) (37 ) (89 ) (536 ) — (662 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — (10 ) — — (10 ) — (10 ) — — (10 ) Economic hedges — (21 ) — — (21 ) — (21 ) — — (21 ) Proprietary trading (4 ) — — — (4 ) (4 ) — — — (4 ) Effect of netting and allocation of collateral 4 19 — — 23 4 19 — — 23 Interest rate and foreign currency derivative liabilities subtotal — (12 ) — — (12 ) — (12 ) — — (12 ) Deferred compensation obligation — (34 ) — — (34 ) — (136 ) — — (136 ) Total liabilities (37 ) (135 ) (278 ) — (450 ) (37 ) (237 ) (536 ) — (810 ) Total net assets $ 5,200 $ 2,724 $ 1,231 $ 3,113 $ 12,268 $ 5,637 $ 2,700 $ 993 $ 3,113 $ 12,443 __________ (a) Generation excludes cash of $259 million and $252 million at December 31, 2017 and 2016 and restricted cash of $127 million and $157 million at December 31, 2017 and 2016 . Exelon excludes cash of $389 million and $360 million at December 31, 2017 and 2016 and restricted cash of $145 million and $180 million at December 31, 2017 and 2016 and includes long-term restricted cash of $85 million and $25 million at December 31, 2017 and 2016 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $77 million and $29 million of cash received from outstanding repurchase agreements at December 31, 2017 and 2016 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of less than $1 million and $(2) million , which have a total notional amount of $811 million and $933 million at December 31, 2017 and 2016 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss. (d) Excludes net liabilities of $82 million and $31 million at December 31, 2017 and 2016 , respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less. (e) Collateral posted/(received) from counterparties totaled $65 million , $320 million and $81 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2017 . Collateral posted/(received) from counterparties totaled $71 million , $197 million and $61 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2016 .
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Text Block]	The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2017 and 2016 : Successor Generation ComEd PHI Exelon For the year ended December 31, 2017 NDT Fund Investments Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Total Balance as of January 1, 2017 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 Total realized / unrealized gains (losses) Included in net income 3 — (90 ) (a) 3 (84 ) — 3 — (81 ) Included in noncurrent payables to affiliates 6 — — — 6 — — (6 ) — Included in payable for Zion Station decommissioning — (8 ) — — (8 ) — — — (8 ) Included in regulatory assets/liabilities — — — — — 2 (b) — 6 8 Change in collateral — — 20 — 20 — — — 20 Purchases, sales, issuances and settlements Purchases 64 1 178 5 248 — — — 248 Sales — — (16 ) — (16 ) — — — (16 ) Issuances — — — — — — (1 ) — (1 ) Settlements (102 ) — (8 ) (c) — (110 ) — — — (110 ) Transfers into Level 3 — — (6 ) — (6 ) — — — (6 ) Transfers out of Level 3 — — (50 ) (11 ) (61 ) — — — (61 ) Other miscellaneous — — 31 (d) (2 ) 29 — — — 29 Balance as of December 31, 2017 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of December 31, 2017 $ 1 $ — $ 254 $ 3 $ 258 $ — $ 3 $ — $ 261 Successor Generation ComEd PHI (f) Exelon For the year ended December 31, 2016 NDT Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts Eliminated in Consolidation Total Balance as of January 1, 2016 $ 670 $ 22 $ 1,051 $ 33 $ 1,776 $ (247 ) $ — $ — $ 1,529 Included due to merger — — — — — — 20 — 20 Total realized / unrealized gains (losses) Included in net income 7 — (568 ) (a) 1 (560 ) — 3 — (557 ) Included in noncurrent payables to affiliates 16 — — — 16 — — (16 ) — Included in regulatory assets/liabilities — — — — — (11 ) (b) — 16 5 Change in collateral — — (141 ) — (141 ) — — — (141 ) Purchases, sales, issuances and settlements Purchases 143 2 342 (e) 7 494 — — — 494 Sales (1 ) (5 ) (9 ) — (15 ) — — — (15 ) Issuances — — — — — — (3 ) — (3 ) Settlements (144 ) — — — (144 ) — — — (144 ) Transfers into Level 3 — — 1 1 2 — — — 2 Transfers out of Level 3 (14 ) — (183 ) — (197 ) — — — (197 ) Balance as of December 31, 2016 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held as of December 31, 2016 $ 5 $ — $ 109 $ — $ 114 $ — $ 2 $ — $ 116 __________ (a) Includes a reduction for the reclassification of $352 million and $677 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2017 and 2016 , respectively. (b) Includes $18 million of decreases in fair value and an increase for realized losses due to settlements of $20 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2017 . Includes $29 million of decreases in fair value and an increase for realized losses due to settlements of $18 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2016 . (c) Exelon includes the settlement value for any open contracts that were net settled prior to their scheduled maturity within this line item. (d) As a result of the bankruptcy filing for EGTP on November 7, 2017, the net mark-to-market commodity contracts were deconsolidated from Exelon's and Generation's consolidated financial statements. (e) Includes $168 million of fair value from contracts acquired as a result of portfolio acquisitions. (f) Successor period represents activity from March 24, 2016 to December 31, 2016 . See tables below for PHI's predecessor periods, as well as activity for Pepco for the years ended December 31, 2017 and 2016 . Predecessor January 1, 2016 to March 23, 2016 PHI Preferred Stock Life Insurance Contracts Beginning Balance $ 18 $ 19 Total realized / unrealized (losses) gains Included in net income (18 ) 1 Ending Balance $ — $ 20 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities for the period $ — $ 1 Life Insurance Contracts For the year ended December 31, Pepco 2017 2016 Balance as of January 1 $ 20 $ 19 Total realized / unrealized gains (losses) Included in net income 3 3 Purchases, sales, issuances and settlements Issuances (1 ) (3 ) Balance as of December 31 $ 22 $ 19 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities for the period $ 3 $ 3
Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis	The following tables present the income statement classification of the total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis during the years ended December 31, 2017 and 2016 : Successor Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Operating and Operating Revenues Purchased Power and Fuel Operating and Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2017 $ 28 $ (126 ) $ 6 $ 3 $ 28 $ (126 ) $ 3 $ 6 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2017 290 (36 ) 4 3 290 (36 ) 3 4 Successor Generation PHI (b) Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the year ended December 31, 2016 $ (477 ) $ (91 ) $ 7 $ 3 $ (477 ) $ (91 ) $ 10 Change in the unrealized gains (losses) relating to assets and liabilities held for the year ended December 31, 2016 154 (45 ) 5 2 154 (45 ) 7 Predecessor PHI Pepco January 1, 2016 to March 23, 2016 December 31, 2017 December 31, 2017 December 31, 2016 Other, net (a) Operating and Maintenance Other, net (a) Total (losses) gains included in net income $ (17 ) $ 3 $ — $ 3 Change in the unrealized gains (losses) relating to assets and liabilities held 1 3 — 3 __________ (a) Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco. (b) Successor period represents activity from March 24, 2016 to December 31, 2016 . See the subsequent table for PHI's predecessor periods, as well as activity for Pepco for the year ended December 31, 2017 and 2016 .
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis, valuation technique	The following tables present the significant inputs to the forward curve used to value these positions: Type of trade Fair Value at December 31, 2017 Valuation Technique Unobservable Input Range Mark-to-market derivatives—Economic hedges (Exelon and Generation) (a)(b) $ 445 Discounted Cash Flow Forward power price $3 - $124 Forward gas price $1.27 - $12.80 Option Model Volatility percentage 11% - 139% Mark-to-market derivatives—Proprietary trading (Exelon and Generation) (a)(b) $ 26 Discounted Cash Flow Forward power price $14 - $94 Mark-to-market derivatives (Exelon and ComEd) $ (256 ) Discounted Cash Flow Forward heat rate (c) 9x - 10x Marketability reserve 4% - 8% Renewable factor 88% - 120% ______ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) The fair values do not include cash collateral posted on level three positions of $81 million as of December 31, 2017 . (c) Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery. Type of trade Fair Value at December 31, 2016 Valuation Technique Unobservable Input Range Mark-to-market derivatives—Economic hedges (Exelon and Generation) (a)(b) $ 435 Discounted Cash Flow Forward power price $11 - $130 Forward gas price $1.72 - $9.20 Option Model Volatility percentage 8% - 173% Mark-to-market derivatives— Proprietary trading (Exelon and Generation) (a)(b) $ (3 ) Discounted Cash Flow Forward power price $19 - $79 Mark-to-market derivatives (Exelon and ComEd) $ (258 ) Discounted Cash Flow Forward heat rate (c) 8x - 9x Marketability reserve 3% - 8% Renewable factor 89% - 121% __________ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) The fair values do not include cash collateral posted on level three positions of $61 million as of December 31, 2016

Derivative Financial Instrume49

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the derivative fair value	Below is a summary of the interest rate and foreign exchange hedge balances as of December 31, 2017 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary Collateral and Netting (a) Subtotal Derivatives Total Mark-to-market derivative assets (current assets) $ — $ 10 $ — $ (7 ) $ 3 $ — $ 3 Mark-to-market derivative assets (noncurrent assets) 3 — — — 3 3 6 Total mark-to-market derivative assets 3 10 — (7 ) 6 3 9 Mark-to-market derivative liabilities (current liabilities) (2 ) (7 ) — 7 (2 ) — (2 ) Mark-to-market derivative liabilities (noncurrent liabilities) — (2 ) — — (2 ) — (2 ) Total mark-to-market derivative liabilities (2 ) (9 ) — 7 (4 ) — (4 ) Total mark-to-market derivative net assets (liabilities) $ 1 $ 1 $ — $ — $ 2 $ 3 $ 5 __________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above. The following table provides a summary of the interest rate and foreign exchange hedge balances recorded by the Registrants as of December 31, 2016 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Proprietary (a) Collateral and Netting (b) Subtotal Derivatives Total Mark-to-market derivative assets (current assets) $ — $ 17 $ 4 $ (13 ) $ 8 $ — $ 8 Mark-to-market derivative assets (noncurrent assets) — 11 1 (8 ) 4 16 20 Total mark-to-market derivative assets — 28 5 (21 ) 12 16 28 Mark-to-market derivative liabilities (current liabilities) (7 ) (13 ) (2 ) 14 (8 ) — (8 ) Mark-to-market derivative liabilities (noncurrent liabilities) (3 ) (8 ) (2 ) 9 (4 ) — (4 ) Total mark-to-market derivative liabilities (10 ) (21 ) (4 ) 23 (12 ) — (12 ) Total mark-to-market derivative net assets (liabilities) $ (10 ) $ 7 $ 1 $ 2 $ — $ 16 $ 16 __________ (a) Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates. (b) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above. The following table provides a summary of the derivative fair value balances related to commodity contracts recorded by the Registrants as of December 31, 2017 : Successor Generation ComEd DPL PHI Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,061 $ 56 $ (2,144 ) $ 973 $ — $ — $ — $ — $ — $ 973 Mark-to-market derivative assets (noncurrent assets) 1,164 12 (845 ) 331 — — — — — 331 Total mark-to-market derivative assets 4,225 68 (2,989 ) 1,304 — — — — — 1,304 Mark-to-market derivative liabilities (current liabilities) (2,646 ) (43 ) 2,480 (209 ) (21 ) (1 ) 1 — — (230 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,137 ) (10 ) 975 (172 ) (235 ) — — — — (407 ) Total mark-to-market derivative liabilities (3,783 ) (53 ) 3,455 (381 ) (256 ) (1 ) 1 — — (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ (1 ) $ 1 $ — $ — $ 667 __________ (a) Exelon, Generation, PHI and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $169 million and $53 million , respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(117) million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances related to commodity contracts recorded by the Registrants as of December 31, 2016 : Successor Generation ComEd DPL PHI Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,623 $ 55 $ (2,769 ) $ 909 $ — $ 2 $ (2 ) $ — $ — $ 909 Mark-to-market derivative assets (noncurrent assets) 1,467 21 (1,016 ) 472 — — — — — 472 Total mark-to-market derivative assets 5,090 76 (3,785 ) 1,381 — 2 (2 ) — — 1,381 Mark-to-market derivative liabilities (current liabilities) (3,165 ) (54 ) 2,964 (255 ) (19 ) — — — — (274 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,274 ) (25 ) 1,150 (149 ) (239 ) — — — — (388 ) Total mark-to-market derivative liabilities (4,439 ) (79 ) 4,114 (404 ) (258 ) — — — — (662 ) Total mark-to-market derivative net assets (liabilities) $ 651 $ (3 ) $ 329 $ 977 $ (258 ) $ 2 $ (2 ) $ — $ — $ 719 __________ (a) Exelon, Generation, PHI and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, and letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $100 million and $72 million , respectively, and current and noncurrent liabilities are shown net of collateral of $95 million and $62 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $329 million at December 31, 2016 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(158) million represents variation margin on the exchanges
Derivative Instruments, Gain (Loss)	For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Operating revenues $ (126 ) $ (490 ) $ 196 Purchased power and fuel (43 ) 459 54 Total Exelon and Generation $ (169 ) $ (31 ) $ 250 Exelon and Generation include the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps as follows: Year Ended December 31, Income Statement Location 2017 2016 2015 2017 2016 2015 Gain (Loss) on Swaps Gain (Loss) on Borrowings Generation Interest expense (a) $ — $ — $ (1 ) $ — $ — $ — Exelon Interest expense (13 ) (9 ) 3 28 23 14 __________ (a) For the year ended December 31, 2015 , the loss on Generation swaps included $(1) million realized in earnings with an immaterial amount excluded from hedge effectiveness testing. For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax mark-to-market gains (losses) in the Consolidated Statements of Operations and Comprehensive Income and are included in “Net fair value changes related to derivatives” in Exelon’s and Generation’s Consolidated Statements of Cash Flows. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Generation Operating Revenues $ (6 ) $ (10 ) $ 7 Generation Interest Expense (3 ) — — Total Generation $ (9 ) $ (10 ) $ 7 For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Exelon Operating Revenues $ (6 ) $ (10 ) $ 7 Exelon Interest Expense (3 ) — 100 Total Exelon $ (9 ) $ (10 ) $ 107
The activity of accumulated OCI related to cash flow hedges	Total Cash Flow Hedge AOCI Activity, Net of Income Tax Generation Exelon For the Year Ended December 31, 2017 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2016 $ (19 ) $ (17 ) Effective portion of changes in fair value (1 ) (1 ) Reclassifications from AOCI to net income Interest expense 4 (a) 4 (a) AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Total Cash Flow Hedge AOCI Activity, Net of Income Tax Generation Exelon For the Year Ended December 31, 2016 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2015 $ (21 ) $ (19 ) Effective portion of changes in fair value (6 ) (6 ) Reclassifications from AOCI to net income Interest expense 8 (b) 8 (b) AOCI derivative loss at December 31, 2016 $ (19 ) $ (17 ) __________ (a) Amount is net of related income tax expense of $1 million for the year ended December 31, 2017 . (b) Amount is net of related income tax expense of $5 million for the year ended December 31, 2016 .
Change in fair value of derivative contracts	For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Operating revenues $ 6 $ 2 $ (6 ) For the years ended December 31, 2017 , 2016 and 2015 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses). For the Years Ended December 31, 2017 2016 2015 Income Statement Location Gain (Loss) Operating revenues $ (1 ) $ (1 ) $ (2 )
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	The table below provides the notional amounts of fixed-to-floating hedges outstanding held by Exelon at December 31, 2017 and 2016 . For the Years Ended December 31, 2017 2016 Fixed-to-floating hedges $ 800 $ 800 The table below provides the notional amounts of floating-to-fixed hedges outstanding held by Exelon and Generation at December 31, 2017 and 2016 . For the Years Ended December 31, 2017 2016 Floating-to-fixed hedges $ 636 $ 659 The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 and 2016 related to foreign currency exchange rate swaps that are marked-to-market to manage the exposure associated with international purchases of commodities in currencies other than U.S. dollars. For the Years Ended December 31, 2017 2016 Foreign currency exchange rate swaps $ 94 $ 85
Disclosure of Credit Derivatives [Table Text Block]	The figures in the tables below exclude credit risk exposure from individual retail counterparties, nuclear fuel procurement contracts and exposure through RTOs, ISOs, NYMEX, ICE, NASDAQ, NGX and Nodal commodity exchanges. Additionally, the figures in the tables below exclude exposures with affiliates, including net receivables with ComEd, PECO, BGE, Pepco, DPL and ACE of $28 million , $22 million , $24 million , $36 million , $12 million and $6 million as of December 31, 2017 , respectively. Rating as of December 31, 2017 Total Exposure Before Credit Collateral Credit Collateral (a) Net Exposure Number of Counterparties Greater than 10% of Net Exposure Net Exposure of Counterparties Greater than 10% of Net Exposure Investment grade $ 738 $ 4 $ 734 1 $ 244 Non-investment grade 90 12 78 — — No external ratings Internally rated — investment grade 253 — 253 — — Internally rated — non-investment grade 83 11 72 — — Total $ 1,164 $ 27 $ 1,137 1 $ 244 Net Credit Exposure by Type of Counterparty December 31, 2017 Financial institutions $ 41 Investor-owned utilities, marketers, power producers 558 Energy cooperatives and municipalities 452 Other 86 Total $ 1,137 __________ (a) As of December 31, 2017 , credit collateral held from counterparties where Generation had credit exposure included $8 million of cash and $19 million of letters of credit. The credit collateral does not include non-liquid collateral.
Fair Value, Concentration of Risk [Table Text Block]	The aggregate fair value of all derivative instruments with credit-risk-related contingent features in a liability position that are not fully collateralized (excluding transactions on the exchanges that are fully collateralized) is detailed in the table below: For the Years Ended December 31, Credit-Risk Related Contingent Feature 2017 2016 Gross fair value of derivative contracts containing this feature (a) $ (926 ) $ (960 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 577 627 Net fair value of derivative contracts containing this feature (c) $ (349 ) $ (333 ) __________ (a) Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features ignoring the effects of master netting agreements. (b) Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral. (c) Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Short-term Debt	The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2017 , 2016 and 2015 . Exelon 2017 2016 2015 Average borrowings $ 823 $ 1,125 $ 499 Maximum borrowings outstanding 2,147 3,076 739 Average interest rates, computed on a daily basis 1.32 % 0.88 % 0.53 % Average interest rates, at December 31 1.24 % 1.12 % 0.88 % Generation 2017 2016 2015 Average borrowings $ 405 $ 536 $ 1 Maximum borrowings outstanding 1,455 1,735 50 Average interest rates, computed on a daily basis 1.23 % 0.94 % 0.49 % Average interest rates, at December 31 1.23 % 1.14 % N/A ComEd 2017 2016 2015 Average borrowings $ 200 $ 256 $ 461 Maximum borrowings outstanding 470 755 684 Average interest rates, computed on a daily basis 1.24 % 0.77 % 0.53 % Average interest rates, at December 31 1.24 % N/A 0.89 % PECO 2017 2016 2015 Average borrowings $ 2 $ — $ — Maximum borrowings outstanding 60 — — Average interest rates, computed on a daily basis 1.13 % N/A N/A Average interest rates, at December 31 1.13 % N/A N/A BGE 2017 2016 2015 Average borrowings $ 54 $ 143 $ 37 Maximum borrowings outstanding 165 369 210 Average interest rates, computed on a daily basis 1.28 % 0.77 % 0.48 % Average interest rates, computed at December 31 1.28 % 0.95 % 0.87 % PHI Corporate Successor Predecessor 2017 2016 2015 Average borrowings N/A $ 153 $ 444 Maximum borrowings outstanding N/A 559 784 Average interest rates, computed on a daily basis N/A 1.03 % 0.90 % Average interest rates, computed at December 31 N/A N/A 1.22 % Pepco 2017 2016 2015 Average borrowings $ 51 $ 4 $ 34 Maximum borrowings outstanding 197 73 190 Average interest rates, computed on a daily basis 1.06 % 0.71 % 0.44 % Average interest rates, computed at December 31 1.06 % 0.90 % 0.68 % DPL 2017 2016 2015 Average borrowings $ 40 $ 33 $ 81 Maximum borrowings outstanding 216 116 179 Average interest rates, computed on a daily basis 1.48 % 0.68 % 0.47 % Average interest rates, computed at December 31 1.48 % N/A 0.79 % ACE 2017 2016 2015 Average borrowings $ 30 $ — $ 175 Maximum borrowings outstanding 133 5 253 Average interest rates, computed on a daily basis 1.43 % 0.65 % 0.46 % Average interest rates, computed at December 31 1.43 % N/A 0.65 % December 31, 2017 and 2016 : Maximum Program Size at December 31, Outstanding Commercial Paper at December 31, Average Interest Rate on Commercial Paper Borrowings for the Year Ended December 31, Commercial Paper Issuer 2017 (a)(b)(c) 2016 (a)(b)(c) 2017 2016 2017 2016 Exelon Corporate $ 600 $ 600 $ — $ — 1.16 % 0.70 % Generation 5,300 5,300 — 620 1.23 % 0.94 % ComEd 1,000 1,000 — — 1.24 % 0.77 % PECO 600 600 — — 1.13 % N/A BGE 600 600 77 45 1.28 % 0.77 % Pepco 500 500 26 23 1.06 % 0.71 % DPL 500 500 216 — 1.48 % 0.68 % ACE 350 350 108 — 1.43 % 0.65 % Total $ 9,450 $ 9,450 $ 427 $ 688 __________ (a) Excludes $480 million and $500 million in bilateral credit facilities that do not back Generation's commercial paper program at December 31, 2017 and 2016 , respectively. (b) Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $34 million , $34 million , $5 million , $2 million , $2 million and $2 million , respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.
Schedule of Line of Credit Facilities	At December 31, 2017 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2017 Borrower Facility Type Aggregate Bank (a)(b) Facility Draws Outstanding Letters of Credit (c) Actual To Support Additional Commercial (b)(d) Exelon Corporate Syndicated Revolver $ 600 $ — $ 45 $ 555 $ 555 Generation Syndicated Revolver 5,300 — 868 4,432 4,432 Generation Bilaterals 480 — 231 249 — ComEd Syndicated Revolver 1,000 — 2 998 998 PECO Syndicated Revolver 600 — 1 599 599 BGE Syndicated Revolver 600 — — 600 523 Pepco Syndicated Revolver 300 — — 300 274 DPL Syndicated Revolver 300 — — 300 84 ACE Syndicated Revolver 300 — — 300 192 Total $ 9,480 $ — $ 1,147 $ 8,333 $ 7,657 __________ (a) Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $34 million , $34 million , $5 million , $2 million , $2 million and $2 million , respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively. (b) Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility. (c) Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Wind. (d) Excludes $480 million in bilateral credit facilities that do not back Generation’s commercial paper program.
Schedule Of Credit Agreement Covenants	The following table summarizes the minimum thresholds reflected in the credit agreements for the year ended December 31, 2017 : Exelon Generation ComEd PECO BGE Pepco DPL ACE Credit agreement threshold 2.50 to 1 3.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 2.00 to 1 At December 31, 2017 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Pepco DPL ACE Interest coverage ratio 6.34 9.02 11.68 7.99 10.50 6.35 8.69 5.57
Schedule of Long-term Debt Instruments	BGE Maturity Date December 31, Rates 2017 2016 Long-term debt Rate stabilization bonds 5.82 % 2017 $ — $ 41 Unsecured notes 2.40 % - 6.35 % 2021 - 2047 2,600 2,300 Total long-term debt 2,600 2,341 Unamortized debt discount and premium, net (6 ) (4 ) Unamortized debt issuance costs (17 ) (15 ) Long-term debt due within one year — (41 ) Long-term debt $ 2,577 $ 2,281 Long-term debt to financing trusts (a) Subordinated debentures to BGE Capital Trust II 6.20 % 2043 $ — $ 258 Total long-term debt to financing trusts — 258 Unamortized debt issuance costs — (6 ) Long-term debt to financing trusts $ — $ 252 __________ (a) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within BGE’s Consolidated Balance Sheets. On August 28, 2017, BGE redeemed all of the outstanding shares of BGE Capital Trust II 6.20% Preferred Securities (“Securities”), pursuant to the optional redemption provisions of the Indenture under which the Securities were issued. The redemption price per share was $25.19, which equaled the stated value per share plus accrued and unpaid dividends to, but excluding, the redemption date. No dividends on the Securities redeemed were accrued on or after the redemption date, nor did any interest accrue on amounts held to pay the redemption price. DPL Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.50 % - 4.15 % 2023 - 2045 $ 1,171 $ 1,196 Unsecured Tax-Exempt Bonds 5.40 % 2024 - 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % 2018 - 2027 26 40 Total long-term debt 1,309 1,348 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (11 ) (10 ) Long-term debt due within one year (83 ) (119 ) Long-term debt $ 1,217 $ 1,221 ComEd Maturity Date December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 2.15 % - 6.45 % 2018 - 2047 $ 7,529 $ 6,954 Notes payable and other (b) 6.95 % - 7.49 % 2018 - 2053 147 147 Total long-term debt 7,676 7,101 Unamortized debt discount and premium, net (23 ) (22 ) Unamortized debt issuance costs (52 ) (46 ) Long-term debt due within one year (840 ) (425 ) Long-term debt $ 6,761 $ 6,608 Long-term debt to financing trust (c) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Total long-term debt to financing trusts 206 206 Unamortized debt issuance costs (1 ) (1 ) Long-term debt to financing trusts $ 205 $ 205 __________ (a) Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture. (b) Includes ComEd’s capital lease obligations of $8 million at both December 31, 2017 and 2016 , respectively. Lease payments of less than $1 million annually will be made from 2018 through expiration at 2053. (c) Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets. The following tables present the outstanding long-term debt at the Registrants as of December 31, 2017 and 2016 : Exelon Maturity Date December 31, Rates 2017 2016 Long-term debt Rate stabilization bonds 5.82 % 2017 $ — $ 41 First mortgage bonds (a) 1.70 % - 7.90 % 2018 - 2047 15,197 14,123 Senior unsecured notes 2.45 % - 7.60 % 2019 - 2046 11,285 11,868 Unsecured notes 2.40 % - 6.35 % 2021 - 2047 2,600 2,300 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 82 105 Notes payable and other (b)(c) 2.61 % - 8.88 % 2018 - 2053 405 576 Junior subordinated notes 3.50 % 2022 1,150 1,150 Contract payment - junior subordinated notes 2.50 % 2017 — 19 Long-term software licensing agreement 3.95 % 2024 79 103 Unsecured Tax-Exempt Bonds 5.40 % — 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % — 2018 - 2027 26 40 Transition bonds 5.05 % - 5.55 % — 2020 - 2023 90 124 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,331 1,400 Variable rates 3.18 % - 4.00 % 2019 - 2024 865 915 Total long-term debt 33,657 33,311 Unamortized debt discount and premium, net (57 ) (68 ) Unamortized debt issuance costs (201 ) (200 ) Fair value adjustment 865 962 Long-term debt due within one year (2,088 ) (2,430 ) Long-term debt $ 32,176 $ 31,575 Long-term debt to financing trusts (d) Subordinated debentures to ComEd Financing III 6.35 % 2033 $ 206 $ 206 Subordinated debentures to PECO Trust III 7.38 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Subordinated debentures to BGE Capital Trust II 6.20 % 2043 — 258 Total long-term debt to financing trusts 390 648 Unamortized debt issuance costs (1 ) (7 ) Long-term debt to financing trusts $ 389 $ 641 __________ (a) Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s, Pepco's, DPL's and ACE's assets are subject to the liens of their respective mortgage indentures. (b) Includes capital lease obligations of $53 million and $69 million at December 31, 2017 and 2016 , respectively. Lease payments of $18 million , $20 million , $5 million , $1 million , $1 million and $8 million will be made in 2018 , 2019 , 2020 , 2021 , 2022 and thereafter, respectively. (c) Includes financing related to Albany Green Energy, LLC (AGE). During the third quarter of 2017, Generation retired $228 million of its outstanding debt balance. As of December 31, 2016, $198 million was outstanding. (d) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. PECO Maturity Date December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2018 - 2047 $ 2,925 $ 2,600 Total long-term debt 2,925 2,600 Unamortized debt discount and premium, net (5 ) (5 ) Unamortized debt issuance costs (17 ) (15 ) Long-term debt due within one year (500 ) — Long-term debt $ 2,403 $ 2,580 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 7.38 % 2028 $ 81 $ 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Long-term debt to financing trusts $ 184 $ 184 __________ (a) Substantially all of PECO’s assets are subject to the lien of its mortgage indenture. (b) Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets. PHI Successor Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2018 - 2045 $ 4,743 $ 4,569 Senior unsecured notes 7.45 % 2017 - 2032 185 266 Unsecured Tax-Exempt Bonds 5.40 % 2031 112 112 Medium-Terms Notes (unsecured) 6.81 % - 7.72 % 2018 - 2027 26 40 Transition bonds (b) 5.05 % - 5.55 % 2020 - 2023 90 124 Notes payable and other (c) 6.20 % - 8.88 % 2018 - 2022 33 46 Total long-term debt 5,189 5,157 Unamortized debt discount and premium, net 5 1 Unamortized debt issuance costs (6 ) (2 ) Fair value adjustment 686 742 Long-term debt due within one year (396 ) (253 ) Long-term debt $ 5,478 $ 5,645 __________ (a) Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture. (b) Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets. (c) Includes Pepco's capital lease obligations of $27 million and $39 million at December 31, 2017 and 2016 , respectively. ACE Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.38 % - 7.75 % 2018 - 2036 $ 1,037 $ 1,038 Transition bonds (b) 5.05 % - 5.55 % 2020 - 2023 90 124 Total long-term debt 1,127 1,162 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (5 ) (6 ) Long-term debt due within one year (281 ) (35 ) Long-term debt $ 840 $ 1,120 __________ (a) Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture. (b) Maturities of ACE's Transition Bonds outstanding at December 31, 2017 are $31 million in 2018, $18 million in 2019, $20 million in 2020 and $21 million in 2021 Generation Maturity Date December 31, Rates 2017 2016 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2019 - 2042 $ 6,019 $ 5,971 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % - 3.35 % 2018 - 2020 82 105 Notes payable and other (a)(b) 2.61 % - 8.88 % 2018 - 2019 223 382 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,331 1,400 Variable rates 3.18 % - 4.00 % 2019 - 2024 865 915 Total long-term debt 8,955 9,208 Unamortized debt discount and premium, net (8 ) (17 ) Unamortized debt issuance costs (60 ) (65 ) Fair value adjustment 103 115 Long-term debt due within one year (346 ) (1,117 ) Long-term debt $ 8,644 $ 8,124 __________ (a) Includes Generation’s capital lease obligations of $18 million and $22 million at December 31, 2017 and 2016 , respectively. Generation will make lease payments of $5 million , $6 million , $5 million , $1 million and $1 million in 2018 , 2019 , 2020 , 2021 and 2022 respectively. Pepco Maturity December 31, Rates 2017 2016 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2043 $ 2,535 $ 2,335 Notes payable and other (b) 6.20 % - 8.88 % 2018 - 2022 35 46 Total long-term debt 2,570 2,381 Unamortized debt discount and premium, net 2 (2 ) Unamortized debt issuance costs (32 ) (30 ) Long-term debt due within one year (19 ) (16 ) Long-term debt $ 2,521 $ 2,333
Schedule of Maturities of Long-term Debt	Long-term debt maturities at Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE in the periods 2018 through 2022 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2018 $ 2,075 $ 346 $ 840 $ 500 $ — $ 383 $ 19 $ 83 $ 281 2019 959 615 300 — — 44 14 12 18 2020 3,564 2,144 500 — — 20 — — 20 2021 1,513 1 350 300 300 262 2 — 260 2022 3,084 1,024 — 350 250 310 310 — — Thereafter 22,852 (a) 4,825 5,892 (b) 1,959 (c) 2,050 4,170 2,225 1,214 548 Total $ 34,047 $ 8,955 $ 7,882 $ 3,109 $ 2,600 $ 5,189 $ 2,570 $ 1,309 $ 1,127 __________ (a) Includes $390 million due to ComEd and PECO financing trusts. (b) Includes $206 million due to ComEd financing trust. (c) Includes $184 million due to PECO financing trusts.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
ScheduleOfRemeasurementsOfDeferredIncomeTaxesDueToTaxReform [Table Text Block]	The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: Successor Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Decrease to Deferred Income Tax Liability Balances $8,624 $1,895 $2,819 $1,407 $1,120 $1,944 $968 $540 $456 Successor Exelon Generation ComEd PECO (c) BGE PHI Pepco DPL ACE Net Regulatory Liability Recorded (a) $7,315 N/A $2,818 $1,394 $1,124 $1,979 $976 $545 $458 Successor Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Deferred Income Tax Benefit/(Expense) Recorded $1,309 $1,895 $1 $13 $(4) $(35) $(8) $(5) $(2) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information.
ScheduleOfCategorizationOfNetRegulatoryLiabilitiesDueToTaxReform [Table Text Block]	The table below sets forth the Registrants’ estimated categorization of their net regulatory liabilities as of December 31, 2017. The amounts in the table below are shown on an after-tax basis reflecting future net cash outflows after taking into consideration the income tax benefits associated with the ultimate settlement with customers. Successor Exelon ComEd PECO (a) BGE PHI PEPCO DPL ACE Subject to IRS Normalization Rules $3,040 $1,400 $533 $459 $648 $299 $195 $153 Subject to Rate Regulator Determination 1,694 573 43 324 754 391 194 170 Net Regulatory Liabilities $4,734 $1,973 $576 $783 $1,402 $690 $389 $ 323 _________ (a) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information.
Schedule of Components of Income Tax Expense (Benefit)	Income tax expense (benefit) from continuing operations is comprised of the following components: For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 194 $ 584 $ (191 ) $ 71 $ 74 $ (60 ) $ (20 ) $ (24 ) $ (12 ) Deferred (469 ) (2,003 ) 523 28 101 250 114 82 34 Investment tax credit amortization (25 ) (21 ) (2 ) — (1 ) (1 ) — — — State Current 14 65 (49 ) 14 (5 ) (4 ) (2 ) — — Deferred 161 — 136 (9 ) 49 32 13 13 4 Total $ (125 ) $ (1,375 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26 Successor Predecessor For the Year Ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Included in operations: Federal Current $ 60 $ 513 $ (135 ) $ 63 $ 51 $ (118 ) $ (88 ) $ (26 ) $ (281 ) $ — Deferred 607 (247 ) 379 72 88 136 97 22 283 10 Investment tax credit amortization (24 ) (20 ) (2 ) — (1 ) — — — (1 ) — State Current 39 45 (4 ) 9 5 7 1 — (11 ) — Deferred 79 (1 ) 63 5 31 16 12 — 13 7 Total $ 761 $ 290 $ 301 $ 149 $ 174 $ 41 $ 22 $ (4 ) $ 3 $ 17 For the Year Ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 407 $ 546 $ (80 ) $ 64 $ 25 $ 12 $ (54 ) $ (27 ) $ (2 ) Deferred 566 16 310 69 126 103 126 73 27 Investment tax credit amortization (22 ) (19 ) (2 ) — (1 ) (1 ) — — — State Current (86 ) (90 ) 7 (10 ) — 17 6 2 3 Deferred 208 49 45 20 39 32 24 1 5 Total $ 1,073 $ 502 $ 280 $ 143 $ 189 $ 163 $ 102 $ 49 $ 33 The following tables represent the net interest and penalties receivable (payable), including interest and penalties related to tax positions reflected in the Registrants’ Consolidated Balance Sheets. Successor Net interest receivable (payable) as of Exelon (a) Generation ComEd (a) PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 233 $ (3 ) $ 4 $ — $ — $ 2 $ — $ — $ — December 31, 2016 (507 ) 46 (384 ) 8 (1 ) 2 1 — 1 Successor Net penalties receivable (payable) as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ (17 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2016 (106 ) — (86 ) — — — — — — __________ (a) Change in balance attributable to Like-Kind Exchange interest payments, see Other Tax Matters for further discussion.
Effective Income Tax Rate Reconciliation	The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: For the Year Ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 2.3 3.0 5.7 0.6 5.4 4.8 3.2 5.4 5.6 Qualified nuclear decommissioning trust fund income 3.8 10.0 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.2 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (a) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.8 ) — — — — — — — Noncontrolling interests 0.1 0.3 — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.7 ) (1.3 ) — — — (9.5 ) (6.3 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.7 ) — — — — — — — Tax Cut and Jobs Act of 2017 (b) (33.1 ) (130.1 ) 0.1 (2.3 ) 0.9 6.4 2.7 2.5 1.6 Other 0.1 (0.4 ) 0.2 (0.1 ) 0.2 (0.1 ) (0.2 ) 0.1 (0.4 ) Effective income tax rate (3.3 )% (96.2 )% 42.4 % 19.3 % 41.5 % 37.5 % 33.9 % 37.0 % 25.2 % Successor Predecessor For the Year Ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL (c) ACE (c) PHI (c) PHI U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit (d) 3.3 3.3 5.6 1.3 5.0 15.7 52.7 6.2 5.8 11.9 Qualified nuclear decommissioning trust fund income 3.4 7.8 — — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (2.3 ) (0.3 ) (0.1 ) (0.1 ) (0.2 ) (3.7 ) 0.8 1.4 (0.9 ) Plant basis differences (4.8 ) — (0.6 ) (9.6 ) (2.7 ) (22.8 ) (25.5 ) 10.3 39.0 (13.5 ) Production tax credits and other credits (3.6 ) (8.2 ) — — — — — — — — Noncontrolling interests (0.2 ) (0.3 ) — — — — — — — — Statute of limitations expiration (0.4 ) (1.7 ) — — — — — — — — Penalties 1.9 — 4.5 — — — — — (0.7 ) — Merger Expenses 5.5 1.1 — — — 23.5 112.9 (44.9 ) (89.0 ) 11.1 Other (e) (0.6 ) (1.5 ) 0.1 (1.2 ) — (1.8 ) (2.2 ) 1.3 3.3 3.6 Effective income tax rate 38.3 % 33.2 % 44.3 % 25.4 % 37.2 % 49.4 % 169.2 % 8.7 % (5.2 )% 47.2 % For the Year Ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % 35.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 3.7 1.0 4.9 1.0 5.3 6.6 6.7 1.7 5.7 Qualified nuclear decommissioning trust fund loss (0.4 ) (0.8 ) — — — — — — — Domestic production activities deduction (0.7 ) (1.3 ) — — — — — — — Health care reform legislation — — — — 0.1 — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (1.5 ) (0.3 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.4 ) (0.6 ) Plant basis differences (1.5 ) — (0.1 ) (8.7 ) (0.7 ) (4.3 ) (5.8 ) (2.3 ) (1.3 ) Production tax credits and other credits (1.9 ) (3.4 ) — — — — — — — Noncontrolling interests 0.3 0.5 — — — — — — — Statute of limitations expiration (1.4 ) (2.4 ) — — — — — — — Other (f) — — 0.2 0.2 — (3.2 ) (0.5 ) 5.2 6.4 Effective income tax rate 32.2 % 27.1 % 39.7 % 27.4 % 39.6 % 33.9 % 35.3 % 39.2 % 45.2 % __________ (a) Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL, and ACE of $ 35 million , $ 3 million , $ 5 million , $ 27 million , $ 14 million , $ 6 million , and $ 7 million , respectively (See Footnote 3 - Regulatory Matters). (b) Included are impacts for TJCA other than the corporate rate change, including revisions further limiting tax deductions for compensation of certain highest paid executives, the write-off of foreign tax credit carryforwards, and loss of a 2015 domestic production activities deduction due to an NOL carryback. (c) DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016 , and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016 . As a result, positive percentages represent an income tax benefit for the periods presented. (d) Includes a remeasurement of uncertain state income tax positions for Pepco and DPL. (e) At PECO, includes a cumulative adjustment related to an anticipated gas repairs tax return accounting method change. The method change request was filed and accepted in 2017. No change to the results recorded as of December 31, 2016. (f) Includes impacts of the PHI Global Settlement for Pepco, DPL, ACE and
Tax Effects of Temporary Differences	rds The tax effects of temporary differences and carryforwards, which give rise to significant portions of the deferred tax assets (liabilities), as of December 31, 2017 and 2016 are presented below:
Summary of Loss Carryforwards	As of December 31, 2017 (a) Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,490 ) $ (2,819 ) $ (3,825 ) $ (1,762 ) $ (1,368 ) $ (2,521 ) $ (1,152 ) $ (717 ) $ (607 ) Accrual based contracts 150 (66 ) — — — 216 — — — Derivatives and other financial instruments (85 ) (66 ) (2 ) — — 3 — — — Deferred pension and postretirement obligation 1,463 (205 ) (285 ) (15 ) (29 ) (130 ) (78 ) (51 ) (18 ) Nuclear decommissioning activities (553 ) (553 ) — — — — — — — Deferred debt refinancing costs 217 26 (8 ) (1 ) (3 ) 203 (4 ) (2 ) (1 ) Regulatory assets and liabilities (688 ) — 489 (90 ) 136 (184 ) 39 88 86 Tax loss carryforward 344 76 33 9 11 156 40 68 35 Tax credit carryforward 861 868 1 — — 6 — — — Investment in partnerships (434 ) (416 ) — — — — — — — Other, net 746 78 141 71 13 193 94 14 16 Deferred income tax liabilities (net) $ (10,469 ) $ (3,077 ) $ (3,456 ) $ (1,788 ) $ (1,240 ) $ (2,058 ) $ (1,061 ) $ (600 ) $ (489 ) Unamortized investment tax credits (732 ) (705 ) (13 ) (1 ) (4 ) (8 ) (2 ) (3 ) (4 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,201 ) $ (3,782 ) $ (3,469 ) $ (1,789 ) $ (1,244 ) $ (2,066 ) $ (1,063 ) $ (603 ) $ (493 ) __________ (a) Includes remeasurement impacts related to the TCJA. As of December 31, 2016 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (17,966 ) $ (4,192 ) $ (5,034 ) $ (3,095 ) $ (1,977 ) $ (3,586 ) $ (1,678 ) $ (973 ) $ (869 ) Accrual based contracts 434 (115 ) — — — 548 — — — Derivatives and other financial instruments (179 ) (162 ) (3 ) — — (1 ) — — — Deferred pension and postretirement obligation 2,287 (316 ) (453 ) (18 ) (43 ) (111 ) (122 ) (74 ) (21 ) Nuclear decommissioning activities (509 ) (509 ) — — — — — — — Deferred debt refinancing costs 325 44 (13 ) (1 ) (3 ) 293 (7 ) (4 ) (2 ) Regulatory assets and liabilities (3,319 ) — (226 ) 10 (240 ) (1,205 ) (194 ) (75 ) (69 ) Tax loss carryforward 189 61 29 — 22 77 27 39 14 Tax credit carryforward 446 493 — — — — — — — Investment in partnerships (650 ) (650 ) — — — — — — — Other, net 1,485 403 351 99 27 225 66 34 34 Deferred income tax liabilities (net) $ (17,457 ) $ (4,943 ) $ (5,349 ) $ (3,005 ) $ (2,214 ) $ (3,760 ) $ (1,908 ) $ (1,053 ) $ (913 ) Unamortized investment tax credits (658 ) (626 ) (15 ) (1 ) (5 ) (9 ) (2 ) (3 ) (4 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (18,115 ) $ (5,569 ) $ (5,364 ) $ (3,006 ) $ (2,219 ) $ (3,769 ) $ (1,910 ) $ (1,056 ) $ (917 ) The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2017 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Federal Federal net operating loss $ 624 (a) $ — $ 156 $ 7 $ — $ 261 $ 82 $ 81 $ 63 Deferred taxes on Federal net operating loss 131 — 33 1 — 55 17 17 13 Federal general business credits carryforwards 861 (b) 868 1 — 1 5 — — — State State net operating losses 3,555 (c) 1,479 (c) — 98 (e) 177 (d) 1,440 (f) 347 (g) 753 (h) 299 (i) Deferred taxes on state tax attributes (net) 233 97 — 8 12 98 23 51 21 Valuation allowance on state tax attributes 29 23 — — 1 5 — — — __________ (a) Exelon's federal net operating loss will begin expiring in 2034. (b) Exelon’s federal general business credit carryforwards will begin expiring in 2033. (c) Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2018. (d) BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026. (e) PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031. (f) PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036. (g) Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2028. (h) DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2027. (i) ACE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2
Reconciliation of Unrecognized Tax Benefits Excluding Amounts Pertaining to Examined Tax Returns Foll Forward	The following tables provide a reconciliation of the Registrants’ unrecognized tax benefits as of December 31, 2017 , 2016 and 2015 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2017 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Increases based on tax positions related to 2017 — — — — — — — — — Decreases based on tax positions related to 2017 — — — — — — — — — Change to positions that only affect timing — — — — — — — — — Increases based on tax positions prior to 2017 28 — 14 — — 14 — — 14 Decreases based on tax positions prior to 2017 (196 ) (17 ) — — — (61 ) (21 ) (16 ) (22 ) Decrease from settlements with taxing authorities (5 ) (5 ) — — — — — — — Decreases from expiration of statute of limitations — — — — — — — — — Unrecognized tax benefits at December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Successor Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2016 $ 1,078 $ 534 $ 142 $ — $ 120 $ 22 $ 8 $ 3 $ — Merger balance transfer 22 5 — — — (5 ) — — — Increases based on tax positions related to 2016 108 10 — — — 59 21 16 22 Decreases based on tax positions related to 2016 — — — — — — — — — Change to positions that only affect timing (332 ) (12 ) (154 ) — — — — — — Increases based on tax positions prior to 2016 88 — — — — 96 51 18 — Decreases based on tax positions prior to 2016 (21 ) (20 ) — — — — — — — Decrease from settlements with taxing authorities (27 ) (27 ) — — — — — — — Decreases from expiration of statute of limitations — — — — — — — — — Unrecognized tax benefits at December 31, 2016 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2015 $ 1,829 $ 1,357 $ 149 $ 44 $ — $ 702 $ — $ — $ — Increases based on tax positions related to 2015 108 — — — 106 — — — — Decreases based on tax positions related to 2015 — — — — — — — — — Change to positions that only affect timing (705 ) (659 ) (7 ) (44 ) — (688 ) — — — Increases based on tax positions prior to 2015 79 65 — — 14 11 8 3 — Decreases based on tax positions prior to 2015 (116 ) (112 ) — — — — — — — Decreases from settlements with taxing authorities (31 ) (31 ) — — — — — — — Decreases from expiration of statute of limitations (86 ) (86 ) — — — (3 ) — — — Unrecognized tax benefits at December 31, 2015 $ 1,078 $ 534 $ 142 $ — $ 120 $ 22 $ 8 $ 3 $ —
Interest Income and Interest Expense Disclosure [Table Text Block]	The following tables set forth the net interest and penalty expense, including interest and penalties related to tax positions, recognized in Interest expense, net and Other, net in Other income and deductions in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Net interest expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2017 $ 37 $ (1 ) $ 11 $ — $ — $ — $ — $ — December 31, 2016 165 (13 ) 117 — — 6 — (1 ) December 31, 2015 (13 ) (31 ) 7 — — (4 ) — — Net penalty expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2017 $ (2 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2016 106 — 86 — — — — — December 31, 2015 — — — — — — — —
Summary of Open Tax Years by Jurisdiction	Description of tax years open to assessment by major jurisdiction

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Nuclear Decommissioning Asset Retirement Obligation Rollforward	The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2016 to December 31, 2017 : Exelon and Generation Nuclear decommissioning ARO at January 1, 2016 $ 8,246 Accretion expense 436 Net increase for changes in and timing of estimated future cash flows 61 Costs incurred related to decommissioning plants (9 ) Nuclear decommissioning ARO at December 31, 2016 (a) 8,734 Accretion Expense 458 Acquisition of FitzPatrick 444 Net increase for changes in and timing of estimated future cash flows 34 Costs incurred related to decommissioning plants (8 ) Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 __________ (a) Includes $ 13 million and $ 10 million as the current portion of the ARO at December 31, 2017 and 2016 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. The following table provides a rollforward of the non-nuclear AROs reflected on the Registrants’ Consolidated Balance Sheets from January 1, 2016 to December 31, 2017 : Successor Exelon Generation ComEd PECO BGE PHI (g) Pepco DPL ACE Non-nuclear AROs at January 1, 2016 $ 355 $ 197 $ 113 $ 27 $ 18 $ — $ — $ — $ — Merger with PHI (a) 8 1 — — — — — — — Net increase due to changes in, and timing of, estimated future cash flows (b) 34 8 4 1 7 14 2 9 3 Development projects (c) 11 11 — — — — — — — Accretion expense (d) 18 10 7 1 — — — — — Sale of generating assets (e) (22 ) (22 ) — — — — — — — Payments (11 ) (6 ) (3 ) (1 ) (1 ) — — — — Non-nuclear AROs at December 31, 2016 (f) 393 199 121 28 24 14 2 9 3 Net increase (decrease) due to changes in, and timing of, estimated future cash flows (b) (11 ) (1 ) (13 ) (1 ) 2 2 1 1 — Development projects (c) 1 1 — — — — — — — Accretion expense (d) 18 10 7 1 — — — — — Deconsolidation of EGTP (h) (7 ) (7 ) — — — — — — — Payments (10 ) (5 ) (2 ) (1 ) (2 ) — — — — Non-nuclear AROs at December 31, 2017 (f) $ 384 $ 197 $ 113 $ 27 $ 24 $ 16 $ 3 $ 10 $ 3 Predecessor PHI (g) 2016 Non-nuclear AROs at January 1, 2016 $ 8 Accretion expense — Non-nuclear AROs at March 23, 2016 $ 8 __________ (a) Following the completion of the PHI merger on March 23, 2016, PHI's AROs related to its unregulated business interests were transferred to Exelon and Generation. (b) During the year ended December 31, 2017 , ComEd recorded a decrease of $1 million in Operating and maintenance expense. Generation, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2017 . During the year ended December 31, 2016 , Generation recorded a increase of $1 million in Operating and maintenance expense. ComEd, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016 . (c) Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites. (d) For ComEd, PECO and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (e) Reflects a reduction to the ARO resulting primarily from the sales of the New Boston generating site and Upstream business in 2016. See Note 4 — Mergers, Acquisitions and Dispositions for further information. (f) Excludes the current portion of the ARO at December 31, 2017 for Generation, ComEd and BGE of $1 million , $2 million and $2 million , respectively. Excludes the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE of $1 million , $2 million and $3 million , respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets. (g) For PHI, the successor period includes activity for the year ended December 31, 2017 and the period of March 24, 2016 through December 31, 2016 . The PHI predecessor periods include activity for the period of January 1, 2016 through March 23, 2016. (h) See Note 4 — Mergers, Acquisitions and Dispositions for additional information.
Unrealized Gains Losses On Nuclear Decommissioning Trust Funds	The following table provides unrealized gains on NDT funds for 2017 , 2016 and 2015 : Exelon and Generation For the Years Ended December 31, 2017 2016 2015 Net unrealized gains (losses) on decommissioning trust funds—Regulatory Agreement Units (a) $ 455 $ 216 $ (282 ) Net unrealized gains (losses) on decommissioning trust funds—Non-Regulatory Agreement Units (b)(c) 521 194 (197 ) __________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $ (10) million , $(1) million and $ 7 million of net unrealized gains (losses) related to the Zion Station pledged assets in 2017 , 2016 and 2015 , respectively. Net unrealized gains related to Zion Station pledged assets are included in the Other current liabilities and Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets in 2017 and 2016, respectively. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.
Nuclear Decommissioning Pledged Assets	The following table provides the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2017 and 2016 : Exelon and Generation 2017 2016 Carrying value of Zion Station pledged assets (a) $ 39 $ 113 Payable to Zion Solutions (b) 37 104 Current portion of payable to Zion Solutions (c) 37 90 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 942 878 __________ (a) Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017. (b) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized. (c) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (d) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Schedule Of Pension And Other Postretirement Participation	The table below shows the pension and other postretirement benefit plans in which employees of each operating company participated at December 31, 2017 : Operating Company (e) Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACE Qualified Pension Plans: Exelon Corporation Retirement Program (a) X X X X X Exelon Corporation Cash Balance Pension Plan (a) X X X X X Exelon Corporation Pension Plan for Bargaining Unit Employees (a) X X X Exelon New England Union Employees Pension Plan (a) X Exelon Employee Pension Plan for Clinton, TMI and Oyster Creek (a) X X X X Pension Plan of Constellation Energy Group, Inc. (b) X X X X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X X X X Nine Mile Point Pension Plan (c) X X Constellation Mystic Power, LLC Union Employees Pension Plan Including Plan A and Plan B (b) X Pepco Holdings LLC Retirement Plan (d) X X X X X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X X X X X Constellation Energy Group, Inc. Senior Executive Supplemental Plan (b) X X X Constellation Energy Group, Inc. Supplemental Pension Plan (b) X X X Constellation Energy Group, Inc. Benefits Restoration Plan (b) X X X X Constellation Energy Nuclear Plan, LLC Executive Retirement Plan (c) X X Constellation Energy Nuclear Plan, LLC Benefits Restoration Plan (c) X X Baltimore Gas & Electric Company Executive Benefit Plan (b) X X X Baltimore Gas & Electric Company Manager Benefit Plan (b) X X X X Pepco Holdings LLC 2011 Supplemental Executive Retirement Plan (d) X X X X X Conectiv Supplemental Executive Retirement Plan (d) X X X X Pepco Holdings LLC Combined Executive Retirement Plan (d) X X X Atlantic City Electric Director Retirement Plan (d) X Operating Company (e) Name of Plan: Generation ComEd PECO BGE BSC PHI Pepco DPL ACE Other Postretirement Benefit Plans: PECO Energy Company Retiree Medical Plan (a) X X X X X Exelon Corporation Health Care Program (a) X X X X X Exelon Corporation Employees’ Life Insurance Plan (a) X X X X X Exelon Corporation Health Reimbursement Arrangement Plan (a) X X X X X Constellation Energy Group, Inc. Retiree Medical Plan (b) X X X X X Constellation Energy Group, Inc. Retiree Dental Plan (b) X X X Constellation Energy Group, Inc. Employee Life Insurance Plan and Family Life Insurance Plan (b) X X X X X Constellation Mystic Power, LLC Post-Employment Medical Account Savings Plan (b) X Exelon New England Union Post-Employment Medical Savings Account Plan (a) X Retiree Medical Plan of Constellation Energy Nuclear Group LLC (c) X X X Retiree Dental Plan of Constellation Energy Nuclear Group LLC (c) X X X Nine Mile Point Nuclear Station, LLC Medical Care and Prescription Drug Plan for Retired Employees (c) X X Pepco Holdings LLC Welfare Plan for Retirees (d) X X X X X ______________________ (a) These plans are collectively referred to as the legacy Exelon plans. (b) These plans are collectively referred to as the legacy Constellation Energy Group (CEG) Plans. (c) These plans are collectively referred to as the legacy CENG plans. (d) These plans are collectively referred to as the legacy PHI plans. (e) Employees generally remain in their legacy benefit plans when transferring between operating companies.
Defined Benefit Plan Change In Benefit Obligation RollForward	The following tables provide a rollforward of the changes in the benefit obligations and plan assets for the most recent two years for all plans combined: Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Change in benefit obligation: Net benefit obligation at beginning of year $ 21,060 $ 17,753 $ 4,457 $ 3,938 Service cost 387 354 106 107 Interest cost 842 830 182 185 Plan participants’ contributions — — 53 54 Actuarial loss (gain) 1,182 567 350 (136 ) Plan amendments 9 (60 ) — — Acquisitions/divestitures (b) 16 2,667 17 589 Settlements (34 ) — — — Gross benefits paid (1,125 ) (1,051 ) (309 ) (280 ) Net benefit obligation at end of year $ 22,337 $ 21,060 $ 4,856 $ 4,457 Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Change in plan assets: Fair value of net plan assets at beginning of year $ 16,791 $ 14,347 $ 2,578 $ 2,293 Actual return on plan assets 2,600 1,061 346 128 Employer contributions 341 347 64 50 Plan participants’ contributions — — 53 54 Gross benefits paid (1,125 ) (1,051 ) (309 ) (280 ) Acquisitions/divestitures (b) — 2,087 — 333 Settlements (34 ) — — — Fair value of net plan assets at end of year $ 18,573 $ 16,791 $ 2,732 $ 2,578 Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Change in benefit obligation: Net benefit obligation at beginning of the period $ 2,490 $ 563 Service cost 12 1 Interest cost 26 6 Actuarial (gain) loss (30 ) (5 ) Gross benefits paid (2 ) (1 ) Net benefit obligation at end of the period $ 2,496 $ 564 Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Change in plan assets: Fair value of net plan assets at beginning of the period $ 2,018 $ 348 Employer and plan participant contributions 4 1 Gross benefits paid by plan (2 ) (1 ) Fair value of net plan assets at end of the period $ 2,020 $ 348 __________ (a) 2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016. (b) Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017. Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans.
Schedule of Amounts Recognized in Balance Sheet	Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2017 2016 (a) Other current liabilities $ 28 $ 21 $ 31 $ 31 Pension obligations 3,736 4,248 — — Non-pension postretirement benefit obligations — — 2,093 1,848 Unfunded status (net benefit obligation less plan assets) $ 3,764 $ 4,269 $ 2,124 $ 1,879 __________ (a) Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.
Schedule of Defined Benefit Plans Disclosures	The following tables present the components of Exelon’s net periodic benefit costs, prior to capitalization, for the years ended December 31, 2017 , 2016 and 2015 and PHI's net periodic benefit costs, prior to capitalization, for the predecessor period of January 1, 2016 to March 23, 2016 . Pension Benefits Other Postretirement Benefits Exelon 2017 (a) 2016 (b) 2015 2017 (a) 2016 (b) 2015 Components of net periodic benefit cost: Service cost $ 387 $ 354 $ 326 $ 106 $ 107 $ 119 Interest cost 842 830 710 182 185 167 Expected return on assets (1,196 ) (1,141 ) (1,026 ) (162 ) (162 ) (151 ) Amortization of: Prior service cost (credit) 1 14 13 (188 ) (185 ) (174 ) Actuarial loss 607 554 571 61 63 80 Settlement and other charges (c) 3 2 2 — — — Net periodic benefit cost $ 644 $ 613 $ 596 $ (1 ) $ 8 $ 41 __________ (a) FitzPatrick net benefit costs are included for the period after acquisition. (b) PHI net periodic benefit costs for the period prior to the merger are not included in the table above. (c) 2016 amount includes an additional termination benefit for PHI. Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Components of net periodic benefit cost: Service cost $ 12 $ 57 $ 1 $ 7 Interest cost 26 109 6 24 Expected return on assets (30 ) (140 ) (5 ) (22 ) Amortization of: Prior service cost (credit) — 2 (3 ) (13 ) Actuarial loss 14 65 2 8 Net periodic benefit cost $ 22 $ 93 $ 1 $ 4 The following table provides the components of gross accumulated other comprehensive loss and regulatory assets (liabilities) that have not been recognized as components of periodic benefit cost at December 31, 2017 and 2016 , respectively, for all plans combined: Exelon Exelon Pension Benefits Other Postretirement Benefits 2017 2016 (a) 2017 2016 (a) Prior service (credit) cost $ (24 ) $ (31 ) $ (522 ) $ (710 ) Actuarial loss 7,556 8,387 829 724 Total (a) $ 7,532 $ 8,356 $ 307 $ 14 Total included in AOCI $ 3,896 $ 4,297 $ 125 $ (42 ) Total included in regulatory assets (liabilities) $ 3,636 $ 4,059 $ 182 $ 56 __________ (a) Effective March 23, 2016 , Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. The following table provides the impact to Exelon’s AOCI and regulatory assets (liabilities) at December 31, 2017 as a result of the components of periodic benefit costs that are expected to be amortized in 2018 . These estimates are subject to the completion of an actuarial valuation of Exelon’s pension and other postretirement benefit obligations, which will reflect actual census data as of January 1, 2018 and actual claims activity as of December 31, 2017 . The valuation is expected to be completed in the first quarter of 2018 for the majority of the benefit plans. Pension Benefits Other Postretirement Benefits Prior service cost (credit) $ 2 $ (186 ) Actuarial loss 640 66 Total (a) $ 642 $ (120 ) __________ (a) Of the $642 million related to pension benefits at December 31, 2017 , $317 million and $325 million are expected to be amortized from AOCI and regulatory assets in 2018 , respectively. Of the $(120) million related to other postretirement benefits at December 31, 2017 , $(65) million and $(55) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2018 , respectively.
Changes In Plan Assets And Benefit Obligations Recognized In OCI And Regulatory Assets	The following tables provide the components of AOCI and regulatory assets (liabilities) for the years ended December 31, 2017 , 2016 and 2015 for all plans combined and the components of PHI's predecessor AOCI and regulatory assets (liabilities) for the period January 1, 2016 to March 23, 2016 . Pension Benefits Other Postretirement Benefits Exelon 2017 2016 (a) 2015 2017 2016 (a) 2015 Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ (222 ) $ 644 $ 476 $ 166 $ (101 ) $ (194 ) Amortization of actuarial loss (607 ) (554 ) (571 ) (61 ) (63 ) (80 ) Current year prior service cost (credit) 9 (60 ) — — — (23 ) Amortization of prior service (cost) credit (1 ) (14 ) (13 ) 188 185 174 Settlements (3 ) — (2 ) — — — Acquisitions — 994 — — 94 — Total recognized in AOCI and regulatory assets (liabilities) $ (824 ) $ 1,010 $ (110 ) $ 293 $ 115 $ (123 ) Total recognized in AOCI $ (401 ) $ 51 $ (64 ) $ 168 $ 20 $ (63 ) Total recognized in regulatory assets (liabilities) $ (423 ) $ 959 $ (46 ) $ 125 $ 95 $ (60 ) Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Changes in plan assets and benefit Current year actuarial loss (gain) $ — $ 50 $ — $ (39 ) Amortization of actuarial loss (14 ) (65 ) (2 ) (8 ) Amortization of prior service (cost) credit — (2 ) 3 13 Total recognized in AOCI and regulatory assets (liabilities) $ (14 ) $ (17 ) $ 1 $ (34 ) Total recognized in AOCI $ (1 ) $ (11 ) $ — $ — Total recognized in regulatory assets (liabilities) $ (13 ) $ (6 ) $ 1 $ (34 )
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]	The following table provides the impact to Exelon’s AOCI and regulatory assets (liabilities) at December 31, 2017 as a result of the components of periodic benefit costs that are expected to be amortized in 2018 . These estimates are subject to the completion of an actuarial valuation of Exelon’s pension and other postretirement benefit obligations, which will reflect actual census data as of January 1, 2018 and actual claims activity as of December 31, 2017 . The valuation is expected to be completed in the first quarter of 2018 for the majority of the benefit plans. Pension Benefits Other Postretirement Benefits Prior service cost (credit) $ 2 $ (186 ) Actuarial loss 640 66 Total (a) $ 642 $ (120 ) __________ (a) Of the $642 million related to pension benefits at December 31, 2017 , $317 million and $325 million are expected to be amortized from AOCI and regulatory assets in 2018 , respectively. Of the $(120) million related to other postretirement benefits at December 31, 2017 , $(65) million and $(55) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2018 , respectively.
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation [Table Text Block]	The following assumptions were used to determine the benefit obligations for the plans at December 31, 2017 , 2016 and 2015 . Assumptions used to determine year-end benefit obligations are the assumptions used to estimate the subsequent year’s net periodic benefit costs. Pension Benefits Other Postretirement Benefits Exelon 2017 2016 2015 2017 2016 2015 Discount rate 3.62 % (a) 4.04 % (b) 4.29 % (c) 3.61 % (a) 4.04 % (b) 4.29 % (c) Rate of compensation increase (d) (e) (e) (d) (e) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% with ultimate trend of 5.00% in 2017 5.00% with 5.50% Predecessor Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 (f) 2015 January 1, 2016 to March 23, 2016 (e) 2015 Discount rate 4.65%/4.55% (g) 4.55 % Rate of compensation 5.00 % 5.00 % Mortality table RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2015 Health care cost trend on covered charges N/A 6.33% pre-65 and 5.40% post-65 __________ (a) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2017. Certain benefit plans used individual rates ranging from 3.49% - 3.65% and 3.57% - 3.68% for pension and other postretirement plans, respectively. (b) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2016. Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively. (c) The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2015. Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (d) 3.25% through 2019 and 3.75% thereafter. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and other postretirement plans used a weighted-average rate of compensation increase of 5% for all periods. (f) Obligation was not remeasured during this period. (g) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively.
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Table Text Block]	The following assumptions were used to determine the net periodic benefit costs for the plans for the years ended December 31, 2017 , 2016 and 2015 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Pension Benefits Other Postretirement Benefits Exelon 2017 2016 2015 2017 2016 2015 Discount rate 4.04 % (a) 4.29 % (b) 3.94 % (c) 4.04 % (a) 4.29 % (b) 3.92 % (c) Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.00 % (d) 6.58 % (d) 6.71 % (d) 6.50 % (d) Rate of compensation increase (e) (e) (e) Mortality table RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) RP-2000 table projected to 2012 with improvement scale AA, with Scale BB-2D improvements (adjusted) Health care cost trend on covered charges N/A N/A N/A 5.00% decreasing to ultimate trend of 5.00% in 2017 5.50% 6.00% decreasing to ultimate trend of 5.00% in 2017 Predecessor Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 2015 January 1, 2016 to March 23, 2016 2015 Discount rate 4.65%/4.55% (f) 4.20 % 4.55 % 4.15 % Expected return on plan assets (g) 6.50 % 6.50 % 6.75 % 6.75 % Rate of compensation 5.00 % 5.00 % 5.00 % 5.00 % Mortality table RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2014 RP-2014 table with improvement scale MP-2015 RP-2014 table with improvement scale MP-2014 Health care cost trend on covered charges N/A N/A 6.33% pre-65 and 5.40% post-65 6.67% pre-65 and 5.50% post-65 __________ (a) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2017 . Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively. (b) The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2016 . Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (c) The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015 . Certain benefit plans used the individual rates ranging from 3.29% - 3.82% and 3.99% - 4.06% for pension and other postretirement plans, respectively. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) The legacy Exelon, CEG and CENG pension and other postretirement plans used a rate of compensation increase of 3.25% through 2019 and 3.75% thereafter, while the legacy PHI pension and other postretirement plans used a weighted-average rate of compensation increase of 5% for all periods. (f) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	A one percentage point change in assumed health care cost trend rates would have the following effects: Effect of a one percentage point increase in assumed health care cost trend: on 2017 total service and interest cost components $ 9 on postretirement benefit obligation at December 31, 2017 125 Effect of a one percentage point decrease in assumed health care cost trend: on 2017 total service and interest cost components (8 ) on postretirement benefit obligation at December 31, 2017 (113 )
Pension And Other Postretirement Benefit Contributions [Table Text Block]	Qualified Pension Plans Non-Qualified Pension Plans Other Exelon $ 301 $ 30 $ 42 Generation 119 11 13 ComEd 38 2 3 PECO 17 1 — BGE 41 1 16 BSC 36 7 1 PHI 50 8 9 Pepco 4 2 8 DPL — 1 — ACE 6 — — PHISCO 40 5 1 The following tables provide contributions to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2017 (a) 2016 (a) 2015 (a) 2017 2016 2015 Exelon $ 341 $ 347 $ 462 $ 64 $ 50 $ 40 Generation 137 140 231 11 12 14 ComEd 36 33 143 5 5 7 PECO 24 30 40 — — — BGE 39 31 1 14 18 16 BSC (b) 38 39 47 2 3 3 Pepco 62 24 — 10 8 2 DPL — 22 — 2 — — ACE — 15 — 20 2 3 PHISCO (c) 5 17 — — 2 — Pension Benefits Other Postretirement Benefits Successor Predecessor Successor Predecessor 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 PHI $ 67 $ 74 $ 4 $ — $ 32 $ 12 $ — $ 5 __________ (a) Exelon's and Generation's pension contributions include $21 million , $25 million and $36 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2017 , 2016 and 2015 , respectively. (b) Includes $4 million , $6 million , and $5 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2017 , 2016 , and 2015 , respectively. (c)
Schedule of Expected Benefit Payments [Table Text Block]	Estimated Future Benefit Payments Estimated future benefit payments to participants in all of the pension plans and postretirement benefit plans at December 31, 2017 were: Pension Benefits Other Postretirement Benefits 2018 $ 1,166 $ 256 2019 1,165 262 2020 1,210 270 2021 1,236 276 2022 1,265 284 2023 through 2027 6,671 1,509 Total estimated future benefit payments through 2027 $ 12,713 $ 2,857
Schedule Of Pension And Other Postretirement Benefit Costs [Table Text Block]	an costs. These amounts include the recognized contractual termination benefit charges, curtailment gains, and settlement charges: For the Years Ended December 31, Exelon Generation (a) ComEd PECO BGE BSC (b) Pepco (c) DPL (c) ACE (c) PHISCO (c)(d) 2017 $ 643 $ 227 $ 176 $ 29 $ 64 $ 53 $ 25 $ 13 $ 13 $ 43 2016 621 218 166 33 68 48 31 18 15 47 2015 637 269 206 39 66 57 30 15 15 37 Successor Predecessor PHI For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Pension and Other Postretirement Benefit Costs $ 94 $ 88 $ 23 $ 97 __________ (a) FitzPatrick net benefit costs are included for the period after acquisition. (b) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE, PHI, Pepco, DPL or ACE amounts
Defined Benefit Plan Weighted Average Asset Allocations And Target Allocations [Table Text Block]	vely. Exelon’s pension and other postretirement benefit plan target asset allocations at December 31, 2017 and 2016 asset allocations were as follows: Pension Plans Exelon Percentage of Plan Assets at December 31, Asset Category Target Allocation 2017 2016 Equity securities 35 % 35 % 33 % Fixed income securities 38 % 39 39 Alternative investments (a) 27 % 26 28 Total 100 % 100 % Other Postretirement Benefit Plans Exelon Percentage of Plan Assets at December 31, Asset Category Target Allocation 2017 2016 Equity securities 46 % 47 % 47 % Fixed income securities 28 % 28 29 Alternative investments (a) 26 % 25 24 Total 100 % 100 % __________ (a) Alternative investments include private equity, hedge funds, real estate, and private credit.
Defined Benefit Plan Fair Value Of Plan Assets [Text Block]	Fair Value Measurements The following tables present pension and other postretirement benefit plan assets measured and recorded at fair value on the Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2017 and 2016 : Exelon December 31, 2017 (a)(b) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 585 $ — $ — $ — $ 585 Equities (c) 3,565 — 2 3,077 6,644 Fixed income: U.S. Treasury and agencies 1,150 159 — — 1,309 State and municipal debt — 64 — — 64 Corporate debt — 3,931 232 — 4,163 Other (c) — 447 — 756 1,203 Fixed income subtotal 1,150 4,601 232 756 6,739 Private equity — — — 1,034 1,034 Hedge funds — — — 1,770 1,770 Real estate — — — 884 884 Private credit — — — 919 919 Pension plan assets subtotal $ 5,300 $ 4,601 $ 234 $ 8,440 $ 18,575 December 31, 2017 (a)(b) Level 1 Level 2 Level 3 Not subject to leveling Total Other postretirement benefit plan assets Cash equivalents $ 29 $ — $ — $ — $ 29 Equities 523 2 — 764 1,289 Fixed income: U.S. Treasury and agencies 13 56 — — 69 State and municipal debt — 136 — — 136 Corporate debt — 47 — — 47 Other 225 71 — 185 481 Fixed income subtotal 238 310 — 185 733 Hedge funds — — — 430 430 Real estate — — — 124 124 Private credit — — — 123 123 Other postretirement benefit plan assets subtotal $ 790 $ 312 $ — $ 1,626 $ 2,728 Total pension and other postretirement benefit plan assets (d) $ 6,090 $ 4,913 $ 234 $ 10,066 $ 21,303 December 31, 2016 (a)(e) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 325 $ — $ — $ — $ 325 Equities (c) 3,144 — 2 2,535 5,681 Fixed income: U.S. Treasury and agencies 1,008 192 — — 1,200 State and municipal debt — 64 — — 64 Corporate debt — 3,641 206 — 3,847 Other (c) — 340 — 748 1,088 Fixed income subtotal 1,008 4,237 206 748 6,199 Private equity — — — 991 991 Hedge funds — — — 1,962 1,962 Real estate — — — 828 828 Private credit — — — 833 833 Pension plan assets subtotal $ 4,477 $ 4,237 $ 208 $ 7,897 $ 16,819 December 31, 2016 (a)(e) Level 1 Level 2 Level 3 Not subject to leveling Total Other postretirement benefit plan assets Cash equivalents $ 24 $ — $ — $ — $ 24 Equities 547 2 — 644 1,193 Fixed income: U.S. Treasury and agencies 9 59 — — 68 State and municipal debt — 134 — — 134 Corporate debt — 43 — — 43 Other 256 60 — 131 447 Fixed income subtotal 265 296 — 131 692 Hedge funds — — — 445 445 Real estate — — — 117 117 Private credit — — — 107 107 Other postretirement benefit plan assets subtotal $ 836 $ 298 $ — $ 1,444 $ 2,578 Total pension and other postretirement benefit plan assets (d) $ 5,313 $ 4,535 $ 208 $ 9,341 $ 19,397 __________ (a) See Note 11 — Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy. (b) Effective March 31, 2017, Exelon became sponsor of FitzPatrick's defined benefit pension and other postretirement benefit plans, and assumed FitzPatrick's benefit plan obligations. (c) Includes derivative instruments of $6 million and $1 million , which have a total notional amount of $3,606 million and $2,918 million at December 31, 2017 and 2016 , respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company’s exposure to credit or market loss. (d) Excludes net assets of $2 million and net liabilities of $28 million at December 31, 2017 and 2016 , respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases. (e) Effective March 23, 2016, Exelon became sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.
Schedule of Changes in Fair Value of Plan Assets [Table Text Block]	rchases. (e) Effective March 23, 2016, Exelon became sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets. The following table presents the reconciliation of Level 3 assets and liabilities measured at fair value for pension and other postretirement benefit plans for the years ended December 31, 2017 and 2016 : Exelon Fixed Income Equities Total Pension Assets Balance as of January 1, 2017 $ 206 $ 2 $ 208 Actual return on plan assets: Relating to assets sold during the period 11 — 11 Purchases, sales and settlements: Purchases 31 — 31 Sales (16 ) — (16 ) Settlements (a) — — — Balance as of December 31, 2017 $ 232 $ 2 $ 234 Fixed income Equities Total Pension Assets Balance as of January 1, 2016 $ 165 $ 2 $ 167 Actual return on plan assets: Relating to assets still held at the reporting date (2 ) — (2 ) Purchases, sales and settlements: Purchases 69 — 69 Sales (14 ) — (14 ) Settlements (a) (12 ) — (12 ) Balance as of December 31, 2016 $ 206 $ 2 $ 208 __________ (a) Represents cash settlements only.
Schedule Of Defined Contributions [Table Text Block]	n limits. The following table presents matching contributions to the savings plan for the years ended December 31, 2017 , 2016 and 2015 : For the Year Ended December 31, Exelon (a) Generation (a) ComEd PECO BGE BSC (b) Pepco (c) DPL (c) ACE PHISCO (c)(d) 2017 $ 128 $ 55 $ 31 $ 10 $ 10 $ 9 $ 3 $ 2 $ 2 $ 6 2016 164 79 34 10 12 19 3 2 2 6 2015 148 80 32 11 14 11 3 2 2 6 Successor Predecessor PHI For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 Saving Plan Matching Contributions $ 13 $ 10 $ 3 $ 14 __________ (a) Includes $13 million and $9 million related to CENG for the years ended December 31, 2016 and December 31, 2015. (b) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, BGE, PHI, Pepco, DPL or ACE amounts above. (c) Pepco's, DPL's and PHISCO's matching contributions include $1 million , $1 million and $1 million , respectively, of costs incurred prior to the closing of Exelon's merger with PHI on March 23, 2016, which is not included in Exelon's matching contributions for the year ended December 31, 2016. (d) These amounts primarily represent amounts billed to Pepco, DPL, and ACE through intercompany allocations. These amounts are not included in Pepco, DPL or ACE amounts above.

Severance (Tables)

Severance (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring and Related Activities [Abstract]
Severance	For the periods ended December 31, 2017 and 2016 , the Registrants have recognized costs to achieve the PHI acquisition as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2017 2016 Exelon $ 16 $ 143 Generation 22 37 ComEd (b) 1 (6 ) PECO 4 5 BGE (b) 4 (1 ) Pepco (b) (6 ) 28 DPL (b) (7 ) 20 ACE (b) (6 ) 19 Successor Predecessor Acquisition, Integration and Financing Costs (a) For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI (b) $ (18 ) $ 69 $ 29 ______________ (a) The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above. (b) For the year ended December 31, 2017 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million , $8 million , $8 million , and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million , $6 million , $11 million , and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information. For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs related to the cost management program within Operating and maintenance expense in their Consolidated Statements of Operations: Exelon Generation ComEd PECO BGE 2017 (a) $ 6 $ 9 $ (1 ) $ (1 ) $ (1 ) 2016 (b) 23 18 3 1 1 __________ (a) The amounts for Generation, ComEd, PECO, and BGE include $(4) million , $(2) million , $(1) million , and $(1) million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017 . (b) The amounts above for Generation, ComEd, PECO and BGE include $7 million , $3 million , $1 million , and $1 million , respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2016 . For the years ended December 31, 2017 and 2016 , the Registrants recorded the following severance costs associated with ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Successor Exelon Generation (a) ComEd (a) PECO (a) BGE (a) PHI (a) Pepco (a) DPL (a) ACE (a) Year ended December 31, 2017 $ 14 $ 6 $ 3 $ 1 $ — $ 4 $ 2 $ 1 $ 1 2016 19 13 3 1 1 1 — — — __________ (a) The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016 . Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017 . Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016	For the year ended December 31, 2016 , the Registrants recorded the following severance costs associated with the identified job reductions within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income, pursuant to the authoritative guidance for ongoing severance plans: Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Severance Benefits Severance costs (a) $ 57 $ 9 $ 2 $ 1 $ 1 $ 44 $ 21 $ 13 $ 10 __________ (a) The amounts above for Generation, ComEd, PECO, BGE, Pepco, DPL, and ACE include $8 million , $2 million , $1 million , $1 million , $20 million , $12 million and $10 million , respectively, for amounts billed by BSC and/or PHISCO through intercompany allocations for the year ended December 31, 2016 .
Severance Liability	Amounts included in the table below represent the severance liability recorded for employees of each Registrant and exclude amounts included at Exelon and billed through intercompany allocations: Successor Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2015 $ 35 $ 23 $ 3 $ — $ 1 $ — $ — $ — $ — Severance charges (a) 99 22 2 — — 56 1 1 — Payments (46 ) (9 ) (2 ) — (1 ) (27 ) (1 ) (1 ) — Balance at December 31, 2016 $ 88 $ 36 $ 3 $ — $ — $ 29 $ — $ — $ — Severance charges (a) 35 31 2 — — 3 — — — Payments (29 ) (9 ) (2 ) — — (12 ) — — — Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits.

Mezzanine Equity Contingently

Mezzanine Equity Contingently Redeemable Noncontrolling Interest (Table)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest Disclosure [Abstract]
Noncontrolling Interest Disclosure [Text Block]	18 . Mezzanine Equity (Exelon, Generation and PHI) Contingently Redeemable Noncontrolling Interests (Exelon and Generation) In November 2015, 2015 ESA Investco, LLC, a wholly owned subsidiary of Generation, entered into an arrangement to sell a portion of its equity to a tax equity investor. Pursuant to the operating agreement, in certain circumstances the equity contributed by the noncontrolling interests holder could be contingently redeemable. These circumstances were outside of the control of Generation and the noncontrolling interests holder resulting in a portion of the noncontrolling interests being considered contingently redeemable and thus was presented in mezzanine equity on the consolidated balance sheet. There were no changes in the contingently redeemable noncontrolling interests for the year ended December 31, 2017 . The following table summarizes the changes in the contingently redeemable noncontrolling interests for the year ended December 31, 2016 : Contingently Redeemable NCI Balance at December 31, 2015 $ 28 Cash received from noncontrolling interests 129 Release of contingency (157 ) Balance at December 31, 2016 $ — Preferred Stock (PHI) In connection with the PHI Merger Agreement, Exelon purchased 18,000 originally issued shares of PHI preferred stock for a purchase price of $180 million . PHI excluded the preferred stock from equity at December 31, 2015 since the preferred stock contained conditions for redemption that were not solely within the control of PHI. Management determined that the preferred stock contained embedded features requiring separate accounting consideration to reflect the potential value to PHI that any issued and outstanding preferred stock could be called and redeemed at a nominal par value upon a termination of the merger agreement under certain circumstances due to the failure to obtain required regulatory approvals. The embedded call and redemption features on the shares of the preferred stock in the event of such a termination were separately accounted for as derivatives. As of December 31, 2015, the fair value of the derivative related to the preferred stock was estimated to be $18 million based on PHI’s updated assessment and was included in current assets with a corresponding increase in preferred stock on the Consolidated Balance Sheet. Immediately prior to the merger date, PHI updated its assessment of the fair value of the derivative and reduced the fair value to zero, recording the $18 million decrease in fair value as a reduction of Other, net within PHI's predecessor period, January 1, 2016 to March 23, 2016 , Statements of Operations and Comprehensive Income. On March 23, 2016 , the preferred stock was cancelled and the $180 million cash consideration previously received by PHI to issue the preferred stock was treated as additional merger purchase price consideration.
Redeemable Noncontrolling Interest [Table Text Block]	The following table summarizes the changes in the contingently redeemable noncontrolling interests for the year ended December 31, 2016 : Contingently Redeemable NCI Balance at December 31, 2015 $ 28 Cash received from noncontrolling interests 129 Release of contingency (157 ) Balance at December 31, 2016 $ —

Shareholders' Equity Sharehold

Shareholders' Equity Shareholder Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Shareholder [Abstract]
Schedule of Common Stock Outstanding Roll Forward [Table Text Block]	The following table presents common stock authorized and outstanding as of December 31, 2017 and 2016 : December 31, 2017 2016 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 963,335,888 924,035,059 ComEd $ 12.50 250,000,000 127,021,246 127,017,157 PECO no par value 500,000,000 170,478,507 170,478,507 BGE no par value 1,500 1,000 1,000 Pepco $ 0.01 200,000,000 100 100 DPL $ 2.25 1,000 1,000 1,000 ACE $ 3.00 25,000,000 8,546,017 8,546,017

Stock-Based Compensation Plan57

Stock-Based Compensation Plans (All Registrants) (Tables)	12 Months Ended
	Dec. 31, 2017
Common Stock [Abstract]
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]	The following tables present the stock-based compensation expense included in Exelon's and PHI’s Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2017 , 2016 and 2015 and PHI's predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2017 2016 (a) 2015 Performance share awards $ 107 $ 93 $ 41 Restricted stock units 77 75 71 Stock options — — 1 Other stock-based awards 7 7 6 Total stock-based compensation expense included in operating and maintenance expense 191 175 119 Income tax benefit (74 ) (68 ) (46 ) Total after-tax stock-based compensation expense $ 117 $ 107 $ 73 __________ (a) 2016 amounts include expense related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016 . PHI Predecessor January 1 to March 23, Year Ended Components of Stock-Based Compensation Expense 2016 2015 Time-based restricted stock units $ 2 $ 7 Performance-based restricted stock units 1 5 Time-based restricted stock awards — 1 Total stock-based compensation expense included in operating and maintenance expense 3 13 Income tax benefit (1 ) (5 ) Total after-tax stock-based compensation expense $ 2 $ 8
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	The following tables present the Registrants' stock-based compensation expense (pre-tax) for the years ended December 31, 2017 , 2016 and 2015 , as well as for the PHI predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Year Ended December 31, Subsidiaries 2017 2016 2015 Exelon $ 191 $ 175 $ 119 Generation 88 78 64 ComEd 7 8 6 PECO 3 3 3 BGE 1 1 3 BSC (a) 88 81 43 PHI Successor (b)(c) 4 4 — Predecessor January 1 to For the Year Ended December 31, 2016 2015 PHI $ 3 $ 13 __________ (a) These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE or PHI amounts above. (b) Pepco's, DPL's and ACE's stock-based compensation expense for the years ended December 31, 2017 and 2016 was not material. (c)
Stock Based Compensation Tax Benefit	The following tables present information regarding Exelon’s and PHI's tax benefits for the years ended December 31, 2017 , 2016 and 2015 and PHI's predecessor periods January 1, 2016 to March 23, 2016 and the year ended December 31, 2015 : Exelon Year Ended December 31, 2017 2016 2015 Realized tax benefit when exercised/distributed: Restricted stock units 35 27 30 Performance share awards 29 18 18 PHI Predecessor January 1 to For the Year Ended December 31, 2016 2015 Realized tax benefit when exercised/distributed: Time-based restricted stock units $ — $ 2 Performance-based restricted stock units — 5
Schedule of Share-based Compensation, Stock Options, Activity	The following table presents information with respect to stock option activity for the year ended December 31, 2017 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2016 12,531,591 $ 46.23 3.50 $ 13 Options exercised (3,093,156 ) 34.69 Options forfeited — — Options expired (2,714,824 ) 55.78 Balance of shares outstanding at December 31, 2017 6,723,611 $ 47.69 2.65 $ 7 Exercisable at December 31, 2017 (a) 6,723,611 $ 47.69 2.65 $ 7 __________ (a) Includes stock options issued to retirement eligible employees.
Stock Options Exercised	The following table summarizes additional information regarding stock options exercised for the years ended December 31, 2017 , 2016 and 2015 : Year Ended 2017 2016 2015 Intrinsic value (a) $ 15 $ 11 $ — Cash received for exercise price 107 19 — __________ (a) The difference between the market value on the date of exercise and the option exercise price.
Schedule of Nonvested Share Activity	.
Schedule of Nonvested Restricted Stock Units Activity	The following table summarizes Exelon’s nonvested restricted stock unit activity for the year ended December 31, 2017 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2016 (a)(c) 3,824,416 $ 30.49 Granted 2,266,199 34.98 Vested (1,736,965 ) 30.98 Forfeited (92,938 ) 33.12 Undistributed vested awards (b) (871,209 ) 34.09 Nonvested at December 31, 2017 (a) 3,389,503 $ 32.24 __________ (a) Excludes 1,488,383 and 1,319,372 of restricted stock units issued to retirement-eligible employees as of December 31, 2017 and 2016 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2017 .
Schedule of Nonvested Performance-based Units Activity	The following table summarizes Exelon’s nonvested performance share awards activity for the year ended December 31, 2017 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2016 (a)(c) 3,116,261 $ 30.77 Granted 1,632,186 35.00 Change in performance 545,793 30.97 Vested (1,111,751 ) 29.11 Forfeited (18,034 ) 33.74 Undistributed vested awards (b) (1,207,489 ) 33.46 Nonvested at December 31, 2017 (a) 2,956,966 $ 32.65 __________ (a) Excludes 2,723,440 and 2,443,409 of performance share awards issued to retirement-eligible employees as of December 31, 2017 and 2016 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2017 . (c) 2016 amounts include activity related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016. The following table summarizes the weighted average grant date fair value and the fair value of performance share awards granted and settled for the years ended December 31, 2017 , 2016 and 2015 : Year Ended 2017 (a) 2016 2015 Weighted average grant date fair value (per share) $ 35.00 $ 28.85 $ 35.88 Fair value of performance shares settled 72 45 46 Fair value of performance shares settled in cash 56 28 29 __________ (a) As of December 31, 2017 , $41 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.5 years.
Not Settled Performance Share Awards Balance Sheet Presentation	The following table presents the balance sheet classification of obligations related to outstanding performance share awards not yet settled: December 31, 2017 2016 Current liabilities (a) $ 57 $ 49 Deferred credits and other liabilities (b) 100 52 Common stock 26 40 Total $ 183 $ 141 __________ (a) Represents the current liability related to performance share awards expected to be settled in cash. (b) Represents the long-term liability related to performance share awards expected to be settled in cash.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Reconciliation of basic and diluted earnings per share	The following table sets forth the components of basic and diluted earnings per share and shows the effect of these stock options, performance share awards and restricted stock awards on the weighted average number of shares outstanding used in calculating diluted earnings per share: Year Ended December 31, 2017 2016 2015 Net income attributable to common shareholders $ 3,770 $ 1,134 $ 2,269 Weighted average common shares outstanding — basic 947 924 890 Assumed exercise and/or distributions of stock-based awards 2 3 3 Weighted average common shares outstanding — diluted 949 927 893

Changes in Accumulated Other 59

Changes in Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule Of Accumulated Other Comprehensive Income (Loss)	The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications (1 ) 6 11 7 6 29 Amounts reclassified from AOCI (b) 4 — 140 — — 144 Net current-period OCI 3 6 151 7 6 173 Ending balance $ (14 ) $ 10 $ (2,459 ) $ (23 ) $ (1 ) $ (2,487 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications (1 ) 1 — 7 6 13 Amounts reclassified from AOCI (b) 4 — — — — 4 Net current-period OCI 3 1 — 7 6 17 Ending balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 For the Year Ended December 31, 2016 Gains and Unrealized Pension and Foreign AOCI of Total Exelon (a) Beginning balance $ (19 ) $ 3 $ (2,565 ) $ (40 ) $ (3 ) $ (2,624 ) OCI before reclassifications (6 ) 1 (182 ) 5 (4 ) (186 ) Amounts reclassified from AOCI (b) 8 — 137 5 — 150 Net current-period OCI 2 1 (45 ) 10 (4 ) (36 ) Ending balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) Generation (a) Beginning balance $ (21 ) $ 1 $ — $ (40 ) $ (3 ) $ (63 ) OCI before reclassifications (6 ) 1 — 5 (4 ) (4 ) Amounts reclassified from AOCI (b) 8 — — 5 — 13 Net current-period OCI 2 1 — 10 (4 ) 9 Ending balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 PHI Predecessor (a) Beginning balance January 1, 2016 $ (8 ) $ — $ (28 ) $ — $ — $ (36 ) OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — 1 — — 1 Net current-period OCI — — 1 — — 1 Ending balance March 23, 2016 (c) $ (8 ) $ — $ (27 ) $ — $ — $ (35 ) __________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) As a result of the PHI Merger, the PHI predecessor balances at March 23, 2016 were reduced to zero on March 24, 2016 due to purchase accounting adjustments applied to PHI.
Reclassification Out Of Accumulated Other Comprehensive Income	The following tables present amounts reclassified out of AOCI to Net income for Exelon, Generation and PHI during the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense Total before tax (5 ) (5 ) Tax benefit 1 1 Net of tax $ (4 ) $ (4 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 92 $ — Actuarial losses (b) (324 ) — Total before tax (232 ) — Tax benefit 92 — Net of tax $ (140 ) $ — Comprehensive Income Total Reclassifications $ (144 ) $ (4 ) Comprehensive income For the Year Ended December 31, 2016 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Predecessor January 1, 2016 to March 23, 2016 Exelon Generation PHI Loss on cash flow hedges Other cash flow hedges $ (13 ) $ (13 ) $ — Interest expense Total before tax (13 ) (13 ) — Tax benefit 5 5 — Net of tax $ (8 ) $ (8 ) $ — Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 78 $ — $ — Actuarial losses (b) (302 ) — (1 ) Total before tax (224 ) — (1 ) Tax benefit 87 — — Net of tax $ (137 ) $ — $ (1 ) Comprehensive Income Losses on foreign currency translation Loss $ (5 ) $ (5 ) $ — Other income and (deductions) Total before tax (5 ) (5 ) — Tax benefit — — — Net of tax $ (5 ) $ (5 ) $ — Total Reclassifications $ (150 ) $ (13 ) $ (1 ) Comprehensive income __________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 16 — Retirement Benefits for additional details).
Schedule of Components of Income Tax Expense (Benefit)	The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2017 and 2016 : For the Year Ended December 31, 2017 2016 2015 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 36 $ 30 $ 30 Actuarial loss reclassified to periodic benefit cost (128 ) (118 ) (140 ) Pension and non-pension postretirement benefit plans valuation adjustment 13 115 62 Change in unrealized loss on cash flow hedges (7 ) — (6 ) Change in unrealized (loss)/gain on equity investments (3 ) 3 1 Change in unrealized loss on marketable securities (1 ) — — Total $ (90 ) $ 30 $ (53 ) Generation Change in unrealized (loss)/gain on cash flow hedges $ (6 ) $ (2 ) $ 2 Change in unrealized (loss)/gain on equity investments (3 ) 3 1 Change in unrealized loss marketable securities (1 ) — — Total $ (10 ) $ 1 $ 3 Predecessor January 1 to For the Year Ended December 31, PHI 2016 2015 Pension and non-pension postretirement benefit plans: Actuarial loss reclassified to periodic cost $ — $ 6

Commitments and Contingencies60

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies [Line Items]
Other Commitments	Commercial Commitments Exelon’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 1,226 $ 1,056 $ 154 $ 16 $ — $ — $ — Surety bonds (b) 1,381 1,293 66 16 6 — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (c) 21 — — — — — 21 Total commercial commitments $ 3,006 $ 2,349 $ 220 $ 32 $ 6 $ — $ 399 __________ (a) Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million , $16 million of which is a guarantee by Pepco, $23 million by DPL and $15 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Generation’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 1,177 $ 1,007 $ 154 $ 16 $ — $ — $ — Surety bonds 1,209 1,164 45 — — — — Total commercial commitments $ 2,386 $ 2,171 $ 199 $ 16 $ — $ — $ — __________ (a) Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties. ComEd’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 10 8 2 — — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 212 $ 10 $ 2 $ — $ — $ — $ 200 __________ (a) Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PECO’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 9 $ 8 $ 1 $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 8 $ 1 $ — $ — $ — $ 178 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. BGE’s commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Letters of credit (non-debt) (a) $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (b) 11 10 1 — — — — Total commercial commitments $ 13 $ 12 $ 1 $ — $ — $ — $ — __________ (a) Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PHI commercial commitments (Successor) as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds $ 63 $ 48 $ 15 $ — $ — $ — $ — Guaranteed lease residual values (a) 21 — — — — — 21 Total commercial commitments $ 84 $ 48 $ 15 $ — $ — $ — $ 21 __________ (a) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. Pepco commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 54 $ 41 $ 13 $ — $ — $ — $ — Guaranteed lease residual values (b) 6 — — — — — 6 Total commercial commitments $ 60 $ 41 $ 13 $ — $ — $ — $ 6 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $16 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. DPL commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds (a) $ 4 $ 3 $ 1 $ — $ — $ — $ — Guaranteed lease residual values (b) 8 — — — — — 8 Total commercial commitments $ 12 $ 3 $ 1 $ — $ — $ — $ 8 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (b) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $23 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote. ACE commercial commitments as of December 31, 2017 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2018 2019 2020 2021 2022 2023 and beyond Surety bonds $ 4 $ 3 $ 1 $ — $ — $ — $ — Guaranteed lease residual values (a) 6 — — — — — 6 Total commercial commitments $ 10 $ 3 $ 1 $ — $ — $ — $ 6 __________ (a) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $15 million . The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Minimum future operating lease payments, including lease payments for contracted generation, vehicles, real estate, computers, rail cars, operating equipment and office equipment, as of December 31, 2017 were: Successor Exelon (a) Generation (a) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2018 $ 188 $ 74 $ 7 $ 5 $ 34 $ 56 $ 8 $ 20 $ 9 2019 129 29 6 5 34 42 7 10 8 2020 147 47 4 5 34 44 6 13 8 2021 142 48 4 5 32 40 5 12 7 2022 119 46 2 5 17 39 4 12 6 Remaining years 787 573 — — 19 194 8 54 19 Total minimum future lease payments $ 1,512 $ 817 $ 23 $ 25 $ 170 $ 415 $ 38 $ 121 $ 57 __________ (a) Includes amounts related to shared use land arrangements. (b) Excludes Generation’s contingent operating lease payments associated with contracted generation agreements. (c) Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd’s, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2018—2022, was $2 million , $5 million , $1 million and $2 million , respectively. Also includes amounts related to shared use land arrangements. (d) Includes all future lease payments on a 99 -year real estate lease that expires in 2106 . (e) The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $25 million , $26 million , $28 million , $28 million and $14 million related to years 2018, 2019, 2020, 2021and 2022, respectively. The following table presents the Registrants’ rental expense under operating leases for the years ended December 31, 2017, 2016 and 2015: For the Year Ended December 31, Exelon Generation (a) ComEd PECO BGE Pepco DPL ACE 2017 $ 709 $ 578 $ 9 $ 9 $ 32 $ 11 $ 16 $ 14 2016 777 667 15 7 22 8 15 13 2015 922 851 12 9 32 7 14 13 Successor Predecessor For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the Year Ended December 31, 2015 PHI Rental expense under operating leases $ 63 $ 49 $ 12 $ 60 __________ (a) Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $508 million , $604 million and $798 million during 2017 , 2016 and 2015 , respectively. Excludes contract amortization associated with purchase accounting and contract acquisitions.
Accrued environmental liabilities	As of December 31, 2017 and 2016 , the Registrants had accrued the following undiscounted amounts for environmental liabilities in Other current liabilities and Other deferred credits and other liabilities within their respective Consolidated Balance Sheets: December 31, 2017 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 466 $ 315 Generation 117 — ComEd 285 283 PECO 30 28 BGE 5 4 PHI 29 — Pepco 27 — DPL 1 — ACE 1 — December 31, 2016 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 429 $ 325 Generation 72 — ComEd 292 291 PECO 33 31 BGE 2 2 PHI 30 1 Pepco 27 — DPL 2 1 ACE 1 —
Schedule of Government Settlement Agreements [Table Text Block]	Under the settlement agreements, Generation has received cumulative cash reimbursements for costs incurred as follows: Total Net (a) Cumulative cash reimbursements (b) $ 1,167 $ 1,006 __________ (a) Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek. (b) Includes $53 and $49 , respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG. As of December 31, 2017 and 2016, the amount of SNF storage costs for which reimbursement has been or will be requested from the DOE under the DOE settlement agreements is as follows: December 31, 2017 December 31, 2016 DOE receivable - current (a) $ 94 $ 109 DOE receivable - noncurrent (b) 15 15 Amounts owed to co-owners (a)(c) (11 ) (13 ) __________ (a) Recorded in Accounts receivable, other. (b) Recorded in Deferred debits and other assets, other (c) Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities.

Supplemental Financial Inform61

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Financial Information [Abstract]
Components of taxes other than income	The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2017 , 2016 and 2015 . For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 898 $ 126 $ 240 $ 125 $ 89 $ 318 $ 300 $ 18 $ — Property 545 269 28 14 132 101 62 32 3 Payroll 230 121 26 15 15 26 6 4 2 Other 58 39 2 — 4 7 3 3 1 Total taxes other than income $ 1,731 $ 555 $ 296 $ 154 $ 240 $ 452 $ 371 $ 57 $ 6 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Taxes other than income Utility (a) $ 753 $ 122 $ 242 $ 136 $ 85 $ 312 $ 18 $ — $ 253 $ 78 Property 483 246 27 13 123 53 31 3 73 18 Payroll 226 117 28 15 17 8 5 3 23 8 Other 114 21 (4 ) — 4 4 1 1 5 1 Total taxes other than income $ 1,576 $ 506 $ 293 $ 164 $ 229 $ 377 $ 55 $ 7 $ 354 $ 105 For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 474 $ 105 $ 236 $ 133 $ 85 $ 326 $ 308 $ 18 $ — Property 407 250 27 11 119 94 57 28 3 Payroll 201 118 28 14 16 27 6 4 2 Other 118 16 5 2 4 8 5 1 2 Total taxes other than income $ 1,200 $ 489 $ 296 $ 160 $ 224 $ 455 $ 376 $ 51 $ 7 __________ (a) Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Components of non-operating income and expenses	For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 455 455 — — — — — — — Non-regulatory agreement units 521 521 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (10 ) (10 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (724 ) (724 ) — — — — — — — Total decommissioning-related activities 939 939 — — — — — — — Investment income 8 6 — — — 2 1 — — Interest income (expense) related to uncertain income tax positions 3 (1 ) — — — — — — — Penalty related to uncertain income tax positions (c) 2 — — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Other 31 4 10 — — 16 8 7 1 Other, net $ 1,056 $ 948 $ 22 $ 9 $ 16 $ 54 $ 32 $ 14 $ 7 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 237 $ 237 $ — $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 126 126 — — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 216 216 — — — — — — — — Non-regulatory agreement units 194 194 — — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (1 ) (1 ) — — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (372 ) (372 ) — — — — — — — — Total decommissioning-related activities 400 400 — — — — — — — — Investment income (loss) 17 8 — (1 ) 2 1 — 1 1 — Long-term lease income 4 — — — — — — — — — Interest income (expense) related to uncertain income tax positions 13 — — — — 1 — — (1 ) — Penalty related to uncertain income tax positions (c) (106 ) — (86 ) — — — — — — — AFUDC—Equity 64 — 14 8 19 19 5 6 23 7 Loss on debt extinguishment (3 ) (2 ) — — — — — — — — Other 24 (5 ) 7 1 — 15 8 2 21 (11 ) Other, net $ 413 $ 401 $ (65 ) $ 8 $ 21 $ 36 $ 13 $ 9 $ 44 $ (4 ) For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 232 $ 232 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 156 156 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (282 ) (282 ) — — — — — — — Non-regulatory agreement units (197 ) (197 ) — — — — — — — Net unrealized gains on pledged assets Zion Station decommissioning 7 7 — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) 21 21 — — — — — — — Total decommissioning-related activities (63 ) (63 ) — — — — — — — Investment income (loss) 8 3 — (2 ) 4 — — — — Long-term lease income 15 — — — — — — — — Interest income related to uncertain income tax positions 1 1 — — — 34 5 — — AFUDC—Equity 24 — 5 5 14 14 12 1 1 Terminated interest rate swaps (d) (26 ) — — — — — — — — PHI merger related debt exchange (e) (22 ) — — — — — — — — Other 17 (1 ) 16 2 — 40 11 9 2 Other, net $ (46 ) $ (60 ) $ 21 $ 5 $ 18 $ 88 $ 28 $ 10 $ 3 __________ (a) Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (c) See Note 14 — Income Taxes for discussion of the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position. (d) In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten-year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from AOCI to Other, net in Exelon's Consolidated Statements of Operations and Comprehensive Income. (e) See Note 13 — Debt and Credit Agreements and Note 4 — Mergers, Acquisitions and Dispositions for additional information on the PHI merger related debt exchange.
Components of depreciation, amortization and accretion, and other, net	The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2017 , 2016 and 2015 . For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment $ 3,293 $ 1,409 $ 777 $ 261 $ 312 $ 457 $ 203 $ 124 $ 89 Regulatory assets 478 — 73 25 161 218 118 43 57 Amortization of intangible assets, net 57 48 — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — Nuclear fuel (b) 1,096 1,096 — — — — — — — ARO accretion (c) 468 468 — — — — — — — Total depreciation, amortization and accretion $ 5,427 $ 3,056 $ 850 $ 286 $ 473 $ 675 $ 321 $ 167 $ 146 Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Depreciation, amortization and accretion Property, plant and equipment $ 3,477 $ 1,835 $ 708 $ 244 $ 299 $ 175 $ 110 $ 82 $ 325 $ 94 Regulatory assets 407 — 67 26 124 120 47 83 190 58 Amortization of intangible assets, net 52 44 — — — — — — — — Amortization of energy contract assets and liabilities (a) 35 35 — — — — — — — — Nuclear fuel (b) 1,159 1,159 — — — — — — — — ARO accretion (c) 446 446 — — — — — — — — Total depreciation, amortization and accretion $ 5,576 $ 3,519 $ 775 $ 270 $ 423 $ 295 $ 157 $ 165 $ 515 $ 152 For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI Depreciation, amortization and accretion Property, plant and equipment $ 2,227 $ 1,007 $ 635 $ 240 $ 289 $ 164 $ 103 $ 76 $ 392 Regulatory assets 170 — 72 20 77 92 45 99 232 Amortization of intangible assets, net 54 47 — — — — — — — Amortization of energy contract assets and liabilities (a) 22 22 — — — — — — — Nuclear fuel (b) 1,116 1,116 — — — — — — — ARO accretion (c) 398 397 — — — — — — — Total depreciation, amortization and accretion $ 3,987 $ 2,589 $ 707 $ 260 $ 366 $ 256 $ 148 $ 175 $ 624 __________ (a) Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Schedule of Cash Flow, Supplemental Disclosure	For the year ended December 31, 2017 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 2,430 $ 391 $ 307 $ 103 $ 96 $ 236 $ 114 $ 49 $ 59 Income taxes (net of refunds) 540 337 83 47 (2 ) (144 ) (104 ) (49 ) (2 ) Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 643 $ 227 $ 176 $ 29 $ 62 $ 94 $ 25 $ 13 $ 13 Loss (Gain) from equity method investments 32 33 — — — (1 ) — — — Provision for uncollectible accounts 125 38 34 26 8 19 8 3 8 Provision for excess and obsolete inventory 56 51 3 — — 2 1 1 — Stock-based compensation costs 88 — — — — — — — — Other decommissioning-related activity (a) (313 ) (313 ) — — — — — — — Energy-related options (b) 7 7 — — — — — — — Amortization of regulatory asset related to debt costs 9 — 4 1 — 4 2 1 1 Amortization of rate stabilization deferral (10 ) — — — 7 (17 ) (17 ) — — Amortization of debt fair value adjustment (18 ) (12 ) — — — (6 ) — — — Merger-related commitments (c) — — — — — (8 ) (6 ) (2 ) — Severance costs 35 31 — — — 3 — — — Amortization of debt costs 64 37 5 2 2 4 2 — 1 Discrete impacts from EIMA and FEJA (d) (52 ) — (52 ) — — — — — — Vacation accrual adjustment (e) (68 ) (35 ) (12 ) — — (8 ) (8 ) — — Long-term incentive plan 109 — — — — — — — — Change in environmental liabilities 44 44 — — — — — — — Other (30 ) 4 6 (4 ) (14 ) (27 ) (12 ) (7 ) (6 ) Total other non-cash operating activities $ 721 $ 112 $ 164 $ 54 $ 65 $ 59 $ (5 ) $ 9 $ 17 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ 42 $ 73 $ (61 ) $ 22 $ 23 $ (12 ) $ 5 $ 4 $ (13 ) Change in PPE related to ARO update 29 29 — — — — — — — Non-cash financing of capital projects 16 16 — — — — — — — Indemnification of like-kind exchange position (f) — — 21 — — — — — — Dividends on stock compensation 7 — — — — — — — — Dissolution of financing trust due to long-term debt retirement 8 — — — 8 — — — — Fair value adjustment of long-term debt due to retirement (5 ) — — — — — — — — Fair value of pension and OPEB obligation transferred in connection with FitzPatrick — 33 — — — — — — — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 4 - Mergers, Acquisitions and Dispositions for more information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 3 — Regulatory Matters for more information. (e) On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that will now be accrued ratably over the year in 2018. (f) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. Successor Predecessor For the year ended December 31, 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 1,340 $ 339 $ 298 $ 104 $ 92 $ 118 $ 47 $ 62 $ 209 $ 43 Income taxes (net of refunds) (441 ) 435 (444 ) 64 31 216 115 200 258 11 Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 619 $ 218 $ 166 $ 33 $ 67 $ 31 $ 18 $ 15 $ 86 $ 23 Loss from equity method investments 24 25 — — — — — — — — Provision for uncollectible accounts 155 19 41 30 1 29 23 32 65 16 Stock-based compensation costs 111 — — — — — — — — 3 Other decommissioning-related activity (a) (384 ) (384 ) — — — — — — — — Energy-related options (b) (11 ) (11 ) — — — — — — — — Amortization of regulatory asset related to debt costs 9 — 4 1 — 2 1 1 3 1 Amortization of rate stabilization deferral 76 — — — 81 (12 ) 2 — (5 ) 5 Amortization of debt fair value adjustment (11 ) (11 ) — — — — — — — — Merger-related commitments (c)(d) 558 53 — — — 125 82 110 317 — Severance costs 99 22 — — — — — — 56 — Discrete impacts from EIMA (e) 8 — 8 — — — — — — — Amortization of debt costs 35 17 4 3 1 — — — 1 — Provision for excess and obsolete inventory 12 6 4 — — 3 1 1 1 1 Lower of cost or market inventory adjustment 37 36 — 1 — — — — — — Baltimore City Conduit Lease Settlement (28 ) — — — (28 ) — — — — — Cash Working Capital Order (13 ) — — — (13 ) — — — — — Asset Retirement Costs 2 — — — — — 1 2 2 — Long-term incentive plan 70 — — — — — — — — — Other (35 ) 25 (12 ) (3 ) (21 ) 5 (14 ) (6 ) (12 ) (3 ) Total other non-cash operating activities $ 1,333 $ 15 $ 215 $ 65 $ 88 $ 183 $ 114 $ 155 $ 514 $ 46 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (128 ) $ 50 $ (91 ) $ (11 ) $ (86 ) $ 27 $ (12 ) $ 11 $ 21 $ 11 Change in PPE related to ARO update 191 191 — — — — — — — — Indemnification of like-kind exchange position (g) — — 158 — — — — — — — Dividends on stock compensation 6 — — — — — — — — — Non-cash financing of capital projects 95 95 — — — — — — — — Sale of Upstream assets (c) 37 37 — — — — — — — — Pending FitzPatrick Acquisition (h) (54 ) (54 ) — — — — — — — — Fair value of net assets contributed to Generation in connection with the PHI merger, net of cash — 119 — — — — — — — — Fair value of net assets distributed to Exelon in connection with the PHI Merger, net of cash (c)(f) — — — — — — — — 127 — Fair value of pension obligation transferred in connection with the PHI Merger (c)(f) — — — — — — — — 53 — Assumption of member purchase liability — — — — — — — — 29 — Assumption of merger commitment liability — — — — — 33 — — 33 — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) See Note 4 - Mergers, Acquisitions and Dispositions for more information. (d) Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts. (e) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information. (f) Immediately following closing of the PHI Merger, the net assets associated with PHI’s unregulated business interests were distributed by PHI to Exelon. Exelon contributed a portion of such net assets to Generation. (g) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. (h) Reflects the transfer of nuclear fuel to Entergy under the cost reimbursement provisions of the FitzPatrick acquisition agreements. See Note 4 - Mergers, Acquisitions and Dispositions for more information. For the year ended December 31, 2015 Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 930 $ 348 $ 308 $ 94 $ 120 $ 268 $ 116 $ 47 $ 63 Income taxes (net of refunds) 342 476 (265 ) 64 73 (13 ) (6 ) (5 ) — Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 637 $ 269 $ 206 $ 39 $ 65 $ 97 $ 30 $ 15 $ 15 Loss from equity method investments 7 8 — — — — — — — Provision for uncollectible accounts 120 22 53 30 15 61 21 20 20 Provision for excess and obsolete inventory 10 9 1 — — 1 — — — Stock-based compensation costs 97 — — — — 13 — — — Other decommissioning-related activity (a) (82 ) (82 ) — — — — — — — Energy-related options (b) 21 21 — — — — — — — Amortization of regulatory asset related to debt costs 7 — 5 2 — 5 2 1 1 Amortization of rate stabilization deferral 73 — — — 73 (2 ) 1 (3 ) — Amortization of debt fair value adjustment (17 ) (17 ) — — — — — — — Discrete impacts from EIMA (c) 144 — 144 — — — — — — Amortization of debt costs 58 15 4 2 2 2 — — — Lower of cost or market inventory adjustment 23 23 — — — — — — — Long-term incentive plan 24 — — — — — — — — Other (13 ) — 3 (3 ) (18 ) (10 ) — — 1 Total other non-cash operating activities $ 1,109 $ 268 $ 416 $ 70 $ 137 $ 167 $ 54 $ 33 $ 37 Non-cash investing and financing activities: Change in PPE related to ARO update $ 885 $ 885 $ — $ — $ — $ — $ — $ — $ — Increase (decrease) in capital expenditures not paid 96 82 34 (13 ) (9 ) 6 (1 ) 3 3 Nuclear fuel procurement (d) 57 57 — — — — — — — Indemnification of like-kind exchange position (e) — — 7 — — — — — — Dividends on stock compensation 6 — — — — — — — — Non-cash financing of capital projects 77 77 — — — — — — — Long-term software licensing agreement (f) 95 — — — — — — — — __________ (a) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning. (b) Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations. (c) Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information. (d) Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 30, 2018, with the final payment being due no later than September 30, 2020. (e) See Note 14 — Income Taxes for discussion of the like-kind exchange tax position. (f) Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 13 - Debt and Credit Agreements .
Supplemental Balance Sheet Disclosures [Text Block]	The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2017 and 2016 . Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 14 $ — $ 6 $ 8 $ — $ — $ — $ — $ — Bloom 206 206 — — — — — — — Net Power 76 76 — — — — — — — Other equity method investments 1 1 — — — — — — — Total equity method investments 297 283 6 8 — — — — — Other investments: Employee benefit trusts and investments (b) 244 51 — 17 5 132 102 — — Other cost method investments 62 62 — — — — — — — Other available for sale investments 37 37 — — — — — — — Total investments $ 640 $ 433 $ 6 $ 25 $ 5 $ 132 $ 102 $ — $ — Successor December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 22 $ — $ 6 $ 8 $ 8 $ — $ — $ — $ — Bloom 216 216 — — — — — — — Net Power 57 57 — — — — — — — Other equity method investments 16 15 — — — — — — — Total equity method investments 311 288 6 8 8 — — — — Other investments: Employee benefit trusts and investments (b) 232 44 — 17 4 133 102 — — Other cost method investments 52 52 — — — — — — — Other available for sale investments 34 34 — — — — — — — Total investments $ 629 $ 418 $ 6 $ 25 $ 12 $ 133 $ 102 $ — $ — __________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) The Registrants’ investments in these marketable securities are recorded at fair market value.
Accrued Liabilities Current	The following tables provide additional information about liabilities of the Registrants at December 31, 2017 and 2016 . Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 978 $ 407 $ 158 $ 64 $ 58 $ 106 $ 29 $ 17 $ 11 Taxes accrued 373 444 60 15 71 61 68 4 5 Interest accrued 328 78 102 33 34 48 23 8 12 Severance accrued 58 30 2 — — 17 — — — Other accrued expenses 98 61 5 2 1 29 17 6 5 Total accrued expenses $ 1,835 $ 1,020 $ 327 $ 114 $ 164 $ 261 $ 137 $ 35 $ 33 Successor December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 1,199 $ 557 $ 199 $ 67 $ 64 $ 112 $ 30 $ 17 $ 11 Taxes accrued 723 239 330 4 78 65 48 4 9 Interest accrued 1,234 82 609 30 31 49 21 8 12 Severance accrued 44 15 2 — — 19 — — — Other accrued expenses 260 96 110 3 2 27 14 7 6 Total accrued expenses $ 3,460 $ 989 $ 1,250 $ 104 $ 175 $ 272 $ 113 $ 36 $ 38 __________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Analysis and reconciliation of reportable segment information	An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the years ended December 31, 2017 , 2016 , and 2015 is as follows: Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Operating revenues (c) : 2017 Competitive businesses electric revenues $ 15,300 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,195 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 591 — — — — — (1 ) 590 Rate-regulated electric revenues — 5,536 2,375 2,489 4,469 — (29 ) 14,840 Rate-regulated natural gas revenues — — 495 687 161 — (10 ) 1,333 Shared service and other revenues — — — — 49 1,831 (1,880 ) — 2016 Competitive businesses electric revenues $ 15,390 $ — $ — $ — $ — $ — $ (1,430 ) $ 13,960 Competitive businesses natural gas revenues 2,146 — — — — — — 2,146 Competitive businesses other revenues 215 — — — — — (4 ) 211 Rate-regulated electric revenues — 5,254 2,531 2,609 3,506 — (31 ) 13,869 Rate-regulated natural gas revenues — — 463 624 92 — (13 ) 1,166 Shared service and other revenues — — — — 45 1,648 (1,686 ) 7 2015 Competitive businesses electric revenues $ 15,944 $ — $ — $ — $ — $ — $ (744 ) $ 15,200 Competitive businesses natural gas revenues 2,433 — — — — — — 2,433 Competitive businesses other revenues 758 — — — — — (1 ) 757 Rate-regulated electric revenues — 4,905 2,486 2,490 — — (5 ) 9,876 Rate-regulated natural gas revenues — — 546 645 — — (15 ) 1,176 Shared service and other revenues — — — — — 1,372 (1,367 ) 5 Intersegment revenues (d) : 2017 $ 1,110 $ 15 $ 7 $ 16 $ 50 $ 1,824 $ (3,020 ) $ 2 2016 1,428 15 8 21 45 1,647 (3,159 ) 5 2015 745 4 2 14 — 1,367 (2,127 ) 5 Depreciation and amortization: 2017 $ 1,457 $ 850 $ 286 $ 473 $ 675 $ 87 $ — $ 3,828 2016 1,879 775 270 423 515 74 — 3,936 2015 1,054 707 260 366 — 63 — 2,450 Operating expenses (c) : 2017 $ 17,993 $ 4,214 $ 2,215 $ 2,562 $ 3,911 $ 1,851 $ (3,026 ) $ 29,720 2016 16,856 4,056 2,292 2,683 3,549 1,928 (3,164 ) 28,200 2015 16,872 3,889 2,404 2,578 — 1,444 (2,131 ) 25,056 Equity in earnings (losses) of unconsolidated affiliates: 2017 $ (33 ) $ — $ — $ — $ — $ 1 $ — $ (32 ) 2016 (25 ) — — — — 1 — (24 ) 2015 (8 ) — — — — 1 — (7 ) Interest expense, net: 2017 $ 440 $ 361 $ 126 $ 105 $ 245 $ 283 $ — $ 1,560 2016 364 461 123 103 195 290 — 1,536 2015 365 332 114 99 — 123 — 1,033 Income (loss) before income taxes: 2017 $ 1,429 $ 984 $ 538 $ 525 $ 578 $ (296 ) $ (2 ) $ 3,756 2016 873 679 587 468 (58 ) (555 ) (5 ) 1,989 2015 1,850 706 521 477 — (219 ) (5 ) 3,330 Income taxes: 2017 $ (1,375 ) $ 417 $ 104 $ 218 $ 217 $ 294 $ — $ (125 ) 2016 290 301 149 174 3 (156 ) — 761 2015 502 280 143 189 — (41 ) — 1,073 Net income (loss): 2017 $ 2,771 $ 567 $ 434 $ 307 $ 362 $ (590 ) $ (2 ) $ 3,849 2016 558 378 438 294 (61 ) (398 ) (5 ) 1,204 2015 1,340 426 378 288 — (177 ) (5 ) 2,250 Capital expenditures: 2017 $ 2,259 $ 2,250 $ 732 $ 882 $ 1,396 $ 65 $ — $ 7,584 2016 3,078 2,734 686 934 1,008 113 — 8,553 2015 3,841 2,398 601 719 — 65 — 7,624 Total assets: 2017 $ 48,387 $ 29,726 $ 10,170 $ 9,104 $ 21,247 $ 8,618 $ (10,552 ) $ 116,700 2016 46,974 28,335 10,831 8,704 21,025 10,369 (11,334 ) 114,904 __________ (a) Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $138 million , sales to BGE of $388 million , sales to Pepco of $255 million , sales to DPL of $179 million and sales to ACE of $29 million in the Mid-Atlantic region, and sales to ComEd of $121 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2016 , intersegment revenues for Generation include revenue from sales to PECO of $ 290 million and sales to BGE of $ 608 million in the Mid-Atlantic region, and sales to ComEd of $ 47 million in the Midwest region, which eliminate upon consolidation. For the Successor period of March 24, 2016 to December 31, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $295 million , sales to DPL of $154 million and sales to ACE of $37 million in the Mid-Atlantic region, which eliminate upon consolidation. For the year ended December 31, 2015 , intersegment revenues for Generation include revenue from sales to PECO of $224 million and sales to BGE of $502 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017 , 2016 and 2015 . (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income. (e) Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2017 . PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor periods, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016 and for the year ended December 31, 2015 . Successor and Predecessor PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : December 31, 2017 - Successor Rate-regulated electric revenues $ 2,158 $ 1,139 $ 1,186 $ — $ (14 ) $ 4,469 Rate-regulated natural gas revenues — 161 — — — 161 Shared service and other revenues — — — 52 (3 ) 49 March 24, 2016 to December 31, 2016 - Successor Rate-regulated electric revenues $ 1,675 $ 850 $ 989 $ 5 $ (13 ) $ 3,506 Rate-regulated natural gas revenues — 92 — — — 92 Shared service and other revenues — — — 45 — 45 January 1, 2016 to March 23, 2016 - Predecessor Rate-regulated electric revenues $ 511 $ 279 $ 268 $ 42 $ (4 ) $ 1,096 Rate-regulated natural gas revenues — 56 — 1 — 57 Shared service and other revenues — — — — — — December 31, 2015 - Predecessor Rate-regulated electric revenues $ 2,129 $ 1,138 $ 1,295 $ 210 $ (2 ) $ 4,770 Rate-regulated natural gas revenues — 164 — 1 — 165 Shared service and other revenues — — — — — — Intersegment revenues: December 31, 2017 - Successor $ 6 $ 8 $ 2 $ 53 $ (19 ) $ 50 March 24, 2016 to December 31, 2016 - Successor 4 5 2 47 (13 ) 45 January 1, 2016 to March 23, 2016 - Predecessor 1 2 1 — (4 ) — December 31, 2015 - Predecessor 5 6 4 — (15 ) — Depreciation and amortization: December 31, 2017 - Successor $ 321 $ 167 $ 146 $ 42 $ (1 ) $ 675 March 24, 2016 to December 31, 2016 - Successor 224 120 128 43 — $ 515 January 1, 2016 to March 23, 2016 - Predecessor 71 37 37 11 (4 ) $ 152 December 31, 2015 - Predecessor 256 148 175 45 — $ 624 Operating expenses: December 31, 2017 - Successor $ 1,760 $ 1,071 $ 1,029 $ 68 $ (17 ) $ 3,911 March 24, 2016 to December 31, 2016 - Successor 1,577 952 1,000 33 (13 ) $ 3,549 January 1, 2016 to March 23, 2016 - Predecessor 443 284 251 73 (3 ) $ 1,048 December 31, 2015 - Predecessor 1,790 1,137 1,161 220 — $ 4,308 Interest expense, net: December 31, 2017 - Successor $ 121 $ 51 $ 61 $ 13 $ (1 ) $ 245 March 24, 2016 to December 31, 2016 - Successor 98 38 47 12 — $ 195 January 1, 2016 to March 23, 2016 - Predecessor 29 12 15 11 (2 ) $ 65 December 31, 2015 - Predecessor 124 50 64 43 (1 ) $ 280 Income (loss) before income taxes: December 31, 2017 - Successor $ 310 $ 192 $ 103 $ 377 $ (404 ) $ 578 March 24, 2016 to December 31, 2016 - Successor 36 (30 ) (51 ) (84 ) 71 $ (58 ) January 1, 2016 to March 23, 2016 - Predecessor 47 43 5 59 (118 ) $ 36 December 31, 2015 - Predecessor 289 125 73 23 (29 ) $ 481 Income taxes: December 31, 2017 - Successor $ 105 $ 71 $ 26 $ 15 $ — $ 217 March 24, 2016 to December 31, 2016 - Successor 26 5 (5 ) (23 ) — $ 3 January 1, 2016 to March 23, 2016 - Predecessor 15 17 1 (16 ) — $ 17 December 31, 2015 - Predecessor 102 49 33 (48 ) 27 $ 163 Net income (loss): December 31, 2017 - Successor $ 205 $ 121 $ 77 $ (91 ) $ 50 $ 362 March 24, 2016 to December 31, 2016 - Successor 10 (35 ) (47 ) (34 ) 45 $ (61 ) January 1, 2016 to March 23, 2016 - Predecessor 32 26 5 (44 ) — $ 19 December 31, 2015 - Predecessor 187 76 40 25 (1 ) $ 327 Capital expenditures: December 31, 2017 - Successor $ 628 $ 428 $ 312 $ 28 $ — $ 1,396 March 24, 2016 to December 31, 2016 - Successor 489 277 218 24 — $ 1,008 January 1, 2016 to March 23, 2016 - Predecessor 97 72 93 11 — 273 December 31, 2015 - Predecessor 544 352 300 34 — 1,230 Total assets: December 31, 2017 - Successor $ 7,832 $ 4,357 $ 3,445 $ 10,600 $ (4,987 ) $ 21,247 December 31, 2016 - Successor 7,335 4,153 3,457 10,804 (4,724 ) 21,025 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017 , 2016 and 2015 . (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. For the predecessor periods presented, Other includes the activity of PHI’s unregulated businesses which were distributed to Exelon and Generation as a result of the PHI Merger.
Analysis and reconciliation of reportable segment revenues for Generation	Generation total revenues: 2017 2016 2015 Revenues from external customers (a) Intersegment revenues Total revenues Revenues from external customers (a) Intersegment revenues Total revenues Revenues from external customers (a) Intersegment revenues Total revenues Mid-Atlantic $ 5,515 $ 25 $ 5,540 $ 6,212 $ (33 ) $ 6,179 $ 5,974 $ (74 ) $ 5,900 Midwest 4,206 (25 ) 4,181 4,402 10 4,412 4,712 (2 ) 4,710 New England 2,010 (8 ) 2,002 1,778 (9 ) 1,769 2,217 (5 ) 2,212 New York 1,535 (17 ) 1,518 1,198 (42 ) 1,156 996 (11 ) 985 ERCOT 958 4 962 831 6 837 863 (6 ) 857 Other Power Regions 1,076 (27 ) 1,049 969 (62 ) 907 1,182 (80 ) 1,102 Total Revenues for Reportable Segments $ 15,300 $ (48 ) $ 15,252 $ 15,390 $ (130 ) $ 15,260 $ 15,944 $ (178 ) $ 15,766 Other (b) 3,166 48 3,214 2,361 130 2,491 3,191 178 3,369 Total Generation Consolidated Operating Revenues $ 18,466 $ — $ 18,466 $ 17,751 $ — $ 17,751 $ 19,135 $ — $ 19,135 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $38 million decrease to revenues, a $ 52 million decrease to revenues, and a $ 7 million increase to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2017 , 2016 , and 2015 , respectively, unrealized mark-to-market losses of $131 million , losses of $500 million , and gains of $203 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively, and elimination of intersegment revenues. Generation total revenues net of purchased power and fuel expense: 2017 2016 2015 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 3,105 $ 109 $ 3,214 $ 3,282 $ 35 $ 3,317 $ 3,556 $ 15 $ 3,571 Midwest 2,810 10 2,820 2,969 2 2,971 2,912 (20 ) 2,892 New England 538 (24 ) 514 467 (29 ) 438 519 (58 ) 461 New York 975 1 976 761 (19 ) 742 584 50 634 ERCOT 575 (243 ) 332 412 (131 ) 281 425 (132 ) 293 Other Power Regions 476 (171 ) 305 483 (147 ) 336 440 (190 ) 250 Total Revenues net of purchased power and fuel expense for Reportable Segments $ 8,479 $ (318 ) $ 8,161 $ 8,374 $ (289 ) $ 8,085 $ 8,436 $ (335 ) $ 8,101 Other (b) 297 318 615 547 289 836 678 335 1,013 Total Generation Revenues net of purchased power and fuel expense $ 8,776 $ — $ 8,776 $ 8,921 $ — $ 8,921 $ 9,114 $ — $ 9,114 __________ (a) Includes purchases and sales from third parties and affiliated sales to the Utility Registrants. (b) Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million decrease in RNF, a $57 million decrease in RNF, and a $8 million increase in RNF for the amortization of intangible assets and liabilities related to commodity contracts for the years ended December 31, 2017 , 2016 , and 2015 , respectively, unrealized mark-to-market losses of $175 million , losses of $41 million , and gains of $257 million for the years ended December 31, 2017 , 2016 , and 2015 , respectively, accelerated nuclear fuel amortization associated with the announced early retirement decision for Clinton and Quad Cities as discussed in Note 8 - Early Nuclear Plant Retirements of $12 million and $60 million for the year ended December 31, 2017 and 2016 , and the elimination of intersegment revenues net of purchased power and fuel expense.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Schedule of Related Party Transactions [Table Text Block]	December 31, 2017 2016 Payables to affiliates (current): Generation (b) $ 36 $ 44 BSC (c) 11 4 DPL — 1 PHISCO (c) 27 25 Total payables to affiliates (current) $ 74 $ 74 __________ ACE The financial statements of ACE include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PHISCO $ 1 $ 2 $ 2 Other 1 1 2 Total operating revenues from affiliates $ 2 $ 3 $ 4 Purchased power from affiliate Generation (a) $ 29 $ 37 $ — Operating and maintenance: PHISCO (b) $ 135 $ 155 $ 143 Operating and maintenance from affiliates: BSC (b) $ 25 $ 15 $ — Other 3 3 3 Total operating and maintenance from affiliates $ 28 $ 18 $ 3 Cash dividends paid to parent $ 68 $ 63 $ 12 Contribution from parent $ — $ 139 $ 95 The financial statements of Pepco include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ — $ 1 $ — PHISCO 6 4 5 Total operating revenues from affiliates $ 6 $ 5 $ 5 Purchased power from affiliate Generation (b) $ 255 $ 295 $ — Operating and maintenance: PHISCO (c) $ 219 $ 263 $ 240 PES (d) 29 39 26 Total operating and maintenance $ 248 $ 302 $ 266 Operating and maintenance from affiliates: BSC (c) $ 53 $ 31 $ — PHISCO (c) 5 4 4 Total operating and maintenance from affiliates $ 58 $ 35 $ 4 Cash dividends paid to parent $ 133 $ 136 $ 146 Contribution from parent $ 161 $ 187 $ 112 December 31, 2017 2016 Prepaid voluntary employee beneficiary association trust (c) $ 2 $ 5 Receivable from affiliates (current): Voluntary employee beneficiary association trust $ 1 $ 2 Generation 12 9 Exelon Corporate (d) — 345 Total receivable from affiliates (current) $ 13 $ 356 Receivable from affiliates (noncurrent): Generation (e) $ 2,528 $ 2,169 Other — 1 Total receivable from affiliates (noncurrent) $ 2,528 $ 2,170 Payables to affiliates (current): Generation (a) $ 28 $ 14 BSC (b) 39 42 ComEd Financing III 4 4 PECO — 2 Exelon Corporate 3 3 Total payables to affiliates (current) $ 74 $ 65 Long-term debt to ComEd financing trust ComEd Financing III $ 205 $ 205 __________ (a) ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information. (b) ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (c) The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets. (d) Represents indemnification from Exelon Corporate related to the like-kind exchange. (e) ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers. December 31, 2017 2016 Receivable from affiliates (current): Other $ 1 $ — Payables to affiliates (current): Generation (b) $ 24 $ 26 BSC (c) 25 22 Exelon Corporate 1 1 PECO — 2 BGE Capital Trust II — 3 Other 2 1 Total payables to affiliates (current) $ 52 $ 55 Long-term debt to BGE financing trust BGE Capital Trust II $ — $ 252 __________ (a) BGE provides energy to Generation for Generation’s own use. (b) BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (c) BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. Successor December 31, 2017 2016 Payables to affiliates (current): Generation $ 54 $ 74 BGE 1 — BSC (a) 24 10 Exelon Corporate 6 6 Other 5 4 Total payables to affiliates (current) $ 90 $ 94 The financial statements of ComEd include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates Generation $ 9 $ 7 $ 4 BSC 6 6 — PECO — 1 — BGE — 1 — Total operating revenues from affiliates $ 15 $ 15 $ 4 Purchased power from affiliate Generation (a) $ 108 $ 47 $ 18 Operating and maintenance from affiliates BSC (b) $ 270 $ 225 $ 195 PECO — 1 — BGE — 1 — Total operating and maintenance from affiliates $ 270 $ 227 $ 195 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 118 $ 112 $ 103 Cash dividends paid to parent $ 422 $ 369 $ 299 Contribution from parent $ 651 $ 315 $ 202 PHI The financial statements of PHI include related party transactions as presented in the tables below: Successor For the Year Ended December 31, March 24, 2016 to December 31, 2017 2016 Operating revenues from affiliates: BSC $ 48 $ 44 PHISCO 2 — Generation — 1 Total operating revenues from affiliates $ 50 $ 45 Purchased power from affiliate Generation $ 463 $ 486 Operating and maintenance from affiliates: BSC (a) $ 145 $ 86 Other 5 3 Total operating and maintenance from affiliates $ 150 $ 89 Cash dividends paid to parent $ 311 $ 273 Contribution from member $ 758 $ 1,251 The financial statements of DPL include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PHISCO $ 6 $ 5 $ 5 Other 2 2 1 Total operating revenues from affiliates $ 8 $ 7 $ 6 Purchased power from affiliate Generation (a) $ 179 $ 154 $ — Operating and maintenance: PHISCO (b) $ 165 $ 194 $ 179 PES (c) 9 8 3 Total operating and maintenance $ 174 $ 202 $ 182 Operating and maintenance from affiliates: BSC (b) $ 31 $ 18 $ — Other 1 1 1 Total operating and maintenance from affiliates $ 32 $ 19 $ 1 Cash dividends paid to parent $ 112 $ 54 $ 92 Contribution from parent $ — $ 152 $ 75 The financial statements of Generation include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: ComEd (a) $ 121 $ 47 $ 18 PECO (b) 138 290 224 BGE (c) 388 608 502 Pepco (d) 255 295 — DPL (e) 179 154 — ACE (f) 29 37 — BSC 1 2 1 Other 4 6 4 Total operating revenues from affiliates $ 1,115 $ 1,439 $ 749 Purchased power and fuel from affiliates: ComEd $ 13 $ — $ — BGE 9 12 14 Other (3 ) — — Total purchased power and fuel from affiliates $ 19 $ 12 $ 14 Operating and maintenance from affiliates: ComEd (g) $ 7 $ 7 $ 4 PECO (g) 1 3 2 BGE (g) 1 1 — Pepco — 1 — PHISCO 1 1 — BSC (h) 689 650 614 Other $ (2 ) $ — $ — Total operating and maintenance from affiliates $ 697 $ 663 $ 620 Interest expense to affiliates, net: Exelon Corporate (i) $ 37 $ 39 $ 43 PCI 1 — — PECO 1 — — Total interest expense to affiliates, net: 39 39 43 Earnings (losses) in equity method investments Qualifying facilities and domestic power projects $ (33 ) $ (25 ) $ (8 ) Capitalized costs BSC (h) $ 98 $ 98 $ 76 Cash distribution paid to member $ 659 $ 922 $ 2,474 Contribution from member $ 102 $ 142 $ 47 The financial statements of PECO include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ 1 $ 3 $ 2 BSC 5 3 — ComEd — 1 — BGE 1 1 — Total operating revenues from affiliates $ 7 $ 8 $ 2 Purchased power from affiliate Generation (b) $ 135 $ 287 $ 220 Operating and maintenance from affiliates: BSC (c) $ 146 $ 142 $ 107 Generation 2 2 3 ComEd — 1 — BGE 1 1 — Total operating and maintenance from affiliates $ 149 $ 146 $ 110 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Generation (1 ) — — Total interest expense to affiliates, net: $ 11 $ 12 $ 12 Capitalized costs BSC (c) $ 59 $ 57 $ 40 Cash dividends paid to parent $ 288 $ 277 $ 279 Contribution from parent $ 16 $ 18 $ 16 December 31, 2017 2016 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 BGE Capital Trust II — 3 Total payables to affiliates (current) $ 5 $ 8 Long-term debt due to financing trusts: ComEd Financing III $ 205 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 BGE Capital Trust II — 252 Total long-term debt due to financing trusts $ 389 $ 641 __________ (a) The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 3 — Regulatory Matters for additional information. December 31, 2017 2016 Receivables from affiliates (current): Pepco $ — $ 1 ACE — 2 Total receivable from affiliates (current) $ — $ 3 Payables to affiliates (current): Generation (a) $ 12 $ 16 BSC (b) 7 3 PHISCO (b) 27 19 Total payables to affiliates (current) $ 46 $ 38 The financial statements of Exelon include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: PECO (a) $ 1 $ 1 $ 1 BGE (a) 4 4 4 Other 2 5 4 Total operating revenues from affiliates $ 7 $ 10 $ 9 Interest expense to affiliates, net: ComEd Financing III $ 14 $ 13 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II 10 16 16 Total interest expense to affiliates, net $ 36 $ 41 $ 41 Earnings (losses) in equity method investments: Qualifying facilities and domestic power projects $ (33 ) $ (25 ) $ (8 ) Other 1 1 1 Total losses in equity method investments $ (32 ) $ (24 ) $ (7 ) December 31, 2017 2016 Payables to affiliates (current): Generation (a) $ 6 $ 9 BSC (b) 5 2 DPL — 2 PHISCO (b) 18 16 Total payables to affiliates (current) $ 29 $ 29 __________ (a) ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. See Note 3 — Regulatory Matters for additional information. (b) ACE receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. December 31, 2017 2016 Prepaid voluntary employee beneficiary association trust (d) $ — $ 1 Receivable from affiliate (current): ComEd $ — $ 2 BGE — 2 Total receivable from affiliates (current) $ — $ 4 Receivable from affiliate (noncurrent): Generation (e) $ 537 $ 438 Payables to affiliates (current): Generation (b) $ 22 $ 33 BSC (c) 29 28 Exelon Corporate 1 1 PECO Trust III 1 1 Total payables to affiliates (current) $ 53 $ 63 Long-term debt to financing trusts: PECO Trust III $ 81 $ 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 184 $ 184 __________ (a) PECO provides energy to Generation for Generation’s own use. (b) PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3 — Regulatory Matters for additional information on AECs. (c) PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (d) The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. (e) PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers. The financial statements of BGE include related party transactions as presented in the tables below: For the Years Ended December 31, 2017 2016 2015 Operating revenues from affiliates: Generation (a) $ 10 $ 13 $ 14 BSC 5 6 — ComEd — 1 — PECO 1 1 — Total operating revenues from affiliates $ 16 $ 21 $ 14 Purchased power from affiliate Generation (b) $ 384 $ 604 $ 498 Operating and maintenance from affiliates: BSC (c) $ 152 $ 130 $ 118 ComEd — 1 — PECO 1 1 — Total operating and maintenance from affiliates $ 153 $ 132 $ 118 Interest expense to affiliates, net: BGE Capital Trust II $ 10 $ 16 $ 16 Capitalized costs BSC (c) $ 54 $ 36 $ 28 Cash dividends paid to parent $ 198 $ 179 $ 158 Contribution from parent $ 184 $ 61 $ 7 December 31, 2017 2016 Receivables from affiliates (current): ComEd (a) $ 28 $ 14 PECO (b) 26 33 BGE (c) 24 26 Pepco (d) 36 44 DPL (e) 12 16 ACE (f) 6 9 PHISCO (h) 1 5 PCI — 8 Other 7 1 Total receivables from affiliates (current) $ 140 $ 156 Intercompany money pool (current): PCI $ 54 $ 55 Payables to affiliates (current): Exelon Corporate (i) $ 21 $ 22 BSC (h) 74 99 ComEd 12 9 PECO (b) 4 — Other 12 7 Total payables to affiliates (current) $ 123 $ 137 Long-term debt due to affiliates (noncurrent): Exelon Corporate (k) $ 910 $ 922 Payables to affiliates (noncurrent): BSC (h) $ — $ 1 ComEd (j) 2,528 2,169 PECO (j) 537 438 Total payables to affiliates (noncurrent) $ 3,065 $ 2,608 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3 — Regulatory Matters for additional information. (b) Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3 — Regulatory Matters for additional information. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (d) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3 — Regulatory Matters for additional information. (e) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3 — Regulatory Matters for additional information. (f) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3 — Regulatory Matters for additional information. (g) Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and BGE and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations. (h) Generation receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized. (i) The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation. (j) Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 15 — Asset Retirement Obligations . (k) In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets.

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Information	The data shown below, which may not equal the total for the year due to the effects of rounding and dilution, includes all adjustments that Exelon considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 8,757 $ 7,573 $ 1,296 $ 483 $ 995 $ 173 June 30 7,623 6,910 232 647 80 267 September 30 8,769 9,002 1,475 1,267 824 490 December 31 8,381 7,875 1,258 714 1,871 204 Average Basic Shares Net Income 2017 2016 2017 2016 Quarter ended: March 31 928 923 $ 1.07 $ 0.19 June 30 934 924 0.09 0.29 September 30 962 925 0.86 0.53 December 31 964 925 1.94 0.22 Net Income 2017 2016 2017 2016 Quarter ended: March 31 930 925 $ 1.07 $ 0.19 June 30 936 926 0.09 0.29 September 30 965 927 0.85 0.53 December 31 967 928 1.93 0.22 The following table presents the New York Stock Exchange—Composite Common Stock Prices and dividends by quarter on a per share basis: 2017 2016 Fourth Quarter Third Quarter Second Quarter First Quarter Fourth Quarter Third Quarter Second Quarter First Quarter High price $ 42.67 $ 38.78 $ 37.44 $ 37.19 $ 36.36 $ 37.70 $ 36.37 $ 35.95 Low price 37.55 35.37 33.30 34.47 29.82 32.86 33.18 26.26 Close 39.41 37.67 36.07 35.98 35.49 33.29 36.36 35.86 Dividends 0.328 0.328 0.328 0.328 0.318 0.318 0.318 0.310 The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 275 $ 291 $ 25 $ (121 ) $ 28 $ (100 ) June 30 270 270 25 19 8 3 September 30 370 421 79 83 41 47 December 31 271 275 28 26 — 8 The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 796 $ 841 $ 192 $ 196 $ 127 $ 124 June 30 630 664 137 152 88 100 September 30 715 788 169 204 112 122 December 31 729 701 157 150 107 92 The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 951 $ 929 $ 228 $ 187 $ 125 $ 98 June 30 674 680 98 59 45 31 September 30 738 812 124 115 62 54 December 31 813 812 163 190 76 103 The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) Common Shareholders 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 530 $ 551 $ 79 $ (105 ) $ 58 $ (108 ) June 30 514 509 84 97 43 49 September 30 604 635 149 132 87 79 December 31 510 491 87 51 17 23 The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 362 $ 362 $ 78 $ (72 ) $ 57 $ (72 ) June 30 282 281 41 30 19 12 September 30 327 331 59 72 31 44 December 31 330 303 52 20 14 7 ACE The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating (Loss) Income Net (Loss) Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 4,888 $ 4,739 $ 387 $ 415 $ 423 $ 310 June 30 4,174 3,589 (467 ) (13 ) (250 ) (8 ) September 30 4,751 5,035 500 342 305 236 December 31 4,654 4,388 501 94 2,215 (41 ) The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 1,298 $ 1,249 $ 314 $ 274 $ 141 $ 115 June 30 1,357 1,286 319 324 118 145 September 30 1,571 1,497 404 389 189 37 December 31 1,309 1,223 286 217 120 80 The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Successor Operating Revenues Operating Income (Loss) Net Income (Loss) Membership Interest 2017 2016 2017 2016 2017 2016 Quarter ended: March 31 $ 1,175 $ 105 (a) $ 180 $ (411 ) (a) $ 140 $ (309 ) (a) June 30 1,074 1,066 148 136 66 52 September 30 1,310 1,394 285 279 153 166 December 31 1,121 1,078 159 90 4 30 Predecessor Operating Revenues Operating Income Net Income Attributable to Membership Interest January 1, 2016 - March 23, 2016 1,153 105 19 __________ (a) Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.

Subsequent Events (Tables)

Subsequent Events (Tables)	12 Months Ended
	Dec. 31, 2017
Subsequent Event [Line Items]
Schedule of Subsequent Events [Table Text Block]	Projected (b) Income statement expense (pre-tax) 2018 Depreciation and Amortization Accelerated depreciation (a) $110 to $140 Accelerated nuclear fuel amortization $40 Operating and Maintenance Increased ARO accretion Up to $5 __________ (a) Includes the accelerated depreciation of plant assets including any ARC. (b) Actual results may differ based on incremental future capital additions, actual units of production for nuclear fuel amortization, future revised ARO assumptions, etc.

Significant Accounting Polici66

Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	100.00%
Third Party interest in ComEd (less than $1 million)	$ 2,275,000,000	$ 1,775,000,000
Minimum expectation of tax position to be realized	50.00%
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
Third Party interest in ComEd (less than $1 million)	$ 1,000,000	1,000,000
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
Exelon Generation Co L L C [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Cost of spent nuclear fuel disposal per kWh of net nuclear generation	$ (0.001)
Utilities Operating Expense, Maintenance and Operations	4,000,000	30,000,000	$ 22,000,000
Development Costs, Period Cost	228,000,000	1,700,000,000
Utilities Operating Expense, Other	$ 13,000,000
Potomac Electric Power Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		4,000,000
Delmarva Power and Light Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		1,000,000
Pepco Holdings LLC [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 34,000,000
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.00%

Significant Accounting Polici67

Significant Accounting Policies - Summary of Capitalized Software Costs (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capitalized Software [Line Items]
Net unamortized software costs	[1]		$ 808	$ 834	$ 808
Amortization of capitalized software costs	[1]			270	255	$ 208
Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					34
Net unamortized software costs			153	133	153
Exelon Generation Co L L C [Member]
Capitalized Software [Line Items]
Net unamortized software costs	[1]		173	173	173
Amortization of capitalized software costs	[1]			73	72	73
Commonwealth Edison Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs			213	227	213
Amortization of capitalized software costs				73	62	47
PECO Energy Co [Member]
Capitalized Software [Line Items]
Net unamortized software costs			91	111	91
Amortization of capitalized software costs				39	33	33
Baltimore Gas and Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs			164	179	164
Amortization of capitalized software costs				46	44	46
Potomac Electric Power Company [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					4
Net unamortized software costs			1	2	1
Amortization of capitalized software costs				0	0	(2)
Delmarva Power and Light Company [Member]
Capitalized Software [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income					1
Net unamortized software costs			1	1	1
Amortization of capitalized software costs				0	0	0
Atlantic City Electric Company [Member]
Capitalized Software [Line Items]
Net unamortized software costs			1	1	1
Amortization of capitalized software costs				0	$ 0	0
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Amortization of capitalized software costs			$ 29	$ 34
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Amortization of capitalized software costs		$ 8				$ 36
[1]	Net unamortized software costs Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACEDecember 31, 2017$834 $173 $227 $111 $179 $133 $2 $1 $1December 31, 2016808 173 213 91 164 153 1 1 1

Significant Accounting Polici68

Significant Accounting Policies - Summary of Total Interest Incurred, Capitalized and Credits to AFUDC (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			$ 1,658	$ 1,678	$ 1,170
Capitalized interest				63	108	79
Credits to AFUDC debt and equity				108	98	44
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			502	472	445
Capitalized interest				63	107	79
Credits to AFUDC debt and equity				0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			369	469	336
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				20	22	9
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			130	127	116
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				12	11	7
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			111	114	113
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				22	30	28
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			133	137	131
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				34	29	19
Delmarva Power and Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			54	52	51
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				10	7	2
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]			64	65	65
Capitalized interest				0	0	0
Credits to AFUDC debt and equity				9	9	$ 2
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]	$ 68			289
Credits to AFUDC debt and equity		$ 10			$ 23
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Total interest incurred	[1]		$ 207	263
Credits to AFUDC debt and equity			$ 35	$ 54
[1]	(a)Includes interest expense to affiliates.

Significant Accounting Polici69

Significant Accounting Policies Balance Sheet Classification of Deferred Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other noncurrent assets	$ 1,322	$ 1,472
Other noncurrent liabilities	2,097	1,827
Commonwealth Edison Co [Member]
Other noncurrent assets	238	325
Other noncurrent liabilities	562	529
Exelon Generation Co L L C [Member]
Other noncurrent assets	662	688
Other noncurrent liabilities	658	595
PECO Energy Co [Member]
Other noncurrent assets	12	20
Other noncurrent liabilities	86	85
Baltimore Gas and Electric Company [Member]
Other noncurrent assets	4	9
Other noncurrent liabilities	$ 56	$ 61

Variable Interest Entities Vari

Variable Interest Entities Variable Interest Entities - Narrative (Details) $ in Millions

1 Months Ended

12 Months Ended

Jul. 31, 2017USD ($)

Nov. 30, 2015

Jun. 30, 2015

Jul. 30, 2014

Dec. 31, 2017USD ($)VIEproject

Dec. 31, 2016USD ($)VIE

Dec. 31, 2015USD ($)

Sep. 30, 2017

Jun. 30, 2017

Mar. 24, 2016USD ($)

Mar. 23, 2016USD ($)

Jun. 09, 2015USD ($)

Jul. 18, 2014USD ($)

Apr. 01, 2014USD ($)

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

$ 1,311

$ 1,274

Number of variable interest entities consolidated | VIE

5

9

Number of variable interest entities not consolidated by equity holders | VIE

7

8

Parental guarantee provided

$ 75

Severance Costs

14

$ 19

Guarantee obligations maximum exposure

56

Investments In Nonconsolidated Variable Interest Entities

[1]

251

248

Variable Interest Entity, Primary Beneficiary [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

205

[2]

199

[3],[4]

2015 ESA Investco, LLC [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

99.00%

Payment Guarantee [Member] | CENG [Member]

Variable Interest Entity [Line Items]

Guarantee obligations maximum exposure

$ 245

Financial Guarantee [Member] | CENG [Member]

Variable Interest Entity [Line Items]

Guarantee obligations maximum exposure

165

Equity interest member [Member] | 2015 ESA Investco, LLC [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

90.00%

Exelon Generation Co L L C [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

937

935

Parental guarantee provided

$ 30

Ownership Percentage Of Consolidated Variable Interest Entities

62.00%

Wind project entities with noncontrolling equity interests | project

6

Noncontrolling equity interest ownership percentage held by third parties

1.00%

Number of projects with significant economic power | project

5

Ownership interests in project entities

99.00%

Severance Costs

[5]

$ 6

13

Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount

$ 8

Exelon Generation Co L L C [Member] | ExGen Renewables Holdings, LLC [Member]

Variable Interest Entity [Line Items]

Proceeds from Sale of Interest in Partnership Unit

$ 400

Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

100.00%

Ownership Percentage Of Consolidated Variable Interest Entities

100.00%

Exelon Generation Co L L C [Member] | Equity Method Investment Variable Interest Entities [Member]

Variable Interest Entity [Line Items]

Parental guarantee provided

$ 275

Exelon Generation Co L L C [Member] | AGE Biomass project [Member]

Variable Interest Entity [Line Items]

Ownership interests in project entities

99.00%

90.00%

Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

205

199

Parental guarantee provided

$ 275

Exelon Generation Co L L C [Member] | CENG [Member]

Variable Interest Entity [Line Items]

Parental guarantee provided

$ 637

Ownership interest

50.01%

Due from Affiliates

$ 333

$ 400

Exelon Generation Co L L C [Member] | Distributed Energy Company [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

90.00%

Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests

227

$ 85

Exelon Generation Co L L C [Member] | Equity interest member [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

69.00%

Exelon Generation Co L L C [Member] | Equity interest member [Member] | ExGen Renewables Holdings, LLC [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

49.00%

Exelon Generation Co L L C [Member] | Equity interest member [Member] | Distributed Energy Company [Member]

Variable Interest Entity [Line Items]

Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage

90.00%

Baltimore Gas and Electric Company [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

40

38

Severance Costs

[5]

0

1

Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]

Variable Interest Entity [Line Items]

Amount Remitted To Variable Interest Entities On Rate Stabilization Bonds

22

86

$ 86

Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

0

Pepco Holdings LLC [Member] | Successor [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

151

116

Severance Costs

[5]

4

1

Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

0

[2]

0

[3]

Atlantic City Electric Company [Member]

Variable Interest Entity [Line Items]

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets

$ 1,200

Severance Costs

[5]

1

0

Guarantee obligations maximum exposure

15

Atlantic City Electric Company [Member] | ATF [Member]

Variable Interest Entity [Line Items]

Cash Remitted To VIE

48

60

$ 61

Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]

Variable Interest Entity [Line Items]

Inventory, Raw Materials and Supplies, Gross

$ 0

$ 0

Pepco Holdings LLC [Member]

Variable Interest Entity [Line Items]

Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets

$ 4,005

[1]

These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

[2]

Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity

[3]

Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

[4]

Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

[5]

The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016

Variable Interest Entities Va71

Variable Interest Entities Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Current assets	[1]	$ 630	$ 954	[2]
Noncurrent assets	[1]	9,317	8,563	[2]
Total assets	[1]	9,947	9,517	[2]
Current liabilities	[1]	306	885	[2]
Noncurrent liabilities	[1]	3,312	2,713	[2]
Total liabilities	[1]	3,618	3,598	[2]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		620	916
Noncurrent assets		9,286	8,525
Total assets		9,906	9,441
Current liabilities		270	802
Noncurrent liabilities		3,246	2,612
Total liabilities		3,516	3,414
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets			23
Noncurrent assets			3
Total assets			26
Current liabilities			42
Noncurrent liabilities			0
Total liabilities			42
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Total assets		41	49
Total liabilities		102	143
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	10	14
Noncurrent assets	[1]	31	35
Total assets	[1]	41	49
Current liabilities	[1]	36	42
Noncurrent liabilities	[1]	66	101
Total liabilities	[1]	102	143
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		6	9
Noncurrent assets		23	23
Total assets		29	32
Current liabilities		32	37
Noncurrent liabilities		58	89
Total liabilities		$ 90	$ 126
[1]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[2]	Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.

Variable Interest Entities Va72

Variable Interest Entities Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Mar. 23, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 898		$ 635			$ 6,502	$ 1,878
Restricted cash		207		253
Customer		4,401		4,158
Other		1,132		1,201
Mark-to-market derivative assets		976		917
Materials and supplies		1,311		1,274
Other current assets		1,242		930
Total current assets		11,834		12,412
Property, plant and equipment, net		74,202		71,555
Nuclear decommissioning trust funds		13,272		11,061
Goodwill		6,677		6,677			2,672
Mark-to-market derivative assets		337		492
Other noncurrent assets		1,322		1,472
Total assets (a)	[1]	116,700		114,904
Long-term debt due within one year		2,088		2,430
Accounts payable		3,532		3,441
Accrued expenses		1,835		3,460
Mark-to-market derivative liabilities		232		282
Unamortized energy contract liabilities		231		407
Other current liabilities		982		981
Total current liabilities		10,796		13,457
Long-term debt		32,176		31,575
Asset retirement obligations		10,029		9,111
Pension obligations		3,736		4,248
Unamortized energy contract liabilities		609		830
Other noncurrent liabilities		2,097		1,827
Total liabilities	[1]	84,568		87,292
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		126	[2]	150	[3],[4]
Restricted cash		64	[2]	59	[3],[4]
Customer		138	[2]	371	[3],[4]
Other		25	[2]	48	[3],[4]
Mark-to-market derivative assets	[3],[4]			31
Materials and supplies		205	[2]	199	[3],[4]
Other current assets		45	[2]	50	[3],[4]
Total current assets		603	[2]	908	[3],[4]
Property, plant and equipment, net		6,186	[2]	5,415	[3],[4]
Nuclear decommissioning trust funds		2,502	[2]	2,185	[3],[4]
Goodwill	[3],[4]			47
Mark-to-market derivative assets	[3],[4]			23
Other noncurrent assets		274	[2]	315	[3],[4]
Total noncurrent assets		8,962	[2]	7,985	[3],[4]
Total assets (a)		9,565	[2]	8,893	[3],[4]
Long-term debt due within one year		102	[2]	181	[3],[4]
Accounts payable		114	[2]	269	[3],[4]
Accrued expenses		65	[2]	119	[3],[4]
Mark-to-market derivative liabilities	[3],[4]			60
Unamortized energy contract liabilities		18	[2]	15	[3],[4]
Other current liabilities		7	[2]	30	[3],[4]
Total current liabilities		306	[2]	674	[3],[4]
Long-term debt		1,154	[2]	641	[3],[4]
Asset retirement obligations		2,035	[2]	1,904	[3],[4]
Pension obligations	[3],[4],[5]			9
Unamortized energy contract liabilities		5	[2]	22	[3],[4]
Other noncurrent liabilities		112	[2]	106	[3],[4]
Noncurrent liabilities		3,306	[2]	2,682	[3],[4]
Total liabilities		3,612	[2]	3,356	[3],[4]
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		416		290			431	780
Restricted cash		138		158
Customer		2,653		2,433
Other		321		558
Mark-to-market derivative assets		976		917
Materials and supplies		937		935
Other current assets		915		701
Total current assets		6,820		6,528
Property, plant and equipment, net		24,906		25,585
Nuclear decommissioning trust funds		13,272		11,061
Goodwill		47		47			47
Mark-to-market derivative assets		334		476
Other noncurrent assets		662		688
Total assets (a)	[6]	48,387		46,974
Long-term debt due within one year		346		1,117
Accounts payable		1,773		1,610
Accrued expenses		1,020		989
Mark-to-market derivative liabilities		211		263
Unamortized energy contract liabilities		43		72
Other current liabilities		265		313
Total current liabilities		4,189		5,683
Long-term debt		7,734		7,202
Asset retirement obligations		9,844		8,922
Unamortized energy contract liabilities		48		80
Other noncurrent liabilities		658		595
Total liabilities	[6]	32,483		33,718
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		126		150
Restricted cash		58		27
Customer		138		371
Other		25		48
Mark-to-market derivative assets				31
Materials and supplies		205		199
Other current assets		41		44
Total current assets		593		870
Property, plant and equipment, net		6,186		5,415
Nuclear decommissioning trust funds		2,502		2,185
Goodwill				47
Mark-to-market derivative assets				23
Other noncurrent assets		243		277
Total noncurrent assets		8,931		7,947
Total assets (a)		9,524		8,817
Long-term debt due within one year		67		99
Accounts payable		114		269
Accrued expenses		64		116
Mark-to-market derivative liabilities				60
Unamortized energy contract liabilities		18		15
Other current liabilities		7		30
Total current liabilities		270		589
Long-term debt		1,088		540
Asset retirement obligations		2,035		1,904
Pension obligations	[5]			9
Unamortized energy contract liabilities		5		22
Other noncurrent liabilities		112		106
Noncurrent liabilities		3,240		2,581
Total liabilities		3,510		3,170
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		17		23			9	64
Restricted cash		1		24
Customer		375		395
Other		94		102
Materials and supplies		40		38
Other current assets		3		7
Total current assets		811		842
Property, plant and equipment, net		7,602		7,040
Other noncurrent assets		4		9
Total assets (a)	[7]	9,104		8,704
Long-term debt due within one year		0		41
Accounts payable		265		205
Accrued expenses		164		175
Other current liabilities		24		26
Total current liabilities		760		707
Long-term debt		2,577		2,281
Asset retirement obligations		23		21
Other noncurrent liabilities		56		61
Total liabilities	[7]	5,963		5,856
Baltimore Gas and Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents				0
Restricted cash				23
Customer				0
Other				0
Mark-to-market derivative assets				0
Materials and supplies				0
Other current assets				0
Total current assets				23
Property, plant and equipment, net				0
Nuclear decommissioning trust funds				0
Goodwill				0
Mark-to-market derivative assets				0
Other noncurrent assets				3
Total noncurrent assets				3
Total assets (a)				26
Long-term debt due within one year				41
Accounts payable				0
Accrued expenses				1
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities				0
Other current liabilities				0
Total current liabilities				42
Long-term debt				0
Asset retirement obligations				0
Pension obligations	[5]			0
Unamortized energy contract liabilities				0
Other noncurrent liabilities				0
Noncurrent liabilities				0
Total liabilities				42
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		30		170
Restricted cash		42		43
Customer		486		496
Other		206		283
Materials and supplies		151		116
Other current assets		75		71
Total current assets		1,551		1,838
Property, plant and equipment, net		12,498		11,598
Goodwill		4,005		4,005		$ 0
Other noncurrent assets		70		81
Total assets (a)	[8]	21,247		21,025
Long-term debt due within one year		396		253
Accounts payable		348		458
Accrued expenses		261		272
Unamortized energy contract liabilities		188		335
Other current liabilities		81		47
Total current liabilities		1,931		2,284
Long-term debt		5,478		5,645
Asset retirement obligations		16		14
Unamortized energy contract liabilities		561		750
Other noncurrent liabilities		389		249
Total liabilities	[8]	12,422		13,009
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	[2]	0	[3]
Restricted cash		6	[2]	9	[3]
Customer		0	[2]	0	[3]
Other		0	[2]	0	[3]
Mark-to-market derivative assets	[3]			0
Materials and supplies		0	[2]	0	[3]
Other current assets		4	[2]	5	[3]
Total current assets		10	[2]	14	[3]
Property, plant and equipment, net		0	[2]	0	[3]
Nuclear decommissioning trust funds		0	[2]	0	[3]
Goodwill	[3]			0
Mark-to-market derivative assets	[3]			0
Other noncurrent assets		31	[2]	35	[3]
Total noncurrent assets		31	[2]	35	[3]
Total assets (a)		41	[2]	49	[3]
Long-term debt due within one year		35	[2]	40	[3]
Accounts payable		0	[2]	0	[3]
Accrued expenses		1	[2]	2	[3]
Mark-to-market derivative liabilities	[3]			0
Unamortized energy contract liabilities		0	[2]	0	[3]
Other current liabilities		0	[2]	0	[3]
Total current liabilities		36	[2]	42	[3]
Long-term debt		66	[2]	101	[3]
Asset retirement obligations		0	[2]	0	[3]
Pension obligations	[3],[5]			0
Unamortized energy contract liabilities		0	[2]	0	[3]
Other noncurrent liabilities		0	[2]	0	[3]
Noncurrent liabilities		66	[2]	101	[3]
Total liabilities		102	[2]	143	[3]
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		2		101			$ 3	$ 2
Restricted cash		6		9
Customer		92		125
Other		56		44
Other current assets		2		2
Total current assets		258		399
Property, plant and equipment, net		2,706		2,521
Other noncurrent assets		45		44
Total assets (a)	[9]	3,445		3,457
Long-term debt due within one year		281		35
Accounts payable		118		132
Accrued expenses		33		38
Other current liabilities		8		8
Total current liabilities		619		320
Long-term debt		840		1,120
Other noncurrent liabilities		25		32
Total liabilities	[9]	2,402		2,423
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0		0
Restricted cash		6		9
Customer		0		0
Other		0		0
Mark-to-market derivative assets				0
Materials and supplies		0		0
Other current assets		0		0
Total current assets		6		9
Property, plant and equipment, net		0		0
Nuclear decommissioning trust funds		0		0
Goodwill				0
Mark-to-market derivative assets				0
Other noncurrent assets		23		23
Total noncurrent assets		23		23
Total assets (a)		29		32
Long-term debt due within one year		31		35
Accounts payable		0		0
Accrued expenses		1		2
Mark-to-market derivative liabilities				0
Unamortized energy contract liabilities		0		0
Other current liabilities		0		0
Total current liabilities		32		37
Long-term debt		58		89
Asset retirement obligations		0		0
Pension obligations	[5]			0
Unamortized energy contract liabilities		0		0
Other noncurrent liabilities		0		0
Noncurrent liabilities		58		89
Total liabilities		$ 90		$ 126
[1]	Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity
[3]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[4]	Includes certain purchase accounting adjustments not pushed down to the BGE standalone entity.
[5]	Includes the CNEG retail gas pension obligation, which is presented as a net asset balance within the Prepaid pension asset line item on Generation’s balance sheet. See Note 16 - Retirement Benefits for additional details.
[6]	Generation’s consolidated assets include $9,524 million and $8,817 million at December 31, 2017 and 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,510 million and $3,170 million at December 31, 2017 and 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[7]	BGE’s consolidated assets include $26 million at December 31, 2016 of BGE’s consolidated VIE that can only be used to settle the liabilities of the VIE. BGE’s consolidated liabilities include $42 million at December 31, 2016 of BGE’s consolidated VIE for which the VIE creditors do not have recourse to BGE. BGE no longer has interests in any VIEs as of December 31, 2017. See Note 2 - Variable Interest Entities.
[8]	PHI’s consolidated total assets include $41 million and $49 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $102 million and $143 million at December 31, 2017 and 2016, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities.
[9]	ACE’s consolidated assets include $29 million and $32 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $90 million and $126 million at December 31, 2017 and 2016, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 - Variable Interest Entities.

Variable Interest Entities Va73

Variable Interest Entities Variable Intereste Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,134	$ 1,205
Total liabilities	[1]	265	502
Exelon's ownership interest in VIE	[1]	251	248
Other ownership interests in VIE	[1]	618	455
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		251	264
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		8	9
Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	3
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	2	9
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	625	638
Total liabilities	[1]	37	215
Exelon's ownership interest in VIE	[1]	0	0
Other ownership interests in VIE	[1]	588	423
Commercial Agreement Variable Interest Entities [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Commercial Agreement Variable Interest Entities [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		8	9
Commercial Agreement Variable Interest Entities [Member] | Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Commercial Agreement Variable Interest Entities [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	2	9
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	509	567
Total liabilities	[1]	228	287
Exelon's ownership interest in VIE	[1]	251	248
Other ownership interests in VIE	[1]	30	32
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		251	264
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Equity Investment VIE [Member] | Debt and payment guarantees
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	3
Equity Investment VIE [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		8
Held-to-maturity Securities Pledged as Collateral		39	113
Accounts Payable, Interest-bearing, Noncurrent	[3]	$ 37	$ 104
[1]	These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.
[2]	These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $39 million and $113 million as of December 31, 2017 and December 31, 2016, respectively; offset by payables to ZionSolutions LLC of $37 million and $104 million as of December 31, 2017 and December 31, 2016, respectively. These items are included to provide information regarding the relative size of the ZionSolutions LLC unconsolidated VIE
[3]	Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters- Narrative (Details) GWh in Millions		Dec. 31, 2030	Feb. 05, 2018USD ($)	Feb. 01, 2018USD ($)	Jan. 02, 2018GWh	Jan. 02, 2018USD ($)	Dec. 19, 2017USD ($)	Dec. 18, 2017USD ($)	Nov. 15, 2017USD ($)	Nov. 07, 2017USD ($)	Oct. 27, 2017USD ($)	Oct. 20, 2017USD ($)	Oct. 18, 2017USD ($)	Sep. 11, 2017USD ($)	Sep. 08, 2017USD ($)	Aug. 24, 2017USD ($)	Aug. 17, 2017USD ($)	Jul. 25, 2017USD ($)	Jul. 24, 2017USD ($)	Jul. 14, 2017USD ($)	Jun. 09, 2017USD ($)	[4]	Apr. 06, 2017USD ($)	Mar. 30, 2017USD ($)	Mar. 24, 2017USD ($)	Mar. 22, 2017USD ($)	Mar. 08, 2017USD ($)	Feb. 15, 2017USD ($)	Feb. 01, 2017USD ($)	Dec. 17, 2016USD ($)	Nov. 30, 2016USD ($)	Nov. 15, 2016USD ($)	Jul. 29, 2016USD ($)	May 17, 2016USD ($)	Feb. 01, 2016USD ($)	Sep. 10, 2015USD ($)	Mar. 27, 2015USD ($)	Jun. 30, 2017USD ($)	Apr. 30, 2016USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)		Dec. 31, 2016USD ($)	May 31, 2007	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)		Dec. 31, 2007USD ($)	Dec. 31, 2023USD ($)	Nov. 30, 2010USD ($)	Nov. 30, 2005USD ($)	Jun. 01, 2019	Jun. 01, 2018	Jul. 21, 2017USD ($)	Jun. 06, 2017USD ($)	Jun. 01, 2017	Mar. 24, 2016USD ($)	Nov. 06, 2015USD ($)	Dec. 31, 2013USD ($)	Mar. 31, 2013USD ($)	Mar. 31, 2011USD ($)	Aug. 31, 2010USD ($)	Dec. 31, 2008USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									$ 137,000,000													$ 137,000,000
Regulatory Assets																																									9,288,000,000				$ 11,388,000,000					$ 11,388,000,000				9,288,000,000		$ 11,388,000,000
Amortization Rate Stabilization Deferral																																																						(10,000,000)		76,000,000		$ 73,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets	[1]																																								35,000,000													35,000,000
Regulatory Liability, Current																																									523,000,000				602,000,000					602,000,000				523,000,000		602,000,000
Regulatory liabilities																																									9,865,000,000				4,187,000,000					4,187,000,000				9,865,000,000		4,187,000,000
Revenues																																									8,381,000,000	$ 8,769,000,000	$ 7,623,000,000	$ 8,757,000,000	7,875,000,000	$ 9,002,000,000	$ 6,910,000,000	$ 7,573,000,000						$ 33,531,000,000		31,360,000,000		29,447,000,000
Document Period End Date																																																						Dec. 31, 2017
License Costs	[2]																																																									95,000,000
Business Combination, Integration Related Costs	[3]																																																					$ 16,000,000		143,000,000
Regulatory Liabilities																																									10,388,000,000				4,789,000,000					4,789,000,000				10,388,000,000		4,789,000,000
Fair Value, Net Asset (Liability)																																																																					$ 2,400,000,000
Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																									81,000,000													81,000,000
Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									63,000,000													63,000,000
Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									111,000,000				134,000,000					134,000,000				111,000,000		134,000,000
Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									112,000,000													112,000,000
Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									30,000,000				47,000,000					47,000,000				30,000,000		47,000,000
DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									190,000,000													190,000,000
Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									244,000,000				188,000,000					188,000,000				244,000,000		188,000,000
CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									8,000,000				11,000,000					11,000,000				8,000,000		11,000,000
Under funded Benefit Post Retirement Obligation [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									953,000,000				1,027,000,000					1,027,000,000				953,000,000		1,027,000,000
AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									640,000,000				701,000,000					701,000,000				640,000,000		701,000,000
Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									82,000,000				89,000,000					89,000,000				82,000,000		89,000,000
Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									45,000,000				25,000,000					25,000,000				45,000,000		25,000,000
COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									5,000,000				8,000,000					8,000,000				5,000,000		8,000,000
Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									596,000,000				621,000,000					621,000,000				596,000,000		621,000,000
Pepco Holdings [Member] | Under funded Benefit Post Retirement Obligation [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									440,000,000				492,000,000					492,000,000				440,000,000		492,000,000
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									513,000,000													513,000,000
Revenues																																																						4,829,000,000		3,785,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization Rate Stabilization Deferral																																																						0		0		0
Revenues																																						$ 12,000,000			4,654,000,000	4,751,000,000	4,174,000,000	4,888,000,000	4,388,000,000	5,035,000,000	3,589,000,000	4,739,000,000						18,466,000,000		17,751,000,000		19,135,000,000
Customer Refund Liability, Noncurrent																																												20,000,000
Purchase Obligation																																																																		$ 235,000,000
License Costs	[2]																																																									0
Business Combination, Integration Related Costs	[3]																																																					22,000,000		37,000,000
Exelon Generation Co L L C [Member] | Conowingo [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs																																																						31,000,000
Exelon Generation Co L L C [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																																							$ 101,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																																									3,000,000													3,000,000
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																																									7,000,000													7,000,000
Exelon Generation Co L L C [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																																																						$ 311,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
SocialCarbonCost																																																						16.50
LowIncomeEnergyAssistanceContributionAnnual																																																						$ 10,000,000
LowIncomeEnergyAssistanceContributionLength																																																						5
Low income sector consumption reduction targets Act 129 Phase II																																																						0.10%
EnergyEfficiencyAnnualCumulativeSavings																																																						6.60%
CumulativeAnnualEnergyEfficiencyGoal | GWh					88
Public Utilities, Requested Rate Increase (Decrease), Amount																					$ (7,000,000)																																	$ 44,000,000	[5]	$ 90,000,000	[5]	$ 68,000,000	[5]
Public Utilities, Approved Equity Capital Structure, Percentage														6.47%																																								8.43%	[6]	8.47%	[6]	8.61%	[6]
Public Utilities, Approved Rate Increase (Decrease), Amount														$ (12,000,000)																																								$ (11,000,000)	[5]	$ (94,000,000)	[5]	$ (86,000,000)	[5]
Public Utilities, Requested Return on Equity, Percentage	[7]																																																					11.50%		11.50%		11.50%
Public Utilities, Approved Return on Equity, Percentage														8.40%
Other Commitment																																									164,000,000													$ 164,000,000
Proposed Capital Expenditure	[5],[8]																																																					0		$ 0		$ 0
Regulatory Assets																																									1,279,000,000				1,167,000,000					1,167,000,000				1,279,000,000		1,167,000,000
Amortization Rate Stabilization Deferral																																																						0		0		0
Amount of Impairment to Carrying Amount of Regulatory Assets																																									3,000,000													3,000,000
Regulatory Liability, Current																																									249,000,000				329,000,000					329,000,000				249,000,000		329,000,000
Regulatory liabilities																																									6,328,000,000				3,369,000,000					3,369,000,000				6,328,000,000		3,369,000,000
Revenues																																									1,309,000,000	1,571,000,000	1,357,000,000	1,298,000,000	1,223,000,000	1,497,000,000	1,286,000,000	1,249,000,000						5,536,000,000		5,254,000,000		4,905,000,000
Purchase Obligation																																																																		$ 170,000,000
License Costs	[2]																																																									0
Business Combination, Integration Related Costs	[3],[9]																																																					1,000,000		(6,000,000)
Regulatory Liabilities																																									6,577,000,000				3,698,000,000					3,698,000,000				6,577,000,000		3,698,000,000
DecouplingImpactOnOperatingRevenuesAndRegulatoryAssets																																																						$ 32,000,000
RenewableEnergyRetailLoad																																																																				50.00%
Commonwealth Edison Co [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
EnergyEfficiencyAnnualCumulativeSavings		21.50%
RenewableEnergyRetailLoad																																																																100.00%	75.00%
Tax Savings From Tax Cuts and Jobs Act				$ 201,000,000
Commonwealth Edison Co [Member] | Energy Related Derivative [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Term of contract																																																						20 years
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																																						$ 78,000,000		$ 134,000,000		$ 85,000,000
Public Utilities, Approved Equity Capital Structure, Percentage																																																						6.45%		6.69%		7.02%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																										$ (18,000,000)																												$ 96,000,000		$ 127,000,000	[10]	$ (67,000,000)
Public Utilities, Approved Rate Increase (Decrease), Amount																																																						$ (18,000,000)		$ 7,000,000		$ 152,000,000
Public Utilities, Requested Return on Equity, Percentage																																																						8.40%		8.64%		9.14%
Public Utilities, Approved Return on Equity, Percentage	[11]																																																					8.34%		8.59%		9.09%
Public Utilities, Requested Equity Capital Structure, Percentage																																																						6.47%		6.71%		7.05%
Commonwealth Edison Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
FutureEnergyEfficiencySpending																																																						$ 350,000,000
EnergyEfficiencyROEAdjustment																																																						20000.00%
Renewable Energy Resources Cumulatively Increase																																																						13.00%
Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
FutureEnergyEfficiencySpending																																																						$ 400,000,000
ResidentialCustomerRateIncrease																																																						0.25
CommercialAndIndustrialCustomerRateIncrease																																																						1.30%
Amount of Impairment to Carrying Amount of Regulatory Assets																																									41,000,000													$ 41,000,000
Renewable Energy Resources Cumulatively Increase																																																						25.00%
Commonwealth Edison Co [Member] | Maximum [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																																						$ 96,000,000		$ 138,000,000		$ (50,000,000)
Commonwealth Edison Co [Member] | Reductions Under TCJA [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									553,000,000													553,000,000
Commonwealth Edison Co [Member] | ACPpayment member [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									41,000,000													41,000,000
Commonwealth Edison Co [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									484,000,000													484,000,000
Commonwealth Edison Co [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																									10,000,000													10,000,000
Regulatory liabilities																																									20,000,000													20,000,000
Regulatory Liabilities																																									63,000,000													63,000,000
Restricted Cash																																									62,000,000													62,000,000
Commonwealth Edison Co [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									47,000,000				60,000,000					60,000,000				47,000,000		60,000,000
Commonwealth Edison Co [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																									14,000,000				30,000,000					30,000,000				14,000,000		30,000,000
Commonwealth Edison Co [Member] | Renewable energy Requirements [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									33,000,000				30,000,000					30,000,000				33,000,000		30,000,000
Commonwealth Edison Co [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									112,000,000													112,000,000
Commonwealth Edison Co [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Commonwealth Edison Co [Member] | EDArefund Member [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									80,000,000													80,000,000
Commonwealth Edison Co [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0													0
Commonwealth Edison Co [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									21,000,000													21,000,000
Commonwealth Edison Co [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									244,000,000				188,000,000					188,000,000				244,000,000		188,000,000
Commonwealth Edison Co [Member] | Electric distribution formula rate | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									186,000,000				134,000,000					134,000,000				186,000,000		134,000,000
Commonwealth Edison Co [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Commonwealth Edison Co [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													22,000,000					22,000,000						22,000,000
Commonwealth Edison Co [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									155,000,000				164,000,000					164,000,000				155,000,000		164,000,000
Commonwealth Edison Co [Member] | Recoverable Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									58,000,000				54,000,000					54,000,000				58,000,000		54,000,000
Commonwealth Edison Co [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									6,000,000				23,000,000					23,000,000				6,000,000		23,000,000
Business Combination, Integration Related Costs																																																								8,000,000
Commonwealth Edison Co [Member] | TransmissionCost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													15,000,000					15,000,000						15,000,000
Commonwealth Edison Co [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Commonwealth Edison Co [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																				$ 127,000,000	$ 190,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage																																					10.95%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																																																						22,000,000
Other Commitment																																									53,000,000													53,000,000
Regulatory Assets																																									410,000,000				1,710,000,000					1,710,000,000				410,000,000		1,710,000,000
Amortization Rate Stabilization Deferral																																																						0		0		0
Regulatory Liability, Current																																									141,000,000				127,000,000					127,000,000				141,000,000		127,000,000
Regulatory liabilities																																									549,000,000				517,000,000					517,000,000				549,000,000		517,000,000
Revenues																																									729,000,000	715,000,000	630,000,000	796,000,000	701,000,000	788,000,000	664,000,000	841,000,000						2,870,000,000		2,994,000,000		3,032,000,000
License Costs	[2]																																																									0
Business Combination, Integration Related Costs	[3]																																																					4,000,000		5,000,000
Regulatory Liabilities																																									690,000,000				644,000,000					644,000,000				$ 690,000,000		644,000,000
Public Utilities, Requested Equity Capital Structure, Percentage																																																						11.00%
PECO Energy Co [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													$ 0
PECO Energy Co [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									60,000,000				56,000,000					56,000,000				60,000,000		56,000,000
PECO Energy Co [Member] | DSP Program costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									36,000,000				34,000,000					34,000,000				36,000,000		34,000,000
PECO Energy Co [Member] | Over Recovered NonBypassable Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									12,000,000													12,000,000
PECO Energy Co [Member] | Over-Recovered Electric Transmission Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									12,000,000				4,000,000					4,000,000				12,000,000		4,000,000
PECO Energy Co [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																													8,000,000					8,000,000						8,000,000
PECO Energy Co [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
PECO Energy Co [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
PECO Energy Co [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0													0
PECO Energy Co [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
PECO Energy Co [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									8,000,000				11,000,000					11,000,000				8,000,000		11,000,000
PECO Energy Co [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									36,000,000				49,000,000					49,000,000				$ 36,000,000		49,000,000
Regulatory Asset, Amortization Period																																																						10 years
PECO Energy Co [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									1,000,000				0					0				$ 1,000,000		0
PECO Energy Co [Member] | Under-Recovered Non-Bypassable Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													10,000,000					10,000,000						10,000,000
PECO Energy Co [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
PECO Energy Co [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									1,000,000				1,000,000					1,000,000				1,000,000		1,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																																						$ 31,000,000	[5]	$ 12,000,000	[5]	$ 0	[5]		$ 242,000,000
Public Utilities, Approved Equity Capital Structure, Percentage	[6]																																																					7.47%		8.09%		8.46%
Public Utilities, Approved Rate Increase (Decrease), Amount	[5]																																																					$ (26,000,000)		$ (28,000,000)		$ (10,000,000)
Public Utilities, Requested Return on Equity, Percentage	[7]																																																					10.50%		10.50%		11.30%
Other Commitment																																									118,000,000													$ 118,000,000
Proposed Capital Expenditure																																																						(8,000,000)	[5],[8]	$ 13,000,000	[5],[8]	$ 13,000,000	[5],[8]		$ 963,000,000
Regulatory Assets																																									571,000,000				712,000,000					712,000,000				571,000,000		712,000,000
Rate Cap Imposed On Public Utility Subsidiary																																																			15.00%
Deferred Purchased Power Costs																																																												$ 306,000,000
Amortization Rate Stabilization Deferral																																																						7,000,000		81,000,000		73,000,000
Estimated number of smart meters to be installed																																																																										2,000,000
Total smart grid smart meter investment grant awarded																																																																										$ 480,000,000
Doe Reimbursements																																																																										$ 200,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																									5,000,000													5,000,000
Captial and OM estimates current year																																									136,000,000													136,000,000
Regulatory Liability, Current																																									62,000,000				50,000,000					50,000,000				62,000,000		50,000,000
Deferred Costs, Noncurrent																																																																								$ 8,000,000	$ 16,000,000
Regulatory liabilities																																									1,101,000,000				110,000,000					110,000,000				1,101,000,000		110,000,000
Revenues																																									813,000,000	738,000,000	674,000,000	951,000,000	812,000,000	812,000,000	680,000,000	929,000,000						3,176,000,000		3,233,000,000		3,135,000,000
Customer Refund Liability, Noncurrent																																																																						$ 30,000,000
License Costs	[2]																																																									0
Business Combination, Integration Related Costs	[3],[9]																																																					4,000,000		(1,000,000)
Site Contingency, Recovery from Third Party of Environmental Remediation Cost																																																														$ 1,000,000	$ 5,000,000
Regulatory Liabilities																																									1,163,000,000				160,000,000					160,000,000				1,163,000,000		160,000,000
Baltimore Gas and Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act				103,000,000
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																																						116,000,000
Projected Investment In Smartmeters																																																																						104,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount																																	$ (44,000,000)
Public Utilities, Requested Return on Equity, Percentage																																	9.75%
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act				72,000,000
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																																						78,000,000
Projected Investment In Smartmeters																																																																						$ 37,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount																																	$ (48,000,000)
Public Utilities, Requested Return on Equity, Percentage																																	9.65%
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act				31,000,000
Baltimore Gas and Electric Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																									22,000,000													22,000,000
Baltimore Gas and Electric Company [Member] | Reductions Under TCJA [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									174,000,000													174,000,000
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									137,000,000													137,000,000
Baltimore Gas and Electric Company [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Baltimore Gas and Electric Company [Member] | Stride Program [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									1,000,000													1,000,000
Baltimore Gas and Electric Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													9,000,000					9,000,000						9,000,000
Regulatory Liabilities																																									0				0					0				0		0
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																													3,000,000					3,000,000						3,000,000
Baltimore Gas and Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									4,000,000				2,000,000					2,000,000				4,000,000		2,000,000
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									10,000,000				1,000,000					1,000,000				10,000,000		1,000,000
Baltimore Gas and Electric Company [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Baltimore Gas and Electric Company [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Baltimore Gas and Electric Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0													0
Baltimore Gas and Electric Company [Member] | Under-Recovered Natural Gas Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									8,000,000				3,000,000					3,000,000				8,000,000		3,000,000
Baltimore Gas and Electric Company [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Baltimore Gas and Electric Company [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													38,000,000					38,000,000						38,000,000
Baltimore Gas and Electric Company [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									214,000,000				230,000,000					230,000,000				214,000,000		230,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																															52,000,000
Baltimore Gas and Electric Company [Member] | Unamortized AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									129,000,000				144,000,000					144,000,000				129,000,000		144,000,000
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									53,000,000				54,000,000		56,000,000			54,000,000				53,000,000		54,000,000
Baltimore Gas and Electric Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									23,000,000				38,000,000					38,000,000				23,000,000		38,000,000
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									7,000,000				4,000,000					4,000,000				7,000,000		4,000,000
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									5,000,000				28,000,000					28,000,000				5,000,000		28,000,000
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									3,000,000													3,000,000
Baltimore Gas and Electric Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									6,000,000				10,000,000					10,000,000				6,000,000		10,000,000																$ 4,000,000
Baltimore Gas and Electric Company [Member] | Non-severance Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																																																							$ 4,000,000
Baltimore Gas and Electric Company [Member] | PHI Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									4,000,000				6,000,000					6,000,000				4,000,000		6,000,000
Baltimore Gas and Electric Company [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Baltimore Gas and Electric Company [Member] | Recoverable Smart Meter Related Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									32,000,000				32,000,000					32,000,000				32,000,000		32,000,000
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									285,000,000				285,000,000					285,000,000				285,000,000		285,000,000
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																												444,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets	[1]																																								27,000,000													27,000,000
Business Combination, Integration Related Costs	[3],[9]																																																					(6,000,000)		28,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									3,047,000,000				3,504,000,000					3,504,000,000				3,047,000,000		3,504,000,000
Amortization Rate Stabilization Deferral																																																		(5,000,000)				(17,000,000)
Regulatory Liability, Current																																									56,000,000				79,000,000					79,000,000				56,000,000		79,000,000
Regulatory liabilities																																									1,872,000,000				158,000,000					158,000,000				1,872,000,000		158,000,000
Revenues																																									1,121,000,000	1,310,000,000	1,074,000,000	1,175,000,000	1,078,000,000	1,394,000,000	1,066,000,000	105,000,000	[12]	3,643,000,000				4,679,000,000
Business Combination, Integration Related Costs	[9],[13]																																																	69,000,000				(18,000,000)
Regulatory Liabilities																																									1,928,000,000				237,000,000					237,000,000				1,928,000,000		237,000,000
Pepco Holdings LLC [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																									18,000,000													18,000,000
Pepco Holdings LLC [Member] | Renewable portfolio standards costs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Pepco Holdings LLC [Member] | Energy and transmission programs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									4,000,000				18,000,000					18,000,000				4,000,000		18,000,000
Pepco Holdings LLC [Member] | Zero emission credit costs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Pepco Holdings LLC [Member] | Pension and other postretirement benefits | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Pepco Holdings LLC [Member] | DC PLUG charge | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									190,000,000													190,000,000
Pepco Holdings LLC [Member] | Electric distribution formula rate | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Pepco Holdings LLC [Member] | CAP arrearage | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Pepco Holdings LLC [Member] | AMI programs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									235,000,000				258,000,000					258,000,000				235,000,000		258,000,000
Pepco Holdings LLC [Member] | Energy and transmission programs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									52,000,000				28,000,000					28,000,000				52,000,000		28,000,000
Pepco Holdings LLC [Member] | Merger integration costs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									39,000,000				15,000,000					15,000,000				39,000,000		15,000,000
Pepco Holdings LLC [Member] | COPCO acquisition adjustment | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									5,000,000				8,000,000					8,000,000				5,000,000		8,000,000
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									310,000,000				335,000,000					335,000,000				310,000,000		335,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									315,000,000													315,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[5]																																																					$ 5,000,000		$ 2,000,000		$ 10,000,000
Public Utilities, Approved Equity Capital Structure, Percentage	[6]																																																					7.92%		7.88%		8.36%
Public Utilities, Approved Rate Increase (Decrease), Amount	[5]																																																					$ (20,000,000)		$ 23,000,000		$ (5,000,000)
Public Utilities, Requested Return on Equity, Percentage	[7]																																																					10.50%		10.50%		11.30%
Other Commitment																																									86,000,000													$ 86,000,000
Projected Capital Expenditures																																										500,000,000
Regulatory Assets																																									891,000,000				852,000,000					852,000,000				891,000,000		$ 852,000,000
Amortization Rate Stabilization Deferral																																																						(17,000,000)		(12,000,000)		$ 1,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																									14,000,000													14,000,000
Regulatory Liability, Current																																									3,000,000				11,000,000					11,000,000				3,000,000		11,000,000
Regulatory liabilities																																									829,000,000				20,000,000					20,000,000				829,000,000		20,000,000
Revenues																																									510,000,000	604,000,000	$ 514,000,000	530,000,000	491,000,000	635,000,000	509,000,000	551,000,000						2,158,000,000		2,186,000,000		2,129,000,000
License Costs	[2]																																																									0
Regulatory Liabilities																																									832,000,000				31,000,000					31,000,000				$ 832,000,000		31,000,000
Alternative Net Capital Requirement																																										250,000,000
Capital ProjectFundedByBonds																																									187,000,000	187,500,000			3,000,000
CapitalProjectFundedByAgency																																										62,500,000
Potomac Electric Power Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capital ProjectFundedByBonds																																																					$ 27,500,000
CapitalProjectFundedByAgency																																																				$ 60,000,000
Tax Savings From Tax Cuts and Jobs Act			$ 31,000,000
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			11,000,000			$ 41,000,000	$ 66,000,000																		$ 69,000,000																						86,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage						10.10%										10.10%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																$ 67,000,000													$ 77,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount											$ (32,000,000)	$ (34,000,000)						$ (37,000,000)														$ (53,000,000)
Public Utilities, Requested Return on Equity, Percentage							10.10%
Public Utilities, Approved Return on Equity, Percentage												9.50%						9.50%											10.60%			9.55%
TaxAdjustmentIncludedInPublicUtilitiesRequestedRateIncreaseDecreaseAmount																18,000,000
Potomac Electric Power Company [Member] | Electric Distribution [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act				$ 39,000,000
Potomac Electric Power Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Return on Equity, Percentage																																																						10.50%
Amount of Impairment to Carrying Amount of Regulatory Assets																																									8,000,000													$ 8,000,000
Potomac Electric Power Company [Member] | Reductions Under TCJA [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									161,000,000													161,000,000
Potomac Electric Power Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									147,000,000													147,000,000
Potomac Electric Power Company [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Potomac Electric Power Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				8,000,000					8,000,000				0		8,000,000
Potomac Electric Power Company [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													3,000,000					3,000,000						3,000,000
Potomac Electric Power Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													5,000,000					5,000,000						5,000,000
Potomac Electric Power Company [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Potomac Electric Power Company [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Potomac Electric Power Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									190,000,000													190,000,000
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInDCServiceTerritory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									9,000,000													9,000,000
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									11,000,000													11,000,000
Potomac Electric Power Company [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Potomac Electric Power Company [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Costs [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													13,000,000					13,000,000						13,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																													3,000,000					3,000,000						3,000,000
Other Income																																																								10,000,000
Potomac Electric Power Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													31,000,000					31,000,000						31,000,000
Potomac Electric Power Company [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									158,000,000				174,000,000					174,000,000				158,000,000		174,000,000
Potomac Electric Power Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									11,000,000				6,000,000					6,000,000				11,000,000		6,000,000
Potomac Electric Power Company [Member] | TransmissionCost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									3,000,000													3,000,000
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									8,000,000													8,000,000
Potomac Electric Power Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									20,000,000				11,000,000					11,000,000				20,000,000		11,000,000
Potomac Electric Power Company [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									229,000,000				250,000,000					250,000,000				229,000,000		250,000,000
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																		$ 26,000,000
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Minimum [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																		6,000,000
Potomac Electric Power Company [Member] | Pepco Holdings [Member] | Maximum [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																		$ 7,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									120,000,000													120,000,000
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[5]																																																					$ 6,000,000		$ 8,000,000		$ 15,000,000
Public Utilities, Approved Equity Capital Structure, Percentage	[6]																																																					7.16%		7.21%		7.80%
Public Utilities, Interim Rate Increase (Decrease), Amount																	$ 2,500,000																													2,500,000
Public Utilities, Approved Rate Increase (Decrease), Amount	[5]																																																					$ (14,000,000)		$ 14,000,000		$ (12,000,000)
Public Utilities, Requested Return on Equity, Percentage	[7]																																																					10.50%		10.50%		11.30%
Public Utilities, Approved Return on Equity, Percentage																	0.00%																										0.00%
Other Commitment																																									27,000,000													$ 27,000,000
Regulatory Assets																																									314,000,000				348,000,000					348,000,000				314,000,000		$ 348,000,000
Amortization Rate Stabilization Deferral																																																						0		2,000,000		$ (3,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets																																									6,000,000													6,000,000
Regulatory Liability, Current																																									42,000,000				43,000,000					43,000,000				42,000,000		43,000,000
Regulatory liabilities																																									593,000,000				97,000,000					97,000,000				593,000,000		97,000,000
Revenues																																									330,000,000	327,000,000	$ 282,000,000	362,000,000	303,000,000	331,000,000	281,000,000	362,000,000						1,300,000,000		1,277,000,000		1,302,000,000
Customer Refund Liability, Noncurrent																																																																			$ 5,000,000
License Costs	[2]																																																									0
Business Combination, Integration Related Costs	[3],[9]																																																					(7,000,000)		20,000,000
Regulatory Liabilities																																									635,000,000				140,000,000					140,000,000				635,000,000		140,000,000
Delmarva Power and Light Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act			26,000,000
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount													$ 31,000,000				$ 24,000,000		$ 27,000,000															$ 63,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									10.10%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount									$ 19,300,000																		$ 60,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount								$ (13,000,000)																			$ (31,500,000)	$ (38,000,000)		$ (30,000,000)																										(32,000,000)
Public Utilities, Approved Return on Equity, Percentage								9.50%																			9.70%	9.60%
Projected Capital Expenditures																												$ 5,000,000
Delmarva Power and Light Company [Member] | Electric Distribution [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act			19,000,000																																					$ 13,000,000
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount										$ 11,000,000							$ 13,000,000																	$ 22,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount																							$ (4,900,000)
Public Utilities, Approved Return on Equity, Percentage																							9.70%							1000000000.00%
Delmarva Power and Light Company [Member] | Gas Distribution [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act			$ 7,000,000
Delmarva Power and Light Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																									7,000,000													7,000,000
Delmarva Power and Light Company [Member] | Reductions Under TCJA [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									160,000,000													160,000,000
Delmarva Power and Light Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									148,000,000													148,000,000
Delmarva Power and Light Company [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Delmarva Power and Light Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									1,000,000				5,000,000					5,000,000				1,000,000		5,000,000
Delmarva Power and Light Company [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													2,000,000					2,000,000						2,000,000
Delmarva Power and Light Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													3,000,000					3,000,000						3,000,000
Delmarva Power and Light Company [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Delmarva Power and Light Company [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Delmarva Power and Light Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0													0
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									4,000,000													4,000,000
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelaware [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									5,000,000													5,000,000
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandAndDelaware [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									1,000,000													1,000,000
Delmarva Power and Light Company [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Delmarva Power and Light Company [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Delmarva Power and Light Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													20,000,000					20,000,000						20,000,000
Delmarva Power and Light Company [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									77,000,000				84,000,000					84,000,000				77,000,000		84,000,000
Delmarva Power and Light Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									15,000,000				5,000,000					5,000,000				15,000,000		5,000,000
Delmarva Power and Light Company [Member] | TransmissionCost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									8,000,000				1,000,000					1,000,000				8,000,000		1,000,000
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									7,000,000				4,000,000					4,000,000				7,000,000		4,000,000
Delmarva Power and Light Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									10,000,000				4,000,000					4,000,000				10,000,000		4,000,000
Delmarva Power and Light Company [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									5,000,000				8,000,000					8,000,000				5,000,000		8,000,000																			$ 41,000,000
Delmarva Power and Light Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									81,000,000				85,000,000					85,000,000				81,000,000		85,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									84,000,000													84,000,000
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[5]																																																					$ 20,000,000		$ 8,000,000		$ 10,000,000
Public Utilities, Approved Equity Capital Structure, Percentage	[6]																																																					8.02%		7.83%		8.51%
Public Utilities, Approved Rate Increase (Decrease), Amount	[5]																																																					$ (42,000,000)		$ 6,000,000		$ (12,000,000)
Public Utilities, Requested Return on Equity, Percentage	[7]																																																					10.50%		10.50%		11.30%
Other Commitment																																									121,000,000													$ 121,000,000
Projected Capital Expenditures																$ 79,000,000
Proposed Capital Expenditure																													$ 29,000,000						$ 9,000,000								32,000,000				19,000,000
Regulatory Assets																																									430,000,000				501,000,000					501,000,000				430,000,000		$ 501,000,000
Amortization Rate Stabilization Deferral																																																						0		0		$ 0
Amount of Impairment to Carrying Amount of Regulatory Assets																																									7,000,000													7,000,000
Regulatory Liability, Current																																									11,000,000				25,000,000					25,000,000				11,000,000		25,000,000
Regulatory liabilities																																									411,000,000				0					0				411,000,000		0
Revenues																																									271,000,000	$ 370,000,000	$ 270,000,000	$ 275,000,000	275,000,000	$ 421,000,000	$ 270,000,000	$ 291,000,000						1,186,000,000		1,257,000,000		1,295,000,000
License Costs	[2]																																																									$ 0
Business Combination, Integration Related Costs	[3],[9]																																																					(6,000,000)		19,000,000
Regulatory Liabilities																																									422,000,000				25,000,000					25,000,000				422,000,000		25,000,000
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 23,000,000
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																								$ 70,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage																				10.10%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				$ 73,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount															$ (43,000,000)																$ (1,000,000)
Public Utilities, Approved Return on Equity, Percentage															9.60%
Atlantic City Electric Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																									3,000,000													3,000,000
Atlantic City Electric Company [Member] | Reductions Under TCJA [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									152,000,000													152,000,000
Atlantic City Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory liabilities																																									147,000,000													147,000,000
Atlantic City Electric Company [Member] | Renewable portfolio standards costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Atlantic City Electric Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									3,000,000				5,000,000					5,000,000				3,000,000		5,000,000
Atlantic City Electric Company [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													1,000,000					1,000,000						1,000,000
Atlantic City Electric Company [Member] | Over Recovered Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liability, Current																																													4,000,000					4,000,000						4,000,000
Atlantic City Electric Company [Member] | Zero emission credit costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0													0
Atlantic City Electric Company [Member] | Pension and other postretirement benefits
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																									0				0					0				0		0
Atlantic City Electric Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0													0
Atlantic City Electric Company [Member] | Electric distribution formula rate
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Atlantic City Electric Company [Member] | Uncollectible deferral Balance [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Other Regulatory Assets																															7,000,000
Atlantic City Electric Company [Member] | Non Utility Deferral [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Increase (Decrease) in Other Regulatory Assets																															$ 10,000,000
Atlantic City Electric Company [Member] | CAP arrearage
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Atlantic City Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																													19,000,000					19,000,000						19,000,000
Atlantic City Electric Company [Member] | AMI programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Atlantic City Electric Company [Member] | Energy and transmission programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									26,000,000				17,000,000					17,000,000				26,000,000		17,000,000
Atlantic City Electric Company [Member] | TransmissionCost [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									11,000,000				6,000,000					6,000,000				11,000,000		6,000,000
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									15,000,000				11,000,000					11,000,000				15,000,000		11,000,000
Atlantic City Electric Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									9,000,000				0					0				9,000,000		0
Atlantic City Electric Company [Member] | COPCO acquisition adjustment
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				0					0				0		0
Atlantic City Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																									0				$ 0					$ 0				0		$ 0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																									$ 111,000,000													$ 111,000,000
[1]	Exelon reflects the consolidated regulatory asset impairments of ComEd, BGE, Pepco, DPL and ACE, and PHI reflects the consolidated regulatory asset impairments of Pepco, DPL and ACE.
[2]	Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 13 - Debt and Credit Agreements.
[3]	The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.
[4]	Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs.
[5]	The time period for any challenges to the annual transmission formula rate update flings expired with no challenges submitted
[6]	Represents to the weighted average debt and equity return on transmission rate bases.
[7]	As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO.
[8]	BGE's transmission revenues include a FERC approved dedicated facilities charge to recover the costs of providing transmission service to specifically designated load by BGE.
[9]	(b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million, $8 million, $8 million, and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million, $6 million, $11 million, and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information.
[10]	On March 22, 2017, the ICC issued an order approving ComEd's proposal to reduce the 2016 revenue requirement by $18 million, which was reflected in customer rates beginning in April 2017. This reduction is not reflected in the 2016 revenue requirement amounts above.
[11]	Includes a reduction of 6 basis points in 2017 and 5 basis points in 2016 and 2015 for a reliability performance metric penalty.
[12]	Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.
[13]	(a)Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.

Regulatory Matters Regulatory75

Regulatory Matters Regulatory Matters - Annual Electric Distribution/Transmission Filings (Details) - USD ($) $ in Millions		Feb. 05, 2018	Jan. 02, 2018	Dec. 19, 2017	Dec. 18, 2017	Nov. 15, 2017	Oct. 27, 2017	Oct. 20, 2017	Oct. 18, 2017	Sep. 11, 2017	Sep. 08, 2017	Aug. 24, 2017	Aug. 17, 2017	Jul. 25, 2017	Jul. 24, 2017	Jul. 14, 2017	Jun. 09, 2017	[1]	Mar. 30, 2017	Mar. 24, 2017	Mar. 22, 2017	Mar. 08, 2017	Feb. 15, 2017	Feb. 01, 2017	Dec. 17, 2016	Nov. 30, 2016	Nov. 15, 2016	Jul. 29, 2016	May 17, 2016	Feb. 01, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2023
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																	$ (7)																$ 44	[2]	$ 90	[2]	$ 68	[2]
Prior Year Revenue Adjustment	[2]																																(33)		4		18
Proposed Capital Expenditure	[2],[3]																																0		0		0
Public Utilities, Approved Rate Increase (Decrease), Amount										$ 12																							$ 11	[2]	$ 94	[2]	$ 86	[2]
Public Utilities, Approved Equity Capital Structure, Percentage										6.47%																							8.43%	[4]	8.47%	[4]	8.61%	[4]
Public Utilities, Requested Return on Equity, Percentage	[5]																																11.50%		11.50%		11.50%
Public Utilities, Approved Return on Equity, Percentage										8.40%
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint																																	55.00%
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																	$ 78		$ 134		$ 85
Public Utilities, Approved Rate Increase (Decrease), Amount																																	18		(7)		(152)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																					$ (18)												$ 96		$ 127	[6]	$ (67)
Public Utilities, Requested Equity Capital Structure, Percentage																																	6.47%		6.71%		7.05%
Public Utilities, Approved Equity Capital Structure, Percentage																																	6.45%		6.69%		7.02%
Public Utilities, Requested Return on Equity, Percentage																																	8.40%		8.64%		9.14%
Public Utilities, Approved Return on Equity, Percentage	[7]																																8.34%		8.59%		9.09%
Commonwealth Edison Co [Member] | Maximum [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																	$ 96		$ 138		$ (50)
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																	31	[2]	12	[2]	0	[2]	$ 242
Prior Year Revenue Adjustment	[2]																																3		3		(3)
Proposed Capital Expenditure																																	(8)	[2],[3]	13	[2],[3]	13	[2],[3]	$ 963
Public Utilities, Approved Rate Increase (Decrease), Amount	[2]																																$ 26		$ 28		$ 10
Public Utilities, Approved Equity Capital Structure, Percentage	[4]																																7.47%		8.09%		8.46%
Public Utilities, Requested Return on Equity, Percentage	[5]																																10.50%		10.50%		11.30%
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																	$ 116
Public Utilities, Approved Rate Increase (Decrease), Amount																												$ 44
Public Utilities, Requested Return on Equity, Percentage																												9.75%
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[2]																																5		$ 2		$ 10
Prior Year Revenue Adjustment	[2]																																15		(10)		(3)
Current Year Revenue Adjustment	[2],[8]																																0		(15)		(2)
Public Utilities, Approved Rate Increase (Decrease), Amount	[2]																																$ 20		$ (23)		$ 5
Public Utilities, Approved Equity Capital Structure, Percentage	[4]																																7.92%		7.88%		8.36%
Public Utilities, Requested Return on Equity, Percentage	[5]																																10.50%		10.50%		11.30%
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 11	$ 41	$ 66																$ 69												$ 86
Public Utilities, Approved Rate Increase (Decrease), Amount							$ 32	$ 34						$ 37													$ 53
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount												$ 67												$ 77
Public Utilities, Requested Return on Equity, Percentage				10.10%
Public Utilities, Approved Return on Equity, Percentage								9.50%						9.50%										10.60%			9.55%
Potomac Electric Power Company [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Return on Equity, Percentage																																	10.50%
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[2]																																$ 6		$ 8		$ 15
Prior Year Revenue Adjustment	[2]																																8		(10)		(1)
Current Year Revenue Adjustment	[2],[8]																																0		(12)		(2)
Public Utilities, Approved Rate Increase (Decrease), Amount	[2]																																$ 14		$ (14)		$ 12
Public Utilities, Approved Equity Capital Structure, Percentage	[4]																																7.16%		7.21%		7.80%
Public Utilities, Requested Return on Equity, Percentage	[5]																																10.50%		10.50%		11.30%
Public Utilities, Approved Return on Equity, Percentage													0.00%																		0.00%
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 31				$ 24		$ 27														$ 63
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 13																	$ 31.5	$ 38		$ 30										$ 32
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 19.3																$ 60
Public Utilities, Approved Return on Equity, Percentage					9.50%																	9.70%	9.60%
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[2]																																$ 20		8		$ 10
Prior Year Revenue Adjustment	[2]																																22		(14)		2
Proposed Capital Expenditure																								$ 29						$ 9	$ 32	$ 19
Current Year Revenue Adjustment	[2],[8]																																0		0		0
Public Utilities, Approved Rate Increase (Decrease), Amount	[2]																																$ 42		$ (6)		$ 12
Public Utilities, Approved Equity Capital Structure, Percentage	[4]																																8.02%		7.83%		8.51%
Public Utilities, Requested Return on Equity, Percentage	[5]																																10.50%		10.50%		11.30%
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																			$ 70
Public Utilities, Approved Rate Increase (Decrease), Amount											$ 43															$ 1
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																$ 73
Public Utilities, Approved Return on Equity, Percentage											9.60%
[1]	Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs.
[2]	The time period for any challenges to the annual transmission formula rate update flings expired with no challenges submitted
[3]	BGE's transmission revenues include a FERC approved dedicated facilities charge to recover the costs of providing transmission service to specifically designated load by BGE.
[4]	Represents to the weighted average debt and equity return on transmission rate bases.
[5]	As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO, and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50-basis-point incentive adder for being a member of a RTO.
[6]	On March 22, 2017, the ICC issued an order approving ComEd's proposal to reduce the 2016 revenue requirement by $18 million, which was reflected in customer rates beginning in April 2017. This reduction is not reflected in the 2016 revenue requirement amounts above.
[7]	Includes a reduction of 6 basis points in 2017 and 5 basis points in 2016 and 2015 for a reliability performance metric penalty.
[8]	In 2012, PJM terminated the MAPP transmission line construction project planned for the Pepco and DPL service territories. Pursuant to a FERC approved settlement agreement, the abandonment costs associated with MAPP were being recovered in transmission rates over a three-year period that ended in May 2016.

Regulatory Matters Regulatory76

Regulatory Matters Regulatory Matters - Schedule of Revenue Increases (Decreases) (Details) - Commonwealth Edison Co [Member] - USD ($) $ in Millions	Sep. 11, 2017	Jun. 09, 2017	[1]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Public Utilities, Requested Rate Increase (Decrease), Amount		$ (7)		$ 44	[2]	$ 90	[2]	$ 68	[2]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 12			$ 11	[2]	$ 94	[2]	$ 86	[2]
Public Utilities, Approved Equity Capital Structure, Percentage	6.47%			8.43%	[3]	8.47%	[3]	8.61%	[3]
Public Utilities, Approved Return on Equity, Percentage	8.40%
[1]	Reflects higher projected PJM capacity revenues compared to projected energy efficiency costs.
[2]	The time period for any challenges to the annual transmission formula rate update flings expired with no challenges submitted
[3]	Represents to the weighted average debt and equity return on transmission rate bases.

Regulatory Matters Schedule of

Regulatory Matters Schedule of Regulatory Asset Impairment (Details) $ in Millions	Dec. 31, 2017USD ($)
Amount of Impairment to Carrying Amount of Regulatory Assets	$ 35	[1]
Commonwealth Edison Co [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	3
Baltimore Gas and Electric Company [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	5
Pepco Holdings LLC [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	27	[1]
Potomac Electric Power Company [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	14
Delmarva Power and Light Company [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	6
Atlantic City Electric Company [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	$ 7
[1]	Exelon reflects the consolidated regulatory asset impairments of ComEd, BGE, Pepco, DPL and ACE, and PHI reflects the consolidated regulatory asset impairments of Pepco, DPL and ACE.

Regulatory Matters Regulatory78

Regulatory Matters Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) $ in Millions	Dec. 31, 2017USD ($)
Other Commitments [Line Items]
Total	$ 137
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Total	164
2,018	36
2,019	60
2,020	44
2,021	24
2,022	0
PECO Energy Co [Member]
Other Commitments [Line Items]
Total	53
2,018	16
2,019	19
2,020	10
2,021	5
2,022	3
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Total	118
2,018	35
2,019	35
2,020	35
2,021	13
2,022	0
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Total	86
2,018	5
2,019	11
2,020	27
2,021	33
2,022	10
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Total	27
2,018	19
2,019	2
2,020	1
2,021	2
2,022	3
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Total	121
2,018	68
2,019	20
2,020	6
2,021	21
2,022	$ 6

Regulatory Matters Regulatory79

Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2013	Dec. 31, 2008
Regulatory Assets [Line Items]
Regulatory Assets	$ 9,288	$ 11,388
Current regulatory assets	1,267	1,342
Noncurrent regulatory assets	8,021	10,046
Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	3,848	4,162
Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	306	2,016
AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	640	701
Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	244	188
Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	166
Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	116	124
Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	758	812
Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	750	1,085
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	109	111
MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	295	305
Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	61	56
Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	258	260
Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	82	89
Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	27	36
Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		10
Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		7
Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	596	621
Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	45	25
Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	55	27
COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	5	8
Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	35	34
Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	19	31
Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	79	138
CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	8	11
Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	529	477
DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	190
Other
Regulatory Assets [Line Items]
Regulatory Assets	67	54
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,279	1,167
Current regulatory assets	225	190
Noncurrent regulatory assets	1,054	977
Commonwealth Edison Co [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	75
Commonwealth Edison Co [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	155	164
Commonwealth Edison Co [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	244	188
Commonwealth Edison Co [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	166
Commonwealth Edison Co [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	37	42
Commonwealth Edison Co [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	73	76
Commonwealth Edison Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	273	278
Commonwealth Edison Co [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	61	56
Commonwealth Edison Co [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	256	258
Commonwealth Edison Co [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	6	23
Commonwealth Edison Co [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0
Commonwealth Edison Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	8	7
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets	410	1,710
Current regulatory assets	29	29
Noncurrent regulatory assets	381	1,681
PECO Energy Co [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	297	1,583
PECO Energy Co [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	36	49
PECO Energy Co [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0
PECO Energy Co [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	1	1
PECO Energy Co [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	22	23
PECO Energy Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	22	26
PECO Energy Co [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	1	0
PECO Energy Co [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	1	1
PECO Energy Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	6	7
PECO Energy Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	8	11
PECO Energy Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0
PECO Energy Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	16	9
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	571	712
Current regulatory assets	174	208
Noncurrent regulatory assets	397	504
Baltimore Gas and Electric Company [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	98
Baltimore Gas and Electric Company [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	214	230
Baltimore Gas and Electric Company [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0
Baltimore Gas and Electric Company [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	11	7
Baltimore Gas and Electric Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	14	12
Baltimore Gas and Electric Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	1
Baltimore Gas and Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	23	38
Baltimore Gas and Electric Company [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	0	1
Baltimore Gas and Electric Company [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		10
Baltimore Gas and Electric Company [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		7
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	285	285
Baltimore Gas and Electric Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	6	10	$ 4
Baltimore Gas and Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	14	3
Baltimore Gas and Electric Company [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	4	10
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	3,047	3,504
Current regulatory assets	554	653
Noncurrent regulatory assets	2,493	2,851
Pepco Holdings LLC [Member] | Pension and other postretirement benefits | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Deferred income taxes | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	9	260
Pepco Holdings LLC [Member] | AMI programs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	235	258
Pepco Holdings LLC [Member] | Electric distribution formula rate | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Energy efficiency costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0
Pepco Holdings LLC [Member] | Debt costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	73	81
Pepco Holdings LLC [Member] | Fair value of long-term debt | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	619	671
Pepco Holdings LLC [Member] | Fair value of PHI's unamortized energy contracts | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	750	1,085
Pepco Holdings LLC [Member] | Asset retirement obligations | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | MGP remediation costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Under-recovered uncollectible accounts | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Renewable energy | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	2	2
Pepco Holdings LLC [Member] | Energy and transmission programs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	52	28
Pepco Holdings LLC [Member] | Deferred storm costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	27	35
Pepco Holdings LLC [Member] | Electric generation-related regulatory asset | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Pepco Holdings LLC [Member] | Rate stabilization deferral | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	310	335
Pepco Holdings LLC [Member] | Merger integration costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	39	15
Pepco Holdings LLC [Member] | Under-recovered revenue decoupling | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	41	24
Pepco Holdings LLC [Member] | COPCO acquisition adjustment | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	5	8
Pepco Holdings LLC [Member] | Workers compensation and long-term disability costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	35	34
Pepco Holdings LLC [Member] | Vacation accrual | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	13	24
Pepco Holdings LLC [Member] | Securitized stranded costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	79	138
Pepco Holdings LLC [Member] | CAP arrearage | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Removal costs | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	529	477
Pepco Holdings LLC [Member] | DC PLUG charge | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	190
Pepco Holdings LLC [Member] | Other | Successor [Member]
Regulatory Assets [Line Items]
Regulatory Assets	39	29
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	891	852
Current regulatory assets	213	162
Noncurrent regulatory assets	678	690
Potomac Electric Power Company [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	9	171
Potomac Electric Power Company [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	158	174
Potomac Electric Power Company [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0
Potomac Electric Power Company [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	15	17
Potomac Electric Power Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	11	6
Potomac Electric Power Company [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	7	12
Potomac Electric Power Company [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		0
Potomac Electric Power Company [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		0
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	229	250
Potomac Electric Power Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	20	11
Potomac Electric Power Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	38	21
Potomac Electric Power Company [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	35	34
Potomac Electric Power Company [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	150	134
Potomac Electric Power Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	190
Potomac Electric Power Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	29	22
Delmarva Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	314	348
Current regulatory assets	69	59
Noncurrent regulatory assets	245	289
Delmarva Power and Light Company [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	38
Delmarva Power and Light Company [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	77	84
Delmarva Power and Light Company [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0
Delmarva Power and Light Company [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	8	9
Delmarva Power and Light Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	1	0
Delmarva Power and Light Company [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	15	5
Delmarva Power and Light Company [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	5	5
Delmarva Power and Light Company [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		0
Delmarva Power and Light Company [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		0
Delmarva Power and Light Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	81	85
Delmarva Power and Light Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	10	4
Delmarva Power and Light Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	3	3
Delmarva Power and Light Company [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	5	8		$ 41
Delmarva Power and Light Company [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	8	14
Delmarva Power and Light Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power and Light Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	93	88
Delmarva Power and Light Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0
Delmarva Power and Light Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	8	5
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets	430	501
Current regulatory assets	71	96
Noncurrent regulatory assets	359	405
Atlantic City Electric Company [Member] | Pension and other postretirement benefits
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	51
Atlantic City Electric Company [Member] | AMI programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric distribution formula rate
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0
Atlantic City Electric Company [Member] | Debt costs
Regulatory Assets [Line Items]
Regulatory Assets	5	6
Atlantic City Electric Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Renewable energy
Regulatory Assets [Line Items]
Regulatory Assets	1	2
Atlantic City Electric Company [Member] | Energy and transmission programs
Regulatory Assets [Line Items]
Regulatory Assets	26	17
Atlantic City Electric Company [Member] | Deferred storm costs
Regulatory Assets [Line Items]
Regulatory Assets	15	18
Atlantic City Electric Company [Member] | Electric generation-related regulatory asset
Regulatory Assets [Line Items]
Regulatory Assets		0
Atlantic City Electric Company [Member] | Rate stabilization deferral
Regulatory Assets [Line Items]
Regulatory Assets		0
Atlantic City Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	9	0
Atlantic City Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | COPCO acquisition adjustment
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Workers compensation and long-term disability costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Vacation accrual
Regulatory Assets [Line Items]
Regulatory Assets	5	10
Atlantic City Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	79	138
Atlantic City Electric Company [Member] | CAP arrearage
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	286	255
Atlantic City Electric Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0
Atlantic City Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	$ 4	$ 4

Regulatory Matters Regulatory80

Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,388	$ 4,789
Regulatory Liability, Current	523	602
Noncurrent regulatory liabilities	9,865	4,187
Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	30	47
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,241
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3,064	2,607
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,573	1,601
Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	36	39
Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	23	185
DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	7	8
Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	35	76
Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	20
Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	111	134
Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	63
Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	112
Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	82	72
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,577	3,698
Regulatory Liability, Current	249	329
Noncurrent regulatory liabilities	6,328	3,369
Commonwealth Edison Co [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,479
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,528	2,169
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,338	1,324
Commonwealth Edison Co [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4	141
Commonwealth Edison Co [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Commonwealth Edison Co [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	47	60
Commonwealth Edison Co [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	63
Regulatory Liability, Current	10
Noncurrent regulatory liabilities	20
Commonwealth Edison Co [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	112
Commonwealth Edison Co [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6	4
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	690	644
Regulatory Liability, Current	141	127
Noncurrent regulatory liabilities	549	517
PECO Energy Co [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	536	438
PECO Energy Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19	41
PECO Energy Co [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	7	8
PECO Energy Co [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	35	76
PECO Energy Co [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	9	20
PECO Energy Co [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60	56
PECO Energy Co [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	24	5
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,163	160
Regulatory Liability, Current	62	50
Noncurrent regulatory liabilities	1,101	110
Baltimore Gas and Electric Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,032
Baltimore Gas and Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	105	141
Baltimore Gas and Electric Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Baltimore Gas and Electric Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	26	19
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,928	237
Regulatory Liability, Current	56	79
Noncurrent regulatory liabilities	1,872	158
Pepco Holdings LLC [Member] | Pension and other postretirement benefits | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Deferred income taxes | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,730
Pepco Holdings LLC [Member] | Nuclear decommissioning | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Removal costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	130	136
Pepco Holdings LLC [Member] | Deferred rent | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	36	39
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	3
Pepco Holdings LLC [Member] | DLC program costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Electric distribution tax repairs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Gas distribution tax repairs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Energy and transmission programs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	4	18
Pepco Holdings LLC [Member] | Renewable portfolio standards costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Zero emission credit costs | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Pepco Holdings LLC [Member] | Under-recovered uncollectible accounts | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Pepco Holdings LLC [Member] | Other | Successor [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	26	41
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	832	31
Regulatory Liability, Current	3	11
Noncurrent regulatory liabilities	829	20
Potomac Electric Power Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	809
Potomac Electric Power Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	20	18
Potomac Electric Power Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	3
Potomac Electric Power Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	8
Potomac Electric Power Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Potomac Electric Power Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3	2
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	635	140
Regulatory Liability, Current	42	43
Noncurrent regulatory liabilities	593	97
Delmarva Power and Light Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	510
Delmarva Power and Light Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	110	118
Delmarva Power and Light Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power and Light Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1	5
Delmarva Power and Light Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Delmarva Power and Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	14	17
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	422	25
Regulatory Liability, Current	11	25
Noncurrent regulatory liabilities	411	0
Atlantic City Electric Company [Member] | Pension and other postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	411
Atlantic City Electric Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Deferred rent
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | DLC program costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Electric distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Gas distribution tax repairs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Atlantic City Electric Company [Member] | Energy and transmission programs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	3	5
Atlantic City Electric Company [Member] | Renewable portfolio standards costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Zero emission credit costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0
Atlantic City Electric Company [Member] | Under-recovered uncollectible accounts
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 6	$ 20

Regulatory Matters Regulatory81

Regulatory Matters Regulatory Matters - Capitalized Ratemaking Amounts Not Recognized (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Document Period End Date		Dec. 31, 2017
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 69	$ 72
Commonwealth Edison Co [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[1]	6	5
PECO Energy Co [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		0	0
Baltimore Gas and Electric Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[2]	53	57
Pepco Holdings LLC [Member] | Successor [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		10	10
Potomac Electric Power Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	6	6
Delmarva Power and Light Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	4	4
Atlantic City Electric Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 0	$ 0
[1]	Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its under-recovered distribution services costs regulatory assets.
[2]	BGE's authorized amounts capitalized for ratemaking purposes primarily relate to earnings on shareholders' investment on its AMI programs
[3]	Pepco's and DPL's authorized amounts capitalized for ratemaking purposes relate to earnings on shareholders' investment on their respective AMI Programs and Energy Efficiency and Demand Response Programs. The earnings on energy efficiency are on Pepco DC and DPL DE programs only.

Regulatory Matters Regulatory82

Regulatory Matters Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Purchase Of Receivables [Line Items]
Document Period End Date		Dec. 31, 2017
Payments to Acquire Other Receivables		$ 298	$ 313
Allowance for Doubtful Accounts Receivable	[1]	(31)	(37)
Payments to Acquire Other Receivables, Net		267	276
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		87	87
Allowance for Doubtful Accounts Receivable	[1]	(14)	(14)
Payments to Acquire Other Receivables, Net		73	73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		70	72
Allowance for Doubtful Accounts Receivable	[1]	(5)	(6)
Payments to Acquire Other Receivables, Net		65	66
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		58	59
Allowance for Doubtful Accounts Receivable	[1]	(3)	(4)
Payments to Acquire Other Receivables, Net		55	55
Pepco Holdings LLC [Member] | Successor [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		83	95
Allowance for Doubtful Accounts Receivable	[1]	(9)	(13)
Payments to Acquire Other Receivables, Net		74	82
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		56	63
Allowance for Doubtful Accounts Receivable	[1]	(5)	(7)
Payments to Acquire Other Receivables, Net		51	56
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		9	10
Allowance for Doubtful Accounts Receivable	[1]	(1)	(2)
Payments to Acquire Other Receivables, Net		8	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		18	22
Allowance for Doubtful Accounts Receivable	[1]	(3)	(4)
Payments to Acquire Other Receivables, Net		$ 15	$ 18
[1]	For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing tariff.

Mergers, Acquisitions and Dis83

Mergers, Acquisitions and Dispositions Mergers, Acquisitions and Dispositions - Narrative (Details)		Nov. 07, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 01, 2016USD ($)	Jun. 16, 2016USD ($)	Mar. 23, 2016USD ($)$ / shares	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)		Mar. 23, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2016USD ($)		Dec. 31, 2018MW	Dec. 31, 2017USD ($)MW		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)	Nov. 30, 2016USD ($)	Mar. 24, 2016USD ($)
Business Acquisition [Line Items]
Deconsolidation, Gain (Loss), Amount		$ 213,000,000																					$ 213,000,000		$ 0		$ 0
Acquisition Costs, Period Cost		$ 60,000,000
Business Combination, Contingent Consideration, Asset																													$ 235,000,000
Payments to Acquire Businesses, Gross																							208,000,000		6,934,000,000		40,000,000
Business Combination, Integration Related Costs	[1]																						16,000,000		143,000,000
Line of credit facility, maximum borrowing capacity																												$ 98
Share price | $ / shares						$ 27.25											$ 27.25
Other Commitment								$ 137,000,000															137,000,000
Payments to Acquire Businesses, Net of Cash Acquired																									(6,962,000,000)		0
Revenues								8,381,000,000	$ 8,769,000,000	$ 7,623,000,000	$ 8,757,000,000	$ 7,875,000,000	$ 9,002,000,000	$ 6,910,000,000	$ 7,573,000,000								33,531,000,000		31,360,000,000		29,447,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000		0		0
Net income (Loss)																							3,849,000,000		1,204,000,000		2,250,000,000
Noncash Merger Related Costs																							0	[2]	558,000,000	[3],[4]
Payments of Debt Restructuring Costs	[5]																										22,000,000
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired																							1,500,000,000
Pepco Holdings [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 7,142,000,000
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets						1,441,000,000											$ 1,441,000,000
Other Commitment								513,000,000															513,000,000
Revenues																							4,829,000,000		3,785,000,000
Net income (Loss)																							$ 364,000,000		(66,000,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent						3,447,000,000											3,447,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets						248,000,000											248,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets						4,005,000,000											4,005,000,000
Total net assets						7,142,000,000											7,142,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt						5,636,000,000											5,636,000,000
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW																						27,000,000	37,000,000
Pepco Holdings LLC [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
OtherNonFinancialCommitment1 | MW																							100,000,000
Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							$ 8,000,000			8,000,000
Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								29,000,000															$ 29,000,000
Pepco Holdings LLC [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Commitment								513,000,000															513,000,000
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 289,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets			60,000,000								60,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent			149,000,000								149,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	[6]		114,000,000								114,000,000
Total net assets			522,000,000								522,000,000
Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other			54,000,000
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			110,000,000
Business Combination, Consideration Transferred, Other			125,000,000
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				$ 257,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets				9,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities				65,000,000
Total net assets				257,000,000
Net Working Capital				$ 204,000,000
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Deconsolidation, Gain (Loss), Amount																							213,000,000		0		0
Membership interest								9,357,000,000				9,261,000,000								$ 9,261,000,000			9,357,000,000		9,261,000,000
Business Combination, Contingent Consideration, Asset																													163,000,000
Payments to Acquire Businesses, Gross																							208,000,000		293,000,000		40,000,000
Business Combination, Integration Related Costs	[1]																						22,000,000		37,000,000
Line of credit facility, maximum borrowing capacity								200,000,000															200,000,000
Gain (Loss) on Disposition of Property Plant Equipment												69,000,000		10,000,000					$ 32,000,000
Proceeds from Sale of Productive Assets					$ 37,000,000
Revenues							12,000,000	4,654,000,000	4,751,000,000	4,174,000,000	4,888,000,000	4,388,000,000	5,035,000,000	3,589,000,000	4,739,000,000								18,466,000,000		17,751,000,000		19,135,000,000
Business Combination, Bargain Purchase, Gain Recognized, Amount																							233,000,000		0		0
Net income (Loss)																							2,771,000,000		558,000,000		1,340,000,000
Noncash Merger Related Costs																							0	[2]	53,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Asset Impairment Charges												23,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			289,000,000
Business Combination, Integration Related Costs																							57,000,000
Business Combination, Consideration Transferred, Other			179,000,000
Total net assets									3,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																							54,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			110,000,000
Payments to Acquire Businesses, Gross									4,000,000														235,000,000
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs	[1],[7]																						(6,000,000)		28,000,000
Gain (Loss) on Disposition of Property Plant Equipment																		$ 37,000,000									9,000,000
Other Commitment			$ 444,000,000								444,000,000
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent																													59,000,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																	0
Business Combination, Integration Related Costs	[7],[8]																29,000,000
Revenues																	1,153,000,000										4,935,000,000
Net income (Loss)																	19,000,000										327,000,000
Noncash Merger Related Costs	[3],[4]																$ 0
Payments of Debt Restructuring Costs																											0
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Membership interest								8,835,000,000				8,077,000,000								8,077,000,000			8,835,000,000		8,077,000,000				7,200,000,000
Business Combination, Contingent Consideration, Asset																													235,000,000
Payments to Acquire Businesses, Gross																				29,000,000
Business Combination, Integration Related Costs	[7],[8]																			69,000,000			(18,000,000)
Business Combination, Consideration Transferred, Other															59,000,000
Revenues								1,121,000,000	1,310,000,000	1,074,000,000	1,175,000,000	1,078,000,000	1,394,000,000	1,066,000,000	105,000,000	[9]				3,643,000,000			4,679,000,000
Net income (Loss)																				(61,000,000)			362,000,000
Noncash Merger Related Costs																				$ 317,000,000	[3],[4]		(8,000,000)	[2]
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Other Commitment								315,000,000															315,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member] | Successor [Member]
Business Acquisition [Line Items]
Other Commitment								6,000,000															6,000,000
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Gain (Loss) on Disposition of Property Plant Equipment																			8,000,000
Other Commitment								86,000,000															86,000,000
Revenues								510,000,000	604,000,000	514,000,000	530,000,000	491,000,000	635,000,000	509,000,000	551,000,000								2,158,000,000		2,186,000,000		2,129,000,000
Net income (Loss)																							205,000,000		42,000,000		187,000,000
Noncash Merger Related Costs																							(6,000,000)	[2]	125,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													1,700,000,000
Potomac Electric Power Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														73,000,000					73,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								120,000,000															120,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							6,000,000			6,000,000
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								1,000,000															1,000,000
Delmarva Power and Light Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Business Combination, Integration Related Costs	[1],[7]																						(7,000,000)		20,000,000
Gain (Loss) on Disposition of Property Plant Equipment												5,000,000	4,000,000
Other Commitment								27,000,000															27,000,000
Revenues								330,000,000	327,000,000	282,000,000	362,000,000	303,000,000	331,000,000	281,000,000	362,000,000								1,300,000,000		1,277,000,000		1,302,000,000
Net income (Loss)																							121,000,000		(9,000,000)		76,000,000
Noncash Merger Related Costs																							(2,000,000)	[2]	82,000,000	[3],[4]
Payments of Debt Restructuring Costs																											0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													1,100,000,000
Delmarva Power and Light Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														46,000,000					46,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								84,000,000															84,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment							$ 2,000,000			2,000,000
Delmarva Power and Light Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								5,000,000															5,000,000
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																									0
Business Combination, Integration Related Costs	[1],[7]																						(6,000,000)		19,000,000
Other Commitment								121,000,000															121,000,000
Revenues								271,000,000	$ 370,000,000	270,000,000	$ 275,000,000	$ 275,000,000	$ 421,000,000	270,000,000	$ 291,000,000								1,186,000,000		1,257,000,000		1,295,000,000
Net income (Loss)																							77,000,000		(42,000,000)		40,000,000
Noncash Merger Related Costs																							0	[2]	$ 110,000,000	[3],[4]
Payments of Debt Restructuring Costs																											$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																													$ 1,200,000,000
Atlantic City Electric Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital														$ 49,000,000					$ 49,000,000
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment								111,000,000															111,000,000
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment								$ 0															0
Preferred Stock [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross																							$ 180,000,000
Preferred Stock [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 180,000,000
Electricity Generation Plant, Non-Nuclear [Member]
Business Acquisition [Line Items]
Impairment of Long-Lived Assets to be Disposed of										$ 460,000,000
[1]	The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.
[2]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[3]	Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.
[4]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[5]	(e)See Note 13—Debt and Credit Agreements and Note 4—Mergers, Acquisitions and Dispositions for additional information on the PHI merger related debt exchange.
[6]	(a)Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23-Commitments and Contingencies for additional background regarding SNF obligations to the DOE.
[7]	(b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million, $8 million, $8 million, and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million, $6 million, $11 million, and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information.
[8]	(a)Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.
[9]	Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.

Mergers, Acquisitions and Dis84

Mergers, Acquisitions and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions		Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Business Acquisition [Line Items]
Business Combination, Bargain Purchase, Gain Recognized, Amount				$ 233	$ 0	$ 0
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets							$ 110
Business Combination, Consideration Transferred		$ 289
Current assets		60	$ 60
Property, plant and equipment		298	298
Unamortized energy contracts		807	807
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	[1]	114	114
Total assets		1,279	1,279
Current liabilities		6	6
Asset retirement obligation		444	444
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent		149	149
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedSpentNuclearFuel			110
Other liabilities		(15)	(15)
Total liabilities		757	757
Total net assets		522	522
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations		33	$ 33
Business Combination, Bargain Purchase, Gain Recognized, Amount				$ 233
Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other		125
Business Combination, Consideration Transferred		110
Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other		$ 54
[1]	(a)Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23-Commitments and Contingencies for additional background regarding SNF obligations to the DOE.

Mergers, Acquisitions and Dis85

Mergers, Acquisitions and Dispositions Purchase Price allocation Table - Con Edison (Details) - USD ($) $ in Millions	Sep. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Combination Segment Allocation [Line Items]
Payments to Acquire Businesses, Gross		$ 208	$ 6,934	$ 40
ConEdison Solutions [Member]
Business Combination Segment Allocation [Line Items]
Payments to Acquire Businesses, Gross	$ 257
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedWorkingCapital	204
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets	6
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEnergyContract	100
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	322
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	65
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	65
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 257

Mergers, Acquisitions and Dis86

Mergers, Acquisitions and Dispositions Merger Commitments Table (Details) - USD ($) $ in Millions	Dec. 31, 2017	Mar. 31, 2017
Other Commitments [Line Items]
Other Commitment	$ 137
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment		$ 444
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	86
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	27
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	121
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	513
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	84
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings LLC [Member] | Rate Bill Credits [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings LLC [Member] | Rate Bill Credits [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	67
Pepco Holdings LLC [Member] | Rate Bill Credits [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	122
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings LLC [Member] | Charitable Contributions [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings LLC [Member] | Charitable Contributions [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings LLC [Member] | Charitable Contributions [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings LLC [Member] | Delivery System Modernization [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delivery System Modernization [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delivery System Modernization [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings LLC [Member] | Workforce Development [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Workforce Development [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Workforce Development [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings LLC [Member] | Other1 [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings LLC [Member] | Other1 [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings LLC [Member] | Other1 [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Successor [Member] | Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	315
Successor [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	259
Successor [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
Successor [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	50
Successor [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
Successor [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
Successor [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
Successor [Member] | Pepco Holdings LLC [Member] | Other1 [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	$ 6

Mergers, Acquisitions and Dis87

Mergers, Acquisitions and Dispositions Merger Transaction Table (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition, Share Price	$ 27.25
Payments to Acquire Businesses, Gross			$ 208	$ 6,934	$ 40
Preferred Stock [Member]
Payments to Acquire Businesses, Gross			$ 180
Pepco Holdings [Member]
Payments to Acquire Businesses, Gross	$ 7,142
Pepco Holdings LLC [Member] | Preferred Stock [Member]
Payments to Acquire Businesses, Gross	180
Pepco Holdings LLC [Member] | Common Stock [Member]
Payments to Acquire Businesses, Gross	$ 6,933
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Deferred Compensation, Share-based Payments [Member]
Stockholders' Equity, Other		$ 29

Mergers, Acquisitions and Dis88

Mergers, Acquisitions and Dispositions Purchase Price Allocation Table - (PHI) (Details) - Pepco Holdings LLC [Member] $ in Millions	Mar. 23, 2016USD ($)
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 21,797
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	2,752
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	1,441
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	11,088
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedAssets	5,015
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets	248
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	4,005
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities	297
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	5,636
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent	3,447
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations	821
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	187
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	14,655
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEnergyContract	1,515
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	$ 7,142

Mergers, Acquisitions and Dis89

Mergers, Acquisitions and Dispositions Merger Integration Related Costs Table (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Business Combination, Integration Related Costs	[1]			$ 16	$ 143
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs	[1]			22	37
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs	[1],[2]			1	(6)
PECO Energy Co [Member]
Business Combination, Integration Related Costs	[1]			4	5
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs	[1],[2]			4	(1)
Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[1],[2]			(6)	28
Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs	[1],[2]			(7)	20
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs	[1],[2]			(6)	19
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[2],[3]	$ 29
Successor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[2],[3]		$ 69	(18)
Regulatory Assets [Member] | Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs					8
Regulatory Assets [Member] | Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs					6
Regulatory Assets [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs			$ 16	24
Regulatory Assets [Member] | Potomac Electric Power Company [Member]
Business Combination, Integration Related Costs				8	11
Regulatory Assets [Member] | Delmarva Power and Light Company [Member]
Business Combination, Integration Related Costs				8	$ 4
Regulatory Assets [Member] | Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs				$ 8
[1]	The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.
[2]	(b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $24 million, $8 million, $8 million, and $8 million incurred at PHI, Pepco, DPL, and ACE, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $8 million, $6 million, $11 million, and $4 million incurred at ComEd, BGE, Pepco, and DPL, respectively, that have been recorded as a regulatory asset for anticipated recovery. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs to achieve distribution synergies related to the PHI acquisition of $16 million incurred at PHI that have been recorded as a regulatory asset for anticipated recovery. See Note 3 - Regulatory Matters for more information.
[3]	(a)Amounts shown reflect the final purchase price allocation and the correction of a reporting error identified and corrected in the second quarter of 2016. The error had resulted in a gross up of certain assets and liabilities related to legacy PHI intercompany and income tax receivable and payable balances.

Mergers, Acquisitions and Dis90

Mergers, Acquisitions and Dispositions Proforma Impact of Merger (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	[3]	Dec. 31, 2016		Dec. 31, 2015
Business Acquisition, Pro Forma Revenue			$ 32,342	[1]	$ 33,823	[2]
Business Acquisition, Pro Forma Net Income (Loss)			$ 1,562	[1]	$ 2,618	[2]
Business Acquisition, Pro Forma Earnings Per Share, Basic			$ 1.69	[1]	$ 2.85	[2]
Business Acquisition, Pro Forma Earnings Per Share, Diluted			$ 1.69	[1]	$ 2.84	[2]
Noncash Merger Related Costs	$ 0		$ 558	[4],[5]
Consolidation, Eliminations [Member]
Business Acquisition, Pro Forma Revenue			171		$ 559
Noncash Merger Related Costs			$ 680		$ 92
[1]	The amounts above exclude non-recurring costs directly related to the merger of $680 million and intercompany revenue of $171 million for the year ended December 31, 2016
[2]	The amounts above exclude non-recurring costs directly related to the merger of $92 million and intercompany revenue of $559 million for the year ended December 31, 2015
[3]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[4]	Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.
[5]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.

Accounts Receivable Schedule of

Accounts Receivable Schedule of Estimated Unbilled Revenues (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		$ 1,858	$ 1,673
Allowance for uncollectible accounts	[1]	(322)	(334)
Regulatory Assets		9,288	11,388
Exelon Generation Co L L C [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues	[2]	1,017	910
Allowance for uncollectible accounts	[1]	(114)	(91)
Commonwealth Edison Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		242	219
Allowance for uncollectible accounts	[1]	(73)	(70)
Regulatory Assets		1,279	1,167
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		162	140
Allowance for uncollectible accounts	[1],[3]	(56)	(61)
Allowance for Doubtful Accounts Receivable, Noncurrent		15	23
Regulatory Assets		410	1,710
Baltimore Gas and Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		205	182
Allowance for uncollectible accounts	[1]	(24)	(32)
Regulatory Assets		571	712
Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charged to Costs and Expenses		10
Pepco Holdings LLC [Member] | Successor [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		232	222
Allowance for uncollectible accounts	[1]	(55)	(80)	[4]
Regulatory Assets		3,047	3,504
Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		133	123
Allowance for uncollectible accounts	[1]	(21)	(29)	[4]
Regulatory Assets		891	852
Charged to Costs and Expenses		6
Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		68	58
Allowance for uncollectible accounts	[1]	(16)	(24)	[4]
Regulatory Assets		314	348
Charged to Costs and Expenses		4
Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unbilled customer revenues		31	41
Allowance for uncollectible accounts	[1]	(18)	(27)	[4]
Regulatory Assets		430	$ 501
PHI Merger [Member] | Pepco Holdings LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(30)
Regulatory Assets		20
PHI Merger [Member] | Potomac Electric Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(14)
Regulatory Assets		8
PHI Merger [Member] | Delmarva Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(8)
Regulatory Assets		4
PHI Merger [Member] | Atlantic City Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for uncollectible accounts		(8)
Regulatory Assets		$ 8
[1]	Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable.
[2]	Represents unbilled portion of retail receivables estimated under Exelon’s unbilled critical accounting policy.
[3]	Excludes the non-current allowance for uncollectible accounts of $15 million and $23 million at December 31, 2017 and 2016, respectively, related to PECO’s current installment plan receivables described below.
[4]	At December 31, 2016, as explained in Note 1 — Significant Accounting Policies, PHI, Pepco, DPL and ACE estimated the allowance for uncollectible accounts on customer receivables by applying loss rates to the outstanding receivable balance by risk segment. The change in estimate resulted in an overall increase of $30 million, $14 million, $8 million, and $8 million in the allowance for uncollectible accounts with $20 million, $8 million, $4 million, and $8 million deferred as a regulatory asset on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets at December 31, 2016, respectively. This also resulted in a $10 million, $6 million, and $4 million pre-tax charge to provision for uncollectible accounts expense for the year ended December 31, 2016, which is included in Operating and maintenance expense on PHI's, Pepco's and DPL's Consolidated Statements of Operations and Comprehensive Income, respectively.

Accounts Receivable Narrative (

Accounts Receivable Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables	$ 11	$ 9
PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve	11	13
Risk Level, Low [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve		1
Risk Level, Medium [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve	3	3
Risk Level, High [Member] | PECO Energy Co [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Installment plan receivables uncollectible accounts reserve	$ 8	$ 9

Property, Plant and Equipment P

Property, Plant and Equipment Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		$ 90,724	$ 95,266	$ 90,724
Less: accumulated depreciation	[1]	19,169	21,064	19,169
Property, plant and equipment, net		71,555	74,202	71,555
Impairment of Long-Lived Assets Held-for-use			573	306	$ 36
Successor [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use		0
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		45,698	$ 49,506	45,698
Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			90 years
Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		27,193	$ 29,019	27,193
Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			2 years
Electric—generation | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			56 years
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		4,642	$ 5,050	4,642
Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			90 years
Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		1,312	$ 1,447	1,312
Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[2]	6,546	$ 6,420	6,546
Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			8 years
Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		4,306	$ 2,825	4,306
Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[3]	1,027	$ 999	1,027
Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			2 years
Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			50 years
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		36,147	$ 36,334	36,147
Less: accumulated depreciation	[4]	10,562	11,428	10,562
Property, plant and equipment, net		25,585	24,906	25,585
Nuclear fuel - work in progress		1,326	1,196	1,326
Capital Leases, Balance Sheet, Assets by Major Class, Net		10	7	10
Capital Leased Assets, Gross		52	47	52
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		42	40	42
Property, Plant, and Equipment, Fair Value Disclosure		17	0	17
Impairment of Long-Lived Assets Held-for-use			510	243	12
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		27,193	29,019	27,193
Impairment of Long-Lived Assets Held-for-use			11
Assets Held-for-sale, Not Part of Disposal Group, Current			$ 6
Exelon Generation Co L L C [Member] | Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			2 years
Exelon Generation Co L L C [Member] | Electric—generation | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			56 years
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[5]	6,546	$ 6,420	6,546
Less: accumulated depreciation		3,186	$ 3,159	3,186
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			8 years
Exelon Generation Co L L C [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		2,332	$ 838	2,332
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[6]	76	$ 57	76
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			2 years
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			3 years
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		23,272	$ 24,992	23,272
Less: accumulated depreciation		3,937	4,269	3,937
Property, plant and equipment, net		19,335	20,723	19,335
Capital Leases, Balance Sheet, Assets by Major Class, Net		7	7	7
Capital Leased Assets, Gross		8	8	8
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		1	1	1
Plant Held for Future Use Amount			44
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		22,636	$ 24,423	22,636
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Commonwealth Edison Co [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			80 years
Commonwealth Edison Co [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		569	$ 517	569
Commonwealth Edison Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[7],[8]	67	$ 52	67
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			36 years
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			50 years
PECO Energy Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		10,818	$ 11,464	10,818
Less: accumulated depreciation		3,253	3,411	3,253
Property, plant and equipment, net		7,565	8,053	7,565
Plant Held for Future Use Amount			21
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		7,591	$ 7,975	7,591
PECO Energy Co [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
PECO Energy Co [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			65 years
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		2,348	$ 2,504	2,348
PECO Energy Co [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
PECO Energy Co [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			70 years
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		670	$ 710	670
PECO Energy Co [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
PECO Energy Co [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			50 years
PECO Energy Co [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		188	$ 254	188
PECO Energy Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[9]	21	$ 21	21
Average Service Life (years)			50 years
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		10,294	$ 11,007	10,294
Less: accumulated depreciation		3,254	3,405	3,254
Property, plant and equipment, net		7,040	7,602	7,040
Plant Held for Future Use Amount			26
Impairment of Long-Lived Assets Held-for-use			7	52	0
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		7,067	$ 7,464	7,067
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			90 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		2,170	$ 2,379	2,170
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			90 years
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		707	$ 771	707
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Baltimore Gas and Electric Company [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			40 years
Baltimore Gas and Electric Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		318	$ 367	318
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[10]	32	$ 26	32
Average Service Life (years)			20 years
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		11,793	$ 12,985	11,793
Less: accumulated depreciation		195	487	195
Property, plant and equipment, net		11,598	12,498	11,598
Impairment of Long-Lived Assets Held-for-use			52
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		10,315	$ 11,517	10,315
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Pepco Holdings LLC [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		414	$ 449	414
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Pepco Holdings LLC [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Pepco Holdings LLC [Member] | Common—electric and gas | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		65	$ 82	65
Pepco Holdings LLC [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Pepco Holdings LLC [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Pepco Holdings LLC [Member] | Construction work in progress | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		892	$ 835	892
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Successor [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[11]	107	$ 102	107
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			3 years
Pepco Holdings LLC [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			43 years
Potomac Electric Power Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		8,621	$ 9,178	8,621
Less: accumulated depreciation		3,050	3,177	3,050
Property, plant and equipment, net		5,571	6,001	5,571
Plant Held for Future Use Amount			59
Impairment of Long-Lived Assets Held-for-use			14	0	0
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		8,018	$ 8,646	8,018
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Potomac Electric Power Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Potomac Electric Power Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		537	$ 473	537
Potomac Electric Power Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[12]	66	$ 59	66
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			25 years
Potomac Electric Power Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			33 years
Delmarva Power and Light Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		4,448	$ 4,826	4,448
Less: accumulated depreciation		1,175	1,247	1,175
Property, plant and equipment, net		3,273	3,579	3,273
Plant Held for Future Use Amount			15
Impairment of Long-Lived Assets Held-for-use			6	0	0
Delmarva Power and Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		3,574	$ 3,875	3,574
Delmarva Power and Light Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power and Light Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			70 years
Delmarva Power and Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		580	$ 614	580
Delmarva Power and Light Company [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power and Light Company [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Delmarva Power and Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		115	$ 117	115
Delmarva Power and Light Company [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power and Light Company [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Delmarva Power and Light Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		163	$ 205	163
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[13]	16	$ 15	16
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			10 years
Delmarva Power and Light Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			43 years
Atlantic City Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		3,537	$ 3,772	3,537
Less: accumulated depreciation		1,016	1,066	1,016
Property, plant and equipment, net		2,521	2,706	2,521
Plant Held for Future Use Amount			27
Impairment of Long-Lived Assets Held-for-use			7	0	$ 0
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		3,341	$ 3,607	3,341
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Atlantic City Electric Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			60 years
Atlantic City Electric Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment		169	$ 138	169
Atlantic City Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[14]	$ 27	$ 27	$ 27
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			13 years
Atlantic City Electric Company [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			15 years
[1]	Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $3,159 million and $3,186 million as of December 31, 2017 and 2016, respectively.
[2]	Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016, respectively.
[3]	Includes Generation’s buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016, respectively. The original cost basis of the buildings was $47 million and $52 million, and total accumulated amortization was $40 million and $42 million, as of December 31, 2017 and 2016, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2017 and 2016, of $7 million. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016. Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $44 million, $21 million, $26 million, $59 million, $15 million and $27 million, respectively, at December 31, 2017. Includes the original cost and progress payments associated with Generation’s turbine equipment held for future use with a carrying value of $0 million and $17 million as of December 31, 2017 and 2016, respectively. Generation's turbine equipment was impaired by $11 million and the remaining $6 million was moved to the assets held for sale account at December 31, 2017.
[4]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million and $3,186 million as of December 31, 2017 and 2016, respectively
[5]	Includes nuclear fuel that is in the fabrication and installation phase of $1,196 million and $1,326 million at December 31, 2017 and 2016, respectively
[6]	Includes buildings under capital lease with a net carrying value of $7 million and $10 million at December 31, 2017 and 2016, respectively. The original cost basis of the buildings was $47 million and $52 million, and total accumulated amortization was $40 million and $42 million, as of December 31, 2017 and 2016, respectively.
[7]	Includes buildings under capital lease with a net carrying value at both December 31, 2017 and 2016 of $7 million. The original cost basis of the buildings was $8 million and total accumulated amortization was $1 million as of both December 31, 2017 and 2016
[8]	Includes land held for future use and non-utility property.
[9]	Represents land held for future use and non-utility property.
[10]	Represents land held for future use and non-utility property
[11]	Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[12]	Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[13]	Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.
[14]	Represents plant held for future use and non-utility property. Utility plant is generally subject to a first mortgage lien.

Property, Plant and Equipment94

Property, Plant and Equipment Property, Plant and Equipment- Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.73%		2.83%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%	[1]	5.94%	[1]	3.47%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.10%		2.17%		2.17%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	7.05%		7.41%		7.79%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.37%		2.32%		2.39%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.89%		1.82%		1.87%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.47%		5.11%		5.16%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.58%		2.56%		2.62%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.33%		2.45%		2.50%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.64%		9.45%		10.35%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.63%		2.52%		2.48%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.07%		2.57%		2.55%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.50%		8.12%		5.19%
Delmarva Power and Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.49%		2.44%
Delmarva Power and Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.07%		2.57%		2.55%
Delmarva Power and Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.14%		4.99%		4.24%
[1]	See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI.

Property, Plant and Equipment95

Property, Plant and Equipment Property, Plant and Equipment- Narrative (Details)	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%	[1]	5.94%	[1]	3.47%
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.75%		2.73%		2.83%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	4.36%		5.94%		3.47%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.99%		3.03%		3.03%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.35%		2.17%		2.13%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.46%		2.45%		2.46%
[1]	See Note 8 — Early Nuclear Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities and TMI.

Impairment of Long-lived Asse96

Impairment of Long-lived Assets Impairment of Long-Lived Assets - Narrative (Details) - USD ($) $ in Millions		1 Months Ended		3 Months Ended			12 Months Ended
		Sep. 30, 2017	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2015
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges					$ 36
Property, plant and equipment, net							$ 74,202	$ 71,555
Gain (Loss) on Contract Termination						$ 4
Interest costs incurred	[1]						1,658	1,678	$ 1,170
Finite-Lived Intangible Assets, Gross							1,228	1,244
Estimated residual value of leased assets			$ 356			356
Proceeds From Lease Termination						$ 360
Wind Assets [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Property, plant and equipment, net					60
Assets held for sale					$ 24
Pepco Holdings LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Finite-Lived Intangible Assets, Gross										$ 25
PHI PEPCO [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment of Long-Lived Assets to be Disposed of				$ 25
Exelon Generation Co L L C [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Property, plant and equipment, net							24,906	25,585
Assets held for sale							0	17
Interest costs incurred	[1]						$ 502	$ 472	$ 445
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment charges		$ 15	$ 119
Electricity Generation Plant, Non-Nuclear [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment of Long-Lived Assets to be Disposed of				$ 460
[1]	(a)Includes interest expense to affiliates.

Early Nuclear Plant Retiremen97

Early Nuclear Plant Retirements Early Nuclear Plant Retirements Narrative (Details)	Dec. 31, 2017
Exelon Generation Co L L C [Member] | Nuclear Plant [Member]
Property, Plant and Equipment [Line Items]
Ownership interest	42.59%

Early Nuclear Plant Retiremen98

Early Nuclear Plant Retirements Early Nuclear Plant Retirements Table (Details) - USD ($) $ in Millions		Dec. 17, 2016	Jun. 16, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Nuclear Fuel Amortization	[1]			$ 1,096	$ 1,159	$ 1,116
Other, net				1,056	413	$ (46)
Inventory, Raw Materials and Supplies, Gross				1,311	1,274
Property, plant and equipment, net				74,202	71,555
Facility Closing [Member] | Clinton and Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation					712
Nuclear Fuel Amortization					60
Other Cost and Expense, Operating		$ (120)	$ 146		26
Accretion Expense, Including Asset Retirement Obligations					2
Other, net					(86)
Other Expenses					$ 714
Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation				250
Nuclear Fuel Amortization				12
Other Cost and Expense, Operating				77
Accretion Expense, Including Asset Retirement Obligations				0
Other, net				0
Other Expenses				339
Facility Closing [Member] | Salem [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials and Supplies, Gross				44
Nuclear Fuel, Net of Amortization				113
Property, plant and equipment, net				439
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress				33
Asset Retirement Obligation				$ (442)
[1]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Jointly Owned Electric Utilit99

Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions		12 Months Ended
		Dec. 31, 2017USD ($)Vmi	Dec. 31, 2016USD ($)
Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		127
Transmission line capacity | V		500
Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		151.3
Transmission line capacity | V		500
Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V		500
Substation capacity | V		500
Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Miles of transmission voltage lines | mi		2.5
Transmission line capacity | V		500
New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Transmission line capacity | V		500
Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[2]	$ 27	$ 27
Accumulated depreciation	[1],[2]	15	15
Construction work in progress	[2]	0	0
Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[3]	102	97
Accumulated depreciation	[1],[3]	52	52
Construction work in progress	[3]	0	0
Other Service [Member] | Other Locations [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[4]	15	15
Accumulated depreciation	[1],[4]	13	13
Construction work in progress	[4]	$ 0	0
Exelon Generation Co L L C [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		44.24%
Exelon Generation Co L L C [Member] | Nuclear Plant [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.59%
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		75.00%
Plant	[1]	$ 1,074	1,054
Accumulated depreciation	[1]	550	515
Construction work in progress		$ 35	0
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		50.00%
Plant	[1]	$ 1,417	1,384
Accumulated depreciation	[1]	461	407
Construction work in progress		$ 18	16
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	[5]	42.59%
Plant	[1],[5]	$ 631	596
Accumulated depreciation	[1],[5]	205	186
Construction work in progress	[5]	$ 33	41
Exelon Generation Co L L C [Member] | Nuclear Plant [Member] | Nine Mile Point [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		82.00%
Plant	[1]	$ 839	830
Accumulated depreciation	[1]	97	68
Construction work in progress		55	37
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant		$ 3
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Wyman [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		5.89%
Plant	[1]	$ 3	3
Accumulated depreciation	[1]	3	3
Construction work in progress		$ 0	$ 0
PECO Energy Co [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		22.00%
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		20.72%
PECO Energy Co [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
Baltimore Gas and Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.00%
Baltimore Gas and Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		10.56%
Potomac Electric Power Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		27.00%
Potomac Electric Power Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		9.72%
Potomac Electric Power Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		11.90%
Delmarva Power and Light Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		9.00%
Delmarva Power and Light Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		1.00%
Delmarva Power and Light Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		3.72%
Delmarva Power and Light Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.45%
Delmarva Power and Light Company [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		4.83%
Delmarva Power and Light Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.40%
Atlantic City Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		8.00%
Atlantic City Electric Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		13.90%
Atlantic City Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		3.83%
Atlantic City Electric Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.45%
Atlantic City Electric Company [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		11.91%
Atlantic City Electric Company [Member] | Valley Forge [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		6.60%
Atlantic City Electric Company [Member] | New Freedom Switching [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		21.78%
[1]	Excludes asset retirement costs.
[2]	PECO, BGE, Pepco, DPL and ACE own a 22%, 7%, 27%, 9% and 8% share, respectively, in 127 miles of 500kV lines located in Pennsylvania as well as a 20.72%, 10.56%, 9.72%, 3.72% and 3.83% share, respectively, of a 500kV substation immediately outside of the Conemaugh fossil-generating station which supplies power to the 500kV lines including, but not limited to, the lines noted above.
[3]	PECO, DPL and ACE own a 42.55%, 1% and 13.9% share, respectively in 151.3 miles of 500kV lines located in New Jersey and Delaware Station. PECO, DPL and ACE also own a 42.55%, 7.45% and 7.45% share, respectively, in 2.5 miles of 500kV line located over the Delaware River. ACE also has a 21.78% share in a 500kV New Freedom Switching
[4]	Generation, DPL and ACE own a 44.24%, 4.83% and 11.91% share, respectively in assets located at Merrill Creek Reservoir located in New Jersey. Pepco, DPL and ACE own a 11.9%, 7.4% and 6.6% share, respectively, in Valley Forge Corporate Center.
[5]	Generation also owns a proportionate share in the fossil-fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2017 and 2016.

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, Gross		$ 8,660,000,000	$ 8,660,000,000	$ 8,660,000,000		$ 4,655,000,000
Accumulated impairment loss		1,983,000,000	1,983,000,000	1,983,000,000		1,983,000,000
Goodwill, beginning balance	$ 2,672,000,000		6,677,000,000	2,672,000,000
Goodwill from business combination			0	4,016,000,000
Impairment losses			0	0
Goodwill, Purchase Accounting Adjustments				(11,000,000)
Goodwill, ending balance		6,677,000,000	6,677,000,000	6,677,000,000
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, Gross		47,000,000	47,000,000	47,000,000		47,000,000
Goodwill, beginning balance	47,000,000		47,000,000	47,000,000
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		47,000,000	47,000,000	47,000,000
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, Gross		4,608,000,000	4,608,000,000	4,608,000,000		4,608,000,000
Accumulated impairment loss		1,983,000,000	1,983,000,000	1,983,000,000		1,983,000,000
Goodwill, beginning balance	2,625,000,000		2,625,000,000	2,625,000,000
Goodwill from business combination			0
Impairment losses			0	0
Goodwill, ending balance		2,625,000,000	2,625,000,000	2,625,000,000
Delmarva Power and Light Company [Member]
Goodwill [Roll Forward]
Goodwill, Gross		8,000,000	8,000,000	8,000,000		8,000,000
Goodwill, beginning balance	8,000,000		8,000,000	8,000,000
Impairment losses			0	0
Goodwill, ending balance		8,000,000	8,000,000	8,000,000
Pepco Holdings LLC [Member]
Goodwill [Roll Forward]
Goodwill from business combination			0
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	1,418,000,000					1,418,000,000
Accumulated impairment loss	12,000,000					$ 12,000,000
Goodwill, beginning balance	1,406,000,000	1,406,000,000		1,406,000,000
Goodwill from business combination	0
Impairment losses	0
Goodwill, ending balance	1,406,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Roll Forward]
Goodwill, Gross	0	4,005,000,000	4,005,000,000	4,005,000,000
Accumulated impairment loss		0	0	0	$ 0
Goodwill, beginning balance		0	4,005,000,000
Goodwill from business combination		4,016,000,000	0
Impairment losses		0	0
Goodwill, Purchase Accounting Adjustments		(11,000,000)	0
Goodwill, ending balance	$ 0	$ 4,005,000,000	$ 4,005,000,000	$ 4,005,000,000

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) - USD ($)		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2016	Mar. 24, 2016
Goodwill [Line Items]
Goodwill			$ 6,677,000,000	$ 6,677,000,000	$ 6,677,000,000	$ 2,672,000,000
Goodwill, Purchase Accounting Adjustments					(11,000,000)
Amortization of Intangible Assets				92,000,000	87,000,000	76,000,000
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill			47,000,000	47,000,000	47,000,000	47,000,000
Amortization of Intangible Assets				83,000,000	79,000,000	69,000,000
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill			2,625,000,000	2,625,000,000	2,625,000,000	2,625,000,000
Amortization of Intangible Assets				7,000,000	7,000,000	7,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							30.00%
Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Line Items]
Goodwill		$ 1,406,000,000				1,406,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Goodwill		0	4,005,000,000	4,005,000,000	4,005,000,000
Goodwill, Purchase Accounting Adjustments			(11,000,000)	0
Potomac Electric Power Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 1,700,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%
Delmarva Power and Light Company [Member]
Goodwill [Line Items]
Goodwill			8,000,000	$ 8,000,000	8,000,000	8,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								1,100,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				50.00%			10.00%
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								$ 1,200,000,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount							10.00%
Unamortized Energy Contracts [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			$ 35,000,000	35,000,000	22,000,000
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			35,000,000	35,000,000	22,000,000
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]	$ 0				0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]		$ 0	0
Unamortized Energy Contracts [Member] | Potomac Electric Power Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Delmarva Power and Light Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			0	0	0
Unamortized Energy Contracts [Member] | Atlantic City Electric Company [Member]
Goodwill [Line Items]
Amortization of Intangible Assets	[1]			$ 0	$ 0	$ 0
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life				10 years
[1]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

Intangible Assets - Schedule102

Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Gross		$ 1,228	$ 1,244
Accumulated Amortization		(1,255)	(1,502)
Net		(27)	(258)
Finite-Lived Intangible Assets, Gross		1,228	1,244
Exelon Enterprise [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	10
2,019	[1]	10
2,020	[1]	10
2,021	[1]	10
2,022	[1]	10
Exelon Enterprise [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[1]	95	95
Accumulated Amortization	[1]	(25)	(15)
Net	[1]	70	80
Finite-Lived Intangible Assets, Gross	[1]	95	95
Exelon Generation Consolidated [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	62
2,019	[1]	57
2,020	[1]	68
2,021	[1]	77
2,022	[1]	54
Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[2],[3]	1,938	1,926
Accumulated Amortization	[2],[3]	(1,574)	(1,543)
Net	[2],[3]	364	383
Finite-Lived Intangible Assets, Gross	[2],[3]	1,938	1,926
Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		305	299
Accumulated Amortization		(133)	(109)
Net		172	190
Finite-Lived Intangible Assets, Gross		305	299
Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		243	243
Accumulated Amortization		(148)	(125)
Net		95	118
Finite-Lived Intangible Assets, Gross		243	243
Exelon Generation Co L L C [Member] | Order or Production Backlog [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		0	9
Accumulated Amortization		0	(7)
Net		0	2
Finite-Lived Intangible Assets, Gross		0	9
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	7
2,019	[1]	7
2,020	[1]	7
2,021	[1]	0
2,022	[1]	0
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		162	162
Accumulated Amortization		(141)	(133)
Net		21	29
Finite-Lived Intangible Assets, Gross		162	162
PHI Service Co Affiliate [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	(189)
2,019	[1]	(119)
2,020	[1]	(115)
2,021	[1]	(92)
2,022	[1]	(89)
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Gross				$ 25
Finite-Lived Intangible Assets, Gross				$ 25
Pepco Holdings LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		(1,515)	(1,515)
Accumulated Amortization		766	430
Net		(749)	(1,085)
Finite-Lived Intangible Assets, Gross		(1,515)	(1,515)
Potomac Electric Power Company [Member] | DC Sponsorship Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		0	25
Accumulated Amortization		0	0
Net		0	25
Finite-Lived Intangible Assets, Gross		$ 0	$ 25
[1]	On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.
[2]	In March 1999 and February 2003, ComEd entered into separate agreements with the City of Chicago and Midwest Generation, LLC. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement.
[3]	Includes unamortized energy contract assets and liabilities on Exelon's, Generations and PHI's Consolidated Balance Sheets.

Intangible Assets - Summary of

Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense			$ 92	$ 87	$ 76
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense			83	79	69
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense			7	7	7
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]		35	35	22
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]		35	35	22
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]		0	$ 0	$ 0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense	[1]	$ 0	$ 0
[1]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

Intangible Assets Renewable and

Intangible Assets Renewable and Alternative Energy Credits (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Exelon Generation Co L L C [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	$ 0	$ 0
Exelon Generation Co L L C [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Exelon Generation Co L L C [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	312	318
Exelon Generation Co L L C [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	27	29
Exelon Consolidations [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	1	1
Exelon Consolidations [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Exelon Consolidations [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	321	330
Exelon Consolidations [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	27	29
PECO Energy Co [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	1	1
PECO Energy Co [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
PECO Energy Co [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
PECO Energy Co [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Delmarva Power and Light Company [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Delmarva Power and Light Company [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Delmarva Power and Light Company [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	8	11
Delmarva Power and Light Company [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Atlantic City Electric Company [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Atlantic City Electric Company [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Atlantic City Electric Company [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	1	1
Atlantic City Electric Company [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Successor [Member] | Pepco Holdings LLC [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Successor [Member] | Pepco Holdings LLC [Member] | Alternative energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0	0
Successor [Member] | Pepco Holdings LLC [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	9	12
Successor [Member] | Pepco Holdings LLC [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	$ 0	$ 0

Fair Value of Financial Asse105

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		$ 865	$ 962
Due to Related Parties, Noncurrent		389	641
Spent Nuclear Fuel Obligation, Noncurrent		1,147	1,024
Debt Issuance Costs, Net		201	200
Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		1	7
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		929	1,267
Long-term debt (including amounts due within one year)(a)	[1]	34,264	34,005
Due to Related Parties, Noncurrent	[2]	389	641
Spent Nuclear Fuel Obligation, Noncurrent		1,147	1,024
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		929	1,267
Long-term debt (including amounts due within one year)(a)	[1]	36,705	34,813
Due to Related Parties, Noncurrent	[2]	431	667
Spent Nuclear Fuel Obligation, Noncurrent		936	732
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	1,113
Due to Related Parties, Noncurrent	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		929	1,267
Long-term debt (including amounts due within one year)(a)	[1]	34,735	31,741
Due to Related Parties, Noncurrent	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		936	732
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	1,970	1,959
Due to Related Parties, Noncurrent	[2]	431	667
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		910	922
Spent Nuclear Fuel Obligation, Noncurrent		1,147	1,024
Debt Issuance Costs, Net		60	64
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		2	699
Long-term debt (including amounts due within one year)(a)	[1]	8,990	9,241
Spent Nuclear Fuel Obligation, Noncurrent		1,147	1,024
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		2	699
Long-term debt (including amounts due within one year)(a)	[1]	9,512	9,152
Spent Nuclear Fuel Obligation, Noncurrent		936	732
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		2	699
Long-term debt (including amounts due within one year)(a)	[1]	7,839	7,482
Spent Nuclear Fuel Obligation, Noncurrent		936	732
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	1,673	1,670
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		205	205
Debt Issuance Costs, Net		52	46
Commonwealth Edison Co [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		1	1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	7,601	7,033
Due to Related Parties, Noncurrent	[2]	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	8,418	7,585
Due to Related Parties, Noncurrent	[2]	227	215
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	8,418	7,585
Due to Related Parties, Noncurrent	[2]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]	227	215
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		184	184
Debt Issuance Costs, Net		17	15
PECO Energy Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	2,903	2,580
Due to Related Parties, Noncurrent		184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	3,194	2,794
Due to Related Parties, Noncurrent		204	192
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent		0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	3,194	2,794
Due to Related Parties, Noncurrent		0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent		204	192
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due to Related Parties, Noncurrent		0	252
Debt Issuance Costs, Net		17	15
Baltimore Gas and Electric Company [Member] | Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net			6
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		77	45
Long-term debt (including amounts due within one year)(a)	[1]	2,577	2,322
Due to Related Parties, Noncurrent	[2]		252
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		77	45
Long-term debt (including amounts due within one year)(a)	[1]	2,825	2,467
Due to Related Parties, Noncurrent	[2]		260
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]		0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		77	45
Long-term debt (including amounts due within one year)(a)	[1]	2,825	2,467
Due to Related Parties, Noncurrent	[2]		0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Due to Related Parties, Noncurrent	[2]		260
Pepco Holdings LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		686
Pepco Holdings LLC [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		6	2
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		350	522
Long-term debt (including amounts due within one year)(a)	[1]	5,874	5,898
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		350	522
Long-term debt (including amounts due within one year)(a)	[1]	6,019	5,809
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		350	522
Long-term debt (including amounts due within one year)(a)	[1]	5,722	5,520
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	297	289
Potomac Electric Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		32	30
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		26	23
Long-term debt (including amounts due within one year)(a)	[1]	2,540	2,349
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		26	23
Long-term debt (including amounts due within one year)(a)	[1]	3,123	2,796
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		26	23
Long-term debt (including amounts due within one year)(a)	[1]	3,114	2,788
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0	0
Long-term debt (including amounts due within one year)(a)	[1]	9	8
Delmarva Power and Light Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		11	11
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		216
Long-term debt (including amounts due within one year)(a)	[1]	1,300	1,340
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		216
Long-term debt (including amounts due within one year)(a)	[1]	1,393	1,383
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		216
Long-term debt (including amounts due within one year)(a)	[1]	1,393	1,383
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Atlantic City Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		5	6
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		108
Long-term debt (including amounts due within one year)(a)	[1]	1,121	1,155
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		108
Long-term debt (including amounts due within one year)(a)	[1]	1,237	1,287
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	[1]	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		108
Long-term debt (including amounts due within one year)(a)	[1]	949	1,007
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(a)	[1]	$ 288	$ 280
[1]	Includes unamortized debt issuance costs which are not fair valued of $201 million, $60 million, $52 million, $17 million, $17 million, $6 million, $32 million, $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2017. Includes unamortized debt issuance costs which are not fair valued of $200 million, $64 million, $46 million, $15 million, $15 million, $2 million, $30 million, $11 million and $6 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2016.
[2]	Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2017. Includes unamortized debt issuance costs which are not fair valued of $7 million, $1 million, and $6 million for Exelon, ComEd and BGE, respectively, as of December 31, 2016.

Fair Value of Financial Asse106

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value Measurement of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		$ (232)	$ (282)
Derivative Liability, Noncurrent		(409)	(392)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, collateral, right to reclaim cash		77	29
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		0	(2)
Derivative Asset, Notional Amount		811	933
Margin Deposit Assets		(117)	(158)
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		389	360
Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		145	180
Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		85	25
Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments		(82)	(31)
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	656	373
FinancialAssetsFairValueDisclosure1		15,716	13,253
Deferred Compensation Liability, Current and Noncurrent		(145)	(136)
Financial Liabilities Fair Value Disclosure		(786)	(810)
FinancialAssetLiabilitiesNetFairValueDisclosure1		14,930	12,443
Alternative Investment, Fair Value Disclosure		3,534	3,113
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(637)	(662)
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(4,040)	(4,697)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(53)	(79)
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	3,456	4,114
Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(4)	(12)
Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(10)
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(9)	(21)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			(4)
Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		7	23
Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	13,431	11,092
Alternative Investment, Fair Value Disclosure	[4]	3,510	3,049
Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	220	129
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7,254	6,014
Alternative Investment, Fair Value Disclosure		2,176	2,011
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,736	3,977
Alternative Investment, Fair Value Disclosure		510	493
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,865	1,804
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,969	1,320
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		82	37
Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		263	264
Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	557	552
Alternative Investment, Fair Value Disclosure	[6]	510	493
Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		528	498
Alternative Investment, Fair Value Disclosure		131	71
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		222	148
Alternative Investment, Fair Value Disclosure		222	148
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		471	326
Alternative Investment, Fair Value Disclosure		471	326
Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		39	113
Alternative Investment, Fair Value Disclosure		24	64
Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	11
Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	2
Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			17
Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		36	83
Alternative Investment, Fair Value Disclosure		24	64
Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		240	224
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		77	74
Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		58	50
Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		93	84
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,304	1,381
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4,225	5,092
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		68	76
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(2,989)	(3,787)
Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		9	28
Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		6	16
Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	28
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			5
Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(7)	(21)
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		37	42
Fair Value, Inputs, Level 1 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		65	71
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	656	373
FinancialAssetsFairValueDisclosure1		6,980	5,674
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(63)	(37)
FinancialAssetLiabilitiesNetFairValueDisclosure1		6,917	5,637
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(64)	(37)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(713)	(1,267)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(3)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	651	1,233
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(1)	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			(4)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		2	4
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	6,215	4,952
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	135	110
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,163	3,551
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,917	1,291
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,917	1,291
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	27
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	11
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			16
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		135	124
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		77	74
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		58	50
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(26)	197
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		557	1,358
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2	3
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(585)	(1,164)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2)	1
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			3
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2)	(2)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		320	197
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
FinancialAssetsFairValueDisclosure1		3,793	2,937
Deferred Compensation Liability, Current and Noncurrent		(145)	(136)
Financial Liabilities Fair Value Disclosure		(329)	(237)
FinancialAssetLiabilitiesNetFairValueDisclosure1		3,464	2,700
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(179)	(89)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2,226)	(2,378)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(42)	(50)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	2,089	2,339
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(5)	(12)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(10)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(8)	(21)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		5	19
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	3,058	2,414
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	85	19
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		915	452
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,058	1,943
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,614	1,554
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		52	29
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		82	37
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		263	264
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	47	59
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	2
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		83	80
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		71	64
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		640	413
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2,378	2,505
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		31	50
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(1,769)	(2,142)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		11	27
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		6	16
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	28
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			2
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5)	(19)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Fair Value, Amount Offset Against Collateral, Net		81	61
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
FinancialAssetsFairValueDisclosure1		1,409	1,529
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(394)	(536)
FinancialAssetLiabilitiesNetFairValueDisclosure1		1,015	993
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(394)	(536)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(1,101)	(1,052)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(9)	(26)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	716	542
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	648	677
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		251	250
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		251	250
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		397	427
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	19
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	19
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	20
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	20
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		690	771
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,290	1,229
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		35	23
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(635)	(481)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		37	42
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		(211)	(263)
Derivative Liability, Noncurrent		(174)	(153)
Derivative liabilities, fair value	[7]	349	333
Exelon Generation Co L L C [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		259	252
Exelon Generation Co L L C [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		127	157
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	168	39
FinancialAssetsFairValueDisclosure1		15,035	12,718
Deferred Compensation Liability, Current and Noncurrent		(38)	(34)
Financial Liabilities Fair Value Disclosure		(423)	(450)
FinancialAssetLiabilitiesNetFairValueDisclosure1		14,612	12,268
Alternative Investment, Fair Value Disclosure		3,534	3,113
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(381)	(404)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(3,783)	(4,439)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(53)	(79)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	3,455	4,114
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(4)	(12)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(10)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(9)	(21)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			(4)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		7	23
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	13,431	11,092
Alternative Investment, Fair Value Disclosure	[4]	3,510	3,049
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	220	129
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7,254	6,014
Alternative Investment, Fair Value Disclosure		2,176	2,011
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,736	3,977
Alternative Investment, Fair Value Disclosure		510	493
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,865	1,804
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,969	1,320
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		82	37
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		263	264
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	557	552
Alternative Investment, Fair Value Disclosure	[6]	510	493
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		528	498
Alternative Investment, Fair Value Disclosure		131	71
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		222	148
Alternative Investment, Fair Value Disclosure		222	148
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		471	326
Alternative Investment, Fair Value Disclosure		471	326
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		39	113
Alternative Investment, Fair Value Disclosure		24	64
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	11
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			17
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		36	83
Alternative Investment, Fair Value Disclosure		24	64
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		50	39
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23	19
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	18
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,304	1,381
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4,225	5,090
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		68	76
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(2,989)	(3,785)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		6	12
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3	0
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	28
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			5
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(7)	(21)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		37	42
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	168	39
FinancialAssetsFairValueDisclosure1		6,385	5,237
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(63)	(37)
FinancialAssetLiabilitiesNetFairValueDisclosure1		6,322	5,200
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(64)	(37)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(712)	(1,267)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(3)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	650	1,233
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(1)	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			(4)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		2	4
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	6,215	4,952
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	135	110
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		4,163	3,551
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,917	1,291
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,917	1,291
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2	27
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			16
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		28	21
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5	2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23	19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(26)	197
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		557	1,356
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(585)	(1,162)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2)	1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(2)	(2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
FinancialAssetsFairValueDisclosure1		3,729	2,859
Deferred Compensation Liability, Current and Noncurrent		(38)	(34)
Financial Liabilities Fair Value Disclosure		(222)	(135)
FinancialAssetLiabilitiesNetFairValueDisclosure1		3,507	2,724
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(179)	(89)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2,226)	(2,378)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(42)	(50)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	2,089	2,339
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(5)	(12)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(2)	(10)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(8)	(21)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		5	19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	3,058	2,414
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	85	19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		915	452
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,058	1,943
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,614	1,554
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		52	29
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		82	37
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		263	264
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	47	59
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1	2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		640	413
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2,378	2,505
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		31	50
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(1,769)	(2,142)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		8	11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		3	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		10	28
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(5)	(19)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0	0
FinancialAssetsFairValueDisclosure1		1,387	1,509
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(138)	(278)
FinancialAssetLiabilitiesNetFairValueDisclosure1		1,249	1,231
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(138)	(278)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(845)	(794)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(9)	(26)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[2],[3]	716	542
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	648	677
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[5]	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		251	250
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		251	250
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[6]	0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		397	427
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		690	771
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,290	1,229
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		35	23
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset	[2],[3]	(635)	(481)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset			0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		37	42
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		(21)	(19)
Derivative Liability, Noncurrent		(235)	(239)
Commonwealth Edison Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		45	36
Commonwealth Edison Co [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure			2
Commonwealth Edison Co [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		62
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	98	20
FinancialAssetsFairValueDisclosure1		98	20
Derivative Liability	[9]	(256)	(258)
Deferred Compensation Liability, Current and Noncurrent		(8)	(8)
Financial Liabilities Fair Value Disclosure		(264)	(266)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(166)	(246)
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	98	20
FinancialAssetsFairValueDisclosure1		98	20
Derivative Liability	[9]	0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		98	20
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability	[9]	0	0
Deferred Compensation Liability, Current and Noncurrent		(8)	(8)
Financial Liabilities Fair Value Disclosure		(8)	(8)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(8)	(8)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		(21)	(19)
Derivative Liability, Noncurrent		(235)	(239)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability	[9]	(256)	(258)
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(256)	(258)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(256)	(258)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		47	22
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	228	45
FinancialAssetsFairValueDisclosure1		245	62
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(11)	(11)
Financial Liabilities Fair Value Disclosure		(11)	(11)
FinancialAssetLiabilitiesNetFairValueDisclosure1		234	51
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		17	17
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	7
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	228	45
FinancialAssetsFairValueDisclosure1		235	52
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		235	52
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		7	7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		10	10
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(11)	(11)
Financial Liabilities Fair Value Disclosure		(11)	(11)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)	(1)
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		10	10
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		17	13
Baltimore Gas and Electric Company [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		1
Baltimore Gas and Electric Company [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure			2
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	36
FinancialAssetsFairValueDisclosure1		6	40
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(5)	(4)
Financial Liabilities Fair Value Disclosure		(5)	(4)
FinancialAssetLiabilitiesNetFairValueDisclosure1		1	36
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	4
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	4
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	36
FinancialAssetsFairValueDisclosure1		6	40
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		6	40
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	4
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		6	4
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(5)	(4)
Financial Liabilities Fair Value Disclosure		(5)	(4)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(5)	(4)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[8]	0	0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Successor [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		12	19
Pepco Holdings LLC [Member] | Successor [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		23	23
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	83	217
Derivative Asset	[11]	0	2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset		0	(2)
Derivative assets, fair value		0	0
FinancialAssetsFairValueDisclosure1		212	348
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(25)	(28)
Financial Liabilities Fair Value Disclosure		(25)	(28)
FinancialAssetLiabilitiesNetFairValueDisclosure1		187	320
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[11]	(1)	0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1	0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		129	131
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		72	73
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		45	42
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	83	217
Derivative Asset	[11]	0	2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset		0	(2)
Derivative assets, fair value		0	0
FinancialAssetsFairValueDisclosure1		155	290
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		155	290
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[11]	(1)	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		72	73
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		72	73
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset	[11]	0	0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset		0	0
Derivative assets, fair value		0	0
FinancialAssetsFairValueDisclosure1		35	38
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(25)	(28)
Financial Liabilities Fair Value Disclosure		(25)	(28)
FinancialAssetLiabilitiesNetFairValueDisclosure1		10	10
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[11]	0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	38
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23	22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset	[11]	0	0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset		0	0
Derivative assets, fair value		0	0
FinancialAssetsFairValueDisclosure1		22	20
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		22	20
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[11]	0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	20
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	20
Potomac Electric Power Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		4	9
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	36	33
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		137	133
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		(4)	(5)
Financial Liabilities Fair Value Disclosure		(4)	(5)
FinancialAssetLiabilitiesNetFairValueDisclosure1		133	128
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		101	100
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		44	43
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		45	41
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	36	33
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		80	76
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		80	76
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		44	43
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		44	43
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		35	38
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		(4)	(5)
Financial Liabilities Fair Value Disclosure		(4)	(5)
FinancialAssetLiabilitiesNetFairValueDisclosure1		31	33
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		35	38
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		12	16
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		23	22
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		22	19
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		22	19
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	19
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22	19
Delmarva Power and Light Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	4
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	42
Derivative Asset	[11]		2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			(2)
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	42
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		(1)	(1)
Financial Liabilities Fair Value Disclosure		(1)	(1)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)	41
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[10]	(1)
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	42
Derivative Asset	[11]		2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			(2)
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	42
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	42
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[10]	(1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		1
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset	[11]		0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		(1)	(1)
Financial Liabilities Fair Value Disclosure		(1)	(1)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)	(1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[10]	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset	[11]		0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability	[10]	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	3
Atlantic City Electric Company [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		23	23
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	29	130
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		29	130
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		29	130
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	29	130
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		29	130
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		29	130
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	[10]	0	0
Derivative Asset			0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset			0
Derivative assets, fair value			0
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability		0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		$ 0	$ 0
[1]	Generation excludes cash of $259 million and $252 million at December 31, 2017 and 2016 and restricted cash of $127 million and $157 million at December 31, 2017 and 2016. Exelon excludes cash of $389 million and $360 million at December 31, 2017 and 2016 and restricted cash of $145 million and $180 million at December 31, 2017 and 2016 and includes long-term restricted cash of $85 million and $25 million at December 31, 2017 and 2016, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[2]	Collateral posted/(received) from counterparties totaled $65 million, $320 million and $81 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2017. Collateral posted/(received) from counterparties totaled $71 million, $197 million and $61 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2016.
[3]	Of the collateral posted/(received), $(117) million and $(158) million represents variation margin on the exchanges as of December 31, 2017 and 2016, respectively.
[4]	Excludes net liabilities of $82 million and $31 million at December 31, 2017 and 2016, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less.
[5]	Includes $77 million and $29 million of cash received from outstanding repurchase agreements at December 31, 2017 and 2016, respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below.
[6]	Includes derivative instruments of less than $1 million and $(2) million, which have a total notional amount of $811 million and $933 million at December 31, 2017 and 2016, respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss.
[7]	Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.
[8]	ComEd excludes cash of $45 million and $36 million at December 31, 2017 and 2016 and restricted cash of $2 million at December 31, 2016 and includes long-term restricted cash of $62 million at December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $47 million and $22 million at December 31, 2017 and 2016. BGE excludes cash of $17 million and $13 million at December 31, 2017 and 2016 and restricted cash of $1 million at December 31, 2017 and includes long-term restricted cash of $2 million at December 31, 2016, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[9]	The Level 3 balance consists of the current and noncurrent liability of $21 million and $235 million, respectively, at December 31, 2017, and $19 million and $239 million, respectively, at December 31, 2016, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[10]	PHI excludes cash of $12 million and $19 million at December 31, 2017 and 2016 and includes long term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $4 million and $9 million at December 31, 2017 and 2016. DPL excludes cash of $2 million and $4 million at December 31, 2017 and 2016. ACE excludes cash of $2 million and $3 million at December 31, 2017 and 2016 and includes long-term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets.
[11]	Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.

Fair Value of Financial Asse107

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value Reconciliation of Level 3 Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2017		Dec. 31, 2016		Jan. 01, 2017	Dec. 31, 2015
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 20	$ 1,015		$ 993			$ 1,529
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			(81)		(557)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			(8)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			8		5
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			20		(141)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			248		494
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			(16)		(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			(1)		(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			(110)		(144)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			(6)		2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			(61)		(197)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			29
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			261		116
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			0		0			0
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			(6)		(16)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			6		16
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0		0
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			1,249		1,231			1,776
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			(84)		(560)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			6		16
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			(8)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			20		(141)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			248		494
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			(16)		(15)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			(110)		(144)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			(6)		2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			(61)		(197)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			29
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			258		114
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			648		677			670
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			3		7
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			6		16
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			64		143
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			(102)		(144)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0		(14)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			1		5
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			12		19			22
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			(8)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			1		2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		(5)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0		0
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			552		493			1,051
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]		(90)		(568)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			20		(141)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			178		342	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			(16)		(9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			(8)	[3]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			(6)		1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			(50)		(183)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous	[4]		31
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			254		109
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings			352		677
Indefinite-lived Intangible Assets Acquired					168
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			37		42			33
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			3		1
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			5		7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			(11)		0
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			(2)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			3		0
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)			20		18
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease)			(18)		(29)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			(256)		(258)			(247)
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets	[5]		2		(11)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0		0
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Successor [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Successor [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		20	22		20	[6]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			3		3	[6]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			0		0	[6]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0		0	[6]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral			0		0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			0		0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales			0		0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			(1)		(3)	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0		0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0		0	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3			0		0	[6]
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous			0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			3		2	[6]
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Predecessor [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		20						19
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		1
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member] | Predecessor [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0						18
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(18)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value			22		19		$ 20	$ 19
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings			3		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases			(1)		(3)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			$ 3		$ 3
[1]	Includes a reduction for the reclassification of $352 million and $677 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2017 and 2016, respectively.
[2]	Includes $168 million of fair value from contracts acquired as a result of portfolio acquisitions.
[3]	Exelon includes the settlement value for any open contracts that were net settled prior to their scheduled maturity within this line item.
[4]	As a result of the bankruptcy filing for EGTP on November 7, 2017, the net mark-to-market commodity contracts were deconsolidated from Exelon's and Generation's consolidated financial statements.
[5]	Includes $18 million of decreases in fair value and an increase for realized losses due to settlements of $20 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2017. Includes $29 million of decreases in fair value and an increase for realized losses due to settlements of $18 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2016.
[6]	Successor period represents activity from March 24, 2016 to December 31, 2016. See tables below for PHI's predecessor periods, as well as activity for Pepco for the years ended December 31, 2017 and 2016.

Fair Value of Financial Asse108

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on Recurring Basis Gain Loss Included in Earnings (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				$ 28	$ (477)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				290	154
Purchased Power And Fuel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				(126)	(91)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				(36)	(45)
Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]			6	10
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]			4	7
Operating and Maintenance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				3
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				28	(477)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				290	154
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				(126)	(91)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				(36)	(45)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]			6	7
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]			4	5
Pepco Holdings LLC [Member] | Other, net [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1],[2]		$ 3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1],[2]		$ 2
Pepco Holdings LLC [Member] | Other, net [Member] | Predecessor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	$ (17)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	1
Pepco Holdings LLC [Member] | Operating and Maintenance [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				3
Potomac Electric Power Company [Member] | Other, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]			0	3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]			0	3
Potomac Electric Power Company [Member] | Operating and Maintenance [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				81	557
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				261	116
Fair Value, Inputs, Level 3 [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				84	560
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				258	114
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				(3)	(3)	[3]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				3	2	[3]
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(1)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		1
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Potomac Electric Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings				(3)	(3)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)				$ 3	$ 3
Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		18
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0
[1]	Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco.
[2]	Successor period represents activity from March 24, 2016 to December 31, 2016. See the subsequent table for PHI's predecessor periods, as well as activity for Pepco for the year ended December 31, 2017 and 2016.
[3]	Successor period represents activity from March 24, 2016 to December 31, 2016. See tables below for PHI's predecessor periods, as well as activity for Pepco for the years ended December 31, 2017 and 2016.

Fair Value of Financial Asse109

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted		$ 81,000,000		$ 61,000,000
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted		497,000,000		347,000,000
Derivative liabilities, fair value	[1]	349,000,000		333,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets, fair value		445,000,000	[2],[3]	435,000,000	[4],[5]
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		3		11
Forward gas price assets		1.27		1.72
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		124		130
Forward gas price assets		$ 12.8		$ 9.2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage		11.00%		8.00%
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage		139.00%		173.00%
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value		$ 26,000,000	[2],[3]	$ (3,000,000)	[4],[5]
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		14		19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		94		79
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities, fair value		$ (256,000,000)		$ (258,000,000)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward heat rate		900.00%	[6]	800.00%	[7]
Marketability Reserve		4.00%		3.00%
Renewable factor		88.00%		89.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward heat rate		1000.00%	[6]	900.00%	[7]
Marketability Reserve		8.00%		8.00%
Renewable factor		120.00%		121.00%
[1]	Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.
[2]	The fair values do not include cash collateral posted on level three positions of $81 million as of December 31, 2017.
[3]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[4]	The fair values do not include cash collateral posted on level three positions of $61 million as of December 31, 2016
[5]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[6]	Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.
[7]	Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.

Fair Value of Financial Asse110

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,147,000,000	$ 1,024,000,000
Forward Power Basis	2.99
Forward Gas Basis	0.42
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,147,000,000	$ 1,024,000,000
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	114,000,000
Exelon Generation Co L L C [Member] | Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	65,000,000
Exelon Generation Co L L C [Member] | Middle market lending [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	363,000,000
Exelon Generation Co L L C [Member] | Private Equity Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	220,000,000
Exelon Generation Co L L C [Member] | Real Estate Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 118,000,000

Derivative Financial Instrum111

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Ineffective portion recognized in income	$ 15,000	$ 14,000	$ 17,000
Cash collateral held	(8,000)
Letters of credit held	19,000
Interest Rate Fair Value Hedge Asset at Fair Value	5,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Credit exposure under off system sales	4,000
Incremental collateral for loss of investment grade credit rating	66,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Letters of credit posted	293,000	284,000
Cash collateral held	(35,000)	(24,000)
Letters of credit held	33,000	28,000
Cash collateral posted	497,000	347,000
Incremental collateral for loss of investment grade credit rating	1,800,000	1,900,000
Interest Rate Fair Value Hedge Asset at Fair Value	2,000
Derivative, Collateral, Obligation to Return Cash	$ 4,000	$ 8,000
Commonwealth Edison Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	10
Commonwealth Edison Company [Member] | Other Contract [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19
Commonwealth Edison Company [Member] | Renewable Energy Program [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	2
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Credit exposure under off system sales	$ 1,000
Incremental collateral for loss of investment grade credit rating	$ 14,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 34,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	11,000
Delmarva Power and Light Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue	$ 2,750
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	85.00%
Expected generation hedged in year two	55.00%
Expected generation hedged in year three	26.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	88.00%
Expected generation hedged in year two	58.00%
Expected generation hedged in year three	29.00%
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 6,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	22,000
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	24,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	36,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	12,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 28,000

Derivative Financial Instrum112

Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		$ 976	$ 917
Mark-to-market derivative assets (noncurrent assets)		337	492
Derivative Liability, Current		232	282
Derivative Liability, Noncurrent		409	392
Total mark-to-market derivative net assets (liabilities)		6	1
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		976	917
Mark-to-market derivative assets (noncurrent assets)		334	476
Derivative Liability, Current		211	263
Derivative Liability, Noncurrent		174	153
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	8
Mark-to-market derivative assets (noncurrent assets)		6	20
Total mark-to-market derivative assets		9	28
Derivative Liability, Current		2	8
Derivative Liability, Noncurrent		2	4
Total mark-to-market derivative liabilities		4	12
Total mark-to-market derivative net assets (liabilities)		5	16
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	8
Mark-to-market derivative assets (noncurrent assets)		3	4
Total mark-to-market derivative assets		6	12
Derivative Liability, Current		2	8
Derivative Liability, Noncurrent		2	4
Total mark-to-market derivative liabilities		4	12
Total mark-to-market derivative net assets (liabilities)		2	0
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	0
Mark-to-market derivative assets (noncurrent assets)		3	0
Total mark-to-market derivative assets		3	0
Derivative Liability, Current		2	7
Derivative Liability, Noncurrent		0	3
Total mark-to-market derivative liabilities		2	10
Total mark-to-market derivative net assets (liabilities)		1	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		10	17
Mark-to-market derivative assets (noncurrent assets)		0	11
Total mark-to-market derivative assets		10	28
Derivative Liability, Current		7	13
Derivative Liability, Noncurrent		2	8
Total mark-to-market derivative liabilities		9	21
Total mark-to-market derivative net assets (liabilities)		1	7
Not Designated as Hedging Instrument, Trading [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	4	[1]
Mark-to-market derivative assets (noncurrent assets)		0	1	[1]
Total mark-to-market derivative assets		0	5	[1]
Derivative Liability, Current		0	2	[1]
Derivative Liability, Noncurrent		0	2	[1]
Total mark-to-market derivative liabilities		0	4	[1]
Total mark-to-market derivative net assets (liabilities)		0	1	[1]
Collateral and Netting | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[2]	(7)	(13)
Mark-to-market derivative assets (noncurrent assets)	[2]	0	(8)
Total mark-to-market derivative assets	[2]	(7)	(21)
Derivative Liability, Current	[2]	(7)	(14)
Derivative Liability, Noncurrent	[2]	0	(9)
Total mark-to-market derivative liabilities	[2]	(7)	(23)
Total mark-to-market derivative net assets (liabilities)	[2]	0	2
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0	0
Mark-to-market derivative assets (noncurrent assets)		3	16
Total mark-to-market derivative assets		3	16
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		0	0
Total mark-to-market derivative liabilities		0	0
Total mark-to-market derivative net assets (liabilities)		$ 3	$ 16
[1]	Generation enters into interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The characterization of the interest rate derivative contracts between the proprietary trading activity in the above table is driven by the corresponding characterization of the underlying commodity position that gives rise to the interest rate exposure. Generation does not utilize proprietary trading interest rate derivatives with the objective of benefiting from shifts or changes in market interest rates.
[2]	Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above.

Derivative Financial Instrum113

Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ (13)	$ (9)	$ 3
Price Risk Derivative [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge	28	23	14
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0	(1)	[1]
Exelon Generation Co L L C [Member] | Price Risk Derivative [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge	$ 0	$ 0	$ 0	[1]
[1]	For the year ended December 31, 2015, the loss on Generation swaps included $(1) million realized in earnings with an immaterial amount excluded from hedge effectiveness testing.

Derivative Financial Instrum114

Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		$ 77		$ 29
Mark-to-market derivative assets (current assets)		976		917
Mark-to-market derivative assets (noncurrent assets)		337		492
Derivative Liability, Current		(232)		(282)
Derivative Liability, Noncurrent		409		392
Total mark-to-market derivative net assets (liabilities)		6		1
Margin Deposit Assets		(117)		(158)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		976		917
Mark-to-market derivative assets (noncurrent assets)		334		476
Derivative Liability, Current		(211)		(263)
Derivative Liability, Noncurrent		174		153
Derivative, Collateral, Obligation to Return Cash		4		8
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current		(21)		(19)
Derivative Liability, Noncurrent		235		239
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		973		909
Mark-to-market derivative assets (noncurrent assets)		331		472
Total mark-to-market derivative assets		1,304		1,381
Derivative Liability, Current		(230)		(274)
Derivative Liability, Noncurrent		(407)		(388)
Total mark-to-market derivative liabilities		637		662
Total mark-to-market derivative net assets (liabilities)		667		719
Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		973	[1]	909	[2]
Mark-to-market derivative assets (noncurrent assets)		331	[1]	472	[2]
Total mark-to-market derivative assets		1,304	[1]	1,381	[2]
Derivative Liability, Current		209	[1]	255	[2]
Derivative Liability, Noncurrent		(172)	[1]	(149)	[2]
Total mark-to-market derivative liabilities		(381)	[1]	(404)	[2]
Total mark-to-market derivative net assets (liabilities)		923	[1]	977	[2]
Commodity Contract [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		0
Mark-to-market derivative assets (noncurrent assets)		0		0
Total mark-to-market derivative assets		0		0
Derivative Liability, Current		0		0
Derivative Liability, Noncurrent		0		0
Total mark-to-market derivative liabilities		0		0
Total mark-to-market derivative net assets (liabilities)		0		0
Commodity Contract [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0		0
Mark-to-market derivative assets (noncurrent assets)		0		0
Total mark-to-market derivative assets		0		0
Derivative Liability, Current		0		0
Derivative Liability, Noncurrent		0		0
Total mark-to-market derivative liabilities		0		0
Total mark-to-market derivative net assets (liabilities)		0		0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3,061		3,623
Mark-to-market derivative assets (noncurrent assets)		1,164		1,467
Total mark-to-market derivative assets		4,225		5,090
Derivative Liability, Current		2,646		3,165
Derivative Liability, Noncurrent		(1,137)		(1,274)
Total mark-to-market derivative liabilities		3,783		4,439
Total mark-to-market derivative net assets (liabilities)		442		651
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Commonwealth Edison Co [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[3]	0		0
Mark-to-market derivative assets (noncurrent assets)	[3]	0		0
Total mark-to-market derivative assets	[3]	0		0
Derivative Liability, Current	[3]	21		19
Derivative Liability, Noncurrent	[3]	(235)		(239)
Total mark-to-market derivative liabilities	[3]	(256)		(258)
Total mark-to-market derivative net assets (liabilities)	[3]	(256)		(258)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[4]	0		2
Mark-to-market derivative assets (noncurrent assets)	[4]	0		0
Total mark-to-market derivative assets	[4]	0		2
Derivative Liability, Current	[4]	1		0
Derivative Liability, Noncurrent	[4]	0		0
Total mark-to-market derivative liabilities	[4]	(1)		0
Total mark-to-market derivative net assets (liabilities)	[4]	(1)		2
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(466)		(329)
Not Designated as Hedging Instrument, Trading [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		56		55
Mark-to-market derivative assets (noncurrent assets)		12		21
Total mark-to-market derivative assets		68		76
Derivative Liability, Current		43		54
Derivative Liability, Noncurrent		10		25
Total mark-to-market derivative liabilities		(53)		(79)
Total mark-to-market derivative net assets (liabilities)		15		(3)
Collateral and Netting | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[5]	(2,144)	[6]	(2,769)	[7]
Mark-to-market derivative assets (noncurrent assets)	[5]	(845)	[6]	(1,016)	[7]
Total mark-to-market derivative assets	[5]	(2,989)	[6]	(3,785)	[7]
Derivative Liability, Current	[5]	(2,480)	[6]	(2,964)	[7]
Derivative Liability, Noncurrent	[5]	975	[6]	1,150	[7]
Total mark-to-market derivative liabilities	[5]	3,455	[6]	4,114	[7]
Total mark-to-market derivative net assets (liabilities)	[5]	466	[6]	329	[7]
Collateral and Netting | Commodity Contract [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[5]	0		(2)
Mark-to-market derivative assets (noncurrent assets)	[5]	0		0
Total mark-to-market derivative assets	[5]	0		(2)
Derivative Liability, Current	[5]	1		0
Derivative Liability, Noncurrent	[5]	0		0
Total mark-to-market derivative liabilities	[5]	1		0
Total mark-to-market derivative net assets (liabilities)	[5]	1		(2)
Other Current Assets [Member] | Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		169		100
Margin Deposit Assets		(117)		(158)
Other Noncurrent Assets [Member] | Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		53		72
Other Current Liabilities [Member] | Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		167		95
Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		$ 77		$ 62
[1]	Current and noncurrent assets are shown net of collateral of $169 million and $53 million, respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017.
[2]	Current and noncurrent assets are shown net of collateral of $100 million and $72 million, respectively, and current and noncurrent liabilities are shown net of collateral of $95 million and $62 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $329 million at December 31, 2016.
[3]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[4]	Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.
[5]	Exelon, Generation, PHI and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.
[6]	Of the collateral posted/(received), $(117) million represents variation margin on the exchanges.
[7]	Of the collateral posted/(received), $(158) million represents variation margin on the exchanges

Derivative Financial Instrum115

Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Derivative [Line Items]
Beginning Balance		$ (2,660)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(144)		$ (150)
Ending Balance		(2,487)		(2,660)
Income Tax Expense (Benefit)		125		(761)		$ (1,073)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance		(54)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(4)		(13)
Ending Balance		(37)		(54)
Income Tax Expense (Benefit)		1,375		(290)		(502)
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(17)		(19)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(1)		(6)
Ending Balance		(14)		(17)		(19)
Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		4	[2]	8	[3]
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance		(19)		(21)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(1)		(6)
Ending Balance		(16)		(19)		$ (21)
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		4	[2]	8	[3]
Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income Tax Expense (Benefit)	[1]			0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income Tax Expense (Benefit)	[1]			0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income Tax Expense (Benefit)		$ 1		$ 5
[1]	Amounts in parenthesis represent a decrease in net income.
[2]	Amount is net of related income tax expense of $1 million for the year ended December 31, 2017.
[3]	Amount is net of related income tax expense of $5 million for the year ended December 31, 2016.

Derivative Financial Instrum116

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (151)	$ (24)	$ 367
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(167)	(40)	249
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	(10)	107
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(3)	0	100
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(169)	(31)	250
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(126)	(490)	196
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(43)	459	54
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	(10)	7
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(6)	(10)	7
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (3)	$ 0	$ 0

Derivative Financial Instrum117

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (151)	$ (24)	$ 367
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(167)	(40)	249
Not Designated as Hedging Instrument, Trading [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	6	2	(6)
Not Designated as Hedging Instrument, Trading [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (1)	$ (1)	$ (2)

Derivative Financial Instrum118

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Cash collateral held		$ 8
Letters of credit held		19
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral held		35	$ 24
Letters of credit held		33	$ 28
Total Exposure Before Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		738
Non-investment grade		90
Internally rated — investment grade		253
Internally rated — non-investment grade		83
Total		1,164
Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		4
Non-investment grade		12
Internally rated — investment grade		0
Internally rated — non-investment grade		11
Total	[1]	27
Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		734
Non-investment grade		78
Internally rated — investment grade		253
Internally rated — non-investment grade		72
Total		1,137
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		1
Non-investment grade		0
Internally rated — investment grade		0
Internally rated — non-investment grade		0
Total		1
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		244
Non-investment grade		0
Internally rated — investment grade		0
Internally rated — non-investment grade		0
Total		$ 244
[1]	As of December 31, 2017, credit collateral held from counterparties where Generation had credit exposure included $8 million of cash and $19 million of letters of credit. The credit collateral does not include non-liquid collateral.

Derivative Financial Instrum119

Derivative Financial Instruments - Net Credit Exposure by Type of Counterparty (Details) - Exelon Generation Co L L C [Member] - Net Exposure [Member] $ in Millions	Dec. 31, 2017USD ($)
Derivative [Line Items]
Financial institutions	$ 41
Investor-owned utilities, marketers, power producers	558
Energy cooperatives and municipalities	452
Other	86
Total	$ 1,137

Derivative Financial Instrum120

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	[1]	$ (926)	$ (960)
Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements	[2]	577	627
Derivative liabilities, fair value	[3]	$ (349)	$ (333)
[1]	Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk-related contingent features ignoring the effects of master netting agreements.
[2]	Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral.
[3]	Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.

Derivative Financial Instrum121

Derivative Financial Instruments - Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative, Notional Amount	$ 3,606	$ 2,918
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	636	659
Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800	800
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 94	$ 85

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Letters of Credit Outstanding, Amount	[1]	$ 1,147,000,000
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	9,450,000,000	$ 9,450,000,000
Outstanding commercial paper		$ 427,000,000	$ 688,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.24%	1.12%		0.88%
Letters of Credit Outstanding, Amount	[1]	$ 45,000,000
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 0	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.16%	0.70%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200,000,000
Average Interest Rate on Commercial Paper Borrowings		1.23%	1.14%
Line of Credit Facility, Current Borrowing Capacity		$ 49,000,000
Exelon Generation Co L L C [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	5,300,000,000	$ 5,300,000,000
Outstanding commercial paper		$ 0	$ 620,000,000
Average Interest Rate on Commercial Paper Borrowings		1.23%	0.94%
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 5,000,000
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.24%			0.89%
Letters of Credit Outstanding, Amount	[1]	$ 2,000,000
Line of Credit Facility, Current Borrowing Capacity		34,000,000
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	1,000,000,000	$ 1,000,000,000
Outstanding commercial paper		$ 0	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.24%	0.77%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.13%
Letters of Credit Outstanding, Amount	[1]	$ 1,000,000
Line of Credit Facility, Current Borrowing Capacity		34,000,000
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 0	$ 0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.28%	0.95%		0.87%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		5,000,000
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600,000,000	$ 600,000,000
Outstanding commercial paper		$ 77,000,000	$ 45,000,000
Average Interest Rate on Commercial Paper Borrowings		1.28%	0.77%
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 2,000,000
Pepco Energy Services [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 2,000,000
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings					1.22%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.06%	0.90%		0.68%
Letters of Credit Outstanding, Amount	[1]	$ 0
Potomac Electric Power Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	500,000,000	$ 500,000,000
Outstanding commercial paper		$ 26,000,000	$ 23,000,000
Average Interest Rate on Commercial Paper Borrowings		1.06%	0.71%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.48%			0.79%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		2,000,000
Delmarva Power and Light Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	500,000,000	$ 500,000,000
Outstanding commercial paper		$ 216,000,000	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.48%	0.68%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		1.43%			0.65%
Letters of Credit Outstanding, Amount	[1]	$ 0
Line of Credit Facility, Current Borrowing Capacity		2,000,000
Atlantic City Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	350,000,000	$ 350,000,000
Outstanding commercial paper		$ 108,000,000	$ 0
Average Interest Rate on Commercial Paper Borrowings		1.43%	0.65%
[1]	Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Win
[2]	Excludes $480 million and $500 million in bilateral credit facilities that do not back Generation's commercial paper program at December 31, 2017 and 2016, respectively
[3]	Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $34 million, $34 million, $5 million, $2 million, $2 million and $2 million, respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Debt and Credit Agreements - Su

Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016	May 26, 2016	Apr. 01, 2016	Jan. 05, 2016	Oct. 23, 2015	Aug. 10, 2013	Aug. 01, 2011
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Facility draws		$ 0
Outstanding letters of credit	[1]	1,147,000,000
Actual available capacity		8,333,000,000
To Support Additional Commercial Paper	[2]	7,657,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity									$ 500,000,000
Exelon Corporate [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	45,000,000
Actual available capacity		555,000,000
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000
To Support Additional Commercial Paper		4,432,000,000
Credit facility agreements with minority and community banks		49,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		480,000,000	$ 500,000,000
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		5,000,000
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity						$ 200,000,000	$ 150,000,000	$ 100,000,000
Actual available capacity		249,000,000
To Support Additional Commercial Paper	[2]	0
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	2,000,000
Actual available capacity		998,000,000
To Support Additional Commercial Paper	[2]	998,000,000
Credit facility agreements with minority and community banks		34,000,000
PECO Energy Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	1,000,000
Actual available capacity		599,000,000
To Support Additional Commercial Paper	[2]	599,000,000
Credit facility agreements with minority and community banks		34,000,000
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		600,000,000
To Support Additional Commercial Paper	[2]	523,000,000
Credit facility agreements with minority and community banks		5,000,000
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		2,000,000
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity					$ 900,000,000					$ 1,500,000,000
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	274,000,000
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	84,000,000
Credit facility agreements with minority and community banks		2,000,000
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit	[1]	0
Actual available capacity		300,000,000
To Support Additional Commercial Paper	[2]	192,000,000
Credit facility agreements with minority and community banks		2,000,000
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	9,480,000,000
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
To Support Additional Commercial Paper	[2]	555,000,000
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		5,300,000,000
Facility draws		0
Outstanding letters of credit		868,000,000
Actual available capacity		4,432,000,000
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	1,000,000,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	600,000,000
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	300,000,000
Revolving Credit Facility [Member] | Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	300,000,000
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[3]	$ 300,000,000
[1]	Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Win
[2]	Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility.
[3]	Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $34 million, $34 million, $5 million, $2 million, $2 million and $2 million, respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Debt and Credit Agreements -124

Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 23, 2017	Jan. 13, 2016	Jun. 30, 2015
Exelon Corporate [Member]
Short-term Debt [Line Items]
Short-term Bank Loans and Notes Payable				$ 500
Average borrowings	$ 823	$ 1,125	$ 499
Maximum borrowings outstanding	$ 2,147	$ 3,076	$ 739
Short-term Debt, Weighted Average Interest Rate, over Time	1.32%	0.88%	0.53%
Average interest rates at year end	1.24%	1.12%	0.88%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 405	$ 536	$ 1
Maximum borrowings outstanding	$ 1,455	$ 1,735	$ 50
Short-term Debt, Weighted Average Interest Rate, over Time	1.23%	0.94%	0.49%
Average interest rates at year end	1.23%	1.14%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 200	$ 256	$ 461
Maximum borrowings outstanding	$ 470	$ 755	$ 684
Short-term Debt, Weighted Average Interest Rate, over Time	1.24%	0.77%	0.53%
Average interest rates at year end	1.24%		0.89%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 2	$ 0	$ 0
Maximum borrowings outstanding	$ 60	0	0
Short-term Debt, Weighted Average Interest Rate, over Time	1.13%
Average interest rates at year end	1.13%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 54	143	37
Maximum borrowings outstanding	$ 165	$ 369	$ 210
Short-term Debt, Weighted Average Interest Rate, over Time	1.28%	0.77%	0.48%
Average interest rates at year end	1.28%	0.95%	0.87%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Short-term Bank Loans and Notes Payable					$ 500	$ 300
Average borrowings		$ 153	$ 444
Maximum borrowings outstanding		$ 559	$ 784
Short-term Debt, Weighted Average Interest Rate, over Time		1.03%	0.90%
Average interest rates at year end			1.22%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 51	$ 4	$ 34
Maximum borrowings outstanding	$ 197	$ 73	$ 190
Short-term Debt, Weighted Average Interest Rate, over Time	1.06%	0.71%	0.44%
Average interest rates at year end	1.06%	0.90%	0.68%
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 40	$ 33	$ 81
Maximum borrowings outstanding	$ 216	$ 116	$ 179
Short-term Debt, Weighted Average Interest Rate, over Time	1.48%	0.68%	0.47%
Average interest rates at year end	1.48%		0.79%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 30	$ 0	$ 175
Maximum borrowings outstanding	$ 133	$ 5	$ 253
Short-term Debt, Weighted Average Interest Rate, over Time	1.43%	0.65%	0.46%
Average interest rates at year end	1.43%		0.65%

Debt and Credit Agreements -125

Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details)	12 Months Ended
	Dec. 31, 2017
Line of Credit Facility [Line Items]
Credit agreement threshold	2.50
Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	27.50%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	12750.00%
Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	3
Exelon Generation Co L L C [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	27.50%
Exelon Generation Co L L C [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	12750.00%
Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Commonwealth Edison Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Commonwealth Edison Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
PECO Energy Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
PECO Energy Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	9000.00%
Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Baltimore Gas and Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
Baltimore Gas and Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10000.00%
Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Potomac Electric Power Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Potomac Electric Power Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
Delmarva Power and Light Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Delmarva Power and Light Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Delmarva Power and Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Atlantic City Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Atlantic City Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%

Debt and Credit Agreements -126

Debt and Credit Agreements - Summary of Interest Coverage Ratios (Details)	12 Months Ended
	Dec. 31, 2017
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	6.34
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	9.02
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	11.68
PECO Energy Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	7.99
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	10.50
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	6.35
Delmarva Power and Light Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	8.69
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	5.57

Debt and Credit Agreements -127

Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2014
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 33,657	$ 33,311
Unamortized debt discount and premium, net			(57)	(68)
Long-term debt (including amounts due within one year)(a)			865	962
Long-term debt due within one year			(2,088)	(2,430)
Long-term debt			32,176	31,575
Long-term debt to financing trusts			389	641
Total long-term debt to financing trusts			390	648
Unamortized Debt Issuance Expense	[1]		(201)	(200)
Repayments of Long-term Debt			2,490	1,936	$ 2,687
2,017			2,075
2,018			959
2,019			3,564
2,020			1,513
2,021			3,084
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			206	206
Long-term debt to financing trusts			$ 205	205
ComEd Financing Three Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.35%
Interest rate on long-term debt			6.35%
PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 81	81
Long-term debt to financing trusts			$ 81	81
PECO Trust Three Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.38%
Interest rate on long-term debt			7.38%
PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 103	103
Long-term debt to financing trusts			$ 103	103
PECO Trust Four Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.75%
Interest rate on long-term debt			5.75%
BGE Trust Member [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 0	258
BGE Trust Member [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.20%
Interest rate on long-term debt			6.20%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,600	2,300
Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.40%
Interest rate on long-term debt			2.40%
Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.35%
Interest rate on long-term debt			6.35%
Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 0	41
Rate Stabilization Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage
Interest rate on long-term debt
Rate Stabilization Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.82%
Interest rate on long-term debt			5.82%
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[2]		$ 15,197	14,123
Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]		1.70%
Interest rate on long-term debt	[2]		1.70%
Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]		7.90%
Interest rate on long-term debt	[2]		7.90%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 11,285	11,868
Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.45%
Interest rate on long-term debt			2.45%
Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.60%
Interest rate on long-term debt			7.60%
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 435	435
Pollution Control Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.70%
Interest rate on long-term debt			2.70%
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 82	105
Notes Payable to Banks [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.15%
Interest rate on long-term debt			3.15%
Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.35%
Interest rate on long-term debt			3.35%
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[3],[4]		$ 405	576
Unamortized Debt Issuance Expense	[1]		$ (1)	(7)
Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		2.61%
Interest rate on long-term debt	[3]		2.61%
Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3]		8.88%
Interest rate on long-term debt	[3]		8.88%
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.497%			2.50%
Long-term Debt, Gross			$ 1,150	1,150
Interest rate on long-term debt			3.497%			2.50%
Junior Subordinated Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.50%
Interest rate on long-term debt			3.50%
contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 0	19
contract Payments Junior Subordinate Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.50%
Interest rate on long-term debt			2.50%
Software License Arrangement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 79	103
Software License Arrangement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.95%
Interest rate on long-term debt			3.95%
Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 112	112
Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.40%
Interest rate on long-term debt			5.40%
Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 26	40
Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.81%
Interest rate on long-term debt			6.81%
Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.72%
Interest rate on long-term debt			7.72%
Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 90	124
Transition Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.05%
Interest rate on long-term debt			5.05%
Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.55%
Interest rate on long-term debt			5.55%
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,331	1,400
Non Recourse Fixed Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.29%
Interest rate on long-term debt			2.29%
Non Recourse Fixed Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.00%
Interest rate on long-term debt			6.00%
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 865	915
Non Recourse Variable Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.18%
Interest rate on long-term debt			3.18%
Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.00%
Interest rate on long-term debt			4.00%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent			$ 53	69
Due in 2015			18
Due in 2016			20
Due in 2017			5
Due in 2018			1
Due in 2019			1
Due in 2020			8
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			8,955	9,208
Unamortized debt discount and premium, net			(8)	(17)
Long-term debt due within one year			(346)	(1,117)
Long-term debt			7,734	7,202
Long-term debt to financing trusts			910	922
Debt and Capital Lease Obligations			8,644	8,124
Unamortized Debt Issuance Expense			(60)	(65)
Capital lease obligations, noncurrent			18	22
Due in 2015			5
Due in 2016			6
Due in 2017			5
Due in 2018			1
Repayments of Long-term Debt			1,261	202	89
2,017			346
2,018			615
2,019			2,144
2,020			1
2,021			1,024
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 6,019	5,971
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.95%
Interest rate on long-term debt			2.95%
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.60%
Interest rate on long-term debt			7.60%
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 435	435
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.50%
Interest rate on long-term debt			2.50%
Exelon Generation Co L L C [Member] | Pollution Control Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.70%
Interest rate on long-term debt			2.70%
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 82	105
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.15%
Interest rate on long-term debt			3.15%
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.35%
Interest rate on long-term debt			3.35%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[5],[6]		$ 223	382
Long-term debt			$ 198
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.61%
Interest rate on long-term debt			2.61%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			8.88%
Interest rate on long-term debt			8.88%
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,331	1,400
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.29%
Interest rate on long-term debt			2.29%
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.00%
Interest rate on long-term debt			6.00%
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 865	915
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.18%
Interest rate on long-term debt			3.18%
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.00%
Interest rate on long-term debt			4.00%
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,570	2,381
Unamortized debt discount and premium, net			2	(2)
Long-term debt			2,521	2,333
Long-term debt due within one year			(19)	(16)
Long-term debt			2,521	2,333
Unamortized Debt Issuance Expense	[7]		(32)	(30)
Due in 2015			13
Due in 2016			14
Repayments of Long-term Debt			13	11	22
2,017			19
2,018			14
2,019			0
2,020			2
2,021			310
Potomac Electric Power Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,535	2,335
Potomac Electric Power Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.05%
Interest rate on long-term debt			3.05%
Potomac Electric Power Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.90%
Interest rate on long-term debt			7.90%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 35	46
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.20%
Interest rate on long-term debt			6.20%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			8.88%
Interest rate on long-term debt			8.88%
Potomac Electric Power Company [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent			$ 27	39
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			7,676	7,101
Unamortized debt discount and premium, net			(23)	(22)
Long-term debt due within one year			(840)	(425)
Long-term debt			6,761	6,608
Long-term debt to financing trusts			205	205
Total long-term debt to financing trusts			206	206
Debt and Capital Lease Obligations			6,761	6,608
Unamortized Debt Issuance Expense	[8]		(52)	(46)
Repayments of Long-term Debt			425	665	260
2,017			840
2,018			300
2,019			500
2,020			350
2,021			0
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			206	206
Long-term debt to financing trusts			205	205
Unamortized Debt Issuance Expense	[8]		$ (1)	(1)
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.35%
Interest rate on long-term debt			6.35%
Commonwealth Edison Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[9]		$ 7,529	6,954
Commonwealth Edison Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[9]		2.15%
Interest rate on long-term debt	[9]		2.15%
Commonwealth Edison Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[9]		6.45%
Interest rate on long-term debt	[9]		6.45%
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[10]		$ 147	147
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[10]		6.95%
Interest rate on long-term debt	[10]		6.95%
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[10]		7.49%
Interest rate on long-term debt	[10]		7.49%
Commonwealth Edison Co [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent			$ 8
Due in 2020			1
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			2,925	2,600
Unamortized debt discount and premium, net			(5)	(5)
Long-term debt			2,403	2,580
Long-term debt to financing trusts			184	184
Long-term debt due within one year			(500)	0
Debt and Capital Lease Obligations			2,403	2,580
Unamortized Debt Issuance Expense	[7]		(17)	(15)
Repayments of Long-term Debt			0	300	0
2,017			500
2,018			0
2,019			0
2,020			300
2,021			350
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts			$ 81	81
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.38%
Interest rate on long-term debt			7.38%
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts			$ 103	103
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.75%
Interest rate on long-term debt			5.75%
PECO Energy Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[11]		$ 2,925	2,600
PECO Energy Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[11]		1.70%
Interest rate on long-term debt	[11]		1.70%
PECO Energy Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[11]		5.95%
Interest rate on long-term debt	[11]		5.95%
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,600	2,341
Unamortized debt discount and premium, net			(6)	(4)
Long-term debt			2,577	2,281
Long-term debt to financing trusts			0	252
Total long-term debt to financing trusts			0	258
Long-term debt due within one year			0	(41)
Long-term debt			2,577	2,281
Unamortized Debt Issuance Expense			(17)	(15)
Repayments of Long-term Debt			41	379	75
2,017			0
2,018			0
2,019			0
2,020			300
2,021			250
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts			0	252
Total long-term debt to financing trusts			0	258
Unamortized Debt Issuance Expense			$ 0	(6)
Baltimore Gas and Electric Company [Member] | BGE Trust Member [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.20%
Interest rate on long-term debt			6.20%
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 0	41
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage
Interest rate on long-term debt
Baltimore Gas and Electric Company [Member] | Rate Stabilization Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.82%
Interest rate on long-term debt			5.82%
Baltimore Gas and Electric Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 2,600	2,300
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			2.40%
Interest rate on long-term debt			2.40%
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.35%
Interest rate on long-term debt			6.35%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 5,189	5,157
Unamortized debt discount and premium, net			5	1
Long-term debt (including amounts due within one year)(a)			686
Long-term debt due within one year			(396)	(253)
Long-term debt			5,478	5,645
Unamortized Debt Issuance Expense	[7]		(6)	(2)
2,017			383
2,018			44
2,019			20
2,020			262
2,021			310
Pepco Holdings LLC [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 185	266
Pepco Holdings LLC [Member] | Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage
Interest rate on long-term debt
Pepco Holdings LLC [Member] | Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.45%
Interest rate on long-term debt			7.45%
Pepco Holdings LLC [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[12]		$ 4,743	4,569
Pepco Holdings LLC [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.05%
Interest rate on long-term debt			3.05%
Pepco Holdings LLC [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.90%
Interest rate on long-term debt			7.90%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[13]		$ 33	46
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.20%
Interest rate on long-term debt			6.20%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			8.88%
Interest rate on long-term debt			8.88%
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 112	112
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.40%
Interest rate on long-term debt			5.40%
Pepco Holdings LLC [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 26	40
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.81%
Interest rate on long-term debt			6.81%
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.72%
Interest rate on long-term debt			7.72%
Pepco Holdings LLC [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[14]		$ 90	124
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.05%
Interest rate on long-term debt			5.05%
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.55%
Interest rate on long-term debt			5.55%
Delmarva Power and Light Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,309	1,348
Unamortized debt discount and premium, net			2	2
Long-term debt due within one year			(79)	(105)
Long-term debt			1,217	1,221
Long-term debt due within one year			(83)	(119)
Long-term debt			1,217	1,221
Unamortized Debt Issuance Expense	[7]		(11)	(10)
Repayments of Long-term Debt			40	100	100
2,017			83
2,018			12
2,019			0
2,020			0
2,021			0
Delmarva Power and Light Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,171	1,196
Delmarva Power and Light Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.50%
Interest rate on long-term debt			3.50%
Delmarva Power and Light Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.15%
Interest rate on long-term debt			4.15%
Delmarva Power and Light Company [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 112	112
Delmarva Power and Light Company [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.40%
Interest rate on long-term debt			5.40%
Delmarva Power and Light Company [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 26	40
Delmarva Power and Light Company [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			6.81%
Interest rate on long-term debt			6.81%
Delmarva Power and Light Company [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.72%
Interest rate on long-term debt			7.72%
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,127	1,162
Unamortized debt discount and premium, net			(1)	(1)
Long-term debt			840	1,120
Long-term debt due within one year			(281)	(35)
Long-term debt			840	1,120
Unamortized Debt Issuance Expense	[7]		(5)	(6)
Repayments of Long-term Debt			35	48	$ 58
2,017			281
2,018			18
2,019			20
2,020			260
2,021			0
Atlantic City Electric Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 1,037	1,038
Atlantic City Electric Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.38%
Interest rate on long-term debt			3.38%
Atlantic City Electric Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.75%
Interest rate on long-term debt			7.75%
Atlantic City Electric Company [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[15]		$ 90	$ 124
2,017			31
2,018			18
2,019			20
2,020			$ 21
Atlantic City Electric Company [Member] | Transition Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.05%
Interest rate on long-term debt			5.05%
Atlantic City Electric Company [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			5.55%
Interest rate on long-term debt			5.55%
AGEPFNotesNov2017 [Member] | AGE Biomass project [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt		$ 228
[1]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[2]	Substantially all of ComEd’s assets other than expressly excepted property and substantially all of PECO’s, Pepco's, DPL's and ACE's assets are subject to the liens of their respective mortgage indentures.
[3]	Includes capital lease obligations of $53 million and $69 million at December 31, 2017 and 2016, respectively. Lease payments of $18 million, $20 million, $5 million, $1 million, $1 million and $8 million will be made in 2018, 2019, 2020, 2021, 2022 and thereafter, respectively.
[4]	Includes financing related to Albany Green Energy, LLC (AGE). During the third quarter of 2017, Generation retired $228 million of its outstanding debt balance. As of December 31, 2016, $198 million was outstanding.
[5]	Includes Generation’s capital lease obligations of $18 million and $22 million at December 31, 2017 and 2016, respectively. Generation will make lease payments of $5 million, $6 million, $5 million, $1 million and $1 million in 2018, 2019, 2020, 2021 and 2022 respectively. The capital lease matures in 2022.
[6]	Includes financing related to Albany Green Energy, LLC (AGE).
[7]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[8]	Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets.
[9]	Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture.
[10]	Includes ComEd’s capital lease obligations of $8 million at both December 31, 2017 and 2016, respectively. Lease payments of less than $1 million annually will be made from 2018 through expiration at 2053.
[11]	Substantially all of PECO’s assets are subject to the lien of its mortgage indenture
[12]	Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture.
[13]	Includes Pepco's capital lease obligations of $27 million and $39 million at December 31, 2017 and 2016, respectively.
[14]	Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets.
[15]	Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture.

Debt and Credit Agreements - Sc

Debt and Credit Agreements - Schedule of Long-term Debt Maturities (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
2,017		$ 2,075
2,018		959
2,019		3,564
2,020		1,513
2,021		3,084
Thereafter	[1]	22,852
Total		34,047
Total long-term debt to financing trusts		390	$ 648
Long-term Debt, Gross		33,657	33,311
ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		206	206
PECO Financing Trusts [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		184
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2,017		346
2,018		615
2,019		2,144
2,020		1
2,021		1,024
Thereafter		4,825
Total		8,955
Long-term Debt, Gross		8,955	9,208
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2,017		840
2,018		300
2,019		500
2,020		350
2,021		0
Thereafter	[2]	5,892
Total		7,882
Total long-term debt to financing trusts		206	206
Long-term Debt, Gross		7,676	7,101
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		206	206
PECO Energy Co [Member]
Debt Instrument [Line Items]
2,017		500
2,018		0
2,019		0
2,020		300
2,021		350
Thereafter	[3]	1,959
Total		3,109
Long-term Debt, Gross		2,925	2,600
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2,017		0
2,018		0
2,019		0
2,020		300
2,021		250
Thereafter		2,050
Total		2,600
Total long-term debt to financing trusts		0	258
Long-term Debt, Gross		2,600	2,341
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
2,017		383
2,018		44
2,019		20
2,020		262
2,021		310
Thereafter		4,170
Total		5,189
Long-term Debt, Gross		5,189	5,157
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2,017		19
2,018		14
2,019		0
2,020		2
2,021		310
Thereafter		2,225
Total		2,570
Long-term Debt, Gross		2,570	2,381
Delmarva Power and Light Company [Member]
Debt Instrument [Line Items]
2,017		83
2,018		12
2,019		0
2,020		0
2,021		0
Thereafter		1,214
Total		1,309
Long-term Debt, Gross		1,309	1,348
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2,017		281
2,018		18
2,019		20
2,020		260
2,021		0
Thereafter		548
Total		1,127
Long-term Debt, Gross		$ 1,127	$ 1,162
[1]	Includes $390 million due to ComEd and PECO financing trusts.
[2]	Includes $206 million due to ComEd financing trust.
[3]	Includes $184 million due to PECO financing trusts.

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions

Sep. 30, 2013MW

Sep. 30, 2014USD ($)

Dec. 31, 2017USD ($)shares

Dec. 31, 2016USD ($)

Dec. 31, 2015USD ($)$ / shares

Nov. 27, 2017USD ($)

Mar. 31, 2017USD ($)

Mar. 23, 2017USD ($)

Nov. 30, 2016USD ($)

Sep. 30, 2016USD ($)

May 26, 2016USD ($)

Apr. 01, 2016USD ($)

Feb. 22, 2016

Jan. 13, 2016USD ($)

Jan. 05, 2016USD ($)

Oct. 23, 2015USD ($)

Sep. 30, 2015USD ($)

Jul. 30, 2015

Jun. 30, 2015USD ($)

Sep. 18, 2014USD ($)

Jun. 30, 2014USD ($)$ / sharesshares

Dec. 31, 2013USD ($)

Aug. 10, 2013USD ($)

Jun. 30, 2013USD ($)

Oct. 31, 2011USD ($)

Aug. 01, 2011USD ($)

Debt Instrument [Line Items]

Long-term Debt, Current Maturities

$ 2,088,000,000

$ 2,430,000,000

Repayments of Long-term Debt

2,490,000,000

1,936,000,000

$ 2,687,000,000

Line of credit facility, maximum borrowing capacity

$ 98

Outstanding letters of credit

[1]

1,147,000,000

Long-term debt, gross

33,657,000,000

33,311,000,000

Long-term debt

34,047,000,000

Collateral amount of debt

3,000,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2.50

Senior Notes [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 11,285,000,000

11,868,000,000

Junior Subordinated Debt [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 1,150,000,000

1,150,000,000

Equity units issued | shares

23

Conversion price | $ / shares

$ 50

Interest rate on long-term debt

3.497%

2.50%

Stock Issued During Period, Shares, Treasury Stock Reissued | shares

33

Junior Subordinated Notes

$ 1,150,000,000

Loss on Reissuance, Treasury Stock

$ 1,050,000,000

Maximum [Member]

Debt Instrument [Line Items]

Basis points adders for prime-based borrowings

9000.00%

Basis points adders for LIBOR-based borrowings

165

Maximum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

7.60%

Maximum [Member] | Junior Subordinated Debt [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

3.50%

Minimum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.45%

Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 9,480,000,000

Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 500,000,000

Exelon Corporate [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

569,000,000

46,000,000

2,263,000,000

Outstanding letters of credit

[1]

45,000,000

Long-term debt, gross

7,039,000,000

7,608,000,000

Long-term debt

7,039,000,000

Outstanding borrowings/facility draws

0

Short-term Bank Loans and Notes Payable

$ 500,000,000

Exelon Corporate [Member] | Junior Subordinated Debt [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 1,150,000,000

1,150,000,000

Interest rate on long-term debt

3.50%

Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

[3]

7.60%

Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

[3]

2.45%

Exelon Corporate [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 600,000,000

Exelon Generation Co L L C [Member]

Debt Instrument [Line Items]

Long-term Debt, Current Maturities

346,000,000

1,117,000,000

Repayments of Long-term Debt

1,261,000,000

202,000,000

89,000,000

Line of credit facility, maximum borrowing capacity

200,000,000

Long-term debt, gross

8,955,000,000

9,208,000,000

Long-term debt

$ 8,955,000,000

Short-term Debt, Percentage Bearing Variable Interest Rate

1.75%

Line of Credit Facility, Description

100

Credit agreement threshold

3

Proceeds from (Repayments of) Restricted Cash, Financing Activities

$ (50,000,000)

Exelon Generation Co L L C [Member] | ExGen Texas Power [Member] | Interest Rate Swap [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.34%

Non-recourse debt, interest rate swap

$ 505,000,000

Exelon Generation Co L L C [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Long-term debt, gross

6,019,000,000

5,971,000,000

Debt Instrument, Face Amount

750,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member]

Debt Instrument [Line Items]

Debt Instrument, Face Amount

$ 675,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | DOE Project Financing, 3.092% January 2, 2037 [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

105,000,000

Non-recourse debt, commitment

$ 646,000,000

Debt, Weighted Average Interest Rate

2.82%

Non-recourse debt

530,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Denver International Airport [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

5.50%

Outstanding borrowings/facility draws

$ 7,000,000

Non-recourse debt

6,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

5.25%

Outstanding borrowings/facility draws

$ 11,000,000

Non-recourse debt

9,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

31,000,000

15,000,000

Escrow Deposit

6,000,000

Gain (Loss) on Sale of Debt Investments

37,000,000

Long-term debt

15,000,000

Outstanding borrowings/facility draws

22,000,000

Proceeds from Sales of Business, Affiliate and Productive Assets

$ 1,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | SolGen [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

3.93%

Debt Instrument, Face Amount

$ 150,000,000

Non-recourse debt

$ 147,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Renewable Power Generation [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

4.11%

Debt Instrument, Face Amount

$ 150,000,000

Non-recourse debt

127,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 131,000,000

Outstanding letters of credit

114,000,000

Interest rate on long-term debt

6.00%

Debt Instrument, Face Amount

$ 613,000,000

Generation capacity of portfolio | MW

667

Aggregate bank commitments under unsecured revolving credit facilities

$ 10,000,000

Non-recourse debt

512,000,000

Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGenRenewablesIVNov2024 [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

3.00%

Long-term debt

$ 850,000,000

Non-recourse debt, interest rate swap

$ 636,000,000

Non-recourse debt, hedge percentage

2.32%

Proceeds from Issuance of Debt

$ 785,000,000

Proceeds from (Repayments of) Restricted Cash, Financing Activities

$ 50,000,000

Exelon Generation Co L L C [Member] | Maximum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

7.60%

Exelon Generation Co L L C [Member] | Minimum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.95%

Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 5,300,000,000

Outstanding letters of credit

868,000,000

Outstanding borrowings/facility draws

0

Exelon Generation Co L L C [Member] | Line of Credit [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

480,000,000

Outstanding letters of credit

[1]

231,000,000

Outstanding borrowings/facility draws

0

Exelon Generation Co L L C [Member] | Line of Credit [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 200,000,000

$ 150,000,000

$ 100,000,000

Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Outstanding letters of credit

480,000,000

500,000,000

Commonwealth Edison Co [Member]

Debt Instrument [Line Items]

Long-term Debt, Current Maturities

840,000,000

425,000,000

Repayments of Long-term Debt

425,000,000

665,000,000

260,000,000

Outstanding letters of credit

[1]

2,000,000

Long-term debt, gross

7,676,000,000

7,101,000,000

Long-term debt

7,882,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2

Commonwealth Edison Co [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 1,000,000,000

PECO Energy Co [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

0

300,000,000

0

Outstanding letters of credit

[1]

1,000,000

Long-term debt, gross

2,925,000,000

2,600,000,000

Long-term debt

3,109,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2

PECO Energy Co [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 600,000,000

Baltimore Gas and Electric Company [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

41,000,000

379,000,000

$ 75,000,000

Outstanding letters of credit

[1]

0

Long-term debt, gross

2,600,000,000

2,341,000,000

Long-term debt

2,600,000,000

Outstanding borrowings/facility draws

$ 0

Preferred Stock, Redemption Price Per Share | $ / shares

$ 100

Credit agreement threshold

2

Baltimore Gas and Electric Company [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Long-term debt, gross

$ 2,600,000,000

2,300,000,000

Baltimore Gas and Electric Company [Member] | Maximum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

6.35%

Baltimore Gas and Electric Company [Member] | Minimum [Member] | Senior Notes [Member]

Debt Instrument [Line Items]

Interest rate on long-term debt

2.40%

Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 600,000,000

Pepco Holdings LLC [Member]

Debt Instrument [Line Items]

Long-term debt, gross

5,189,000,000

5,157,000,000

Long-term debt

5,189,000,000

Repayments of Bank Debt

300,000,000

Short-term Bank Loans and Notes Payable

$ 500,000,000

$ 300,000,000

Short-term Debt, Percentage Bearing Variable Interest Rate

1.00%

950000.00%

Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

$ 900,000,000

$ 1,500,000,000

Potomac Electric Power Company [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

13,000,000

11,000,000

$ 22,000,000

Outstanding letters of credit

[1]

0

Long-term debt, gross

2,570,000,000

2,381,000,000

Long-term debt

2,570,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2

Potomac Electric Power Company [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 300,000,000

Delmarva Power and Light Company [Member]

Debt Instrument [Line Items]

Long-term Debt, Current Maturities

79,000,000

105,000,000

Repayments of Long-term Debt

40,000,000

100,000,000

100,000,000

Outstanding letters of credit

[1]

0

Long-term debt, gross

1,309,000,000

1,348,000,000

Long-term debt

1,309,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2

Delmarva Power and Light Company [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 300,000,000

Atlantic City Electric Company [Member]

Debt Instrument [Line Items]

Repayments of Long-term Debt

35,000,000

48,000,000

$ 58,000,000

Outstanding letters of credit

[1]

0

Long-term debt, gross

1,127,000,000

$ 1,162,000,000

Long-term debt

1,127,000,000

Outstanding borrowings/facility draws

$ 0

Credit agreement threshold

2

Atlantic City Electric Company [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Line of credit facility, maximum borrowing capacity

[2]

$ 300,000,000

[1]

Excludes nonrecourse debt letters of credit, see discussion below on Antelope Valley Solar Ranch One and Continental Win

[2]

Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $34 million, $34 million, $5 million, $2 million, $2 million and $2 million, respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

[3]

Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets.

Income Taxes Deferred Tax Revis

Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities		$ 10,388	$ 4,789
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability	[1]	8,624
Regulatory Liabilities	[2]	7,315
Deferred Income Tax Expense (Benefit)	[1]	1,309
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		3,040
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		1,694
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		4,734
Exelon Generation Co L L C [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		1,895
Deferred Income Tax Expense (Benefit)		1,895
Commonwealth Edison Co [Member]
Regulatory Liabilities		6,577	3,698
Commonwealth Edison Co [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		2,819
Regulatory Liabilities	[2]	2,818
Deferred Income Tax Expense (Benefit)		1
Commonwealth Edison Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		1,400
Commonwealth Edison Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		573
Commonwealth Edison Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		1,973
PECO Energy Co [Member]
Regulatory Liabilities		690	644
PECO Energy Co [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		1,407
Regulatory Liabilities	[2]	1,394
Deferred Income Tax Expense (Benefit)		13
PECO Energy Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities	[3]	533
PECO Energy Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities	[3]	43
PECO Energy Co [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities	[3]	576
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities		1,163	160
Baltimore Gas and Electric Company [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		1,120
Regulatory Liabilities	[2]	1,124
Deferred Income Tax Expense (Benefit)		(4)
Baltimore Gas and Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		459
Baltimore Gas and Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		324
Baltimore Gas and Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		783
Pepco Holdings LLC [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Deferred Income Tax Expense (Benefit)		(35)
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Liabilities		1,928	237
Pepco Holdings LLC [Member] | Successor [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		1,944
Regulatory Liabilities	[2]	1,979
Pepco Holdings LLC [Member] | Successor [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		648
Pepco Holdings LLC [Member] | Successor [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		754
Pepco Holdings LLC [Member] | Successor [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		1,402
Potomac Electric Power Company [Member]
Regulatory Liabilities		832	31
Potomac Electric Power Company [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		968
Regulatory Liabilities	[2]	976
Deferred Income Tax Expense (Benefit)		(8)
Potomac Electric Power Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		299
Potomac Electric Power Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		391
Potomac Electric Power Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		690
Delmarva Power and Light Company [Member]
Regulatory Liabilities		635	140
Delmarva Power and Light Company [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		540
Regulatory Liabilities	[2]	545
Deferred Income Tax Expense (Benefit)		(5)
Delmarva Power and Light Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		195
Delmarva Power and Light Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		194
Delmarva Power and Light Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		389
Atlantic City Electric Company [Member]
Regulatory Liabilities		422	$ 25
Atlantic City Electric Company [Member] | RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability		456
Regulatory Liabilities	[2]	458
Deferred Income Tax Expense (Benefit)		(2)
Atlantic City Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities		153
Atlantic City Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities		170
Atlantic City Electric Company [Member] | NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities		$ 323
[1]	Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans.
[2]	Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers.
[3]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information.

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Income taxes			$ (125)	$ 761	$ 1,073
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes			(1,375)	290	502
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes			417	301	280
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes			104	149	143
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes			218	174	189
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes			105	41	102
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Income taxes			71	22	49
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes			26	(4)	33
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Income taxes		$ 3	217
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Income taxes	$ 17				163
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current			194	60	407
Deferred			(469)	607	566
Investment Tax Credit			(25)	(24)	(22)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current			584	513	546
Deferred			(2,003)	(247)	16
Investment Tax Credit			(21)	(20)	(19)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current			(191)	(135)	(80)
Deferred			523	379	310
Investment Tax Credit			(2)	(2)	(2)
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current			71	63	64
Deferred			28	72	69
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current			74	51	25
Deferred			101	88	126
Investment Tax Credit			(1)	(1)	(1)
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current			(20)	(118)	(54)
Deferred			114	136	126
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Current			(24)	(88)	(27)
Deferred			82	97	73
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current			(12)	(26)	(2)
Deferred			34	22	27
Investment Tax Credit			0	0	0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Current		(281)	(60)
Deferred		283	250
Investment Tax Credit		(1)	(1)
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Current	0				12
Deferred	10				103
Investment Tax Credit	0				(1)
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current			14	39	(86)
Deferred			161	79	208
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current			65	45	(90)
Deferred			0	(1)	49
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current			(49)	(4)	7
Deferred			136	63	45
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current			14	9	(10)
Deferred			(9)	5	20
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current			(5)	5	0
Deferred			49	31	39
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current			(2)	7	6
Deferred			13	16	24
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Current			0	1	2
Deferred			13	12	1
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current			0	0	3
Deferred			4	$ 0	5
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Current		(11)	(4)
Deferred		$ 13	$ 32
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Current	0				17
Deferred	$ 7				$ 32

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016	[7]	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Income Taxes [Line Items]
U.S. Federal statutory rate						21.00%	35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							2.30%		3.30%	[1]	3.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							3.80%		(3.40%)		0.40%
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											(0.70%)
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.90%)		(1.20%)		0.90%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(1.70%)		(4.80%)		(1.50%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							(1.80%)		(3.60%)		(1.90%)
Noncontrolling interests							0.10%		0.20%		0.30%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							(1.20%)		0.40%		(1.40%)
EffectiveIncomeTaxRateReconciliationPenalties							(3.70%)		1.90%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							(2.20%)		5.50%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(33.10%)
Other (e)							0.10%		(0.60%)	[3]	0.00%	[4]
Effective income tax rate							(3.30%)		38.30%		32.20%
Amount of Impairment to Carrying Amount of Regulatory Assets	[5]						$ 35
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							3.00%		3.30%	[1]	1.00%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							10.00%		(7.80%)		0.80%
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											(1.30%)
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(2.20%)		(2.30%)		(1.50%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.00%	[6]	0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							(4.80%)		(8.20%)		(3.40%)
Noncontrolling interests							(0.30%)		0.30%		(0.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		(1.70%)		(2.40%)
EffectiveIncomeTaxRateReconciliationPenalties							(1.30%)		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							(5.70%)		(1.10%)
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(130.10%)
Other (e)							0.40%		1.50%	[3]	0.00%	[4]
Effective income tax rate							(96.20%)		33.20%		27.10%
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							5.70%		5.60%	[1]	4.90%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.20%)		(0.30%)		(0.30%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.30%	[6]	(0.60%)		(0.10%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							1.30%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		4.50%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						0.10%
Other (e)							0.20%		0.10%	[3]	0.20%	[4]
Effective income tax rate							42.40%		44.30%		39.70%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 3
PECO Energy Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							0.60%		1.30%	[1]	1.00%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)		(0.10%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(13.80%)	[6]	(9.60%)		(8.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(2.30%)
Other (e)							(0.10%)		(1.20%)	[3]	0.20%	[4]
Effective income tax rate							19.30%		25.40%		27.40%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							5.40%		5.00%	[1]	5.30%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											0.10%
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)		(0.10%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.10%	[6]	(2.70%)		(0.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						0.90%
Other (e)							0.20%		0.00%	[3]	0.00%	[4]
Effective income tax rate							41.50%		37.20%		39.60%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 5
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							3.20%		15.70%	[1]	6.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)	[7]	(0.20%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(0.40%)	[6]	(22.80%)		(5.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(6.30%)		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		23.50%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						2.70%
Other (e)							(0.20%)		(1.80%)	[3]	(0.50%)	[4]
Effective income tax rate							33.90%		49.40%		35.30%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 14
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%	[7]	35.00%
State income taxes, net of Federal income tax benefit (d)							5.40%		52.70%	[1],[7]	1.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)	[7]	(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.20%)	[7]	(3.70%)	[7]	(0.40%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							2.00%	[6]	(25.50%)	[7]	(2.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%	[7]	0.00%
Noncontrolling interests							0.00%		0.00%	[7]	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%	[7]	0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(7.80%)		0.00%	[7]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		112.90%	[7]
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						2.50%
Other (e)							0.10%		(2.20%)	[3],[7]	5.20%	[4]
Effective income tax rate							37.00%		169.20%	[7]	39.20%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 6
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%	[7]	35.00%
State income taxes, net of Federal income tax benefit (d)							5.60%		6.20%	[1],[7]	5.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)	[7]	(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.40%)	[7]	0.80%	[7]	(0.60%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							3.60%	[6]	10.30%	[7]	(1.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%	[7]	0.00%
Noncontrolling interests							0.00%		0.00%	[7]	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%	[7]	0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(19.80%)		0.00%	[7]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		(44.90%)	[7]
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						1.60%
Other (e)							(0.40%)		1.30%	[3],[7]	6.40%	[4]
Effective income tax rate							25.20%		8.70%	[7]	45.20%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 7
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets	[5]						$ 27
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate				35.00%			35.00%
State income taxes, net of Federal income tax benefit (d)				5.80%	[1]		4.80%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent				(0.00%)			(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference				1.40%			(0.20%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent				39.00%			1.10%	[6]
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent				0.00%			0.00%
Noncontrolling interests				0.00%			0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent				0.00%			0.00%
EffectiveIncomeTaxRateReconciliationPenalties				(0.70%)			(9.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent				(89.00%)			0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						6.40%
Other (e)				3.30%	[3]		(0.10%)
Effective income tax rate				(5.20%)			37.50%
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate		35.00%									35.00%
State income taxes, net of Federal income tax benefit (d)		11.90%	[1]								6.60%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent		(0.00%)									(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.90%)									(0.20%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent		(13.50%)									(4.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent		0.00%									0.00%
Noncontrolling interests		0.00%									0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%									0.00%
EffectiveIncomeTaxRateReconciliationPenalties		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		11.10%
Other (e)		3.60%	[3]								(3.20%)	[4]
Effective income tax rate		47.20%									33.90%
[1]	Includes a remeasurement of uncertain state income tax positions for Pepco and DPL.
[2]	Included are impacts for TJCA other than the corporate rate change, including revisions further limiting tax deductions for compensation of certain highest paid executives, the write-off of foreign tax credit carryforwards, and loss of a 2015 domestic production activities deduction due to an NOL carryback.
[3]	At PECO, includes a cumulative adjustment related to an anticipated gas repairs tax return accounting method change. The method change request was filed and accepted in 2017. No change to the results recorded as of December 31, 2016
[4]	Includes impacts of the PHI Global Settlement for Pepco, DPL, ACE and PHI.
[5]	Exelon reflects the consolidated regulatory asset impairments of ComEd, BGE, Pepco, DPL and ACE, and PHI reflects the consolidated regulatory asset impairments of Pepco, DPL and ACE.
[6]	Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL, and ACE of $35 million, $3 million, $5 million, $27 million, $14 million, $6 million, and $7 million, respectively (See Footnote 3 - Regulatory Matters).
[7]	DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016, and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016. As a result, positive percentages represent an income tax benefit for the periods presented.

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (12,490)	$ (17,966)
Deferred Tax Liabilities, Other Finite-Lived Assets	150	434
Derivatives and other financial instruments	(85)	(179)
Deferred pension and postretirement obligation	1,463	2,287
Deferred Tax Liabilities, Investments	(553)	(509)
Deferred debt refinancing costs	217	325
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(688)	(3,319)
Tax loss carryforward	344	189
Tax credit carryforward	861	446
Investment in partnerships	(434)	(650)
Other, net	746	1,485
Deferred income tax liabilities (net)	(10,469)	(17,457)
Unamortized investment tax credits	(732)	(658)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(11,201)	(18,115)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,819)	(4,192)
Deferred Tax Liabilities, Other Finite-Lived Assets	(66)	(115)
Derivatives and other financial instruments	(66)	(162)
Deferred pension and postretirement obligation	(205)	(316)
Deferred Tax Liabilities, Investments	(553)	(509)
Deferred debt refinancing costs	26	44
Deferred Tax Liabilities, Regulatory Assets and Liabilities	0	0
Tax loss carryforward	76	61
Tax credit carryforward	868	493
Investment in partnerships	(416)	(650)
Other, net	78	403
Deferred income tax liabilities (net)	(3,077)	(4,943)
Unamortized investment tax credits	(705)	(626)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,782)	(5,569)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(3,825)	(5,034)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	(2)	(3)
Deferred pension and postretirement obligation	(285)	(453)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(8)	(13)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	489	(226)
Tax loss carryforward	33	29
Tax credit carryforward	1	0
Investment in partnerships	0	0
Other, net	141	351
Deferred income tax liabilities (net)	(3,456)	(5,349)
Unamortized investment tax credits	(13)	(15)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,469)	(5,364)
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,762)	(3,095)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(15)	(18)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(1)	(1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(90)	10
Tax loss carryforward	9	0
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	71	99
Deferred income tax liabilities (net)	(1,788)	(3,005)
Unamortized investment tax credits	(1)	(1)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,789)	(3,006)
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,368)	(1,977)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(29)	(43)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(3)	(3)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	136	(240)
Tax loss carryforward	11	22
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	13	27
Deferred income tax liabilities (net)	(1,240)	(2,214)
Unamortized investment tax credits	(4)	(5)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,244)	(2,219)
Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,521)	(3,586)
Deferred Tax Liabilities, Other Finite-Lived Assets	216	548
Derivatives and other financial instruments	3	(1)
Deferred pension and postretirement obligation	(130)	(111)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	203	293
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(184)	(1,205)
Tax loss carryforward	156	77
Tax credit carryforward	6	0
Investment in partnerships	0	0
Other, net	193	225
Deferred income tax liabilities (net)	(2,058)	(3,760)
Unamortized investment tax credits	(8)	(9)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,066)	(3,769)
Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(607)	(869)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(18)	(21)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(1)	(2)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	86	(69)
Tax loss carryforward	35	14
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	16	34
Deferred income tax liabilities (net)	(489)	(913)
Unamortized investment tax credits	(4)	(4)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(493)	(917)
Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(717)	(973)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(51)	(74)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(2)	(4)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	88	(75)
Tax loss carryforward	68	39
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	14	34
Deferred income tax liabilities (net)	(600)	(1,053)
Unamortized investment tax credits	(3)	(3)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(603)	(1,056)
Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,152)	(1,678)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(78)	(122)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(4)	(7)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	39	(194)
Tax loss carryforward	40	27
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	94	66
Deferred income tax liabilities (net)	(1,061)	(1,908)
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	$ (1,063)	$ (1,910)

Income Taxes - Schedule of Carr

Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	Dec. 31, 2017USD ($)
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 624	[1]
Deferred Tax Assets, Operating Loss Carryforwards	131
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred Tax Assets, Operating Loss Carryforwards	0
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	156
Deferred Tax Assets, Operating Loss Carryforwards	33
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	7
Deferred Tax Assets, Operating Loss Carryforwards	1
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred Tax Assets, Operating Loss Carryforwards	0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	261
Deferred Tax Assets, Operating Loss Carryforwards	55
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	82
Deferred Tax Assets, Operating Loss Carryforwards	17
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	81
Deferred Tax Assets, Operating Loss Carryforwards	17
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	63
Deferred Tax Assets, Operating Loss Carryforwards	13
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	861	[2]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	868
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	1
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	1
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	5
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	3,555	[3]
Deferred taxes on state tax attributes (net)	233
Valuation allowance on state tax attributes	29
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,479	[3]
Deferred taxes on state tax attributes (net)	97
Valuation allowance on state tax attributes	23
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred taxes on state tax attributes (net)	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	98	[4]
Deferred taxes on state tax attributes (net)	8
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	177	[5]
Deferred taxes on state tax attributes (net)	12
Valuation allowance on state tax attributes	1
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,440	[6]
Deferred taxes on state tax attributes (net)	98
Valuation allowance on state tax attributes	5
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	347	[7]
Deferred taxes on state tax attributes (net)	23
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	753	[8]
Deferred taxes on state tax attributes (net)	51
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	299	[9]
Deferred taxes on state tax attributes (net)	21
Valuation allowance on state tax attributes	$ 0
[1]	Exelon's federal net operating loss will begin expiring in 2034.
[2]	Exelon’s federal general business credit carryforwards will begin expiring in 2033.
[3]	Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2018.
[4]	PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031.
[5]	BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026.
[6]	PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036.
[7]	Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2028.
[8]	DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2027.
[9]	ACE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031.

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 916		$ 1,078	$ 1,829
Unrecognized Tax Benefits, Increase Resulting from Acquisition			22
Increases based on tax positions related to current year	0		108	108
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		(332)	(705)
Decreases based on tax positions prior to current year	28		88	79
Unrecognized Tax Benefits, Period Increase (Decrease)	(196)	[1]	(21)	(116)
Decrease from settlements with taxing authorities	(5)		(27)	(31)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	(86)
Unrecognized tax benefits - ending balance	743		916	1,078
Exelon Generation Co L L C [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	490		534	1,357
Unrecognized Tax Benefits, Increase Resulting from Acquisition			5
Increases based on tax positions related to current year	0		10	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		(12)	(659)
Decreases based on tax positions prior to current year	0		0	65
Unrecognized Tax Benefits, Period Increase (Decrease)	(17)	[1]	(20)	(112)
Decrease from settlements with taxing authorities	(5)		(27)	(31)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	(86)
Unrecognized tax benefits - ending balance	468		490	534
Commonwealth Edison Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	(12)		142	149
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		0	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		(154)	(7)
Decreases based on tax positions prior to current year	14		0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	2		(12)	142
PECO Energy Co [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0		0	44
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		0	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		0	(44)
Decreases based on tax positions prior to current year	0		0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	0		0	0
Baltimore Gas and Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	120		120	0
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		0	106
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		0	0
Decreases based on tax positions prior to current year	0		0	14
Unrecognized Tax Benefits, Period Increase (Decrease)	0	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	120		120	120
Potomac Electric Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	80		8	0
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		21	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		0	0
Decreases based on tax positions prior to current year	0		51	8
Unrecognized Tax Benefits, Period Increase (Decrease)	(21)	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	59		80	8
Delmarva Power and Light Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	37		3	0
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		16	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		0	0
Decreases based on tax positions prior to current year	0		18	3
Unrecognized Tax Benefits, Period Increase (Decrease)	(16)	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	21		37	3
Atlantic City Electric Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	22		0	0
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Increases based on tax positions related to current year	0		22	0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0	0
Increases based on tax positions prior to current year	0		0	0
Decreases based on tax positions prior to current year	14		0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	(22)	[1]	0	0
Decrease from settlements with taxing authorities	0		0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0	0
Unrecognized tax benefits - ending balance	14		22	0
Pepco Holdings LLC [Member] | Successor [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	172		22
Unrecognized Tax Benefits, Increase Resulting from Acquisition			(5)
Increases based on tax positions related to current year	0		59
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions	0		0
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	14		96
Unrecognized Tax Benefits, Period Increase (Decrease)	(61)	[1]	0
Decrease from settlements with taxing authorities	0		0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0		0
Unrecognized tax benefits - ending balance	$ 125		172	22
Pepco Holdings LLC [Member] | Predecessor [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance			$ 22	702
Increases based on tax positions related to current year				0
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions				0
Increases based on tax positions prior to current year				(688)
Decreases based on tax positions prior to current year				11
Unrecognized Tax Benefits, Period Increase (Decrease)				0
Decrease from settlements with taxing authorities				0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations				(3)
Unrecognized tax benefits - ending balance				$ 22
[1]	Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACEUnrecognized tax benefits at January 1, 2015$1,829 $1,357 $149 $44 $— $702 $— $— $—Increases based on tax positions related to 2015108 — — — 106 — — — —Decreases based on tax positions related to 2015— — — — — — — — —Change to positions that only affect timing(705) (659) (7) (44) — (688) — — —Increases based on tax positions prior to 201579 65 — — 14 11 8 3 —Decreases based on tax positions prior to 2015(116) (112) — — — — — — —Decreases from settlements with taxing authorities(31) (31) — — — — — — —Decreases from expiration of statute of limitations(86) (86) — — — (3) — — —Unrecognized tax benefits at December 31, 2015$1,078 $534 $142 $— $120$22$8$3$—

Income Taxes - Summary of Inter

Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Document Period End Date		Dec. 31, 2017
Net Interest Receivable Payable Related To Uncertain Tax Positions		$ 233	$ (507)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		(17)	(106)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		(3)	46
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	[1]	4	(384)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	(86)
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	8
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	(1)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		2	2
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	1
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	1
Unrecognized Tax Benefits, Income Tax Penalties Accrued		$ 0	$ 0
[1]	Change in balance attributable to Like-Kind Exchange interest payments, see Other Tax Matters for further discussion.

Income Taxes - Summary of In137

Income Taxes - Summary of Interest Expense (Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Document Period End Date			Dec. 31, 2017
Unrecognized Tax Benefits, Income Tax Penalties Expense			$ (2)	$ 106	$ 0
Net interest (income) expense recognized related to uncertain tax positions			37	165	(13)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			(1)	(13)	(31)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	86	0
Net interest (income) expense recognized related to uncertain tax positions			11	117	7
PECO Energy Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			0	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			0	0	0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions		$ (2)	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 0				(34)
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			0	6	(4)
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			0	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	0
Net interest (income) expense recognized related to uncertain tax positions			$ 0	$ (1)	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended	9 Months Ended			12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Mar. 23, 2016	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2016		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	Jul. 01, 2017	Jun. 29, 2017	Dec. 15, 2016	Jun. 30, 2016	Mar. 24, 2016	Dec. 15, 2015	Dec. 31, 2014	Dec. 31, 1999
Income Taxes [Line Items]
Document Period End Date												Dec. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent											21.00%	35.00%		35.00%		35.00%
LimitationonDeductibleInterestExpense											100.00%
AllowableExpensingForCostOfQualifiedProperty											30.00%
BonusDepreciationPercentage											50.00%
Unrecognized Tax Benefits	$ 743			$ 916					$ 916			$ 743		$ 916		$ 1,078							$ 1,829
Unrecognized Tax Benefits, Income Tax Penalties Expense												(2)		106		0
Unrecognized Tax Benefits, Interest on Income Taxes Expense					$ 94
Unrecognized Tax Benefits, Period Increase (Decrease)												(196)	[1]	(21)		(116)
Taxes accrued	373			723					723			373		723
Unrecognized Tax Benefits, Income Tax Penalties Accrued	(17)			(106)					(106)			(17)		(106)
Tax positions for which there is uncertainty about the timing of tax benefits	7			83					83			7		83		415
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	523			633					633			523		$ 633		$ 538
Income Tax Expense (Benefit), Intraperiod Tax Allocation			$ 28
Like kind exchange [Member]
Income Taxes [Line Items]
Income Taxes Receivable							$ 369
Payments for Other Taxes	20											950
Deferred gain on sale of property																								$ 1,200
Unrecognized Tax Benefits, Income Tax Penalties Expense												90
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 39						$ 39
Expected non-cash charge to earnings							26											$ 50
Unrecognized Tax Benefits, Period Increase (Decrease)							2
Investment Agreement, Early Termination Fee				1,250
Taxes accrued		335	106					335												$ 360
Unrecognized Tax Benefits, Income Tax Penalties Accrued	1,300											$ 1,300
Deferred								350
Tax Adjustments, Settlements, and Unusual Provisions								150
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%		35.00%
Unrecognized Tax Benefits	468			490					490			$ 468		$ 490		$ 534							1,357
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												(17)	[1]	(20)		(112)
Taxes accrued	444			239					239			444		239
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			0		0
Tax positions for which there is uncertainty about the timing of tax benefits																20
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	461			483					483			461		483		509
Allocation of federal tax benefit under tax sharing agreement	102			94					94			$ 102		$ 94		$ 57
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%		35.00%
Unrecognized Tax Benefits	2			(12)					(12)			$ 2		$ (12)		$ 142							149
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		86		0
Unrecognized Tax Benefits, Interest on Income Taxes Expense					$ 64
Unrecognized Tax Benefits, Period Increase (Decrease)												0	[1]	0		0
Taxes accrued	60			330					330			60		330
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			(86)					(86)			0		$ (86)
Tax positions for which there is uncertainty about the timing of tax benefits																$ 142
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	2											2
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		2						2
Expected non-cash charge to earnings							23											$ 15
Unrecognized Tax Benefits, Period Increase (Decrease)							$ 8
Investment Agreement, Early Termination Fee												300
Taxes accrued			86
Deferred												$ 300
PECO Energy Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%		35.00%
Unrecognized Tax Benefits	0			0					0			$ 0		$ 0		$ 0							44
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												0	[1]	0		0
Taxes accrued	15			4					4			15		4
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			0		0
Allocation of federal tax benefit under tax sharing agreement	16			18					18			$ 16		$ 18		$ 16
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%		35.00%
Unrecognized Tax Benefits	120			120					120			$ 120		$ 120		$ 120			$ 120			$ 120	0
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												0	[1]	0		0
Taxes accrued	71			78					78			71		78
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			0		0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate																120
Allocation of federal tax benefit under tax sharing agreement	10			8					8			$ 10		$ 8		$ 7
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%		35.00%
Unrecognized Tax Benefits	59			80					80			$ 59		$ 80		$ 8			59			59	0
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												(21)	[1]	0		0
Taxes accrued	68			48					48			68		48
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			$ 0		0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				21					21					$ 21		$ 8
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%	[2]	35.00%
Unrecognized Tax Benefits	21			37					37			$ 21		$ 37		$ 3			21			21	0
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												(16)	[1]	0		0
Taxes accrued	4			4					4			4		4
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			$ 0		0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				16					16					$ 16		$ 3
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent												35.00%		35.00%	[2]	35.00%
Unrecognized Tax Benefits	14			22					22			$ 14		$ 22		$ 0			14				0
Unrecognized Tax Benefits, Income Tax Penalties Expense												0		0		0
Unrecognized Tax Benefits, Period Increase (Decrease)												(22)	[1]	0		0
Taxes accrued	5			9					9			5		9
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			$ 0		0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				22					$ 22					22
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent																					$ 59
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent									35.00%	[2]		35.00%
Unrecognized Tax Benefits	125			172					$ 172			$ 125		172		$ 22			$ 94
Unrecognized Tax Benefits, Period Increase (Decrease)												(61)	[1]	0
Taxes accrued	61			65					65			61		65
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0			0					0			0		0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	32											32
Allocation of federal tax benefit under tax sharing agreement	7											7
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent						35.00%										35.00%
Unrecognized Tax Benefits																$ 22						$ 80	$ 702
Unrecognized Tax Benefits, Period Increase (Decrease)																0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				$ 93					93					93		11
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Deferred												(469)		607		566
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	146											146
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred												(2,003)		(247)		16
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	19											19
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred												523		379		310
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred												28		72		69
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred												101		88		126
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred												114		136		126
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	21											21
Internal Revenue Service (IRS) [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Deferred												82		97		73
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	16											16
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred												34		22		27
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	22											22
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Deferred									283			250
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	59											59
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						$ 10										103
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Deferred Tax Assets, State Taxes		272	8					272
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities			20
Deferred												161		79		208
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	683											683
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	462											462
Other, net		250
Deferred State and Local Income Tax Expense (Benefit)								20
IllinoisCorporateIncomeTaxRate							7.75%										9.50%
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred												0		(1)		49
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	469											469
Other, net		20
Deferred State and Local Income Tax Expense (Benefit)								$ 20
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred												136		63		45
Other, net		$ 270
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred												(9)		5		20
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred												49		31		39
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	120											120
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred												13		16		24
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	59											59
Other, net			8
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Deferred												13		12		1
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	21											21
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred												4		$ 0		5
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	14											14
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Deferred									$ 13			32
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 94											$ 94
Other, net			$ 8
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						$ 7										$ 32
[1]	Predecessor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACEUnrecognized tax benefits at January 1, 2015$1,829 $1,357 $149 $44 $— $702 $— $— $—Increases based on tax positions related to 2015108 — — — 106 — — — —Decreases based on tax positions related to 2015— — — — — — — — —Change to positions that only affect timing(705) (659) (7) (44) — (688) — — —Increases based on tax positions prior to 201579 65 — — 14 11 8 3 —Decreases based on tax positions prior to 2015(116) (112) — — — — — — —Decreases from settlements with taxing authorities(31) (31) — — — — — — —Decreases from expiration of statute of limitations(86) (86) — — — (3) — — —Unrecognized tax benefits at December 31, 2015$1,078 $534 $142 $— $120$22$8$3$—
[2]	DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016, and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016. As a result, positive percentages represent an income tax benefit for the periods presented.

Asset Retirement Obligations -

Asset Retirement Obligations - Nuclear Decommissioning Asset Retirement Obligation Rollforward (Details) - USD ($) $ in Millions		3 Months Ended					9 Months Ended	12 Months Ended
		Dec. 31, 2017		Sep. 30, 2016	Mar. 31, 2016		Sep. 30, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]							$ 468		$ 446		$ 398
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]							0		0		0
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]							468		446		397
Asset Retirement Obligation, Revision of Estimate							$ 61	1		1
Asset Retirement Obligation, Period Increase (Decrease)		$ 180		$ 165			288			488
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					$ 8,246		8,246	8,734	[2]	8,246
Asset Retirement Obligation, Accretion Expense								458		436
Asset Retirement Obligation, Revision of Estimate								444
Asset Retirement Obligation, Period Increase (Decrease)								34		61
Costs incurred to decommission retired plants								(8)		(9)
ARO ending balance		9,662						9,662		8,734	[2]	8,246
Asset Retirement Obligation, Current		13						13		10
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0	3		0
Asset Retirement Obligation, Accretion Expense								0		0
Asset Retirement Obligation, Revision of Estimate					0	[3]		0	[4]	3	[4]
Asset Retirement Obligation, Period Increase (Decrease)								0		0	[5]
ARO ending balance		3						3		3		0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					197		$ 197	199	[6]	197
Asset Retirement Obligation, Accretion Expense								10		10
Asset Retirement Obligation, Revision of Estimate					$ 1	[3]		(1)	[4]	8	[4]
Asset Retirement Obligation, Period Increase (Decrease)								7		(22)	[5]
ARO ending balance		197	[6]					197	[6]	199	[6]	$ 197
Asset Retirement Obligation, Current		$ 1						$ 1		$ 1
[1]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes $13 million and $10 million as the current portion of the ARO at December 31, 2017 and 2016, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	Following the completion of the PHI merger on March 23, 2016, PHI's AROs related to its unregulated business interests were transferred to Exelon and Generation.
[4]	During the year ended December 31, 2017, ComEd recorded a decrease of $1 million in Operating and maintenance expense. Generation, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2017. During the year ended December 31, 2016, Generation recorded a increase of $1 million in Operating and maintenance expense. ComEd, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016.
[5]	Reflects a reduction to the ARO resulting primarily from the sales of the New Boston generating site and Upstream business in 2016. See Note 4—Mergers, Acquisitions and Dispositions for further information.
[6]	Excludes the current portion of the ARO at December 31, 2017 for Generation, ComEd and BGE of $1 million, $2 million and $2 million, respectively. Excludes the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE of $1 million, $2 million and $3 million, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

Asset Retirement Obligations140

Asset Retirement Obligations - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations, Noncurrent	$ 10,029,000,000					$ 10,029,000,000	$ 9,111,000,000
Percent of additional decommissioning shortfall with recourse	50.00%					50.00%
Nuclear decommissioning trust funds	$ 13,272,000,000					$ 13,272,000,000	11,061,000,000
Spent Nuclear Fuel Obligation, Noncurrent	1,147,000,000					1,147,000,000	1,024,000,000
Line of credit facility, maximum borrowing capacity								$ 98
Decommissioning Liability, Noncurrent	0					0	14,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)	180,000,000		$ 165,000,000		$ 288,000,000		488,000,000
Asset Retirement Obligations, Noncurrent	9,844,000,000					9,844,000,000	8,922,000,000
Asset Retirement Obligation, Revision of Estimate					$ 61,000,000	1,000,000	1,000,000
Shortfall of decommissioning funds with recourse	$ 50,000,000					$ 50,000,000
Percent of additional decommissioning shortfall with recourse	5.00%					5.00%
Nuclear decommissioning trust funds	$ 13,272,000,000					$ 13,272,000,000	11,061,000,000
Spent Nuclear Fuel Obligation, Noncurrent	1,147,000,000					1,147,000,000	1,024,000,000
ZionSolutions rent payable						1
Line of credit facility, maximum borrowing capacity	200,000,000					$ 200,000,000
Annual average accretion of the ARO						5.00%
Number of years used in present value measurement						30 years
Historical five-year annual average after-tax return on NDT funds						8.00%
Decommissioning Liability, Noncurrent	$ 0					$ 0	14,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						2.00%
Years after cessation of plant operations						10 years
Estimated annual after tax return on nuclear decommissioning funds	4.80%					4.80%
Exelon Generation Co L L C [Member] | Maximum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						3.00%
Years after cessation of plant operations						70 years
Estimated annual after tax return on nuclear decommissioning funds	6.40%					6.40%
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)				$ 138,000,000		$ 928,000,000	436,000,000
Asset Retirement Obligation, Revision of Estimate	$ 178,000,000
Nuclear decommissioning
Asset Retirement Obligations [Line Items]
Proceeds from Customers		$ 4,000,000				24,000,000
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)						34,000,000	$ 61,000,000
Asset Retirement Obligation, Revision of Estimate						444,000,000
Zion Station [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent	$ 114,000,000					$ 114,000,000

Asset Retirement Obligations141

Asset Retirement Obligations - Unrealized Gain on NDT Funds (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		$ 13,272	$ 11,061
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		13,272	11,061
Unrealized Gain (Loss) on Investments		(10)	(1)	$ 7
Collateral Pledged [Member] | Unregulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	[1],[2]	521	194	(197)
Collateral Pledged [Member] | Regulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	[3]	455	$ 216	$ (282)
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments		$ 13,349
[1]	Excludes $(10) million, $(1) million and $7 million of net unrealized gains (losses) related to the Zion Station pledged assets in 2017, 2016 and 2015, respectively. Net unrealized gains related to Zion Station pledged assets are included in the Other current liabilities and Payable for Zion Station decommissioning on Exelon’s and Generation’s Consolidated Balance Sheets
[2]	Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.
[3]	Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets.

Asset Retirement Obligations142

Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2016
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity				$ 98
Carrying value of Zion Station pledged assets		$ 0	$ 113,000,000
Decommissioning Liability, Noncurrent		0	14,000,000
Asset Retirement Obligations, Noncurrent		10,029,000,000	9,111,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000
Held-to-maturity Securities Pledged as Collateral		39,000,000	113,000,000
Accounts Payable, Interest-bearing, Noncurrent	[1]	37,000,000	104,000,000
Asset Retirement Obligation, Cash Paid to Settle	[2]	942,000,000	878,000,000
Carrying value of Zion Station pledged assets		0	113,000,000
Decommissioning Liability, Noncurrent		0	14,000,000
Asset Retirement Obligations, Noncurrent		9,844,000,000	8,922,000,000
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligations [Line Items]
Accounts Payable, Interest-bearing, Current	[3]	$ 37,000,000	$ 90,000,000
[1]	Included in Other current assets within Exelon’s and Generation’s Consolidated Balance Sheets in 2017
[2]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT Funds. The NDT Funds will be utilized to satisfy the tax obligations as gains and losses are realized.

Asset Retirement Obligations143

Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended			12 Months Ended
		Dec. 31, 2017		Sep. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016		Sep. 30, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										$ 468		$ 446		$ 398
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										$ 61	1		1
Asset Retirement Obligation, Accretion Expense	[1]										468		446		397
Asset Retirement Obligation, Period Increase (Decrease)		$ 180		$ 165						288			488
Payments	[2]										(942)		(878)
Asset Retirement Obligation, Revision of Estimate										61	1		1
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]							$ 0			0
Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]						$ 0								0
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Delmarva Power and Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					$ 197		197			197	199	[3]	197
Asset Retirement Obligation, Revision of Estimate					1	[4]					(1)	[5]	8	[5]
Development projects	[6]										1		11
Asset Retirement Obligation, Accretion Expense											10		10
Asset Retirement Obligation, Period Increase (Decrease)											7		(22)	[7]
Payments											(5)		(6)
ARO ending balance		197	[3]					199	[3]		197	[3]	199	[3]	197
Asset Retirement Obligation, Revision of Estimate					1	[4]					(1)	[5]	8	[5]
Asset Retirement Obligation, Current		1						1			1		1
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					27		27			27	28		27
Asset Retirement Obligation, Revision of Estimate					0	[4]					(1)	[5]	1	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										1		1
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(1)		(1)
ARO ending balance		27						28			27		28		27
Asset Retirement Obligation, Revision of Estimate					0	[4]					(1)	[5]	1	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					18		18			18	24	[3]	18
Asset Retirement Obligation, Revision of Estimate					0	[4]					2	[5]	7	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(2)		(1)
ARO ending balance		24	[3]					24	[3]		24	[3]	24	[3]	18
Asset Retirement Obligation, Revision of Estimate					0	[4]					2	[5]	7	[5]
Asset Retirement Obligation, Current		2						3			2		3
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	[9]				0		0			0	14		0
Asset Retirement Obligation, Revision of Estimate	[9]				0	[4]					2	[5]	14	[5]
Development projects	[6],[9]						0				0
Asset Retirement Obligation, Accretion Expense	[9]										0		0
Asset Retirement Obligation, Period Increase (Decrease)	[9]										0	[10]	0	[7]
Payments	[9]										0		0
ARO ending balance	[9]	16						14			16		14		0
Asset Retirement Obligation, Revision of Estimate	[9]				0	[4]					2	[5]	14	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	[9]				8		8	8		8			8
ARO ending balance	[9]						8								8
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	2		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	2	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		3						2			3		2		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	2	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power and Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	9		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	9	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		10						9			10		9		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	9	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	3		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					0	[5]	3	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		3						3			3		3		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					0	[5]	3	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[7]												(22)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					113		113			113	121	[3]	113
Asset Retirement Obligation, Revision of Estimate					0	[4]					(13)	[5]	4	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										7		7
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(2)		(3)
ARO ending balance		113	[3]					121	[3]		113	[3]	121	[3]	113
Asset Retirement Obligation, Revision of Estimate					0	[4]					(13)	[5]	4	[5]
Asset Retirement Obligation, Current		2						2			2		2
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					8,246		8,246			8,246	8,734	[11]	8,246
Asset Retirement Obligation, Revision of Estimate											444
Asset Retirement Obligation, Accretion Expense											458		436
Asset Retirement Obligation, Period Increase (Decrease)											34		61
ARO ending balance		9,662						8,734	[11]		9,662		8,734	[11]	8,246
Asset Retirement Obligation, Revision of Estimate											444
Asset Retirement Obligation, Current		13						10			13		10
Nuclear decommissioning | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					355		$ 355			$ 355	393		355
Asset Retirement Obligation, Revision of Estimate					8	[4]					(11)	[5]	34	[5]
Development projects	[6]										1		11
Asset Retirement Obligation, Accretion Expense											18		18
Asset Retirement Obligation, Period Increase (Decrease)											7
Payments											(10)		(11)
ARO ending balance		$ 384						$ 393			384		393		$ 355
Asset Retirement Obligation, Revision of Estimate					$ 8	[4]					$ (11)	[5]	$ 34	[5]
[1]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	Excludes the current portion of the ARO at December 31, 2017 for Generation, ComEd and BGE of $1 million, $2 million and $2 million, respectively. Excludes the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE of $1 million, $2 million and $3 million, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.
[4]	Following the completion of the PHI merger on March 23, 2016, PHI's AROs related to its unregulated business interests were transferred to Exelon and Generation.
[5]	During the year ended December 31, 2017, ComEd recorded a decrease of $1 million in Operating and maintenance expense. Generation, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2017. During the year ended December 31, 2016, Generation recorded a increase of $1 million in Operating and maintenance expense. ComEd, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016.
[6]	Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.
[7]	Reflects a reduction to the ARO resulting primarily from the sales of the New Boston generating site and Upstream business in 2016. See Note 4—Mergers, Acquisitions and Dispositions for further information.
[8]	Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites.
[9]	For PHI, the successor period includes activity for the year ended December 31, 2017 and the period of March 24, 2016 through December 31, 2016. The PHI predecessor periods include activity for the period of January 1, 2016 through March 23, 2016.
[10]	See Note 4—Mergers, Acquisitions and Dispositions for additional information.
[11]	Includes $13 million and $10 million as the current portion of the ARO at December 31, 2017 and 2016, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.

Retirement Benefits Retirement

Retirement Benefits Retirement Benefits- Narrative (Details) - USD ($) $ in Millions		Jan. 01, 2016	Sep. 30, 2017	Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount	[1]								$ 128		$ 164		$ 148
Increase (Decrease) in Obligation, Pension Benefits				$ 92
Benefit obligation increase (decrease) reflecting actual census data				(57)
AOCI valuation adjustment				(59)
Regulatory asset increase (decrease) due to updated valuation adjustment				57
Defined benefit plan, amounts recognized In regulatory liabilities, before tax				$ 4
Expected qualified pension plan contributions	[2]								301
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								30
Expected other postretirement benefit plan contributions	[4]								$ 42
Fitzpatrick [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase (Decrease) in Obligation, Pension Benefits			$ 16
Benefit obligation increase (decrease) reflecting actual census data			$ (17)
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage						80.00%			83.00%		80.00%
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Funded Percentage						84.00%			88.00%		84.00%
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount	[1]								$ 55		$ 79		80
Expected qualified pension plan contributions	[2]								119
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								11
Expected other postretirement benefit plan contributions	[4]								13
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount									31		34		32
Expected qualified pension plan contributions	[2]								38
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								2
Expected other postretirement benefit plan contributions	[4]								3
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount									10		10		11
Expected qualified pension plan contributions	[2]								17
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								1
Expected other postretirement benefit plan contributions	[4]								0
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount									10		12		14
Expected qualified pension plan contributions	[2]								41
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								1
Expected other postretirement benefit plan contributions	[4]								16
Pepco Holdings LLC [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected qualified pension plan contributions	[2]								50
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								8
Expected other postretirement benefit plan contributions	[4]								9
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount					$ 3						14
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount						$ 10			13
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount					1				3	[5]	3	[5]	3	[5]
Expected qualified pension plan contributions	[2]								4
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								2
Expected other postretirement benefit plan contributions	[4]								8
Delmarva Power and Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount					1				2	[5]	2	[5]	2	[5]
Expected qualified pension plan contributions	[2]								0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								1
Expected other postretirement benefit plan contributions	[4]								0
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount	[5]								2		2		2
Expected qualified pension plan contributions	[2]								6
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[3]								0
Expected other postretirement benefit plan contributions	[4]								0
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Amortization of Gain (Loss)									607	[6]	554	[7]	$ 571
Actual return on plan assets									2,600		$ 1,061	[8]
Defined Contribution Plan, Employer Discretionary Contribution Amount									$ 300
Discount rate						4.04%	[9]		3.62%	[10]	4.04%	[9]	4.29%	[11]
Current year actuarial (gain) loss									$ (222)		$ 644	[12]	$ 476
Regulatory asset increase (decrease) due to updated valuation adjustment									$ (423)		$ 959	[12]	$ (46)
Expected return on plan assets								7.00%	7.00%		7.00%	[13]	7.00%	[13]
Discount rate									4.04%	[14]	4.29%	[15]	3.94%	[16]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months									$ 1,166
Amortization of actuarial loss									(607)		$ (554)	[12]	$ (571)
Current year prior service cost (credit)									9		(60)	[12]	0
Amortization of prior service (cost) credit									(1)		(14)	[12]	(13)
Settlements									(3)		0	[12]	(2)
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[12]								(824)		1,010		(110)
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Amortization of Gain (Loss)					(14)						(65)
Current year actuarial (gain) loss					0						50
Regulatory asset increase (decrease) due to updated valuation adjustment					$ (13)						$ (6)
Expected return on plan assets	[17]				6.50%						6.50%
Discount rate											4.20%
Amortization of actuarial loss					$ (14)						$ (65)
Amortization of prior service (cost) credit					0						(2)
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[12]				$ (14)						$ (17)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase					5.00%						5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Amortization of Gain (Loss)									61	[6]	$ 63	[7]	$ 80
Actual return on plan assets									$ 346		$ 128	[8]
Discount rate						4.04%	[9]		3.61%	[10]	4.04%	[9]	4.29%	[11]
Current year actuarial (gain) loss									$ 166		$ (101)	[12]	$ (194)
Regulatory asset increase (decrease) due to updated valuation adjustment									$ 125		$ 95	[12]	$ (60)
Expected return on plan assets								6.60%	6.58%		6.71%	[13]	6.50%	[13]
Discount rate									4.04%	[14]	4.29%	[15]	3.92%	[16]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months									$ 256
Amortization of actuarial loss									(61)		$ (63)	[12]	$ (80)
Current year prior service cost (credit)									0		0	[12]	(23)
Amortization of prior service (cost) credit									188		185	[12]	174
Settlements									0		0	[12]	0
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[12]								$ 293		115		$ (123)
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Amortization of Gain (Loss)					$ (2)						$ (8)
Discount rate						4.55%					4.55%
Current year actuarial (gain) loss					0						$ (39)
Regulatory asset increase (decrease) due to updated valuation adjustment					$ 1						$ (34)
Expected return on plan assets	[17]				6.75%						6.75%
Discount rate					4.55%						4.15%
Amortization of actuarial loss					$ (2)						$ (8)
Amortization of prior service (cost) credit					3						13
Defined Benefit Plan Accumulated Other Comprehensive Income And Regulatory Assets Before Tax	[12]				$ 1						$ (34)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase					5.00%						5.00%
Change in Assumptions for Defined Benefit Plans [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets									7.00%
Discount rate									4.04%
Change in Assumptions for Defined Benefit Plans [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected return on plan assets		6.58%
Discount rate									4.04%
Assets [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate									16.10%
Assets [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate									14.70%
[1]	Includes $13 million and $9 million related to CENG for the years ended December 31, 2016 and December 31, 2015.
[2]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[3]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[4]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[5]	Pepco's, DPL's and PHISCO's matching contributions include $1 million, $1 million and $1 million, respectively, of costs incurred prior to the closing of Exelon's merger with PHI on March 23, 2016, which is not included in Exelon's matching contributions for the year ended December 31, 2016.
[6]	FitzPatrick net benefit costs are included for the period after acquisition.
[7]	PHI net periodic benefit costs for the period prior to the merger are not included in the table above.
[8]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[9]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2016. Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively.
[10]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2017. Certain benefit plans used individual rates ranging from 3.49% - 3.65% and 3.57% - 3.68% for pension and other postretirement plans, respectively.
[11]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2015. Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively.
[12]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[13]	Not applicable to pension and other postretirement benefit plans that do not have plan asset
[14]	)The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2017. Certain benefit plans used individual rates ranging from 3.66%-4.11% and 4.00%-4.17% for pension and other postretirement plans, respectivel
[15]	The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2016. Certain benefit plans used individual rates ranging from 3.68%-4.14% and 4.32%-4.43% for pension and other postretirement plans, respectively.
[16]	The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015. Certain benefit plans used the individual rates ranging from 3.29%-3.82% and 3.99%-4.06% for pension and other postretirement plans, respectively.
[17]	Expected return on other postretirement benefit plan assets is pre-tax.

Retirement Benefits Retireme145

Retirement Benefits Retirement Benefits - Summary of Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Employer contributions						$ 13		$ 9
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement				$ 34		0	[1]
Net benefit obligation at beginning of year	[1]	$ 17,753		21,060		17,753
Service cost				387	[2]	354	[1],[3]	326
Interest cost				842	[2]	830	[1],[3]	710
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant				0		0	[1]
Actuarial loss (gain)				1,182		567	[1]
Plan amendments				9		(60)	[1]
Acquisitions/divestitures(b)	[4]			16		2,667	[1]
Defined Benefit Plan, Benefit Obligation, Benefits Paid				(1,125)		(1,051)	[1]
Net benefit obligation at end of year				22,337		21,060	[1]	17,753	[1]
Fair value of net plan assets at beginning of year	[1]	14,347		16,791		14,347
Actual return on plan assets				2,600		1,061	[1]
Employer contributions				341		347	[1]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant				0		0	[1]
Defined Benefit Plan, Plan Assets, Benefits Paid				(1,125)		(1,051)	[1]
Acquisitions/divestitures(b)	[4]			0		2,087	[1]
Defined Benefit Plan, Fair Value of Plan Assets				18,573		16,791	[1]	14,347	[1]
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year				2,490
Service cost		12				57
Interest cost		26				109
Actuarial loss (gain)		(30)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(2)
Net benefit obligation at end of year		2,496				2,490
Fair value of net plan assets at beginning of year				2,018
Employer contributions		4
Defined Benefit Plan, Plan Assets, Benefits Paid		(2)
Defined Benefit Plan, Fair Value of Plan Assets		2,020				2,018
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement				0		0	[1]
Net benefit obligation at beginning of year		3,938	[1]	4,457		3,938	[1]
Service cost				106	[2]	107	[1],[3]	119
Interest cost				182	[2]	185	[1],[3]	167
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant				53		54	[1]
Actuarial loss (gain)				350		(136)	[1]
Plan amendments				0		0	[1]
Acquisitions/divestitures(b)	[4]			17		589	[1]
Defined Benefit Plan, Benefit Obligation, Benefits Paid				(309)		(280)	[1]
Net benefit obligation at end of year				4,856		4,457		3,938	[1]
Fair value of net plan assets at beginning of year	[1]	2,293		2,578		2,293
Actual return on plan assets				346		128	[1]
Employer contributions				64		50	[1]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant				53		54	[1]
Defined Benefit Plan, Plan Assets, Benefits Paid				(309)		(280)	[1]
Acquisitions/divestitures(b)	[4]			0		333	[1]
Defined Benefit Plan, Fair Value of Plan Assets				2,732		2,578	[1]	$ 2,293	[1]
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Net benefit obligation at beginning of year				563
Service cost		1				7
Interest cost		6				24
Actuarial loss (gain)		(5)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(1)
Net benefit obligation at end of year		564				563
Fair value of net plan assets at beginning of year				$ 348
Employer contributions		1
Defined Benefit Plan, Plan Assets, Benefits Paid		(1)
Defined Benefit Plan, Fair Value of Plan Assets		$ 348				$ 348
[1]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[2]	FitzPatrick net benefit costs are included for the period after acquisition.
[3]	PHI net periodic benefit costs for the period prior to the merger are not included in the table above.
[4]	Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017. Effective March 23, 2016, Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans.

Retirement Benefits Retireme146

Retirement Benefits Retirement Benefits - Balance Sheet locations of Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	[1]
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	$ 28	$ 21
Pension obligations	3,736	4,248
Non-pension postretirement benefit obligations	0	0
Unfunded status (net benefit obligation less plan assets)	3,764	4,269
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	31	31
Pension obligations	0	0
Non-pension postretirement benefit obligations	2,093	1,848
Unfunded status (net benefit obligation less plan assets)	$ 2,124	$ 1,879
[1]	Effective March 23, 2016, Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.

Retirement Benefits Reitrement

Retirement Benefits Reitrement Benefits- Projected Benefit Obligations and Accumulated Benefit Obligations in Excess of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 22,337	$ 21,060
Fair value of net plan assets	18,573	16,791
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 21,153	$ 19,930

Retirement Benefits Retireme148

Retirement Benefits Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 1,182		$ 567	[1]
Service cost		387	[2]	354	[1],[3]	$ 326
Interest cost		842	[2]	830	[1],[3]	710
Expected return on assets		(1,196)	[2]	(1,141)	[3]	(1,026)
Prior service cost (credit)		1	[2]	14	[3]	13
Actuarial loss		607	[2]	554	[3]	571
Settlement and other charges(c)		3	[2],[4]	2	[3],[4]	2
Net periodic benefit cost		644	[2]	613	[3]	596
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ (30)
Service cost	12			57
Interest cost	26			109
Expected return on assets	30			140
Prior service cost (credit)	0			2
Actuarial loss	(14)			(65)
Net periodic benefit cost	22			93
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		350		(136)	[1]
Service cost		106	[2]	107	[1],[3]	119
Interest cost		182	[2]	185	[1],[3]	167
Expected return on assets		(162)	[2]	(162)	[3]	(151)
Prior service cost (credit)		(188)	[2]	(185)	[3]	(174)
Actuarial loss		61	[2]	63	[3]	80
Settlement and other charges(c)		0	[2],[4]	0	[3],[4]	0
Net periodic benefit cost		$ (1)	[2]	8	[3]	$ 41
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(5)
Service cost	1			7
Interest cost	6			24
Expected return on assets	5			22
Prior service cost (credit)	(3)			(13)
Actuarial loss	(2)			(8)
Net periodic benefit cost	$ 1			$ 4
[1]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[2]	FitzPatrick net benefit costs are included for the period after acquisition.
[3]	PHI net periodic benefit costs for the period prior to the merger are not included in the table above.
[4]	2016 amount includes an additional termination benefit for PHI.

Retirement Benefits Retireme149

Retirement Benefits Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets (Liabilities) related to Retirement Plans (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, amounts recognized in regulatory assets, before tax		$ 57
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss				$ (222)	$ 644	[1]	$ 476
Amortization of actuarial loss				(607)	(554)	[1]	(571)
Current year prior service cost (credit)				9	(60)	[1]	0
Amortization of prior service (cost) credit				(1)	(14)	[1]	(13)
Settlements				3	0	[1]	2
DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeAndRegulatoryAssetsAcqusition				0	994	[1]	0
Total recognized in AOCI and regulatory assets (liabilities)	[1]			(824)	1,010		(110)
Defined benefit plan, amounts recognized in OCI, before tax				(401)	51	[1]	(64)
Defined benefit plan, amounts recognized in regulatory assets, before tax				(423)	959	[1]	(46)
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss			$ 0		50
Amortization of actuarial loss			(14)		(65)
Amortization of prior service (cost) credit			0		(2)
Total recognized in AOCI and regulatory assets (liabilities)	[1]		(14)		(17)
Defined benefit plan, amounts recognized in OCI, before tax			(1)		(11)
Defined benefit plan, amounts recognized in regulatory assets, before tax			(13)		(6)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss				166	(101)	[1]	(194)
Amortization of actuarial loss				(61)	(63)	[1]	(80)
Current year prior service cost (credit)				0	0	[1]	(23)
Amortization of prior service (cost) credit				188	185	[1]	174
Settlements				0	0	[1]	0
DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeAndRegulatoryAssetsAcqusition				0	94	[1]	0
Total recognized in AOCI and regulatory assets (liabilities)	[1]			293	115		(123)
Defined benefit plan, amounts recognized in OCI, before tax				168	20	[1]	(63)
Defined benefit plan, amounts recognized in regulatory assets, before tax				$ 125	95	[1]	$ (60)
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss			0		(39)
Amortization of actuarial loss			(2)		(8)
Amortization of prior service (cost) credit			3		13
Total recognized in AOCI and regulatory assets (liabilities)	[1]		1		(34)
Defined benefit plan, amounts recognized in OCI, before tax			0		0
Defined benefit plan, amounts recognized in regulatory assets, before tax			$ 1		$ (34)
[1]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.

Retirement Benefits Retireme150

Retirement Benefits Retirement Benefits - Gross Accumulated Other Comprehensive Loss and Regulatory Assets (Liabilities) not Recognized as Components of Periodic Benefit Cost (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	[1]
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	$ (24)	$ (31)
Actuarial loss	7,556	8,387
Total	7,532	8,356
Benefits included in accumulated other comprehensive income	3,896	4,297
Benefits included in regulatory assets	3,636	4,059
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	(522)	(710)
Actuarial loss	829	724
Total	307	14
Benefits included in accumulated other comprehensive income	125	(42)
Benefits included in regulatory assets	$ 182	$ 56
[1]	Effective March 23, 2016, Exelon became the sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.

Retirement Benefits Retireme151

Retirement Benefits Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets expected to be Amortized as Components of Periodic Benefit Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	$ 2
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	640
Benefits included in accumulated other comprehensive income	642	[1]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	317
Pension Plan, Defined Benefit [Member] | Regulatory Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	325
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year	(186)
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year	66
Benefits included in accumulated other comprehensive income	(120)	[1]
Benefits included in regulatory assets	(55)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	$ (65)
[1]	Of the $642 million related to pension benefits at December 31, 2017, $317 million and $325 million are expected to be amortized from AOCI and regulatory assets in 2018, respectively. Of the $(120) million related to other postretirement benefits at December 31, 2017, $(65) million and $(55) million are expected to be amortized from AOCI and regulatory assets (liabilities) in 2018, respectively.

Retirement Benefits Retireme152

Retirement Benefits Retirement Benefits - Assumptions Used in Calculations (Details)		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Document Period End Date				Dec. 31, 2017
CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.66%		3.68%		3.29%
CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.11%		4.14%		3.82%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				4.04%	[1]	4.29%	[2]	3.94%	[3]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			7.00%	7.00%		7.00%	[4]	7.00%	[4]
Discount rate				3.62%	[5]	4.04%	[6]	4.29%	[7]
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.49%		3.66%		3.68%
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.65%		4.11%		4.14%
Pension Plan, Defined Benefit [Member] | Period One [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.25%
Pension Plan, Defined Benefit [Member] | Period One [Member] | CENG Legacy Benefit Plans [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.25%
Pension Plan, Defined Benefit [Member] | Period Two [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.75%
Pension Plan, Defined Benefit [Member] | Period Two [Member] | CENG Legacy Benefit Plans [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.75%
Pension Plan, Defined Benefit [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase						5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate						4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[8]	6.50%				6.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%				5.00%
Qualified Plan [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate						4.65%
Non-Qualified Pension Plan [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate						4.55%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Health care cost trend rate						5.50%		5.50%		6.00%
Ultimate health care cost trend rate										5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				4.04%	[1]	4.29%	[2]	3.92%	[3]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			6.60%	6.58%		6.71%	[4]	6.50%	[4]
Discount rate				3.61%	[5]	4.04%	[6]	4.29%	[7]
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.00%		4.32%		3.99%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.17%		4.43%		4.06%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.57%		4.00%		4.32%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.68%		4.17%		4.43%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Health care cost trend rate						5.40%		5.40%		5.50%
Ultimate health care cost trend rate										5.00%
DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYearAge				0.0633		0.0633		0.0667
Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase						5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.55%				4.15%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[8]	6.75%				6.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%				5.00%
Discount rate						4.55%
[1]	)The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2017. Certain benefit plans used individual rates ranging from 3.66%-4.11% and 4.00%-4.17% for pension and other postretirement plans, respectivel
[2]	The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2016. Certain benefit plans used individual rates ranging from 3.68%-4.14% and 4.32%-4.43% for pension and other postretirement plans, respectively.
[3]	The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015. Certain benefit plans used the individual rates ranging from 3.29%-3.82% and 3.99%-4.06% for pension and other postretirement plans, respectively.
[4]	Not applicable to pension and other postretirement benefit plans that do not have plan asset
[5]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2017. Certain benefit plans used individual rates ranging from 3.49% - 3.65% and 3.57% - 3.68% for pension and other postretirement plans, respectively.
[6]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2016. Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively.
[7]	The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2015. Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively.
[8]	Expected return on other postretirement benefit plan assets is pre-tax.

Retirement Benefits Retireme153

Retirement Benefits Retirement Benefits - Effects of One Percentage Point Change in Assumed Health Care Cost Trend Rates (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Retirement Benefits [Abstract]
Effect of a one percentage point increase in assumed healthcare cost trend on 2010 total service and interest cost components	$ 9
Effect of a one percentage point increase in assumed healthcare cost trend on postretirement benefit obligation at December 31, 2010	125
Effect of a one percentage point decrease in assumed healthcare cost trend on 2010 total service and interest cost components	(8)
Effect of a one percentage point decrease in assumed healthcare cost trend on postretirement benefit obligation at December 31, 2010	$ (113)

Retirement Benefits Retireme154

Retirement Benefits Retirement Benefits - Contributions made to Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended	12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					$ 405		$ 397		$ 502
Expected qualified pension plan contributions	[1]				301
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				30
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				42
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions	[1]				36
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				7
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				1
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[4]				21		25		36
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					148		152		245
Expected qualified pension plan contributions	[1]				119
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				11
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				13
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					41		38		150
Expected qualified pension plan contributions	[1]				38
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				3
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					24		30		40
Expected qualified pension plan contributions	[1]				17
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				0
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					53		49		17
Expected qualified pension plan contributions	[1]				41
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				16
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions	[1]				50
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				8
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				9
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions	[1]				40
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				5
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				1
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				$ 86	99
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		$ 4							21
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					72		32		14
Expected qualified pension plan contributions	[1]				4
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				8
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					2		22		0
Expected qualified pension plan contributions	[1]				0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				0
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					20		17		2
Expected qualified pension plan contributions	[1]				6
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	[2]				0
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year	[3]				0
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				341		347		462
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1,166
Pension Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[4],[5]				38		39		47
Pension Plan, Defined Benefit [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				137		140		231
Pension Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				36		33		143
Pension Plan, Defined Benefit [Member] | PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				24		30		40
Pension Plan, Defined Benefit [Member] | Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				39		31		1
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		4	[4]		5	[5],[6]	17	[5],[6]	0	[5],[6]
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				74	67
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		4					0
Pension Plan, Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					4	[4]	6		5
Pension Plan, Defined Benefit [Member] | Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				62		24		0
Pension Plan, Defined Benefit [Member] | Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				0		22		0
Pension Plan, Defined Benefit [Member] | Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[5]				0		15		0
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					64		50		40
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					256
Other Postretirement Benefit Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[4]				2		3		3
Other Postretirement Benefit Plan, Defined Benefit [Member] | Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					11		12		14
Other Postretirement Benefit Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					5		5		7
Other Postretirement Benefit Plan, Defined Benefit [Member] | PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					0		0		0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					14		18		16
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[6]				0		2		0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				$ 12	32
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		$ 0					5
Other Postretirement Benefit Plan, Defined Benefit [Member] | Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					10		8		2
Other Postretirement Benefit Plan, Defined Benefit [Member] | Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					2		0		0
Other Postretirement Benefit Plan, Defined Benefit [Member] | Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					$ 20		$ 2		$ 3
[1]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[2]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[3]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051
[4]	Includes $4 million, $6 million, and $5 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2017, 2016, and 2015, respectively.
[5]	Exelon's and Generation's pension contributions include $21 million, $25 million and $36 million related to the legacy CENG plans that was funded by CENG as provided in an Employee Matters Agreement (EMA) between Exelon and CENG for the years ended December 31, 2017, 2016 and 2015, respectively.
[6]	PHISCO’s pension contributions for the year ended December 31, 2016 include $4 million of contributions made prior to the closing of Exelon’s merger with PHI on March 23, 2016.

Retirement Benefits Retireme155

Retirement Benefits Retirement Benefits - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2017USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	$ 30	[1]
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	1,166
2,019	1,165
2,020	1,210
2,021	1,236
2,022	1,265
2022 through 2026	6,671
Total estimated future benefit payments through 2027	12,713
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	256
2,019	262
2,020	270
2,021	276
2,022	284
2022 through 2026	1,509
Total estimated future benefit payments through 2027	$ 2,857
[1]	Qualified Pension PlansNon-Qualified Pension PlansOtherPostretirementBenefitsExelon$301$30$42Generation1191113ComEd3823PECO171—BGE41116BSC3671PHI5089Pepco428DPL—1—ACE6——PHISCO4051

Retirement Benefits Retireme156

Retirement Benefits Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense				$ 643		$ 621		$ 637
Corporate, Non-Segment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	[1]			53		48		57
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense	[2]			227		218		269
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense				176		166		206
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense				29		33		39
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense				64		68		66
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense			$ 94
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		$ 88				23		97
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		9		43	[3],[4]	47	[3],[4]	37	[3],[4]
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		7		25	[3]	31	[3]	30	[3]
Delmarva Power and Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		4		13	[3]	18	[3]	15	[3]
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense		$ 3		$ 13	[3]	$ 15	[3]	$ 15	[3]
[1]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE, PHI, Pepco, DPL or ACE amounts above.
[2]	FitzPatrick net benefit costs are included for the period after acquisition.
[3]	Pepco's, DPL's, ACE's and PHISCO's pension and postretirement benefit costs for the year ended December 31, 2016 include $7 million, $4 million, $3 million and $9 million, respectively, of costs incurred prior to the closing of Exelon’s merger with PHI on March 23, 2016.
[4]	These amounts represent amounts billed to Pepco, DPL and ACE through intercompany allocations. These amounts are not included in Pepco, DPL or ACE amounts above.

Retirement Benefits Retireme157

Retirement Benefits Retirement Benefits - Pension and Other Postretirement Benefit Plan Target Asset Allocations (Details)		Dec. 31, 2017	Dec. 31, 2016
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		100.00%	100.00%
Pension Plan, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		35.00%
Percentage of Plan Assets		35.00%	33.00%
Pension Plan, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		38.00%
Percentage of Plan Assets		39.00%	39.00%
Pension Plan, Defined Benefit [Member] | Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	27.00%
Percentage of Plan Assets	[1]	26.00%	28.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of Plan Assets		100.00%	100.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		46.00%
Percentage of Plan Assets		47.00%	47.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage		28.00%
Percentage of Plan Assets		28.00%	29.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Target asset allocation percentage	[1]	26.00%
Percentage of Plan Assets	[1]	25.00%	24.00%
[1]	Alternative investments include private equity, hedge funds, real estate, and private credit.

Retirement Benefits Retireme158

Retirement Benefits Retirement Benefits - Fair Value Measurements of Pension and Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Fair Value, Net		$ 6		$ 1
Derivative, Notional Amount		3,606		2,918
Net assets pending transactions excluded		2		(28)
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2],[3]	21,303	[1]	19,397	[4]
Alternative Investment, Fair Value Disclosure		3,534		3,113
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2],[3]	6,090	[1]	5,313	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2],[3]	4,913	[1]	4,535	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2],[3]	234	[1]	208	[4]
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		18,573		16,791	[5]	$ 14,347	[5]
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		234		208		167
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		232		206		165
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	18,575	[1]	16,819	[4]
Alternative Investment, Fair Value Disclosure	[3]	8,440	[1]	7,897	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	585	[1]	325	[4]
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	6,644	[1]	5,681	[4]
Alternative Investment, Fair Value Disclosure	[3],[6]	3,077	[1]	2,535	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	1,309	[1]	1,200	[4]
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	64	[1]	64	[4]
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	4,163	[1]	3,847	[4]
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	1,203	[1]	1,088	[4]
Alternative Investment, Fair Value Disclosure	[3],[6]	756	[1]	748	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	6,739	[1]	6,199	[4]
Alternative Investment, Fair Value Disclosure	[3]	756	[1]	748	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	1,034	[1]	991	[4]
Alternative Investment, Fair Value Disclosure	[3]	1,034	[1]	991	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	1,770	[1]	1,962	[4]
Alternative Investment, Fair Value Disclosure	[3]	1,770	[1]	1,962	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	884	[1]	828	[4]
Alternative Investment, Fair Value Disclosure	[3]	884	[1]	828	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	919	[1]	833	[4]
Alternative Investment, Fair Value Disclosure	[3]	919	[1]	833	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	5,300	[1]	4,477	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	585	[1]	325	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	3,565	[1]	3,144	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	1,150	[1]	1,008	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	1,150	[1]	1,008	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	4,601	[1]	4,237	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	159	[1]	192	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	64	[1]	64	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	3,931	[1]	3,641	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Debt Obligations [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	447	[1]	340	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	4,601	[1]	4,237	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	234	[1]	208	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0	[4]
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3],[6]	2	[1]	2	[4]
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Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Real Estate Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
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Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	$ 0	[1]	$ 0	[4]
[1]	Effective March 31, 2017, Exelon became sponsor of FitzPatrick's defined benefit pension and other postretirement benefit plans, and assumed FitzPatrick's benefit plan obligations.
[2]	Excludes net assets of $2 million and net liabilities of $28 million at December 31, 2017 and 2016, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases.
[3]	See Note 11—Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy.
[4]	Effective March 23, 2016, Exelon became sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.
[5]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[6]	Includes derivative instruments of $6 million and $1 million, which have a total notional amount of $3,606 million and $2,918 million at December 31, 2017 and 2016, respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company’s exposure to credit or market loss.

Retirement Benefits Retireme159

Retirement Benefits Retirement Benefits - Reconciliation of Level 3 Assets and Liabilities measured at Fair Value for Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	[1]	$ 16,791		$ 14,347
Defined Benefit Plan, Fair Value of Plan Assets		18,573		16,791	[1]
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year		208		167
Relating to assets still held at the reporting date		11		(2)
Defined Benefit Plan Purchases		31		69
Defined Benefit Plan Sales		16		14
Settlements	[2]	0		(12)
Defined Benefit Plan, Fair Value of Plan Assets		234		208
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year		206		165
Relating to assets still held at the reporting date		11		(2)
Defined Benefit Plan Purchases		31		69
Defined Benefit Plan Sales		16		14
Settlements	[2]	0		(12)
Defined Benefit Plan, Fair Value of Plan Assets		232		206
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Security Individually Held [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year		2		2
Relating to assets still held at the reporting date		0		0
Defined Benefit Plan Purchases		0		0
Defined Benefit Plan Sales		0		0
Settlements	[2]	0		0
Defined Benefit Plan, Fair Value of Plan Assets		2		2
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment, Fair Value Disclosure		3,534		3,113
Fair value of net plan assets at beginning of year	[3],[4],[5]	19,397
Defined Benefit Plan, Fair Value of Plan Assets	[4],[5]	21,303	[6]	19,397	[3]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	[3],[4],[5]	208
Defined Benefit Plan, Fair Value of Plan Assets	[4],[5]	234	[6]	208	[3]
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment, Fair Value Disclosure	[5]	8,440	[6]	7,897	[3]
Fair value of net plan assets at beginning of year	[3],[5]	16,819
Defined Benefit Plan, Fair Value of Plan Assets	[5]	18,575	[6]	16,819	[3]
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment, Fair Value Disclosure	[5]	756	[6]	748	[3]
Fair value of net plan assets at beginning of year	[3],[5]	6,199
Defined Benefit Plan, Fair Value of Plan Assets	[5]	6,739	[6]	6,199	[3]
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	[3],[5]	208
Defined Benefit Plan, Fair Value of Plan Assets	[5]	234	[6]	208	[3]
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	[3],[5]	206
Defined Benefit Plan, Fair Value of Plan Assets	[5]	$ 232	[6]	$ 206	[3]
[1]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[2]	Represents cash settlements only.
[3]	Effective March 23, 2016, Exelon became sponsor of PHI's defined benefit pension and other postretirement benefit plans, and assumed PHI's benefit plan obligations and related assets.
[4]	Excludes net assets of $2 million and net liabilities of $28 million at December 31, 2017 and 2016, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables related to pending securities sales, interest and dividends receivable, and payables related to pending securities purchases.
[5]	See Note 11—Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy.
[6]	Effective March 31, 2017, Exelon became sponsor of FitzPatrick's defined benefit pension and other postretirement benefit plans, and assumed FitzPatrick's benefit plan obligations.

Retirement Benefits Retireme160

Retirement Benefits Retirement Benefits - Summary of Defined Contribution Savings Plan (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[1]			$ 128		$ 164		$ 148
Employer contributions						13		9
Corporate, Non-Segment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[2]			9		19		11
Exelon Generation Co L L C [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[1]			55		79		80
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				31		34		32
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				10		10		11
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				10		12		14
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		$ 1		6	[3],[4]	6	[3],[4]	6	[3],[4]
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions			$ 10	13
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		3				14
Potomac Electric Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		1		3	[3]	3	[3]	3	[3]
Delmarva Power and Light Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		$ 1		2	[3]	2	[3]	2	[3]
Atlantic City Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[3]			$ 2		$ 2		$ 2
[1]	Includes $13 million and $9 million related to CENG for the years ended December 31, 2016 and December 31, 2015.
[2]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These costs are not included in the Generation, ComEd, PECO, BGE, PHI, Pepco, DPL or ACE amounts above.
[3]	Pepco's, DPL's and PHISCO's matching contributions include $1 million, $1 million and $1 million, respectively, of costs incurred prior to the closing of Exelon's merger with PHI on March 23, 2016, which is not included in Exelon's matching contributions for the year ended December 31, 2016.
[4]	These amounts primarily represent amounts billed to Pepco, DPL, and ACE through intercompany allocations. These amounts are not included in Pepco, DPL or ACE amounts above.

Severance Severance - Ongoing S

Severance Severance - Ongoing Severance Plans (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 14	$ 19
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	6	13
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	3	3
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	1
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	4	1
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	0
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 1	$ 0
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016

Severance Severance - Cost Mana

Severance Severance - Cost Management Program-Related (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 14		$ 19
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		6		23
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	6		13
Exelon Generation Co L L C [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		9	[2]	18	[3]
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(4)	[2]	7	[3]
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	3		3
Commonwealth Edison Co [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(1)	[2]	3	[3]
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(2)	[2]	3	[3]
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1		1
PECO Energy Co [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(1)	[2]	1	[3]
PECO Energy Co [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(1)	[2]	1	[3]
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0		1
Baltimore Gas and Electric Company [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		(1)	[2]	1	[3]
Baltimore Gas and Electric Company [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ (1)	[2]	$ 1	[3]
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016
[2]	The amounts for Generation, ComEd, PECO, and BGE include $(4) million, $(2) million, $(1) million, and $(1) million, respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017.
[3]	The amounts above for Generation, ComEd, PECO and BGE include $7 million, $3 million, $1 million, and $1 million, respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2016.

Severance Severance - PHI Merge

Severance Severance - PHI Merger (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 14	$ 19
PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			57
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	6	13
Exelon Generation Co L L C [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		9
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			8
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	3	3
Commonwealth Edison Co [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		2
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			2
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	1
PECO Energy Co [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		1
PECO Energy Co [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Baltimore Gas and Electric Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		1
Baltimore Gas and Electric Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	4	1
Pepco Holdings LLC [Member] | Successor [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		44
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	0
Potomac Electric Power Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		21
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			20
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Delmarva Power and Light Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		13
Delmarva Power and Light Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			12
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 1	0
Atlantic City Electric Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		10
Atlantic City Electric Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			$ 10
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016
[2]	The amounts above for Generation, ComEd, PECO, BGE, Pepco, DPL, and ACE include $8 million, $2 million, $1 million, $1 million, $20 million, $12 million and $10 million, respectively, for amounts billed by BSC and/or PHISCO through intercompany allocations for the year ended December 31, 2016.

Severance Severance - Liabiliti

Severance Severance - Liabilities Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 88	$ 35
Severance Costs		14	19
Payments		(29)	(46)
Ending Balance		94	88
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	35	99
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		36	23
Severance Costs	[2]	6	13
Payments		(9)	(9)
Ending Balance		58	36
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	31	22
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		3	3
Severance Costs	[2]	3	3
Payments		(2)	(2)
Ending Balance		3	3
Commonwealth Edison Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	2
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	1
Payments		0	0
Ending Balance		0	0
PECO Energy Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	1
Severance Costs	[2]	0	1
Payments		0	(1)
Ending Balance		0	0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		29	0
Severance Costs	[2]	4	1
Payments		(12)	(27)
Ending Balance		20	29
Pepco Holdings LLC [Member] | Successor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	3	56
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	2	0
Payments		0	(1)
Ending Balance		0	0
Potomac Electric Power Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	0
Payments		0	(1)
Ending Balance		0	0
Delmarva Power and Light Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	0
Payments		0	0
Ending Balance		0	0
Atlantic City Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 0	$ 0
[1]	Includes salary continuance and health and welfare severance benefits.
[2]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016

Severance Severance - Narrative

Severance Severance - Narrative (Details) - USD ($) $ in Millions		1 Months Ended		12 Months Ended
		Jun. 30, 2017	Aug. 31, 2015	Dec. 31, 2017		Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs				$ 14		$ 19
Effect on Future Earnings, Amount			$ 400	250
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				6		23
Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 17
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			6		13
Exelon Generation Co L L C [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				9	[2]	18	[3]
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				$ (4)	[2]	$ 7	[3]
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016
[2]	The amounts for Generation, ComEd, PECO, and BGE include $(4) million, $(2) million, $(1) million, and $(1) million, respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017.
[3]	The amounts above for Generation, ComEd, PECO and BGE include $7 million, $3 million, $1 million, and $1 million, respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2016.

Mezzanine Equity Contingent166

Mezzanine Equity Contingently Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	18,000
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	$ (407)	$ (239)
Payments to Acquire Businesses, Gross	208	6,934	$ 40
Preferred Stock [Member]
Noncontrolling Interest [Line Items]
Payments to Acquire Businesses, Gross	180
Pepco Holdings LLC [Member]
Noncontrolling Interest [Line Items]
Derivative Asset, Not Subject to Master Netting Arrangement	18
Exelon Generation Co L L C [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	(407)	(239)	(1)
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		0	28
Temporary Equity, Accretion to Redemption Value		129
Temporary Equity, Other Changes		(157)
Payments to Acquire Businesses, Gross	$ 208	$ 293	$ 40

Shareholders' Equity Schedule

Shareholders' Equity Schedule of Common Stock Authorized and Outstanding (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	963,335,888	924,035,059
Common Stock [Member] | Commonwealth Edison Co [Member]
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 12.50	$ 12.50
Common stock, shares authorized	250,000,000	250,000,000
Common Stock, Shares, Outstanding	127,021,246	127,017,157
Common Stock [Member] | PECO Energy Co [Member]
Class of Stock [Line Items]
Common stock, shares authorized	500,000,000	500,000,000
Common Stock, Shares, Outstanding	170,478,507	170,478,507
Common Stock [Member] | Baltimore Gas and Electric Company [Member]
Class of Stock [Line Items]
Common stock, shares authorized	1,500	1,500
Common Stock, Shares, Outstanding	1,000	1,000
Common Stock [Member] | Potomac Electric Power Company [Member]
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common Stock, Shares, Outstanding	100	100
Common Stock [Member] | Delmarva Power and Light Company [Member]
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 2.25	$ 2.25
Common stock, shares authorized	1,000	1,000
Common Stock, Shares, Outstanding	1,000	1,000
Common Stock [Member] | Atlantic City Electric Company [Member]
Class of Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 3	$ 3
Common stock, shares authorized	25,000,000	25,000,000
Common Stock, Shares, Outstanding	8,546,017	8,546,017

Shareholders' Equity Shareholde

Shareholders' Equity Shareholder Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jun. 01, 2017	Sep. 19, 2016	Sep. 18, 2016	Jul. 03, 2016	Jul. 03, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2016	Jul. 30, 2015	Jun. 30, 2014
Schedule of Capitalization, Equity [Line Items]
Temporary Equity, Share Subscriptions										57,500,000	57,500,000
Sale of Stock, Price Per Share										$ 32.48
Treasury Stock, Number of Shares Held						2,000,000	35,000,000
Treasury stock, at cost						$ 123	$ 2,327
Stock Repurchased During Period, Value							$ 0	$ 0
Stock Repurchased During Period, Shares							0	0
Stock Redeemed or Called During Period, Value							$ (193)
Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						100,000,000	100,000,000
Preferred Stock, Shares Outstanding						0	0
Equity units issued [Member]
Schedule of Capitalization, Equity [Line Items]
Stock Issued During Period, Shares, Treasury Stock Reissued	33,000,000
Minimum [Member]
Schedule of Capitalization, Equity [Line Items]
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value										$ 1,870
Commonwealth Edison Co [Member]
Schedule of Capitalization, Equity [Line Items]
Class of Warrant or Right, Outstanding						60,584	72,859
Commonwealth Edison Co [Member] | Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Common Stock Shares Reserved For Warrant Conversion						20,195	24,286
Commonwealth Edison Co [Member] | Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						850,000	850,000
Preferred Stock, Shares Outstanding						0	0
Commonwealth Edison Co [Member] | Cumulative Preferred Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Shares Authorized						6,810,451	6,810,451
Preferred Stock, Shares Outstanding						0	0
Baltimore Gas and Electric Company [Member]
Schedule of Capitalization, Equity [Line Items]
Preferred Stock, Value, Outstanding								$ 190
Preferred Stock, Redemption Price Per Share								$ 100
Stock Redeemed or Called During Period, Shares		400,000	500,000	600,000	400,000
Preferred Stock, Dividend Rate, Percentage		6.70%	6.97%	6.99%	7.125%
Stock Redeemed or Called During Period, Value			$ 90		$ 100		$ (190)
Junior Subordinated Debt [Member]
Schedule of Capitalization, Equity [Line Items]
Shares Issued, Price Per Share									$ 35
Junior Subordinated Notes											$ 1,150
Equity units issued											23,000,000
Stock Issued During Period, Shares, Treasury Stock Reissued						33,000,000

Stock-Based Compensation Pla169

Stock-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Common Stock Narrative Information [Line Items]
Obligations of outstanding restricted stock not settled		$ 108		$ 101
Settlement of restricted stock		88		68	$ 75
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		41
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Deferred Credits And Other Liabilities	[1]	$ 100		$ 52
Pepco Holdings LLC [Member]
Common Stock Narrative Information [Line Items]
Settlement of restricted stock					$ 6
Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Granted, Weighted Average Grant Date Fair Value (in usd per share)		$ 35	[2]	$ 28.85	$ 35.88
Percentage to be settled as common stock		50.00%
Percentage to be settled as cash		50.00%
Percentage to be settled as cash if ownership requirements are met		100.00%
Performance Shares [Member] | Pepco Holdings LLC [Member]
Common Stock Narrative Information [Line Items]
Granted, Weighted Average Grant Date Fair Value (in usd per share)					26.10
Employee Stock Option [Member]
Common Stock Narrative Information [Line Items]
Requisite service period		4 years
Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		1 year 8 months 12 days
Restricted Stock Units (RSUs) [Member]
Common Stock Narrative Information [Line Items]
Granted, Weighted Average Grant Date Fair Value (in usd per share)		$ 34.98		$ 28.14	36.55
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 51
Restricted Stock Units (RSUs) [Member] | Pepco Holdings LLC [Member]
Common Stock Narrative Information [Line Items]
Granted, Weighted Average Grant Date Fair Value (in usd per share)					$ 27.40
Performance based RSU [Member] | Pepco Holdings LLC [Member]
Common Stock Narrative Information [Line Items]
Settlement of restricted stock					$ 15
Granted, Weighted Average Grant Date Fair Value (in usd per share)					$ 26.08
Minimum [Member] | Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Requisite service period		3 years
Maximum [Member] | Restricted Stock [Member]
Common Stock Narrative Information [Line Items]
Requisite service period		5 years
LTIP [Member]
Common Stock Narrative Information [Line Items]
Shares authorized		13
[1]	Represents the long-term liability related to performance share awards expected to be settled in cash.
[2]	(a)As of December 31, 2017, $41 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.5 years.

Stock-Based Compensation Pla170

Stock-Based Compensation Plans - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 191	$ 175	[1]	$ 119
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense			(18)		(3)
Allocated Share-based Compensation Expense, Net of Tax		117	107	[1]	73
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		107	93	[1]	41
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		(29)	(18)		(18)
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		77	75	[1]	71
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		(35)	(27)		(30)
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0	0	[1]	1
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		7	7	[1]	6
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		$ (74)	$ (68)	[1]	(46)
Predecessor [Member] | Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 3				13
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	(1)				(5)
Allocated Share-based Compensation Expense, Net of Tax	2				8
Predecessor [Member] | Pepco Holdings LLC [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	1				5
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	0				5
Predecessor [Member] | Pepco Holdings LLC [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	2				7
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	0				2
Predecessor [Member] | Pepco Holdings LLC [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 0				$ 1
[1]	(a)2016 amounts include expense related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016.

Stock-Based Compensation Pla171

Stock-Based Compensation Plans - Schedule of Pre-Tax Stock-based Compensation Expense (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			$ 191	$ 175	[1]	$ 119
Exelon Generation Co L L C [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			88	78		64
Commonwealth Edison Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			7	8		6
PECO Energy Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			3	3		3
Baltimore Gas and Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			1	1		3
Pepco Holdings LLC [Member] | Predecessor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 3				13
Corporate, Non-Segment [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	[2]		88	81		43
Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	[2],[3]		$ 4			$ 0
Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	[2],[3]			$ 4
[1]	(a)2016 amounts include expense related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016.
[2]	These amounts primarily represent amounts billed to Exelon’s subsidiaries through intercompany allocations. These amounts are not included in the Generation, ComEd, PECO, BGE or PHI amounts above.
[3]	's stock-based compensation expense for the years ended December 31, 2017 and 2016 was not material. (c)

Stock-Based Compensation Pla172

Stock-Based Compensation Plans - Components of Tax Benefits from Stock-based Compensation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation			$ (18)	$ (3)
Restricted Stock Units (RSUs) [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation		$ (35)	(27)	(30)
Performance Shares [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation		$ (29)	$ (18)	(18)
Pepco Holdings LLC [Member] | Predecessor [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	$ (1)			(5)
Pepco Holdings LLC [Member] | Predecessor [Member] | Restricted Stock Units (RSUs) [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	0			2
Pepco Holdings LLC [Member] | Predecessor [Member] | Performance Shares [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	$ 0			$ 5

Stock-Based Compensation Pla173

Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
December 31, 2016		12,531,591
Options exercised		(3,093,156)
Options forfeited		0
Options expired		(2,714,824)
December 31, 2017		6,723,611	12,531,591
Weighted Average Exercise Price (in usd per share)		$ 47.69	$ 46.23
Options Exercised, Weighted Average Exercise Price (in usd per share)		34.69
Options Forfeited, Weighted Average Exercise Price (in usd per share)		0
Options Expired, Weighted Average Exercise Price (in usd per share)		$ 55.78
Shares Outstanding, Weighted Average Remaining Contractual Life		2 years 7 months 23 days	3 years 6 months
Exercisable at December 31, 2017	[1]	6,723,611
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	[1]	$ 47.69
Shares Exercisable, Weighted Average Remaining Contractual Life	[1]	2 years 7 months 23 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	[1]	$ 7	$ 13
Shares Exercisable, Aggregate Intrinsic Value		$ 7
[1]	Includes stock options issued to retirement eligible employees.

Stock-Based Compensation Pla174

Stock-Based Compensation Plans - Summary of Information of Stock Options Exercised (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock [Abstract]
Aggregate value	[1]	$ 15	$ 11	$ 0
Cash received for exercise price		$ 107	$ 19	$ 0
[1]	The difference between the market value on the date of exercise and the option exercise price.

Stock-Based Compensation Pla175

Stock-Based Compensation Plans - Summary of Nonvested Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1],[2]	3,824,416
Granted		2,266,199
Vested		(1,736,965)
Forfeited		(92,938)
Undistributed vested awards	[3]	(871,209)
Ending Balance	[2]	3,389,503	3,824,416	[1]
Nonvested, Weighted Average Exercise Price (in usd per share)	[1],[2]	$ 30.49
Granted, Weighted Average Grant Date Fair Value (in usd per share)		34.98	$ 28.14		$ 36.55
Vested, Weighted Average Exercise Price (in usd per share)		30.98
Forfeited, Weighted Average Exercise Price (in usd per share)		33.12
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[3]	34.09
Nonvested, Weighted Average Exercise Price (in usd per share)	[2]	$ 32.24	$ 30.49	[1]
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		1,488,383	1,319,372
Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted, Weighted Average Grant Date Fair Value (in usd per share)					$ 27.40
[1]	(c)2016 amounts include activity related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016.
[2]	Excludes 1,488,383 and 1,319,372 of restricted stock units issued to retirement-eligible employees as of December 31, 2017 and 2016, respectively, as they are fully vested.
[3]	Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2017.

Stock-Based Compensation Pla176

Stock-Based Compensation Plans - Summary of Nonvested Performance Share Awards Activity (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 41
Weighted Average Period Non Vested Performance Share Awards Are Expected To Be Recognized Over		1 year 6 months
Fair Value Of Settled Performance Share Awards		$ 72	[1]	$ 45		$ 46
Performance Share Awards Obligations Settled In Cash		$ 56	[1]	$ 28		$ 29
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[2],[3]	3,116,261
Granted		1,632,186
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)		545,793
Vested		(1,111,751)
Forfeited		(18,034)
Undistributed vested awards	[4]	(1,207,489)
Ending Balance	[3]	2,956,966		3,116,261	[2]
Nonvested, Weighted Average Exercise Price (in usd per share)	[3]	$ 32.65		$ 30.77	[2]
Granted, Weighted Average Grant Date Fair Value (in usd per share)		35	[1]	$ 28.85		$ 35.88
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Change in Performance, Weighted Average Grant Date Fair Value		30.97
Vested, Weighted Average Exercise Price (in usd per share)		29.11
Forfeited, Weighted Average Exercise Price (in usd per share)		33.74
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[4]	$ 33.46
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		2,723,440		2,443,409
Performance Shares [Member] | Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted, Weighted Average Grant Date Fair Value (in usd per share)						$ 26.10
[1]	(a)As of December 31, 2017, $41 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.5 years.
[2]	(c)2016 amounts include activity related to stock-based compensation granted to eligible PHI employees since the merger date of March 23, 2016.
[3]	Excludes 2,723,440 and 2,443,409 of performance share awards issued to retirement-eligible employees as of December 31, 2017 and 2016, respectively, as they are fully vested.
[4]	Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2017.

Stock-Based Compensation Pla177

Stock-Based Compensation Plans - Balance Sheet Classification of Obligations related to Outstanding Performance Share Awards Not Yet Settled (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Current Liabilities	[1]	$ 57	$ 49
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Deferred Credits And Other Liabilities	[2]	100	52
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Common Stock		26	40
Total Balance Sheet Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled		$ 183	$ 141
[1]	Represents the current liability related to performance share awards expected to be settled in cash.
[2]	Represents the long-term liability related to performance share awards expected to be settled in cash.

Earnings Per Share Earnings 178

Earnings Per Share Earnings Per Share - Schedule of Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 1,871	$ 824	$ 80	$ 995	$ 204	$ 490	$ 267	$ 173	$ 3,770	$ 1,134	$ 2,269
Weighted average common shares outstanding — basic	964	962	934	928	925	925	924	923	947	924	890
Assumed exercise and/or distributions of stock-based awards									2	3	3
Weighted average common shares outstanding — diluted	967	965	936	930	928	927	926	925	949	927	893

Earnings Per Share Earnings 179

Earnings Per Share Earnings Per Share - Narrative (Details) - shares shares in Millions	Jun. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity units issued [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock Issued During Period, Shares, Treasury Stock Reissued	33
Pepco Holdings [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger)		0	0	3
Employee Stock Option [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stock options not included in the calculation of diluted common shares outstanding (less than 1 million related to PHI merger)		8	12	16

Changes in Accumulated Other180

Changes in Accumulated Other Comprehensive Income Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		$ 27,294				$ 27,612		$ 27,294		$ 24,133
Amounts reclassified from AOCI	[1]					144		150
Other comprehensive income (loss)						171		(36)		60
Ending Balance				$ 27,612		32,132		27,612		27,294
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	[1]					4		13
Other comprehensive income (loss)						15		9		(27)
Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(19)				(17)		(19)
OCI before reclassifications	[2]					(1)		(6)
Amounts reclassified from AOCI	[2],[3]					4		8
Other comprehensive income (loss)	[2]					3		2
Ending Balance	[2]			(17)		(14)		(17)		(19)
Gains and (Losses) on Cash Flow Hedges | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(21)				(19)		(21)
OCI before reclassifications	[2]					(1)		(6)
Amounts reclassified from AOCI	[2],[3]					4		8
Other comprehensive income (loss)	[2]					3		2
Ending Balance	[2]			(19)		(16)		(19)		(21)
Gains and (Losses) on Cash Flow Hedges | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0				0		0
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			0		0		0		0
Gains and (Losses) on Cash Flow Hedges | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(8)		(8)	[4]			(8)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	(8)	[4]							(8)
Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	3				4		3
OCI before reclassifications	[2]					6		1
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		1
Ending Balance	[2]			4		10		4		3
Unrealized Gains and (losses) on Marketable Securities | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	1				2		1
OCI before reclassifications	[2]					1		1
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					1		1
Ending Balance	[2]			2		3		2		1
Unrealized Gains and (losses) on Marketable Securities | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	1				1		1
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			1		1		1		1
Unrealized Gains and (losses) on Marketable Securities | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0		0	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							0
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(2,565)				(2,610)		(2,565)
OCI before reclassifications	[2]					11		(182)
Amounts reclassified from AOCI	[1],[2],[3]					140		137
Other comprehensive income (loss)	[2]					151		(45)
Ending Balance	[2]			(2,610)		(2,459)		(2,610)		(2,565)
Pension and Non-Pension Postretirement Benefit Plan Items | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0				0		0
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[1],[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			0		0		0		0
Pension and Non-Pension Postretirement Benefit Plan Items | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0				0		0
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			0		0		0		0
Pension and Non-Pension Postretirement Benefit Plan Items | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(28)		(27)	[4]			(28)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	1
Other comprehensive income (loss)	[2]	1
Ending Balance	[2]	(27)	[4]							(28)
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(40)				(30)		(40)
OCI before reclassifications	[2]					7		5
Amounts reclassified from AOCI	[2],[3]					0		5
Other comprehensive income (loss)	[2]					7		10
Ending Balance	[2]			(30)		(23)		(30)		(40)
Foreign Currency Items | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(40)				(30)		(40)
OCI before reclassifications	[2]					7		5
Amounts reclassified from AOCI	[2],[3]					0		5
Other comprehensive income (loss)	[2]					7		10
Ending Balance	[2]			(30)		(23)		(30)		(40)
Foreign Currency Items | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0				0		0
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			0		0		0		0
Foreign Currency Items | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0		0	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							0
AOCI of Equity Investments
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(3)				(7)		(3)
OCI before reclassifications	[2]					6		(4)
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		(4)
Ending Balance	[2]			(7)		(1)		(7)		(3)
AOCI of Equity Investments | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(3)				(7)		(3)
OCI before reclassifications	[2]					6		(4)
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					6		(4)
Ending Balance	[2]			(7)		(1)		(7)		(3)
AOCI of Equity Investments | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0				0		0
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			0		0		0		0
AOCI of Equity Investments | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	0		0	[4]			0
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	0
Other comprehensive income (loss)	[2]	0
Ending Balance	[2]	0	[4]							0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(2,624)	[2]			(2,660)	[2]	(2,624)	[2]	(2,684)
OCI before reclassifications	[2]					29		(186)
Amounts reclassified from AOCI	[2],[3]					144		150
Other comprehensive income (loss)						173	[2]	(36)	[2]	60
Ending Balance	[2]			(2,660)		(2,487)		(2,660)		(2,624)
Total | Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(63)				(54)		(63)
OCI before reclassifications	[2]					13		(4)
Amounts reclassified from AOCI	[2],[3]					4		13
Other comprehensive income (loss)						17	[2]	9	[2]	(27)
Ending Balance	[2]			(54)		(37)		(54)		(63)
Total | PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	1				1		1
OCI before reclassifications	[2]					0		0
Amounts reclassified from AOCI	[2],[3]					0		0
Other comprehensive income (loss)	[2]					0		0
Ending Balance	[2]			1		$ 1		1		1
Total | PEPCO Holdings Inc [Member] | Predecessor [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(36)		$ (35)	[4]			$ (36)
OCI before reclassifications	[2]	0
Amounts reclassified from AOCI	[2],[3]	1
Other comprehensive income (loss)	[2]	1
Ending Balance	[2]	$ (35)	[4]							$ (36)
[1]	Amounts in parenthesis represent a decrease in net income.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	As a result of the PHI Merger, the PHI predecessor balances at March 23, 2016 were reduced to zero on March 24, 2016 due to purchase accounting adjustments applied to PHI.

Changes in Accumulated Other181

Changes in Accumulated Other Comprehensive Income Changes in Accumulated Other Comprehensive Income - Reclassifications out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss			$ 1,056	$ 413	$ (46)
Total before tax			3,756	1,989	3,330
Income Tax Expense (Benefit)			(125)	761	1,073
Net Income (Loss)			3,849	1,204	2,250
Amounts reclassified from AOCI	[1]		(144)	(150)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss	[1]			(5)
Total before tax	[1]			(5)
Income Tax Expense (Benefit)	[1]			0
Net Income (Loss)	[1]			(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Tax Expense (Benefit)			(1)	(5)
Gains and (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amounts reclassified from AOCI	[2],[3]		(4)	(8)
Gains and (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other cash flow hedges	[1]		(5)	(13)
Total before tax	[1]		(5)	(13)
Income Tax Expense (Benefit)	[1]		1	5
Net of tax	[1]		(4)	(8)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]		92	78
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]		(324)	(302)
Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]		(232)	(224)
Tax benefit	[1]		92	87
Amounts reclassified from AOCI	[1],[2],[3]		(140)	(137)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss			948	401	(60)
Income Tax Expense (Benefit)			(1,375)	290	502
Net Income (Loss)			2,771	558	1,340
Amounts reclassified from AOCI	[1]		(4)	(13)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss	[1]			(5)
Total before tax	[1]			(5)
Income Tax Expense (Benefit)	[1]			0
Net Income (Loss)	[1]			(5)
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amounts reclassified from AOCI	[2],[3]		(4)	(8)
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other cash flow hedges	[1]		(5)	(13)
Total before tax	[1]		(5)	(13)
Income Tax Expense (Benefit)	[1]		1	5
Net of tax	[1]		(4)	(8)
Exelon Generation Co L L C [Member] | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]		0	0
Exelon Generation Co L L C [Member] | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]		0	0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]		0	0
Tax benefit	[1]		0	0
Amounts reclassified from AOCI	[1],[2],[3]		$ 0	$ 0
Pepco Holdings LLC [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss		$ (4)			88
Income Tax Expense (Benefit)		17			163
Net of tax		19			318
Net Income (Loss)		19			$ 327
Amounts reclassified from AOCI	[1]	(1)
Pepco Holdings LLC [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loss	[1]	0
Total before tax	[1]	0
Income Tax Expense (Benefit)	[1]	0
Net Income (Loss)	[1]	0
Pepco Holdings LLC [Member] | Gains and (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other cash flow hedges	[1]	0
Total before tax	[1]	0
Income Tax Expense (Benefit)	[1]	0
Net of tax	[1]	0
Pepco Holdings LLC [Member] | Prior service costs | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	0
Pepco Holdings LLC [Member] | Actuarial losses | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	(1)
Pepco Holdings LLC [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	(1)
Tax benefit	[1]	0
Amounts reclassified from AOCI	[1]	$ (1)
[1]	Amounts in parenthesis represent a decrease in net income.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 16 — Retirement Benefits for additional details).

Changes in Accumulated Other182

Changes in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		$ (90)	$ 30	$ (53)
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		36	30	30
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		(128)	(118)	(140)
Pension and Non-Pension Postretirement Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		13	115	62
Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		(7)	0	(6)
Unrealized Gains and (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gain (loss) on equity investments taxes		(3)	3	1
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax		(1)	0	0
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		(10)	1	3
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes		(6)	(2)	2
Exelon Generation Co L L C [Member] | Unrealized Gains and (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gain (loss) on equity investments taxes		(3)	3	1
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax		$ (1)	$ 0	0
Predecessor [Member] | PEPCO Holdings Inc [Member] | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, income taxes	$ 0			$ 6

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Dec. 31, 2017USD ($)
Guarantor Obligations [Line Items]
Contractual Obligation	$ 3,006
Contractual Obligation, Due in Next Fiscal Year	2,349
Contractual Obligation, Due in Second Year	220
Contractual Obligation, Due in Third Year	32
Contractual Obligation, Due in Fourth Year	6
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	399
Guarantee obligations maximum exposure	56
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	2,386
Contractual Obligation, Due in Next Fiscal Year	2,171
Contractual Obligation, Due in Second Year	199
Contractual Obligation, Due in Third Year	16
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	0
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	212
Contractual Obligation, Due in Next Fiscal Year	10
Contractual Obligation, Due in Second Year	2
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	200
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	187
Contractual Obligation, Due in Next Fiscal Year	8
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	178
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	13
Contractual Obligation, Due in Next Fiscal Year	12
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	0
Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	60
Contractual Obligation, Due in Next Fiscal Year	41
Contractual Obligation, Due in Second Year	13
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	6
Guarantee obligations maximum exposure	16
Delmarva Power and Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	12
Contractual Obligation, Due in Next Fiscal Year	3
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	8
Guarantee obligations maximum exposure	23
Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	10
Contractual Obligation, Due in Next Fiscal Year	3
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	6
Guarantee obligations maximum exposure	15
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	1,226	[1]
Contractual Obligation, Due in Next Fiscal Year	1,056	[1]
Contractual Obligation, Due in Second Year	154	[1]
Contractual Obligation, Due in Third Year	16	[1]
Contractual Obligation, Due in Fourth Year	0	[1]
Contractual Obligation, Due in Fifth Year	0	[1]
Contractual Obligation, Due after Fifth Year	0	[1]
Financial Standby Letter of Credit [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	1,177	[2]
Contractual Obligation, Due in Next Fiscal Year	1,007	[2]
Contractual Obligation, Due in Second Year	154	[2]
Contractual Obligation, Due in Third Year	16	[2]
Contractual Obligation, Due in Fourth Year	0	[2]
Contractual Obligation, Due in Fifth Year	0	[2]
Contractual Obligation, Due after Fifth Year	0	[2]
Financial Standby Letter of Credit [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	2	[3]
Contractual Obligation, Due in Next Fiscal Year	2	[3]
Contractual Obligation, Due in Second Year	0	[3]
Contractual Obligation, Due in Third Year	0	[3]
Contractual Obligation, Due in Fourth Year	0	[3]
Contractual Obligation, Due in Fifth Year	0	[3]
Contractual Obligation, Due after Fifth Year	0	[3]
Financial Standby Letter of Credit [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	2	[4]
Contractual Obligation, Due in Next Fiscal Year	2	[4]
Contractual Obligation, Due in Second Year	0	[4]
Contractual Obligation, Due in Third Year	0	[4]
Contractual Obligation, Due in Fourth Year	0	[4]
Contractual Obligation, Due in Fifth Year	0	[4]
Contractual Obligation, Due after Fifth Year	0	[4]
Surety Bond [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	1,381	[5]
Contractual Obligation, Due in Next Fiscal Year	1,293	[5]
Contractual Obligation, Due in Second Year	66	[5]
Contractual Obligation, Due in Third Year	16	[5]
Contractual Obligation, Due in Fourth Year	6	[5]
Contractual Obligation, Due in Fifth Year	0	[5]
Contractual Obligation, Due after Fifth Year	0	[5]
Surety Bond [Member] | Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	1,209
Contractual Obligation, Due in Next Fiscal Year	1,164
Contractual Obligation, Due in Second Year	45
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	0
Surety Bond [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	10	[6]
Contractual Obligation, Due in Next Fiscal Year	8	[6]
Contractual Obligation, Due in Second Year	2	[6]
Contractual Obligation, Due in Third Year	0	[6]
Contractual Obligation, Due in Fourth Year	0	[6]
Contractual Obligation, Due in Fifth Year	0	[6]
Contractual Obligation, Due after Fifth Year	0	[6]
Surety Bond [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	9	[7]
Contractual Obligation, Due in Next Fiscal Year	8	[7]
Contractual Obligation, Due in Second Year	1	[7]
Contractual Obligation, Due in Third Year	0	[7]
Contractual Obligation, Due in Fourth Year	0	[7]
Contractual Obligation, Due in Fifth Year	0	[7]
Contractual Obligation, Due after Fifth Year	0	[7]
Surety Bond [Member] | Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	11	[8]
Contractual Obligation, Due in Next Fiscal Year	10	[8]
Contractual Obligation, Due in Second Year	1	[8]
Contractual Obligation, Due in Third Year	0	[8]
Contractual Obligation, Due in Fourth Year	0	[8]
Contractual Obligation, Due in Fifth Year	0	[8]
Contractual Obligation, Due after Fifth Year	0	[8]
Surety Bond [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	54	[9]
Contractual Obligation, Due in Next Fiscal Year	41	[9]
Contractual Obligation, Due in Second Year	13	[9]
Contractual Obligation, Due in Third Year	0	[9]
Contractual Obligation, Due in Fourth Year	0	[9]
Contractual Obligation, Due in Fifth Year	0	[9]
Contractual Obligation, Due after Fifth Year	0	[9]
Surety Bond [Member] | Delmarva Power and Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	4	[10]
Contractual Obligation, Due in Next Fiscal Year	3	[10]
Contractual Obligation, Due in Second Year	1	[10]
Contractual Obligation, Due in Third Year	0	[10]
Contractual Obligation, Due in Fourth Year	0	[10]
Contractual Obligation, Due in Fifth Year	0	[10]
Contractual Obligation, Due after Fifth Year	0	[10]
Surety Bond [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	4
Contractual Obligation, Due in Next Fiscal Year	3
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	0
Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	378
Contractual Obligation, Due in Next Fiscal Year	0
Contractual Obligation, Due in Second Year	0
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	378
Trust Preferred Securities [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	200
Contractual Obligation, Due in Next Fiscal Year	0
Contractual Obligation, Due in Second Year	0
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	200
Trust Preferred Securities [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	178
Contractual Obligation, Due in Next Fiscal Year	0
Contractual Obligation, Due in Second Year	0
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	178
GuaranteedLeaseResidualValues [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	21	[11]
Contractual Obligation, Due in Next Fiscal Year	0	[11]
Contractual Obligation, Due in Second Year	0	[11]
Contractual Obligation, Due in Third Year	0	[11]
Contractual Obligation, Due in Fourth Year	0	[11]
Contractual Obligation, Due in Fifth Year	0	[11]
Contractual Obligation, Due after Fifth Year	21	[11]
GuaranteedLeaseResidualValues [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	6	[12]
Contractual Obligation, Due in Next Fiscal Year	0	[12]
Contractual Obligation, Due in Second Year	0	[12]
Contractual Obligation, Due in Third Year	0	[12]
Contractual Obligation, Due in Fourth Year	0	[12]
Contractual Obligation, Due in Fifth Year	0	[12]
Contractual Obligation, Due after Fifth Year	6	[12]
GuaranteedLeaseResidualValues [Member] | Delmarva Power and Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	8	[13]
Contractual Obligation, Due in Next Fiscal Year	0	[13]
Contractual Obligation, Due in Second Year	0	[13]
Contractual Obligation, Due in Third Year	0	[13]
Contractual Obligation, Due in Fourth Year	0	[13]
Contractual Obligation, Due in Fifth Year	0	[13]
Contractual Obligation, Due after Fifth Year	8	[13]
GuaranteedLeaseResidualValues [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	6	[14]
Contractual Obligation, Due in Next Fiscal Year	0	[14]
Contractual Obligation, Due in Second Year	0	[14]
Contractual Obligation, Due in Third Year	0	[14]
Contractual Obligation, Due in Fourth Year	0	[14]
Contractual Obligation, Due in Fifth Year	0	[14]
Contractual Obligation, Due after Fifth Year	6	[14]
Successor [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	84
Contractual Obligation, Due in Next Fiscal Year	48
Contractual Obligation, Due in Second Year	15
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	21
Successor [Member] | Surety Bond [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	63
Contractual Obligation, Due in Next Fiscal Year	48
Contractual Obligation, Due in Second Year	15
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	0
Contractual Obligation, Due in Fifth Year	0
Contractual Obligation, Due after Fifth Year	0
Successor [Member] | GuaranteedLeaseResidualValues [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	21	[15]
Contractual Obligation, Due in Next Fiscal Year	0	[15]
Contractual Obligation, Due in Second Year	0	[15]
Contractual Obligation, Due in Third Year	0	[15]
Contractual Obligation, Due in Fourth Year	0	[15]
Contractual Obligation, Due in Fifth Year	0	[15]
Contractual Obligation, Due after Fifth Year	$ 21	[15]
[1]	Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[2]	Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties.
[3]	Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[4]	Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[5]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[6]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[7]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[8]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[9]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[10]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[11]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million, $16 million of which is a guarantee by Pepco, $23 million by DPL and $15 million by ACE. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
[12]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $16 million. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
[13]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $23 million. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
[14]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $15 million. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.
[15]	Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $56 million. The minimum lease term associated with these assets ranges from 1 to 4 years. Historically, payments under the guarantees have not been made and PHI believes the likelihood of payments being required under the guarantees is remote.

Commitments and Contingencie184

Commitments and Contingencies Commitments and Contingencies - Schedule of Minimum Future Operating Lease Payments (Details) - USD ($) $ in Millions		Dec. 31, 2017		Nov. 30, 2016
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[1]	$ 188
2,019	[1]	129
2,020	[1]	147
2,021	[1]	142
2,022	[1]	119
Remaining Years	[1]	787
Total minimum future lease payments	[1]	1,512
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[1]	74
2,019	[1]	29
2,020	[1]	47
2,021	[1]	48
2,022	[1]	46
Remaining Years	[1]	573
Total minimum future lease payments	[1]	817
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	7
2,019	[2]	6
2,020	[2]	4
2,021	[2]	4
2,022	[2]	2
Remaining Years	[2]	0
Total minimum future lease payments	[2]	23
Commonwealth Edison Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		2
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	5
2,019	[2]	5
2,020	[2]	5
2,021	[2]	5
2,022	[2]	5
Remaining Years	[2]	0
Total minimum future lease payments	[2]	25
PECO Energy Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		5
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018		34	[2],[3],[4]	$ 25
2,019		34	[2],[3],[4]	26
2,020		34	[2],[3],[4]	28
2,021		32	[2],[3],[4]	28
2,022		17	[2],[3],[4]	$ 14
Remaining Years	[2],[3],[4]	19
Total minimum future lease payments	[2],[3],[4]	170
Baltimore Gas and Electric Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		1
Pepco Holdings LLC [Member] | Successor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018		56
2,019		42
2,020		44
2,021		40
2,022		39
Remaining Years		194
Total minimum future lease payments		415
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018		8
2,019		7
2,020		6
2,021		5
2,022		4
Remaining Years		8
Total minimum future lease payments		38
Delmarva Power and Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	20
2,019	[2]	10
2,020	[2]	13
2,021	[2]	12
2,022	[2]	12
Remaining Years	[2]	54
Total minimum future lease payments	[2]	121
Delmarva Power and Light Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		2
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018		9
2,019		8
2,020		8
2,021		7
2,022		6
Remaining Years		19
Total minimum future lease payments		$ 57
[1]	Excludes Generation’s contingent operating lease payments associated with contracted generation agreements.
[2]	Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd’s, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2018—2022, was $2 million, $5 million, $1 million and $2 million, respectively.
[3]	Includes all future lease payments on a 99-year real estate lease that expires in 2106.
[4]	The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $25 million, $26 million, $28 million , $28 million and $14 million related to years 2018, 2019, 2020, 2021and 2022, respectively.

Commitments and Contingencie185

Commitments and Contingencies Commitments and Contingencies - Schedule of Future Rental Expense under Operating Leases (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				$ 709	$ 777	$ 922
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	[1]			578	667	851
Long Term Contract For Purchase Of Electric Power Capacity			$ 604	508	604	798
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				9	15	12
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				9	7	9
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				32	22	32
Pepco Holdings LLC [Member] | Successor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense			$ 49	63
Pepco Holdings LLC [Member] | Predecessor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		$ 12				60
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				11	8	7
Delmarva Power and Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				16	15	14
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				$ 14	$ 13	$ 13
[1]	Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $508 million, $604 million and $798 million during 2017, 2016 and 2015, respectively. Excludes contract amortization associated with purchase accounting and contract acquisitions.

Commitments and Contingencie186

Commitments and Contingencies Commitments and Contingencies - Settlement Agreements (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Nontrade Receivables, Current	[1]		$ 94	$ 109
Nontrade Receivables, Noncurrent	[2]		15	15
Accounts Payable, Other, Current	[1],[3]		(11)	$ (13)
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement	[4]		1,167
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[4],[5]		$ 1,006
Exelon Generation Co L L C [Member] | Department of Energy [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement		$ 53
Spent Nuclear Fuel Storage Reimbursement Net Co Owners		$ 49
[1]	Recorded in Accounts receivable, other.
[2]	Recorded in Deferred debits and other assets, other
[3]	Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities.
[4]	Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG.
[5]	Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek.

Commitments and Contingencie187

Commitments and Contingencies Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 466	$ 429
Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	315	325
Exelon Generation Co L L C [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	117	72
Exelon Generation Co L L C [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Commonwealth Edison Co [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	285	292
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	283	291
PECO Energy Co [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	30	33
PECO Energy Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	28	31
Baltimore Gas and Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	5	2
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	4	2
Pepco Holdings LLC [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	29	30
Pepco Holdings LLC [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	1
Potomac Electric Power Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	27
Potomac Electric Power Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Delmarva Power and Light Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	2
Delmarva Power and Light Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	1
Atlantic City Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0

Commitments and Contingencie188

Commitments and Contingencies Commitments and Contingencies - Narrative (Details)		Nov. 04, 2016	Nov. 01, 2015USD ($)	Sep. 23, 2015USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)MW	Dec. 31, 2017USD ($)MW	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2017	Dec. 31, 2017claimant	Dec. 31, 2017MGPSite	Dec. 31, 2017employee	Jun. 30, 2016USD ($)	Feb. 17, 2012USD ($)
Commitments and Contingencies [Line Items]
Document Period End Date									Dec. 31, 2017
Direct Investment Commitment																		$ 1,000,000,000
Power Volume | MW								10	220
BusinessAcquisitionResidualcommitment | MW								55
Loss Contingency, Loss in Period										$ 50,000,000
Nontrade Receivables, Current	[1]				$ 94,000,000			$ 109,000,000	$ 94,000,000	109,000,000
Nontrade Receivables, Noncurrent	[2]				15,000,000			15,000,000	15,000,000	15,000,000
Accounts Payable, Other, Current	[1],[3]				(11,000,000)			(13,000,000)	(11,000,000)	(13,000,000)
DOE Spent Nuclear Fuel One Time Fee					34,000,000				34,000,000
Operating Expenses	[4]								29,720,000,000	28,200,000,000	$ 25,056,000,000
Loss Contingency, Damages Awarded, Value												$ 14,000,000
Maximum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					10,000,000				10,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Entity Number of Employees | employee																1,500
Leasehold Improvements, Gross								110,000,000		110,000,000
Lessee, Operating Lease, Term of Contract		20 years
Costs Incurred, Development Costs									457,000,000
Nuclear financial protection pool value					450,000,000				450,000,000
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses					13,000,000,000				13,000,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident					2,800,000,000				2,800,000,000
Mutual Insurance Total Retrospective Premium Obligation					360,000,000				360,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation					3,200,000,000				3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation					0.001				0.001
Spent Nuclear Fuel Storage Reimbursement	[5]								1,167,000,000
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[5],[6]								1,006,000,000
DOE Spent Nuclear Fuel One Time Fee					277,000,000				277,000,000
DOE Spent Nuclear Fuel One Time Fee With Interest					1,147,000,000			1,024,000,000	$ 1,147,000,000	1,024,000,000
Spent Nuclear Fuel Treasury Interest Rate									1.149%
Total cost of remediation to be shared by PRPs									$ 90,000,000
Loss Contingency Accrual, Provision					20,000,000
Environmental loss contingencies								90,000,000		90,000,000
Asbestos Liability Reserve					78,000,000			83,000,000	78,000,000	83,000,000
Asbestos Liability Reserve related to open claims					21,000,000				21,000,000
Open Asbestos Liability Claims | claimant														230
Asbestos liability reserve related to anticipated claims							$ 57,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Direct Investment Commitment					450,000,000				$ 450,000,000
Business Acquisition, Expected New Generation Mwh | MW									285
Exelon Generation Co L L C [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Direct Investment Commitment					500,000,000				$ 500,000,000
Business Acquisition, Expected New Generation Mwh | MW									300
Exelon Generation Co L L C [Member] | West Lake [Member]
Commitments and Contingencies [Line Items]
Loss Contingency Accrual, Provision					340,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident					13,400,000,000				$ 13,400,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 420,000,000
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members					60,000,000			21,000,000	60,000,000	21,000,000	$ 21,000,000
Exelon Generation Co L L C [Member] | Unasserted Claim [Member]
Commitments and Contingencies [Line Items]
Accrued Liabilities and Other Liabilities																	$ 14,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															42
Sites approved for clean-up | MGPSite															19
Sites under study/remediation | MGPSite															23
Other Increase (Decrease) in Environmental Liabilities						13,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															26
Sites approved for clean-up | MGPSite															17
Sites under study/remediation | MGPSite															9
Other Increase (Decrease) in Environmental Liabilities						$ 2,000,000
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															13
Sites approved for clean-up | MGPSite															11
Sites under study/remediation													13,000,000		2
Common Equity Tier One Capital Ratio													48.00%
Occupancy, Net			$ 42,000,000	$ 12,000,000
Operating Leases, Income Statement, Initial Direct Costs								25,000,000
Oil and Gas Property, Lease Operating Expense								29,000,000
Operating Expenses								28,000,000
Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Number of Real Estate Properties | MGPSite															9
Environmental Remediation Expense							$ 10,000,000
Pepco Holdings LLC [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					7,000,000				7,000,000
Pepco Holdings LLC [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					18,000,000				18,000,000
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Common Equity Tier One Capital Ratio													48.00%
Accrued Liabilities and Other Liabilities					$ 28,000,000			$ 0	$ 28,000,000	$ 0
Delmarva Power and Light Company [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															3
Sites approved for clean-up | MGPSite															2
Common Equity Tier One Capital Ratio													48.00%
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Common Equity Tier One Capital Ratio													48.00%
[1]	Recorded in Accounts receivable, other.
[2]	Recorded in Deferred debits and other assets, other
[3]	Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities.
[4]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.
[5]	Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG.
[6]	Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek.

Supplemental Financial Infor189

Supplemental Financial Information - Summary of Taxes other than Income (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			$ 898	$ 753	$ 474
Property				545	483	407
Payroll				230	226	201
Other				58	114	118
Total taxes other than income				1,731	1,576	1,200
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			126	122	105
Property				269	246	250
Payroll				121	117	118
Other				39	21	16
Total taxes other than income				555	506	489
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			240	242	236
Property				28	27	27
Payroll				26	28	28
Other				2	(4)	5
Total taxes other than income				296	293	296
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			125	136	133
Property				14	13	11
Payroll				15	15	14
Other				0	0	2
Total taxes other than income				154	164	160
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			89	85	85
Property				132	123	119
Payroll				15	17	16
Other				4	4	4
Total taxes other than income				240	229	224
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			300	312	308
Property				62	53	57
Payroll				6	8	6
Other				3	4	5
Total taxes other than income				371	377	376
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			18	18	18
Property				32	31	28
Payroll				4	5	4
Other				3	1	1
Total taxes other than income				57	55	51
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			0	0	0
Property				3	3	3
Payroll				2	3	2
Other				1	1	2
Total taxes other than income				6	$ 7	7
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]		$ 253	318
Property			73	101
Payroll			23	26
Other			5	7
Total taxes other than income			$ 354	$ 452
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]	$ 78				326
Property		18				94
Payroll		8				27
Other		1				8
Total taxes other than income		$ 105				$ 455
[1]	Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Supplemental Financial Infor190

Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					$ 488		$ 237		$ 232
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]					209		126		156
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						455		216		(282)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						521		194		(197)
Net unrealized income (losses) on pledged assets						(10)		(1)		7
Regulatory offset to decommissioning trust fund-related activities	[2]					(724)		(372)		21
Total decommissioning-related activities						939		400		(63)
Investment income (loss)						8		17		8
Long-term lease income								4		15
Interest income related to uncertain income tax positions						3		13		1
Income Tax Examination, Penalties and Interest Expense						2		(106)	[3]
AFUDC—Equity						73		64		24
Terminated interest rate swaps(d)	[4]							(3)		(26)
Payments of Debt Restructuring Costs	[5]									(22)
Gain (Loss) on Disposition of Assets						3		(48)		18
Other						31		24		17
Other, net						1,056		413		(46)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Other, net	[6]							(5)
Gain (Loss) on Sale of Derivatives						26
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					488		237		232
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]					209		126		156
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						455		216		(282)
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						521		194		(197)
Net unrealized income (losses) on pledged assets						(10)		(1)		7
Regulatory offset to decommissioning trust fund-related activities	[2]					(724)		(372)		21
Total decommissioning-related activities						939		400		(63)
Investment income (loss)						6		8		3
Long-term lease income								0		0
Interest income related to uncertain income tax positions						(1)		0		1
Income Tax Examination, Penalties and Interest Expense						0		0	[3]
AFUDC—Equity						0		0		0
Terminated interest rate swaps(d)								(2)		0
Payments of Debt Restructuring Costs										0
Gain (Loss) on Disposition of Assets						2		(59)		12
Other						4		(5)		(1)
Other, net						948		401		(60)
Exelon Generation Co L L C [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Other, net	[6]							(5)
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Supplemental Financial Information Tables [Line Items]
Debt Instrument, Face Amount						750
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]					0		0		0
Total decommissioning-related activities						0		0		0
Investment income (loss)						0		0		0
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		0		0
Income Tax Examination, Penalties and Interest Expense						0		(86)	[3]
AFUDC—Equity						12		14		5
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Other						10		7		16
Other, net						22		(65)		21
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0		0
Regulatory offset to decommissioning trust fund-related activities						0	[2]	0	[2]	0
Total decommissioning-related activities						0		0		0
Investment income (loss)						0		(1)		(2)
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		0		0
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity						9		8		5
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Other						0		1		2
Other, net						9		8		5
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]					0		0		0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0		0
Regulatory offset to decommissioning trust fund-related activities	[2]					0		0		0
Total decommissioning-related activities						0		0		0
Investment income (loss)						0		2		4
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		0		0
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity						16		19		14
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Other						0		0		0
Other, net						16		21		18
Pepco Holdings LLC [Member]
Supplemental Financial Information Tables [Line Items]
Total decommissioning-related activities						0
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]			$ 0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units				0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units				0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement				0		0
Net unrealized income (losses) on pledged assets				0	[2]	0
Regulatory offset to decommissioning trust fund-related activities				0		0	[2]
Total decommissioning-related activities								0
Investment income (loss)				1		2
Long-term lease income				0
Interest income related to uncertain income tax positions				(1)		0
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity				23		36
Terminated interest rate swaps(d)								0
Gain (Loss) on Disposition of Assets				(1)		1
Other				21		16
Other, net				$ 44		54
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	$ 0								0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0								0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0								0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0								0
Net unrealized income (losses) on pledged assets		0	[2]							0
Regulatory offset to decommissioning trust fund-related activities		0								0	[2]
Total decommissioning-related activities								0		0
Investment income (loss)		0								0
Long-term lease income		0								0
Interest income related to uncertain income tax positions		0								34
Income Tax Examination, Penalties and Interest Expense								0
AFUDC—Equity		7								14
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Gain (Loss) on Disposition of Assets		0								46
Other		(11)								40
Other, net		(4)								88
Pepco Holdings LLC [Member] | Predecessor [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Supplemental Financial Information Tables [Line Items]
Other, net	[6]	$ 0
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units						0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0	[2]	0
Regulatory offset to decommissioning trust fund-related activities						0	[2]	0		0	[2]
Total decommissioning-related activities						0		0		0
Investment income (loss)						1		1		0
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		1		5
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity						23		19		12
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Gain (Loss) on Disposition of Assets						(1)		8		46
Other						8		15		11
Other, net						32		36		28
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units						0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0	[2]	0
Regulatory offset to decommissioning trust fund-related activities						0	[2]	0		0	[2]
Total decommissioning-related activities						0		0		0
Investment income (loss)						0		0		0
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		0		0
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity						7		5		1
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Other						7		8		9
Other, net						14		13		10
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]					0		0		0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units						0	[1]	0		0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units						0		0		0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement						0		0		0
Net unrealized income (losses) on pledged assets						0		0	[2]	0
Regulatory offset to decommissioning trust fund-related activities						0	[2]	0		0	[2]
Total decommissioning-related activities						0		0		0
Investment income (loss)						0		1		0
Long-term lease income								0		0
Interest income related to uncertain income tax positions						0		0		0
Income Tax Examination, Penalties and Interest Expense						0		0
AFUDC—Equity						6		6		1
Terminated interest rate swaps(d)								0		0
Payments of Debt Restructuring Costs										0
Other						1		2		2
Other, net						$ 7		$ 9		$ 3
[1]	Includes investment income and realized gains and losses on sales of investments within the nuclear decommissioning trust funds.
[2]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[3]	See Note 14—Income Taxes for discussion of the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position.
[4]	In January 2015, in connection with Generation's $750 million issuance of five-year Senior Unsecured Notes, Exelon terminated certain floating-to-fixed interest rate swaps. As the original forecasted transactions were a series of future interest payments over a ten-year period, a portion of the anticipated interest payments are probable not to occur. As a result, $26 million of anticipated payments were reclassified from AOCI to Other, net in Exelon's Consolidated Statements of Operations and Comprehensive Income.
[5]	(e)See Note 13—Debt and Credit Agreements and Note 4—Mergers, Acquisitions and Dispositions for additional information on the PHI merger related debt exchange.
[6]	Amounts in parenthesis represent a decrease in net income.

Supplemental Financial Infor191

Supplemental Financial Information - Summary of Depreciation, Amortization, Accretion and Depletion (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				$ 3,293	$ 3,477	$ 2,227
Regulatory assets				478	407	170
Amortization of Intangible Assets				92	87	76
Nuclear fuel	[1]			1,096	1,159	1,116
ARO accretion	[2]			468	446	398
Total depreciation, amortization and accretion				5,427	5,576	3,987
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				1,409	1,835	1,007
Regulatory assets				0	0	0
Amortization of Intangible Assets				83	79	69
Nuclear fuel	[1]			1,096	1,159	1,116
ARO accretion	[2]			468	446	397
Total depreciation, amortization and accretion				3,056	3,519	2,589
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				777	708	635
Regulatory assets				73	67	72
Amortization of Intangible Assets				7	7	7
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				850	775	707
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				261	244	240
Regulatory assets				25	26	20
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				286	270	260
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				312	299	289
Regulatory assets				161	124	77
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				473	423	366
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment			$ 325	457
Regulatory assets			190	218
Nuclear fuel	[1]		0	0
ARO accretion	[2]		0	0
Total depreciation, amortization and accretion			515	675
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment		$ 94				392
Regulatory assets		58				232
Nuclear fuel	[1]	0				0
ARO accretion	[2]	0				0
Total depreciation, amortization and accretion		152				624
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				203	175	164
Regulatory assets				118	120	92
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				321	295	256
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				124	110	103
Regulatory assets				43	47	45
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				167	157	148
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Property, plant and equipment				89	82	76
Regulatory assets				57	83	99
Nuclear fuel	[1]			0	0	0
ARO accretion	[2]			0	0	0
Total depreciation, amortization and accretion				146	165	175
Unamortized Energy Contracts [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			35	35	22
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			35	35	22
Unamortized Energy Contracts [Member] | Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]		0	0
Unamortized Energy Contracts [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]	0				0
Unamortized Energy Contracts [Member] | Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Unamortized Energy Contracts [Member] | Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets	[3]			0	0	0
Other Intangible Assets [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				57	52	54
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				48	44	47
Other Intangible Assets [Member] | Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets			$ 0	0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets		$ 0				0
Other Intangible Assets [Member] | Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				0	0	0
Other Intangible Assets [Member] | Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Amortization of Intangible Assets				$ 0	$ 0	$ 0
[1]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[3]	Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

Supplemental Financial Infor192

Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($)		3 Months Ended		9 Months Ended			12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016		Sep. 30, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							$ 2,430,000,000		$ 1,340,000,000		$ 930,000,000
Income taxes (net of refunds)							540,000,000		(441,000,000)		342,000,000
Pension and non-pension postretirement benefit costs							643,000,000		619,000,000		637,000,000
Income (Loss) from Equity Method Investments							32,000,000		24,000,000		7,000,000
Provision for uncollectible accounts							125,000,000		155,000,000		120,000,000
Provision for excess and obsolete inventory							56,000,000		12,000,000		10,000,000
Stock-based compensation costs							88,000,000		111,000,000		97,000,000
Other decommissioning related-activity							(313,000,000)	[1]	(384,000,000)	[2]	(82,000,000)	[3]
Energy-related options							7,000,000	[4]	(11,000,000)	[5]	21,000,000	[6]
Amortization of regulatory asset related to debt costs							9,000,000		9,000,000		7,000,000
Amortization of rate stabilization deferral							(10,000,000)		76,000,000		73,000,000
Amortization of debt fair value adjustment							(18,000,000)		(11,000,000)		(17,000,000)
Merger-related commitments (c)							0	[7]	558,000,000	[8],[9]
Restructuring Costs							35,000,000		99,000,000
Amortization of Debt Issuance Costs							64,000,000		8,000,000	[10]	58,000,000
Discrete impacts from EIMA							(52,000,000)	[11]	35,000,000		144,000,000	[12]
Lower of cost or market inventory adjustment									37,000,000		23,000,000
Environmental Expense and Liabilities							44,000,000
Litigation Settlement, Amount Awarded from Other Party									(28,000,000)
Proceeds from Collection of Other Receivables									13,000,000
Increase (Decrease) in Accrued Liabilities							109,000,000		70,000,000		24,000,000
Other							(30,000,000)		(35,000,000)		(13,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							721,000,000		1,333,000,000		1,109,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(42,000,000)		(128,000,000)		(96,000,000)
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross							208,000,000		6,934,000,000		40,000,000
Change in PPE related to ARO update				$ 191,000,000			29,000,000		191,000,000		885,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							16,000,000		$ 54,000,000	[14]
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								37
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							(8,000,000)
Other Noncash Expense							(68,000,000)	[16]	$ 95,000,000		77,000,000
License Costs	[17]										95,000,000
noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									2,000,000
NonCashFairValueAdjustment									0
Payments to Acquire Businesses, Gross									0
Predecessor [Member]
Supplemental Cash Flow Information [Line Items]
Income (Loss) from Equity Method Investments											0
Other decommissioning related-activity	[3]										0
Energy-related options	[6],[18]										0
Amortization of debt fair value adjustment											0
Discrete impacts from EIMA	[12]										0
Change in PPE related to ARO update											0
Contribution of Property	[15]										0
Other Noncash Expense											0
License Costs	[17]										0
Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										57,000,000
Contribution of Property							0	[19]	0	[20]
Non Cash Licensing Agreement							(5,000,000)
Exelon Generation Co L L C [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							391,000,000		339,000,000		348,000,000
Income taxes (net of refunds)							337,000,000		435,000,000		476,000,000
Pension and non-pension postretirement benefit costs							227,000,000		218,000,000		269,000,000
Income (Loss) from Equity Method Investments											8,000,000
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions							33,000,000		25,000,000		8,000,000
Provision for uncollectible accounts							38,000,000		19,000,000		22,000,000
Provision for excess and obsolete inventory							51,000,000		6,000,000		9,000,000
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							(313,000,000)	[1]	(384,000,000)	[2]	(82,000,000)	[3]
Energy-related options							7,000,000	[4]	(11,000,000)	[5]	21,000,000	[6]
Amortization of regulatory asset related to debt costs							0		0		0
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							(12,000,000)		(11,000,000)		(17,000,000)
Merger-related commitments (c)							0	[7]	53,000,000	[8],[9]
Restructuring Costs							31,000,000		22,000,000
Asset Retirement Obligation, Revision of Estimate						$ 61,000,000	1,000,000		1,000,000
Amortization of Debt Issuance Costs							37,000,000		17,000,000		15,000,000
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									36,000,000		23,000,000
Environmental Expense and Liabilities							44,000,000
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							4,000,000		25,000,000		0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							112,000,000		15,000,000		268,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(73,000,000)		50,000,000		(82,000,000)
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							33,000,000
Payments to Acquire Businesses, Gross							208,000,000		293,000,000		40,000,000
Change in PPE related to ARO update				191,000,000			29,000,000		191,000,000		885,000,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							16,000,000		$ 54,000,000	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								37
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							(35,000,000)	[16]	$ 95,000,000		77,000,000
License Costs	[17]										0
Exelon Generation Co L L C [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									0
NonCashFairValueAdjustment									119,000,000
Payments to Acquire Businesses, Gross									0
Exelon Generation Co L L C [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										57,000,000
Contribution of Property							0	[19]	0	[20]
Non Cash Licensing Agreement							0
Commonwealth Edison Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							307,000,000		298,000,000		308,000,000
Income taxes (net of refunds)							83,000,000		(444,000,000)		(265,000,000)
Pension and non-pension postretirement benefit costs							176,000,000		166,000,000		206,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							34,000,000		41,000,000		53,000,000
Provision for excess and obsolete inventory							3,000,000		4,000,000		1,000,000
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							4,000,000		4,000,000		5,000,000
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							0	[7]	0	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							5,000,000		4,000,000		4,000,000
Discrete impacts from EIMA							(52,000,000)	[11]	8,000,000	[10]	144,000,000	[12]
Lower of cost or market inventory adjustment									0		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							6,000,000		(12,000,000)		3,000,000
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							164,000,000		215,000,000		416,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							61,000,000		(91,000,000)		(34,000,000)
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										7,000,000
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							(12,000,000)	[16]	$ 0		0
License Costs	[17]										0
Commonwealth Edison Co [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Commonwealth Edison Co [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Asset Retirement Obligation, Revision of Estimate									0
NonCashFairValueAdjustment									0
Commonwealth Edison Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										0
Contribution of Property		$ 0	[20]				21,000,000	[19]	158,000,000	[20]
Non Cash Licensing Agreement							0
PECO Energy Co [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							103,000,000		104,000,000		94,000,000
Income taxes (net of refunds)							47,000,000		64,000,000		64,000,000
Pension and non-pension postretirement benefit costs							29,000,000		33,000,000		39,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							26,000,000		30,000,000		30,000,000
Provision for excess and obsolete inventory							0		0		0
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							1,000,000		1,000,000		2,000,000
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							0	[7]	0	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							2,000,000		3,000,000		2,000,000
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									1,000,000		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							(4,000,000)		(3,000,000)		(3,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							54,000,000		65,000,000		70,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(22,000,000)		(11,000,000)		13,000,000
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							0	[16]	$ 0		0
License Costs	[17]										0
PECO Energy Co [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									0
NonCashFairValueAdjustment									0
PECO Energy Co [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										0
Contribution of Property							0	[19]	0	[20]
Non Cash Licensing Agreement							0
Baltimore Gas and Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							96,000,000		92,000,000		120,000,000
Income taxes (net of refunds)							(2,000,000)		31,000,000		73,000,000
Pension and non-pension postretirement benefit costs							62,000,000		67,000,000		65,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							8,000,000		1,000,000		15,000,000
Provision for excess and obsolete inventory							0		0		0
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							0		0		0
Amortization of rate stabilization deferral							7,000,000		81,000,000		73,000,000
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							0	[7]	0	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							2,000,000		1,000,000		2,000,000
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									0		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									(28,000,000)
Proceeds from Collection of Other Receivables									13,000,000
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							(14,000,000)		(21,000,000)		(18,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							65,000,000		88,000,000		137,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(23,000,000)		(86,000,000)		9,000,000
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Licensing Agreement							0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							8,000,000
Other Noncash Expense							0	[16]	$ 0		0
License Costs	[17]										0
Baltimore Gas and Electric Company [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									0
NonCashFairValueAdjustment									0
Baltimore Gas and Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										0
Contribution of Property							0	[19]	0	[20]
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)				209,000,000			236,000,000
Income taxes (net of refunds)				258,000,000			(144,000,000)
Pension and non-pension postretirement benefit costs				86,000,000			94,000,000
Income (Loss) from Equity Method Investments				0			1,000,000
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				0			(1,000,000)
Provision for uncollectible accounts				65,000,000			19,000,000
Provision for excess and obsolete inventory				1,000,000			2,000,000
Stock-based compensation costs				0			0
Other decommissioning related-activity				0	[2]		0	[1]
Energy-related options				0	[5]		0	[4]
Amortization of regulatory asset related to debt costs				3,000,000			4,000,000
Amortization of rate stabilization deferral				(5,000,000)			(17,000,000)
Amortization of debt fair value adjustment				0			(6,000,000)
Merger-related commitments (c)				317,000,000	[8],[9]		(8,000,000)	[7]
Restructuring Costs				56,000,000			3,000,000
Amortization of Debt Issuance Costs				1,000,000			4,000,000
Discrete impacts from EIMA	[11]						0
Lower of cost or market inventory adjustment				0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0
Other				(12,000,000)			(27,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities				514,000,000			59,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash				21,000,000			(12,000,000)
NonCashFairValueAdjustment	[9],[13]			127,000,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]			53,000,000
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross				29,000,000
Change in PPE related to ARO update							0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				$ 0	[14]		0
Dividends, Stock							0
Contribution of Property	[19]						0
Noncash or Part Noncash Divestiture, Description	[9]			0
Non Cash Licensing Agreement							0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense				$ 0			(8,000,000)	[16]
Pepco Holdings LLC [Member] | Successor [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)				33,000,000
Asset Retirement Obligation, Revision of Estimate				2,000,000
NonCashFairValueAdjustment				0
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)		43,000,000									268,000,000
Income taxes (net of refunds)		11,000,000									(13,000,000)
Pension and non-pension postretirement benefit costs		23,000,000									97,000,000
Income (Loss) from Equity Method Investments		0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		0									0
Provision for uncollectible accounts		16,000,000									61,000,000
Provision for excess and obsolete inventory		1,000,000									1,000,000
Stock-based compensation costs		3,000,000									13,000,000
Other decommissioning related-activity	[2]	0
Energy-related options	[5]	0
Amortization of regulatory asset related to debt costs		1,000,000									5,000,000
Amortization of rate stabilization deferral		5,000,000									(2,000,000)
Amortization of debt fair value adjustment		0
Merger-related commitments (c)	[8],[9]	0
Restructuring Costs		0
Amortization of Debt Issuance Costs		0									2,000,000
Discrete impacts from EIMA	[10]	0
Lower of cost or market inventory adjustment		0									0
Litigation Settlement, Amount Awarded from Other Party		0
Proceeds from Collection of Other Receivables		0
Increase (Decrease) in Accrued Liabilities									0		0
Other		(3,000,000)									(10,000,000)
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities		46,000,000									167,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash		11,000,000									(6,000,000)
NonCashFairValueAdjustment	[9],[13]	0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]	0
Payments to Acquire Businesses, Gross		0
Change in PPE related to ARO update				0					0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[14]	$ 0
Noncash or Part Noncash Divestiture, Description	[9]	0
Other Noncash Expense		$ 0
Pepco Holdings LLC [Member] | Predecessor [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)		0
Asset Retirement Obligation, Revision of Estimate		0
NonCashFairValueAdjustment		$ 0
Pepco Holdings LLC [Member] | Indemnification Agreement [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[20]			0
Potomac Electric Power Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							114,000,000		118,000,000		116,000,000
Income taxes (net of refunds)							(104,000,000)		216,000,000		(6,000,000)
Pension and non-pension postretirement benefit costs							25,000,000		31,000,000		30,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							8,000,000		29,000,000		21,000,000
Provision for excess and obsolete inventory							1,000,000		3,000,000		0
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							2,000,000		2,000,000		2,000,000
Amortization of rate stabilization deferral							(17,000,000)		(12,000,000)		1,000,000
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							(6,000,000)	[7]	125,000,000	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							2,000,000		0		0
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									0		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							(12,000,000)		5,000,000		0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							(5,000,000)		183,000,000		54,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(5,000,000)		27,000,000		(1,000,000)
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							(8,000,000)	[16]	$ 0		0
License Costs	[17]										0
Potomac Electric Power Company [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									33,000,000
Asset Retirement Obligation, Revision of Estimate									0
NonCashFairValueAdjustment									0
Potomac Electric Power Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										0
Contribution of Property							0	[19]	0	[20]
Non Cash Licensing Agreement							0
Delmarva Power and Light Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							49,000,000		47,000,000		47,000,000
Income taxes (net of refunds)							(49,000,000)		115,000,000		(5,000,000)
Pension and non-pension postretirement benefit costs							13,000,000		18,000,000		15,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							3,000,000		23,000,000		20,000,000
Provision for excess and obsolete inventory							1,000,000		1,000,000		0
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							1,000,000		1,000,000		1,000,000
Amortization of rate stabilization deferral							0		2,000,000		(3,000,000)
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							(2,000,000)	[7]	82,000,000	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							0		0		0
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									0		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							(7,000,000)		(14,000,000)		0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							9,000,000		114,000,000		33,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							(4,000,000)		(12,000,000)		3,000,000
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							0	[16]	$ 0		0
License Costs	[17]										0
Delmarva Power and Light Company [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									1,000,000
NonCashFairValueAdjustment									0
Delmarva Power and Light Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										0
Contribution of Property							0	[19]	0	[20]
Non Cash Licensing Agreement							0
Atlantic City Electric Company [Member]
Supplemental Cash Flow Information [Line Items]
Interest (net of amount capitalized)							59,000,000		62,000,000		63,000,000
Income taxes (net of refunds)							(2,000,000)		200,000,000		0
Pension and non-pension postretirement benefit costs							13,000,000		15,000,000		15,000,000
Income (Loss) from Equity Method Investments							0		0		0
Provision for uncollectible accounts							8,000,000		32,000,000		20,000,000
Provision for excess and obsolete inventory							0		1,000,000		0
Stock-based compensation costs							0		0		0
Other decommissioning related-activity							0	[1]	0	[2]	0	[3]
Energy-related options							0	[4]	0	[5]	0	[6]
Amortization of regulatory asset related to debt costs							1,000,000		1,000,000		1,000,000
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments (c)							0	[7]	110,000,000	[8],[9]
Restructuring Costs							0		0
Amortization of Debt Issuance Costs							1,000,000		0		0
Discrete impacts from EIMA							0	[11]	0	[10]	0	[12]
Lower of cost or market inventory adjustment									0		0
Environmental Expense and Liabilities							0
Litigation Settlement, Amount Awarded from Other Party									0
Proceeds from Collection of Other Receivables									0
Increase (Decrease) in Accrued Liabilities							0		0		0
Other							(6,000,000)		(6,000,000)		1,000,000
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities							17,000,000		155,000,000		37,000,000
Fair value of net assets contributed to Generation in connection with the PHI Merger, net of cash							13,000,000		11,000,000		3,000,000
NonCashFairValueAdjustment	[9],[13]								0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	[9],[13]								0
Business Combination, Contingent Consideration, Liability, Noncurrent							0
Payments to Acquire Businesses, Gross									0
Change in PPE related to ARO update				0			0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired							0		$ 0	[14]
Dividends, Stock							0
Contribution of Property	[15]										0
Noncash or Part Noncash Divestiture, Description	[9]								0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement							0
Other Noncash Expense							0	[16]	$ 0		0
License Costs	[17]										0
Atlantic City Electric Company [Member] | noncash member [Member]
Supplemental Cash Flow Information [Line Items]
Merger-related commitments (c)									0
Asset Retirement Obligation, Revision of Estimate									2,000,000
NonCashFairValueAdjustment									0
Atlantic City Electric Company [Member] | Indemnification Agreement [Member]
Supplemental Cash Flow Information [Line Items]
Energy-related options	[18]										$ 0
Contribution of Property							0	[19]	$ 0	[20]
Non Cash Licensing Agreement							$ 0
Severance [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Cash Flow Information [Line Items]
Discrete impacts from EIMA	[10]			$ 0
[1]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[2]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[3]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations for additional information regarding the accounting for nuclear decommissioning.
[4]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[5]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[6]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[7]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[8]	Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.
[9]	See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[10]	Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information.
[11]	Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 3 — Regulatory Matters for more information.
[12]	Reflects the change in distribution rates pursuant to EIMA, which allows for the recovery of costs by a utility through a pre-established performance-based formula rate. See Note 3 — Regulatory Matters for more information.
[13]	Immediately following closing of the PHI Merger, the net assets associated with PHI’s unregulated business interests were distributed by PHI to Exelon. Exelon contributed a portion of such net assets to Generation.
[14]	Reflects the transfer of nuclear fuel to Entergy under the cost reimbursement provisions of the FitzPatrick acquisition agreements. See Note 4 - Mergers, Acquisitions and Dispositions for more information.
[15]	See Note 14 — Income Taxes for discussion of the like-kind exchange tax position.
[16]	On December 1, 2017, Exelon adopted a single, standard vacation accrual policy for all non-represented, non-craft (represented and craft policies remained unchanged) employees effective January 1, 2018. To reflect the new policy, Exelon recorded a one-time, $68 million pre-tax credit to expense to reverse 2018 vacation cost originally accrued throughout 2017 that will now be accrued ratably over the year in 2018.
[17]	Relates to a long-term software license agreement entered into on May 30, 2015. Exelon is required to make payments starting August of 2015 through May of 2024. See Note 13 - Debt and Credit Agreements.
[18]	Relates to the nuclear fuel procurement contracts for the purchase of fixed quantities of uranium, which was delivered to Generation in 2015. Generation is required to make payments starting September 30, 2018, with the final payment being due no later than September 30, 2020.
[19]	See Note 14 — Income Taxes for discussion of the like-kind exchange tax position.
[20]	See Note 14 — Income Taxes for discussion of the like-kind exchange tax position.

Supplemental Financial Infor193

Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		$ 297,000,000	$ 311,000,000
Investments		640,000,000	629,000,000
Compensation-related accruals	[1]	978,000,000	1,199,000,000
Taxes accrued		373,000,000	723,000,000
Interest accrued		328,000,000	1,234,000,000
Severance accrued		58,000,000	44,000,000
Other accrued expenses		98,000,000	260,000,000
Accrued Liabilities		1,835,000,000	3,460,000,000
Total accrued expenses		1,835,000,000	3,460,000,000
Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	14,000,000	22,000,000
Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		206,000,000	216,000,000
Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		76,000,000	57,000,000
Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		1,000,000	16,000,000
Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[3]	244,000,000	232,000,000
Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		62,000,000	52,000,000
Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		37,000,000	34,000,000
Exelon Generation Co L L C [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		283,000,000	288,000,000
Investments		433,000,000	418,000,000
Compensation-related accruals	[1]	407,000,000	557,000,000
Taxes accrued		444,000,000	239,000,000
Interest accrued		78,000,000	82,000,000
Severance accrued		30,000,000	15,000,000
Other accrued expenses		61,000,000	96,000,000
Total accrued expenses		1,020,000,000	989,000,000
Exelon Generation Co L L C [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	0
Exelon Generation Co L L C [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		206,000,000	216,000,000
Exelon Generation Co L L C [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		76,000,000	57,000,000
Exelon Generation Co L L C [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		1,000,000	15,000,000
Exelon Generation Co L L C [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[3]	51,000,000	44,000,000
Exelon Generation Co L L C [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		62,000,000	52,000,000
Exelon Generation Co L L C [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		37,000,000	34,000,000
Commonwealth Edison Co [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		6,000,000	6,000,000
Investments		6,000,000	6,000,000
Compensation-related accruals	[1]	158,000,000	199,000,000
Taxes accrued		60,000,000	330,000,000
Interest accrued		102,000,000	609,000,000
Severance accrued		2,000,000	2,000,000
Other accrued expenses		5,000,000	110,000,000
Total accrued expenses		327,000,000	1,250,000,000
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	6,000,000	6,000,000
Commonwealth Edison Co [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[3]	0	0
Commonwealth Edison Co [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Commonwealth Edison Co [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
PECO Energy Co [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		8,000,000	8,000,000
Investments		25,000,000	25,000,000
Compensation-related accruals	[1]	64,000,000	67,000,000
Taxes accrued		15,000,000	4,000,000
Interest accrued		33,000,000	30,000,000
Severance accrued		0	0
Other accrued expenses		2,000,000	3,000,000
Total accrued expenses		114,000,000	104,000,000
PECO Energy Co [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	8,000,000	8,000,000
PECO Energy Co [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
PECO Energy Co [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
PECO Energy Co [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
PECO Energy Co [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[3]	17,000,000	17,000,000
PECO Energy Co [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
PECO Energy Co [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
Baltimore Gas and Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	8,000,000
Investments		5,000,000	12,000,000
Compensation-related accruals	[1]	58,000,000	64,000,000
Taxes accrued		71,000,000	78,000,000
Interest accrued		34,000,000	31,000,000
Severance accrued		0	0
Other accrued expenses		1,000,000	2,000,000
Total accrued expenses		164,000,000	175,000,000
Baltimore Gas and Electric Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	8,000,000
Baltimore Gas and Electric Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments	[3]	5,000,000	4,000,000
Baltimore Gas and Electric Company [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Baltimore Gas and Electric Company [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		132,000,000	133,000,000
Compensation-related accruals	[1]	106,000,000	112,000,000
Taxes accrued		61,000,000	65,000,000
Interest accrued		48,000,000	49,000,000
Severance accrued		17,000,000	19,000,000
Other accrued expenses		29,000,000	27,000,000
Total accrued expenses		261,000,000	272,000,000
Pepco Holdings LLC [Member] | Financing Trusts [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	0
Pepco Holdings LLC [Member] | Bloom Energy [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Net Power [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Other Equity Method Investments [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Employee Benefit Trusts and Investments [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments		132,000,000	133,000,000
Pepco Holdings LLC [Member] | Other Cost Method Investments [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Pepco Holdings LLC [Member] | Other Available For Sale Investments [Member] | Successor [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
Potomac Electric Power Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		102,000,000	102,000,000
Compensation-related accruals	[1]	29,000,000	30,000,000
Taxes accrued		68,000,000	48,000,000
Interest accrued		23,000,000	21,000,000
Severance accrued		0	0
Other accrued expenses		17,000,000	14,000,000
Total accrued expenses		137,000,000	113,000,000
Potomac Electric Power Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	0
Potomac Electric Power Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments		102,000,000	102,000,000
Potomac Electric Power Company [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Potomac Electric Power Company [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
Delmarva Power and Light Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		0	0
Compensation-related accruals	[1]	17,000,000	17,000,000
Taxes accrued		4,000,000	4,000,000
Interest accrued		8,000,000	8,000,000
Severance accrued		0	0
Other accrued expenses		6,000,000	7,000,000
Total accrued expenses		35,000,000	36,000,000
Delmarva Power and Light Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	0
Delmarva Power and Light Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Delmarva Power and Light Company [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments		0	0
Delmarva Power and Light Company [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Delmarva Power and Light Company [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		0	0
Atlantic City Electric Company [Member]
Supplemental Balance Sheet Information [Line Items]
Total equity method investments		0	0
Investments		0	0
Compensation-related accruals	[1]	11,000,000	11,000,000
Taxes accrued		5,000,000	9,000,000
Interest accrued		12,000,000	12,000,000
Severance accrued		0	0
Other accrued expenses		5,000,000	6,000,000
Total accrued expenses		33,000,000	38,000,000
Atlantic City Electric Company [Member] | Financing Trusts [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments	[2]	0	0
Atlantic City Electric Company [Member] | Bloom Energy [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Net Power [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Other Equity Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Employee Benefit Trusts and Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Employee benefit trusts and investments		0	0
Atlantic City Electric Company [Member] | Other Cost Method Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other cost method investments		0	0
Atlantic City Electric Company [Member] | Other Available For Sale Investments [Member]
Supplemental Balance Sheet Information [Line Items]
Other available for sale investments		$ 0	$ 0
[1]	Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.
[2]	Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments on the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information.
[3]	The Registrants’ investments in these marketable securities are recorded at fair market value.

Segment Information Segment Inf

Segment Information Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2017Reportable_segment
Segment Reporting Information [Line Items]
Number of reportable segments	12
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	6
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	3

Segment Information Segment 195

Segment Information Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended		12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				$ 14,195		$ 13,960		$ 15,200
Competitive businesses natural gas revenues	[1]				2,575		2,146		2,433
Competitive businesses other revenues	[1]				590		211		757
Rate-regulated electric revenues	[1]				14,840		13,869		9,876
Rate-regulated natural gas revenues	[1]				1,333		1,166		1,176
Shared service and other revenues	[1]				0		7		5
Operating revenues from affiliates					7		10		9
Depreciation and amortization					3,828		3,936		2,450
Operating Expenses	[1]				29,720		28,200		25,056
Equity in losses of unconsolidated affiliates					(32)		(24)		(7)
Interest expense, net					1,560		1,536		1,033
Income (loss) before income taxes					3,756		1,989		3,330
Income taxes					(125)		761		1,073
Net Income (Loss)					3,849		1,204		2,250
Capital expenditures					7,584		8,553		7,624
Assets	[2]		$ 114,904		116,700		114,904
Predecessor [Member]
Segment Reporting Information [Line Items]
Equity in losses of unconsolidated affiliates									0
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					1,115		1,439		749
Equity in losses of unconsolidated affiliates									(8)
Income (loss) before income taxes					1,429		873		1,850
Income taxes					(1,375)		290		502
Net Income (Loss)					2,771		558		1,340
Capital expenditures					2,259		3,078		3,841
Assets	[3]		46,974		48,387		46,974
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[4]				121		47		18
PECO Energy Co Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[5]				1		1		1
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]				138		290		224
Baltimore Gas And Electric Company Affiliate [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[5]				4		4		4
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[7]				388		608		502
Potomac Electric Power Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					255	[8]	295	[9]	0	[8]
Delmarva Power and Light Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					179	[10]	154	[8]	0	[10]
Atlantic City Electric Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					29	[9]	37	[10]	0	[9]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				(1,105)		(1,430)		(744)
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				(1)		(4)		(1)
Rate-regulated electric revenues	[1]				(29)		(31)		(5)
Rate-regulated natural gas revenues	[1]				(10)		(13)		(15)
Shared service and other revenues	[1]				(1,880)		(1,686)		(1,367)
Operating revenues from affiliates	[11]				2		5		5
Depreciation and amortization					0		0		0
Operating Expenses	[1]				(3,026)		(3,164)		(2,131)
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					0		0		0
Income (loss) before income taxes					(2)		(5)		(5)
Income taxes					0		0		0
Net Income (Loss)					(2)		(5)		(5)
Capital expenditures					0		0		0
Assets			(11,334)		(10,552)		(11,334)
Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		(13)		(14)
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		(3)
Operating revenues from affiliates			(13)		(19)
Depreciation and amortization			0		(1)
Operating Expenses			(13)		(17)
Interest expense, net			0		(1)
Income (loss) before income taxes			71		(404)
Income taxes			0		0
Net Income (Loss)			45		50
Capital expenditures			0		0
Assets			(4,724)		(4,987)		(4,724)
Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	$ (4)							(2)
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Operating revenues from affiliates		(4)							(15)
Depreciation and amortization		(4)							0
Operating Expenses		(3)							0
Interest expense, net		(2)							(1)
Income (loss) before income taxes		(118)							(29)
Income taxes		0							27
Net Income (Loss)		0							(1)
Capital expenditures		0							0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[13]				15,300		15,390		15,944
Competitive businesses natural gas revenues	[1],[13]				2,575		2,146		2,433
Competitive businesses other revenues	[1],[13]				591		215		758
Rate-regulated electric revenues	[1],[13]				0		0		0
Rate-regulated natural gas revenues	[1],[13]				0		0		0
Shared service and other revenues	[1],[13]				0		0		0
Depreciation and amortization	[13]				1,457		1,879		1,054
Operating Expenses	[1],[13]				17,993		16,856		16,872
Equity in losses of unconsolidated affiliates	[13]				(33)		(25)		(8)
Interest expense, net	[13]				440		364		365
Income (loss) before income taxes	[13]				1,429		873		1,850
Income taxes	[13]				(1,375)		290		502
Net Income (Loss)	[13]				2,771		558		1,340
Capital expenditures	[13]				2,259		3,078		3,841
Assets	[13]		46,974		48,387		46,974
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[13]				1,110		1,428		745
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				5,536		5,254		4,905
Rate-regulated natural gas revenues	[1]				0		0		0
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					850		775		707
Operating Expenses	[1]				4,214		4,056		3,889
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					361		461		332
Income (loss) before income taxes					984		679		706
Income taxes					417		301		280
Net Income (Loss)					567		378		426
Capital expenditures					2,250		2,734		2,398
Assets			28,335		29,726		28,335
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				15		15		4
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				2,375		2,531		2,486
Rate-regulated natural gas revenues	[1]				495		463		546
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					286		270		260
Operating Expenses	[1]				2,215		2,292		2,404
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					126		123		114
Income (loss) before income taxes					538		587		521
Income taxes					104		149		143
Net Income (Loss)					434		438		378
Capital expenditures					732		686		601
Assets			10,831		10,170		10,831
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				7		8		2
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]				0		0		0
Competitive businesses natural gas revenues	[1]				0		0		0
Competitive businesses other revenues	[1]				0		0		0
Rate-regulated electric revenues	[1]				2,489		2,609		2,490
Rate-regulated natural gas revenues	[1]				687		624		645
Shared service and other revenues	[1]				0		0		0
Depreciation and amortization					473		423		366
Operating Expenses	[1]				2,562		2,683		2,578
Equity in losses of unconsolidated affiliates					0		0		0
Interest expense, net					105		103		99
Income (loss) before income taxes					525		468		477
Income taxes					218		174		189
Net Income (Loss)					307		294		288
Capital expenditures					882		934		719
Assets			8,704		9,104		8,704
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				16		21		14
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[14]		0		0				0
Competitive businesses natural gas revenues	[1],[14]		0		0				0
Competitive businesses other revenues	[1],[14]		0		0				0
Rate-regulated electric revenues	[1],[14]		3,506	[12]	4,469	[12]			0
Rate-regulated natural gas revenues	[1],[14]		92	[12]	161	[12]			0
Shared service and other revenues	[1],[14]		45	[12]	49	[12]			0
Depreciation and amortization	[14]		515		675				0
Operating Expenses	[1],[14]		3,549		3,911				0
Equity in losses of unconsolidated affiliates	[14]		0		0				0
Interest expense, net	[14]		195		245				0
Income (loss) before income taxes	[14]		(58)		578				0
Income taxes	[14]		3		217				0
Net Income (Loss)	[14]		(61)		362				0
Capital expenditures	[14]		1,008		1,396				0
Assets	[14]		21,025		21,247		21,025
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	1,096							4,770
Rate-regulated natural gas revenues	[12]	57							165
Shared service and other revenues	[12]	0							0
Depreciation and amortization		152							624
Operating Expenses		1,048							4,308
Interest expense, net		65							280
Income (loss) before income taxes		36							481
Income taxes		17							163
Net Income (Loss)		19							327
Capital expenditures		273							1,230
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[14]		45		50				0
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0							0
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		1,675		2,158
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		0
Depreciation and amortization			224		321
Operating Expenses			1,577		1,760
Interest expense, net			98		121
Income (loss) before income taxes			36		310
Income taxes			26		105
Net Income (Loss)			10		205
Capital expenditures			489		628
Assets			7,335		7,832		7,335
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	511							2,129
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Depreciation and amortization		71							256
Operating Expenses		443							1,790
Interest expense, net		29							124
Income (loss) before income taxes		47							289
Income taxes		15							102
Net Income (Loss)		32							187
Capital expenditures		97							544
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			4		6
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1							5
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		850		1,139
Rate-regulated natural gas revenues	[12]		92		161
Shared service and other revenues	[12]		0		0
Depreciation and amortization			120		167
Operating Expenses			952		1,071
Interest expense, net			38		51
Income (loss) before income taxes			(30)		192
Income taxes			5		71
Net Income (Loss)			(35)		121
Capital expenditures			277		428
Assets			4,153		4,357		4,153
Delmarva Power and Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	279							1,138
Rate-regulated natural gas revenues	[12]	56							164
Shared service and other revenues	[12]	0							0
Depreciation and amortization		37							148
Operating Expenses		284							1,137
Interest expense, net		12							50
Income (loss) before income taxes		43							125
Income taxes		17							49
Net Income (Loss)		26							76
Capital expenditures		72							352
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			5		8
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2							6
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]		989		1,186
Rate-regulated natural gas revenues	[12]		0		0
Shared service and other revenues	[12]		0		0
Depreciation and amortization			128		146
Operating Expenses			1,000		1,029
Interest expense, net			47		61
Income (loss) before income taxes			(51)		103
Income taxes			(5)		26
Net Income (Loss)			(47)		77
Capital expenditures			218		312
Assets			3,457		3,445		3,457
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12]	268							1,295
Rate-regulated natural gas revenues	[12]	0							0
Shared service and other revenues	[12]	0							0
Depreciation and amortization		37							175
Operating Expenses		251							1,161
Interest expense, net		15							64
Income (loss) before income taxes		5							73
Income taxes		1							33
Net Income (Loss)		5							40
Capital expenditures		93							300
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates			2		2
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1							4
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[15]				0		0		0
Competitive businesses natural gas revenues	[1],[15]				0		0		0
Competitive businesses other revenues	[1],[15]				0		0		0
Rate-regulated electric revenues	[1],[15]				0		0		0
Rate-regulated natural gas revenues	[1],[15]				0		0		0
Shared service and other revenues	[1],[15]				1,831		1,648		1,372
Depreciation and amortization	[15]				87		74		63
Operating Expenses	[1],[15]				1,851		1,928		1,444
Equity in losses of unconsolidated affiliates	[15]				1		1		1
Interest expense, net	[15]				283		290		123
Income (loss) before income taxes	[15]				(296)		(555)		(219)
Income taxes	[15]				294		(156)		(41)
Net Income (Loss)	[15]				(590)		(398)		(177)
Capital expenditures	[15]				65		113		65
Assets	[15]		10,369		8,618		10,369
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12],[16]		5		0
Rate-regulated natural gas revenues	[12],[16]		0		0
Shared service and other revenues	[12],[16]		45		52
Depreciation and amortization	[16]		43		42
Operating Expenses	[16]		33		68
Interest expense, net	[16]		12		13
Income (loss) before income taxes	[16]		(84)		377
Income taxes	[16]		(23)		15
Net Income (Loss)	[16]		(34)		(91)
Capital expenditures	[16]		24		28
Assets	[16]		10,804		10,600		10,804
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[12],[16]	42							210
Rate-regulated natural gas revenues	[12],[16]	1							1
Shared service and other revenues	[12],[16]	0							0
Depreciation and amortization	[16]	11							45
Operating Expenses	[16]	73							220
Interest expense, net	[16]	11							43
Income (loss) before income taxes	[16]	59							23
Income taxes	[16]	(16)							(48)
Net Income (Loss)	[16]	(44)							25
Capital expenditures	[16]	11							34
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11],[15]				1,824		1,647		1,367
Corporate and Other [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[16]		$ 47		53
Corporate and Other [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[16]	$ 0							0
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					25		(33)		(74)
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates					(25)		10		(2)
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]				$ (3,020)		$ (3,159)		$ (2,127)
[1]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.
[2]	Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.
[3]	Generation’s consolidated assets include $9,524 million and $8,817 million at December 31, 2017 and 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,510 million and $3,170 million at December 31, 2017 and 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities.
[4]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[5]	The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 3—Regulatory Matters for additional information.
[6]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3—Regulatory Matters for additional information.
[7]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[8]	(d)Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3—Regulatory Matters for additional information.
[9]	Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3—Regulatory Matters for additional information.
[10]	(e)Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[11]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[12]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.
[13]	Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. For the year ended December 31, 2017, intersegment revenues for Generation include revenue from sales to PECO of $138 million, sales to BGE of $388 million, sales to Pepco of $255 million, sales to DPL of $179 million and sales to ACE of $29 million in the Mid-Atlantic region, and sales to ComEd of $121 million in the Midwest region, which eliminate upon consolidation. For the year ended December 31, 2016, intersegment revenues for Generation include revenue from sales to PECO of $290 million and sales to BGE of $608 million in the Mid-Atlantic region, and sales to ComEd of $47 million in the Midwest region, which eliminate upon consolidation. For the Successor period of March 24, 2016 to December 31, 2016, intersegment revenues for Generation include revenue from sales to Pepco of $295 million, sales to DPL of $154 million and sales to ACE of $37 million in the Mid-Atlantic region, which eliminate upon consolidation. For the year ended December 31, 2015, intersegment revenues for Generation include revenue from sales to PECO of $224 million and sales to BGE of $502 million in the Mid-Atlantic region, and sales to ComEd of $18 million in the Midwest region, which eliminate upon consolidation.
[14]	Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2017. PHI includes the three reportable segments: Pepco, DPL and ACE. See tables below for PHI's predecessor periods, including Pepco, DPL and ACE, for January 1, 2016 to March 23, 2016 and for the year ended December 31, 2015.
[15]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[16]	Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. For the predecessor periods presented, Other includes the activity of PHI’s unregulated businesses which were distributed to Exelon and Generation as a result of the PHI Merger.

Segment Information Segment 196

Segment Information Segment Information- Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues		$ 8,381	$ 8,769	$ 7,623	$ 8,757	$ 7,875	$ 9,002	$ 6,910	$ 7,573	$ 33,531	$ 31,360	$ 29,447
Operating revenues from affiliates										7	10	9
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,540	6,179	5,900
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,181	4,412	4,710
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,002	1,769	2,212
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										1,518	1,156	985
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										962	837	857
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues										1,049	907	1,102
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										15,252	15,260	15,766
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									3,214	2,491	3,369
Unrealized Gain (Loss) on Securities										(131)	(500)	203
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										18,466	17,751	19,135
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									5,515	6,212	5,974
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									4,206	4,402	4,712
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									2,010	1,778	2,217
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									1,535	1,198	996
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									958	831	863
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									1,076	969	1,182
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									15,300	15,390	15,944
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts										(38)	(52)	7
Unrealized Gain (Loss) on Securities										(175)	(41)	257
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									18,466	17,751	19,135
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[2]									3,166	2,361	3,191
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[3]									2	5	5
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										25	(33)	(74)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(25)	10	(2)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(8)	(9)	(5)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(17)	(42)	(11)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										4	6	(6)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(27)	(62)	(80)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										(48)	(130)	(178)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]									48	130	178
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										$ 0	$ 0	$ 0
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Also includes a $38 million decrease to revenues, a $52 million decrease to revenues, and a $7 million increase to revenues for the amortization of intangible assets related to commodity contracts recorded at fair value for the years ended December 31, 2017, 2016, and 2015, respectively, unrealized mark-to-market losses of $131 million, losses of $500 million, and gains of $203 million for the years ended December 31, 2017, 2016, and 2015, respectively, and elimination of intersegment revenues.
[2]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants
[3]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

Segment Information Segment 197

Segment Information Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Nuclear Fuel Amortization	[1]	$ 1,096	$ 1,159	$ 1,116
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Total RNF		3,214	3,317	3,571
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Total RNF		2,820	2,971	2,892
Generation New England [Member]
Segment Reporting Information [Line Items]
Total RNF		514	438	461
Generation New York [Member]
Segment Reporting Information [Line Items]
Total RNF		976	742	634
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Total RNF		332	281	293
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Total RNF		305	336	250
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Total RNF		8,161	8,085	8,101
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Total RNF	[2]	615	836	1,013
Unrealized Gain (Loss) on Securities		(131)	(500)	203
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Total RNF		8,776	8,921	9,114
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	3,105	3,282	3,556
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	2,810	2,969	2,912
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	538	467	519
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	975	761	584
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	575	412	425
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	476	483	440
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	8,479	8,374	8,436
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2],[3]	297	547	678
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel		(54)	(57)	8
Unrealized Gain (Loss) on Securities		(175)	(41)	257
Nuclear Fuel Amortization		12	60
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[3]	8,776	8,921	9,114
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		109	35	15
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		10	2	(20)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(24)	(29)	(58)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		1	(19)	50
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(243)	(131)	(132)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(171)	(147)	(190)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		(318)	(289)	(335)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment RNF	[2]	318	289	335
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment RNF		$ 0	$ 0	$ 0
[1]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million decrease in RNF, a $57 million decrease in RNF, and a $8 million increase in RNF for the amortization of intangible assets and liabilities related to commodity contracts for the years ended December 31, 2017, 2016, and 2015, respectively, unrealized mark-to-market losses of $175 million, losses of $41 million, and gains of $257 million for the years ended December 31, 2017, 2016, and 2015, respectively, accelerated nuclear fuel amortization associated with the announced early retirement decision for Clinton and Quad Cities as discussed in Note 8 - Early Nuclear Plant Retirements of $12 million and $60 million for the year ended December 31, 2017 and 2016, and the elimination of intersegment revenues net of purchased power and fuel expense.
[3]	Includes purchases and sales from third parties and affiliated sales to the Utility Registrants.

Related Party Transactions - Re

Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Related Party Transaction [Line Items]
Operating revenues from affiliates				$ 7		$ 10		$ 9
Interest expense to affiliates, net				36		41		41
Income (Loss) from Equity Method Investments				(32)		(24)		(7)
Cash dividends paid to parent				1,236		1,166		1,105
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]			1		1		1
Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]			4		4		4
Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		5		4
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				1		1		1
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				14		13		13
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				10		16		16
Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1,115		1,439		749
Related Party Transaction, Purchases from Related Party				19		12		14
Operating and maintenance from affiliates				697		663		620
Interest expense to affiliates, net				39		39		43
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Income (Loss) from Equity Method Investments								(8)
Cash distribution paid to member				659		922		2,474
Cash contributions received from affiliates				102		142		47
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[2]			121		47		18
Related Party Transaction, Purchases from Related Party				13		0		0
Operating and maintenance from affiliates	[3]			7		7		4
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[4]			138		290		224
Operating and maintenance from affiliates	[3]			1		3		2
Interest expense to affiliates, net				1		0		0
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[5]			388		608		502
Related Party Transaction, Purchases from Related Party				9		12		14
Operating and maintenance from affiliates	[3]			1		1		0
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				255	[6]	295	[7]	0	[6]
Operating and maintenance from affiliates				0		1		0
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				179	[8]	154	[6]	0	[8]
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				29	[7]	37	[8]	0	[7]
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		2		1
Operating and maintenance from affiliates	[9]			689		650		614
Capitalized costs	[9]			98		98		76
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				4		6		4
Related Party Transaction, Purchases from Related Party				(3)		0		0
Operating and maintenance from affiliates				(2)		0		0
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net	[10]			37		39		43
Cash distribution paid to member				659		922		2,474
Cash contributions received from affiliates				102		142		47
Exelon Generation Co L L C [Member] | Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions				(33)		(25)		(8)
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates				1		1		0
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				1		0		0
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				15		15		4
Related Party Transaction, Purchases from Related Party				108		47		18
Operating and maintenance from affiliates				270		227		195
Interest expense to affiliates, net				13		13		13
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				422		369		299
Proceeds from Contributions from Parent				651		315		202
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				9		7		4
Related Party Transaction, Purchases from Related Party	[11]			108		47		18
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		6		0
Operating and maintenance from affiliates	[12]			270		225		195
Capitalized costs	[12]			118		112		103
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				13		13		13
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				422		369		299
Proceeds from Contributions from Parent				651		315		202
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				7		8		2
Related Party Transaction, Purchases from Related Party				135		287		220
Operating and maintenance from affiliates				149		146		110
Interest expense to affiliates, net				11		12		12
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				288		277		279
Proceeds from Contributions from Parent				16		18		16
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		0
Operating and maintenance from affiliates				1		1		0
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[13]			1		3		2
Related Party Transaction, Purchases from Related Party	[14]			135		287		220
Operating and maintenance from affiliates				2		2		3
Interest income from affiliates, net				(1)		0		0
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				5		3		0
Operating and maintenance from affiliates	[15]			146		142		107
Capitalized costs	[15]			59		57		40
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				6		6		6
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				288		277		279
Proceeds from Contributions from Parent				16		18		16
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				16		21		14
Related Party Transaction, Purchases from Related Party				384		604		498
Operating and maintenance from affiliates				153		132		118
Interest expense to affiliates, net				10		16		16
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				198		179		158
Proceeds from Contributions from Parent				184		61		7
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				0		1		0
Operating and maintenance from affiliates				0		1		0
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		0
Operating and maintenance from affiliates				1		1		0
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[16]			10		13		14
Related Party Transaction, Purchases from Related Party	[17]			384		604		498
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				5		6		0
Operating and maintenance from affiliates	[18]			152		130		118
Capitalized costs	[18]			54		36		28
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net				10		16		16
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				198		179		158
Proceeds from Contributions from Parent				184		61		7
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party		$ 0						0
Pepco Holdings LLC [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			$ 45	50
Related Party Transaction, Purchases from Related Party			486	463
Operating and maintenance from affiliates			89	150
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			0	1
Income (Loss) from Equity Method Investments			0	(1)
Cash distribution paid to member			273	311
Cash dividends paid to parent			0	0
Proceeds from Contributions from Parent			1,251	758
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0
Related Party Transaction, Purchases from Related Party			486	463
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			44	48
Operating and maintenance from affiliates	[19]		86	145
Pepco Holdings LLC [Member] | Other Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates			3	5
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			273	311
Proceeds from Contributions from Parent			1,251	758
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			$ 0	2
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		5		5
Related Party Transaction, Purchases from Related Party				255		295		0
Operating and maintenance from affiliates				58		35		4
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				133		136		146
Proceeds from Contributions from Parent				161		187		112
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance				248		302		266
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[20]			0		1		0
Related Party Transaction, Purchases from Related Party	[21]			255		295		0
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[22]			53		31		0
Potomac Electric Power Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				133		136		146
Proceeds from Contributions from Parent				161		187		112
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[23]			29		39		26
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		4		5
Operating and maintenance from affiliates	[22]			5		4		4
Operating and maintenance	[22]			219		263		240
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				8		7		6
Related Party Transaction, Purchases from Related Party				179		154		0
Operating and maintenance from affiliates				32		19		1
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				112		54		92
Proceeds from Contributions from Parent				0		152		75
Delmarva Power and Light Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance				174		202		182
Delmarva Power and Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[24]			179		154		0
Delmarva Power and Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[25]			31		18		0
Delmarva Power and Light Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		2		1
Operating and maintenance from affiliates				1		1		1
Delmarva Power and Light Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				112		54		92
Proceeds from Contributions from Parent				0		152		75
Delmarva Power and Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[26]			9		8		3
Delmarva Power and Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				6		5		5
Operating and maintenance	[25]			165		194		179
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				2		3		4
Related Party Transaction, Purchases from Related Party				29		37		0
Operating and maintenance from affiliates				28		18		3
Income (Loss) from Equity Method Investments				0		0		0
Cash dividends paid to parent				68		63		12
Proceeds from Contributions from Parent				0		139		95
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[27]			29		37		0
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[28]			25		15		0
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		1		2
Operating and maintenance from affiliates				3		3		3
Atlantic City Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent				68		63		12
Cash contributions received from affiliates				0		139		95
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates				1		2		2
Operating and maintenance	[28]			$ 135		$ 155		$ 143
[1]	The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 3—Regulatory Matters for additional information.
[2]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[3]	Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and BGE and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations.
[4]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3—Regulatory Matters for additional information.
[5]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[6]	(d)Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3—Regulatory Matters for additional information.
[7]	Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3—Regulatory Matters for additional information.
[8]	(e)Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[9]	Generation receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[10]	The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation.
[11]	ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 12—Derivative Financial Instruments for additional information.
[12]	ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[13]	PECO provides energy to Generation for Generation’s own use.
[14]	PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.
[15]	PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[16]	BGE provides energy to Generation for Generation’s own use.
[17]	BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[18]	BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[19]	PHI receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[20]	Pepco provides energy to Generation for Generation’s own use.
[21]	Pepco procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[22]	Pepco receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[23]	PES performs underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco.
[24]	DPL procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[25]	DPL receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[26]	PES performs underground transmission construction services, including services that are treated as capital costs, for DPL.
[27]	(a)ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. See Note 3—Regulatory Matters for additional information.
[28]	ACE receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

Related Party Transactions -199

Related Party Transactions - Related Party Transactions included in Consolidated Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		$ 5	$ 8
Due to Related Parties, Noncurrent		389	641
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		4	4
Due to Related Parties, Noncurrent		205	205
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		1	1
Due to Related Parties, Noncurrent		81	81
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Noncurrent		103	103
BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	3
Due to Related Parties, Noncurrent		0	252
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		140	156
Notes Payable, Related Parties, Current		54	55
Accounts Payable, Related Parties, Current		123	137
Due to Related Parties, Noncurrent		910	922
Due to Affiliate, Noncurrent		3,065	2,608
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[1]	26	33
Accounts Payable, Related Parties, Current	[1]	4	0
Due to Affiliate, Noncurrent	[2]	537	438
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[3]	28	14
Accounts Payable, Related Parties, Current		12	9
Due to Affiliate, Noncurrent	[2]	2,528	2,169
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[4]	12	16
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[5]	36	44
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[6]	6	9
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[7]	24	26
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[8]	1	5
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	8
Notes Payable, Related Parties, Current		54	55
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		7	1
Accounts Payable, Related Parties, Current		12	7
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[9]	21	22
Due to Related Parties, Noncurrent	[10]	910	922
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[8]	74	99
Due to Affiliate, Noncurrent	[8]	0	1
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		13	356
Total receivable from affiliates (noncurrent)		2,528	2,170
Accounts Payable, Related Parties, Current		74	65
Due to Related Parties, Noncurrent		205	205
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		12	9
Total receivable from affiliates (noncurrent)	[11]	2,528	2,169
Accounts Payable, Related Parties, Current	[12]	28	14
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	2
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		4	4
Due to Related Parties, Noncurrent		205	205
Commonwealth Edison Co [Member] | Voluntary Employee Beneficiary Association Trust Affiliate [Member]
Related Party Transaction [Line Items]
Prepaid Expense Other, Noncurrent	[13]	2	5
Receivables from affiliates		1	2
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)		0	1
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates	[14]	0	345
Accounts Payable, Related Parties, Current		3	3
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[15]	39	42
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		1
Accounts Payable, Related Parties, Current		52	55
Due to Related Parties, Noncurrent		0	252
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[16]	24	26
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	2
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	3
Due to Related Parties, Noncurrent		0	252
Baltimore Gas and Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		1	0
Accounts Payable, Related Parties, Current		2	1
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		1	1
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[17]	25	22
Pepco Holdings LLC [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		90	94
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		54	74
Pepco Holdings LLC [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		1	0
Pepco Holdings LLC [Member] | Other Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		5	4
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		6	6
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[18]	24	10
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		74	74
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[19]	36	44
Potomac Electric Power Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	1
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[20]	27	25
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[20]	11	4
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	3
Accounts Payable, Related Parties, Current		46	38
Delmarva Power and Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[21]	12	16
Delmarva Power and Light Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	1
Delmarva Power and Light Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	2
Delmarva Power and Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[22]	27	19
Delmarva Power and Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[22]	7	3
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		29	29
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[23]	6	9
Atlantic City Electric Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		0	2
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[24]	18	16
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[24]	5	2
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	4
Total receivable from affiliates (noncurrent)		537	438
Accounts Payable, Related Parties, Current		53	63
Due to Related Parties, Noncurrent		184	184
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	[25]	537	438
Accounts Payable, Related Parties, Current	[26]	22	33
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	2
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		1	1
Due to Related Parties, Noncurrent		81	81
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Due to Related Parties, Noncurrent		103	103
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates		0	2
PECO Energy Co [Member] | Voluntary Employee Beneficiary Association Trust Affiliate [Member]
Related Party Transaction [Line Items]
Prepaid Expense Other, Noncurrent	[27]	0	1
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current		1	1
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	[28]	$ 29	$ 28
[1]	Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has a ten-year agreement with PECO to sell solar AECs. See Note 3—Regulatory Matters for additional information.
[2]	Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 15—Asset Retirement Obligations.
[3]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.
[4]	(e)Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[5]	(d)Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. See Note 3—Regulatory Matters for additional information.
[6]	Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. See Note 3—Regulatory Matters for additional information.
[7]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[8]	Generation receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[9]	The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation.
[10]	In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets.
[11]	ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers.
[12]	ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 12—Derivative Financial Instruments for additional information.
[13]	The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.
[14]	Represents indemnification from Exelon Corporate related to the like-kind exchange.
[15]	ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[16]	BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[17]	BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[18]	PHI receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[19]	Pepco procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[20]	Pepco receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[21]	DPL procures a portion of its electricity and gas supply requirements from Generation under its MDPSC and DPSC approved market based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.
[22]	DPL receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[23]	(a)ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. See Note 3—Regulatory Matters for additional information.
[24]	ACE receives a variety of corporate support services from BSC and PHISCO, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.
[25]	PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers.
[26]	PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.
[27]	The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time.
[28]	PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

Quarterly Data (Unaudited) - Qu

Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended										9 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Line Items]
Operating Revenues		$ 8,381	$ 8,769	$ 7,623	$ 8,757	$ 7,875	$ 9,002	$ 6,910	$ 7,573				$ 33,531	$ 31,360	$ 29,447
Operating Income (Loss)		1,258	1,475	232	1,296	714	1,267	647	483				4,260	3,112	4,409
Net Income (Loss) Attributable to Common Stockholders		1,871	824	80	995	204	490	267	173				3,770	1,134	2,269
Net Income (Loss)													3,849	1,204	2,250
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 12	4,654	4,751	4,174	4,888	4,388	5,035	3,589	4,739				18,466	17,751	19,135
Operating Income (Loss)		501	500	(467)	387	94	342	(13)	415				921	836	2,275
Net (Loss) Income Attributable to Membership Interest		2,215	305	(250)	423	(41)	236	(8)	310
Net Income (Loss)													2,771	558	1,340
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		1,309	1,571	1,357	1,298	1,223	1,497	1,286	1,249				5,536	5,254	4,905
Operating Income (Loss)		286	404	319	314	217	389	324	274				1,323	1,205	1,017
Net Income (Loss)		120	189	118	141	80	37	145	115				567	378	426
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		729	715	630	796	701	788	664	841				2,870	2,994	3,032
Operating Income (Loss)		157	169	137	192	150	204	152	196				655	702	630
Net Income (Loss) Attributable to Common Stockholders		107	112	88	127	92	122	100	124				434	438	378
Net Income (Loss)													434	438	378
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		813	738	674	951	812	812	680	929				3,176	3,233	3,135
Operating Income (Loss)		163	124	98	228	190	115	59	187				614	550	558
Net Income (Loss) Attributable to Common Stockholders		76	62	45	125	103	54	31	98				307	286	275
Net Income (Loss)													307	294	288
Pepco Holdings LLC [Member] | Predecessor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues											$ 1,153				4,935
Operating Income (Loss)											105				673
Net (Loss) Income Attributable to Membership Interest											19
Net Income (Loss)											$ 19				327
Pepco Holdings LLC [Member] | Successor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		1,121	1,310	1,074	1,175	1,078	1,394	1,066	105	[1]		$ 3,643	4,679
Operating Income (Loss)		159	285	148	180	90	279	136	(411)	[1]		93	769
Net (Loss) Income Attributable to Membership Interest		4	153	66	140	30	166	52	(309)	[1]
Net Income (Loss)												$ (61)	362
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		510	604	514	530	491	635	509	551				2,158	2,186	2,129
Operating Income (Loss)		87	149	84	79	51	132	97	(105)				399	174	385
Net Income (Loss) Attributable to Common Stockholders		17	87	43	58	23	79	49	(108)
Net Income (Loss)													205	42	187
Delmarva Power and Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		330	327	282	362	303	331	281	362				1,300	1,277	1,302
Operating Income (Loss)		52	59	41	78	20	72	30	(72)				229	50	165
Net Income (Loss) Attributable to Common Stockholders		14	31	19	57	7	44	12	(72)
Net Income (Loss)													121	(9)	76
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		271	370	270	275	275	421	270	291				1,186	1,257	1,295
Operating Income (Loss)		28	79	25	25	26	83	19	(121)				157	7	134
Net Income (Loss) Attributable to Common Stockholders		$ 0	$ 41	$ 8	$ 28	$ 8	$ 47	$ 3	$ (100)
Net Income (Loss)													$ 77	$ (42)	$ 40
[1]	Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.

Quarterly Data (Unaudited) -201

Quarterly Data (Unaudited) - Quarterly Per Share Information (Details) - $ / shares shares in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Weighted average common shares outstanding — basic	964	962	934	928	925	925	924	923	947	924	890
Net Income per Basic Share	$ 1.94	$ 0.86	$ 0.09	$ 1.07	$ 0.22	$ 0.53	$ 0.29	$ 0.19	$ 3.98	$ 1.23	$ 2.55
Weighted average common shares outstanding — diluted	967	965	936	930	928	927	926	925	949	927	893
Net Income per Diluted Share	$ 1.93	$ 0.85	$ 0.09	$ 1.07	$ 0.22	$ 0.53	$ 0.29	$ 0.19	$ 3.97	$ 1.22	$ 2.54

Quarterly Data (Unaudited) -202

Quarterly Data (Unaudited) - Quarterly Composite Common Stock Prices and Dividends (Details) - $ / shares	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
Class of Stock [Line Items]
Dividends	$ 0.328	$ 0.328	$ 0.328	$ 0.328	$ 0.318	$ 0.318	$ 0.318	$ 0.31
Close	39.41	37.67	36.07	35.98	35.49	33.29	36.36	35.86
Maximum [Member]
Class of Stock [Line Items]
Close	42.67	38.78	37.44	37.19	36.36	37.70	36.37	35.95
Minimum [Member]
Class of Stock [Line Items]
Close	$ 37.55	$ 35.37	$ 33.30	$ 34.47	$ 29.82	$ 32.86	$ 33.18	$ 26.26

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended									12 Months Ended
		Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Revenues				$ 8,381	$ 8,769	$ 7,623	$ 8,757	$ 7,875	$ 9,002	$ 6,910	$ 7,573		$ 33,531	$ 31,360	$ 29,447
Nuclear Fuel Amortization	[1]												1,096	1,159	1,116
Exelon Generation Co L L C [Member]
Subsequent Event [Line Items]
Revenues		$ 12		$ 4,654	$ 4,751	$ 4,174	$ 4,888	$ 4,388	$ 5,035	$ 3,589	$ 4,739		18,466	17,751	19,135
Nuclear Fuel Amortization	[1]												1,096	$ 1,159	$ 1,116
Zero emission credit costs | Exelon Generation Co L L C [Member]
Subsequent Event [Line Items]
Revenues													$ 311
Subsequent Event [Member] | Facility Closing [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member]
Subsequent Event [Line Items]
Nuclear Fuel Amortization												$ 40
Subsequent Event [Member] | Facility Closing [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member] | Minimum [Member]
Subsequent Event [Line Items]
Other Nonrecurring Expense			$ 25
Other Restructuring Costs			5
Restructuring and Related Cost, Accelerated Depreciation												110
Subsequent Event [Member] | Facility Closing [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member] | Maximum [Member]
Subsequent Event [Line Items]
Other Nonrecurring Expense			35
Other Restructuring Costs			10
Restructuring and Related Cost, Accelerated Depreciation												140
Accretion Expense, Including Asset Retirement Obligations												$ 5
Subsequent Event [Member] | Facility Closing [Member] | Oyster Creek [Member] | Zero emission credit costs | Exelon Generation Co L L C [Member]
Subsequent Event [Line Items]
Revenues			150
Increase (Decrease) in Regulatory Liabilities			$ 100
[1]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Schedule I - Condensed Finan204

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Operations and Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended								9 Months Ended	12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Expenses [Abstract]
Total operating expenses											$ 29,720	$ 28,200	$ 25,056
Operating Income (Loss)		$ 1,258	$ 1,475	$ 232	$ 1,296	$ 714	$ 1,267	$ 647	$ 483		4,260	3,112	4,409
Other income and (deductions)
Interest expense, net											(1,524)	(1,495)	(992)
Equity in losses of unconsolidated affiliates											(32)	(24)	(7)
Other, net											1,056	413	(46)
Total other income and (deductions)											(504)	(1,123)	(1,079)
Income before income taxes											3,756	1,989	3,330
Income taxes											(125)	761	1,073
Net Income (Loss)											3,849	1,204	2,250
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax											56	48	46
Actuarial loss reclassified to periodic cost, net of tax											197	184	220
Unrealized gain (loss) on cash flow hedges, net of taxes										$ 0	3	2	9
Unrealized gain (loss) on marketable securities, net of taxes											4	(4)	(3)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax											6	1	0
Unrealized gain (loss) on foreign currency translation, net of taxes											7	10	(21)
Other comprehensive income (loss)											171	(36)	60
Comprehensive income											3,943	1,098	2,329
Exelon Corporate [Member]
Operating Expenses [Abstract]
Operating and maintenance											10	221	0
Operating and maintenance from affiliates	[1]										25	51	43
Other											4	4	4
Total operating expenses											39	276	47
Operating Income (Loss)											(39)	(276)	(47)
Other income and (deductions)
Interest expense, net											(315)	(312)	(168)
Equity in losses of unconsolidated affiliates											4,398	1,521	2,461
Interest income from affiliates, net											40	39	43
Other, net											1	7	(43)
Total other income and (deductions)											4,124	1,255	2,293
Income before income taxes											4,085	979	2,246
Income taxes											315	(155)	(23)
Net Income (Loss)											3,770	1,134	2,269
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost, net of tax											56	48	46
Actuarial loss reclassified to periodic cost, net of tax											197	184	220
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax											(10)	181	99
Unrealized gain (loss) on cash flow hedges, net of taxes											3	2	9
Unrealized gain (loss) on marketable securities, net of taxes											6	(4)	(3)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax											6	1	0
Unrealized gain (loss) on foreign currency translation, net of taxes											7	10	(21)
Other comprehensive income (loss)											173	(36)	60
Comprehensive income											$ 3,943	$ 1,098	$ 2,329
[1]	Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead.

Schedule I - Condensed Finan205

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net cash flows provided by operating activities	$ 7,480	$ 8,445	$ 7,616
Cash flows from investing activities
Payments to Acquire Businesses, Net of Cash Acquired		6,962	0
Proceeds from Sale and Collection of Lease Receivables	0	360	0
Capital expenditures	(7,584)	(8,553)	(7,624)
Change in restricted cash	(50)	(42)	66
Other investing activities	(43)	(153)	(119)
Net cash flows used in investing activities	(7,934)	(15,503)	(7,822)
Cash flows from financing activities
Changes in short-term borrowings	621	240	0
Issuance of long-term debt	3,470	4,716	6,709
Retirement of long-term debt	(2,490)	(1,936)	(2,687)
Proceeds from Issuance of Common Stock	0	0	1,868
Dividends paid on common stock	(1,236)	(1,166)	(1,105)
Proceeds from employee stock plans	150	55	32
Other financing activities	(83)	(85)	(99)
Net cash flows provided by financing activities	717	1,191	4,830
Increase (Decrease) in cash and cash equivalents	263	(5,867)	4,624
Cash and cash equivalents at beginning of period	635	6,502	1,878
Cash and cash equivalents at end of period	898	635	6,502
Exelon Corporate [Member]
Net cash flows provided by operating activities	1,921	1,029	3,071
Cash flows from investing activities
Payments to Acquire Businesses, Net of Cash Acquired	0
Increase (Decrease) Due from Affiliates	(129)	1,390	(1,217)
Increase (Decrease) in Due from Affiliates, Current	0	0	550
Investment in affiliates	(1,717)	(1,757)	(212)
Other investing activities	(5)	5	(55)
Net cash flows used in investing activities	(1,851)	(7,324)	(934)
Cash flows from financing activities
Issuance of long-term debt	0	1,800	4,200
Retirement of long-term debt	(569)	(46)	(2,263)
Proceeds from Issuance of Common Stock	0	0	1,868
Dividends paid on common stock	(1,236)	(1,166)	(1,105)
Proceeds from employee stock plans	150	55	32
Other financing activities	(9)	(20)	(58)
Net cash flows provided by financing activities	(14)	623	2,674
Increase (Decrease) in cash and cash equivalents	56	(5,672)	4,811
Cash and cash equivalents at beginning of period	18	5,690	879
Cash and cash equivalents at end of period	$ 74	$ 18	$ 5,690

Schedule I - Condensed Finan206

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 17, 2012
Current assets
Cash and cash equivalents		$ 898	$ 635	$ 6,502	$ 1,878
Prepaid Taxes		0	1,250
Accounts receivable, net
Other		1,132	1,201
Regulatory assets		1,267	1,342
Other		1,242	930
Total current assets		11,834	12,412
Property, plant and equipment, net		74,202	71,555
Deferred debits and other assets
Regulatory assets		8,021	10,046
Other		1,322	1,472
Total assets (a)	[1]	116,700	114,904
Current liabilities
Short-term Debt		929	1,267
Due to Affiliate, Current		360	706
Long-term debt due within one year		2,088	2,430
Accounts payable		3,532	3,441
Unamortized energy contract liabilities		231	407
Accrued expenses		1,835	3,460
Regulatory liabilities		523	602
Other		982	981
Total current liabilities		10,796	13,457
Long-term debt		32,176	31,575
Deferred credits and other liabilities
Regulatory liabilities		9,865	4,187
Pension obligations		3,736	4,248
Non-pension postretirement benefit obligations		2,093	1,848
Other		2,097	1,827
Total liabilities	[1]	84,568	87,292
Commitments and Contingencies						$ 1,000
Shareholders’ equity
Common stock		18,964	18,794
Treasury stock, at cost (2 shares and 35 shares at December 31, 2017 and 2016, respectively)		(123)	(2,327)
Retained earnings		13,503	12,030
Accumulated other comprehensive loss, net		(2,487)	(2,660)
Total shareholders’ equity		29,857	25,837
Liabilities and Equity		116,700	114,904
Exelon Corporate [Member]
Current assets
Cash and cash equivalents		74	18	$ 5,690	$ 879
Accounts receivable, net
Other		431	73
Accounts receivable from affiliates		33	48
Receivables from affiliates		217	88
Regulatory assets		284	263
Other		4	1,250
Total current assets		1,043	1,740
Property, plant and equipment, net		50	51
Deferred debits and other assets
Regulatory assets		3,697	4,033
Investments in affiliates		39,272	34,869
Deferred income taxes		1,431	2,107
Receivable from affiliates		910	922
Other		234	256
Total deferred debits and other assets		45,544	42,187
Total assets (a)		46,637	43,978
Current liabilities
Short-term Debt		500	0
Due to Affiliate, Current		360	706
Long-term debt due within one year		0	570
Accounts payable		2	2
Accrued expenses		99	489
Regulatory liabilities		16	16
Liability, Defined Benefit Plan, Current		65	58
Other		46	50
Total current liabilities		1,088	1,891
Long-term debt		7,161	7,193
Deferred credits and other liabilities
Regulatory liabilities		15	31
Pension obligations		7,792	8,608
Non-pension postretirement benefit obligations		322	7
Deferred income taxes		220	226
Other		180	182
Deferred Credits and Other Liabilities, Noncurrent		8,529	9,054
Total liabilities		16,778	18,138
Commitments and Contingencies
Shareholders’ equity
Common stock		18,966	18,797
Treasury stock, at cost (2 shares and 35 shares at December 31, 2017 and 2016, respectively)		(123)	(2,327)
Retained earnings		13,503	12,030
Accumulated other comprehensive loss, net		(2,487)	(2,660)
Total shareholders’ equity		29,859	25,840
Liabilities and Equity		$ 46,637	$ 43,978
[1]	Exelon’s consolidated assets include $9,565 million and $8,893 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,612 million and $3,356 million at December 31, 2017 and December 31, 2016, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities.

Schedule I - Condensed Finan207

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet - Phantom (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Treasury Stock, Shares held	2,000,000	35,000,000
Exelon Corporate [Member]
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Treasury Stock, Shares held	35,000,000	35,000,000

Schedule I - Condensed Finan208

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Basis of Presentation - Narrative (Details) - Exelon Corporate [Member]	Dec. 31, 2017
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	100.00%
Commonwealth Edison Co [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	99.00%
Baltimore Gas and Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	100.00%
Baltimore Gas and Electric Company [Member] | Preferred Stock [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	0.00%

Schedule I - Condensed Finan209

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Narrative (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Mar. 23, 2017	Nov. 30, 2016
Line of Credit Facility [Line Items]
Document Period End Date		Dec. 31, 2017
Maximum Program Size				$ 98
Line of Credit Facility, Capacity Available for Trade Purchases	[1]	$ 7,657,000,000
Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Short-term Bank Loans and Notes Payable			$ 500,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum Program Size	[2]	9,480,000,000
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Maximum Program Size	[2]	600,000,000
Line of Credit Facility, Capacity Available for Trade Purchases	[1]	$ 555,000,000
[1]	Pepco, DPL and ACE's revolving credit facility is subject to available borrowing capacity. The borrowing capacity may be increased or decreased during the term of the facility, except that (i) the sum of the borrowing capacity must equal the total amount of the facility, and (ii) the aggregate amount of credit used at any given time by each of Pepco, DPL or ACE may not exceed $900 million or the maximum amount of short-term debt the company is permitted to have outstanding by its regulatory authorities. The total number of the borrowing reallocations may not exceed eight per year during the term of the facility.
[2]	Excludes additional credit facility agreements for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $34 million, $34 million, $5 million, $2 million, $2 million and $2 million, respectively, arranged with minority and community banks located primarily within utilities' service territories. These facilities expire on October 12, 2018. These facilities are solely utilized to issue letters of credit. As of December 31, 2017, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Schedule I - Condensed Finan210

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Outstanding Long-term Debt (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2014
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 33,657	$ 33,311
Unamortized debt discount and premium, net		(57)	(68)
Unamortized Debt Issuance Expense	[1]	(201)	(200)
Long-term debt		32,176	31,575
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 1,150	1,150
Debt Instrument, Interest Rate, Stated Percentage		3.497%		2.50%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 11,285	11,868
contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 0	19
Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.50%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		7.60%
Maximum [Member] | contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.50%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.45%
Exelon Corporate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 7,039	7,608
Unamortized debt discount and premium, net		(8)	(8)
Unamortized Debt Issuance Expense		(49)	(57)
Fair value adjustment of consolidated subsidiary		179	220
Long-term debt due within one year		0	(570)
Long-term debt		7,161	7,193
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 1,150	1,150
Debt Instrument, Interest Rate, Stated Percentage		3.50%
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Unsecured Long Term Debt	[2]	$ 5,889	6,439
Exelon Corporate [Member] | contract Payments Junior Subordinate Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 0	$ 19
Debt Instrument, Interest Rate, Stated Percentage		2.50%
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]	7.60%
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]	2.45%
[1]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[2]	Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets.

Schedule I - Condensed Finan211

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Debt Maturities (Details) $ in Millions	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
2,017	$ 2,075
2,018	959
2,019	3,564
2,020	1,513
2,021	3,084
Thereafter	22,852	[1]
Total	34,047
Exelon Corporate [Member]
Debt Instrument [Line Items]
2,017	0
2,018	0
2,019	1,450
2,020	300
2,021	1,150
Thereafter	4,139
Total	$ 7,039
[1]	Includes $390 million due to ComEd and PECO financing trusts.

Schedule I - Condensed Finan212

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Related Party Transactions - Summary of Related Party Transactions (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments		$ (32)	$ (24)	$ (7)
Due to Affiliate, Current		360	706
Exelon Corporate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[1]	25	51	43
Interest income from affiliates, net		40	39	43
Income (Loss) from Equity Method Investments		4,398	1,521	2,461
Cash contributions received from affiliates		1,879	1,912	3,209
Accounts receivable from affiliates		33	48
Receivables from affiliates		217	88
Investments in affiliates		39,272	34,869
Total receivable from affiliates (noncurrent)		910	922
Due to Affiliate, Current		360	706
Exelon Corporate [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[1]	23	51	43
Interest income from affiliates, net		3	0	0
Income (Loss) from Equity Method Investments		1	1	0
Accounts receivable from affiliates	[1]	1	15
Receivables from affiliates	[1]	217	88
Investments in affiliates	[1]	196	194
Exelon Corporate [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates		2	0	0
Investments in affiliates		(6)	(6)
Exelon Corporate [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Interest income from affiliates, net		37	39	43
Income (Loss) from Equity Method Investments		2,694	496	1,371
Accounts receivable from affiliates		21	22
Investments in affiliates		13,635	11,488
Total receivable from affiliates (noncurrent)	[2]	910	922
Exelon Corporate [Member] | Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		3	3
Due to Affiliate, Current		0	345
Exelon Corporate [Member] | PECO Energy Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		1	1
Exelon Corporate [Member] | Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		1	1
Exelon Corporate [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates		6	6
Exelon Corporate [Member] | Exelon Energy Delivery Company LLC [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments	[3]	1,670	1,041	1,079
Investments in affiliates	[3]	25,082	23,003
Exelon Corporate [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments		1	6	0
Investments in affiliates		78	77
Exelon Corporate [Member] | UII LLC [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments		41	(9)	20
Investments in affiliates		268	92
Due to Affiliate, Current		360	361
Exelon Corporate [Member] | Exelon Transmission Company LLC [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments		(10)	(13)	(8)
Investments in affiliates		1	5
Exelon Corporate [Member] | VEBA [Member]
Related Party Transaction [Line Items]
Investments in affiliates		(4)	(5)
Exelon Corporate [Member] | Exelon Enterprise [Member]
Related Party Transaction [Line Items]
Income (Loss) from Equity Method Investments		1	(1)	$ (1)
Investments in affiliates		$ 22	$ 21
[1]	Exelon Corporate receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead.
[2]	In connection with the debt obligations assumed by Exelon as part of the Constellation merger, Exelon and subsidiaries of Generation (former Constellation subsidiaries) assumed intercompany loan agreements that mirror the terms and amounts of the third-party debt obligations of Exelon, resulting in intercompany notes payable included in Long-Term Debt to affiliate on Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation on Exelon’s Consolidated Balance Sheets.
[3]	Exelon Energy Delivery Company, LLC consists of ComEd, PECO, BGE, PHI, Pepco, DPL and ACE.

Schedule II - Valuation and 213

Schedule II - Valuation and Qualifying Accounts Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 284		$ 334	$ 284		$ 311
Charged to Costs and Expenses	[1]			126	162		113
Charged to Other Accounts	[1],[2]			27	99	[3]	27
Deductions	[1],[4]			165	211		167
Balance at End of Period	[1]		$ 334	322	334		284
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		13		20	13		50
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				17	10	[3]	(27)
Deductions				0	3		10
Balance at End of Period			20	37	20		13
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		105		113	105		95
Charged to Costs and Expenses				56	12		10
Charged to Other Accounts				10	1	[3]	2
Deductions				5	5		2
Balance at End of Period			113	174	113		105
Exelon Generation Co L L C [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		77		91	77		60
Charged to Costs and Expenses				34	19		22
Charged to Other Accounts				0	3		0
Deductions				11	8		5
Balance at End of Period			91	114	91		77
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		11		9	11		48
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				14	0		(27)
Deductions				0	2		10
Balance at End of Period			9	23	9		11
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		102		106	102		93
Charged to Costs and Expenses				51	6		9
Charged to Other Accounts				9	0		0
Deductions				0	2		0
Balance at End of Period			106	166	106		102
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		75		70	75		84
Charged to Costs and Expenses				39	45		39
Charged to Other Accounts	[5]			20	23		18
Deductions	[6]			56	73		66
Balance at End of Period			70	73	70		75
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		3		4	3		2
Charged to Costs and Expenses				3	4		1
Charged to Other Accounts				1	1		2
Deductions				3	4		2
Balance at End of Period			4	5	4		3
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[7]	83		61	83		100
Charged to Costs and Expenses	[7]			26	32		37
Charged to Other Accounts	[7],[8]			4	7		9
Deductions	[7],[9]			35	61		63
Balance at End of Period	[7]		61	56	61		83
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		2	1		1
Charged to Costs and Expenses				0	1		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			2	2	2		1
PECO Energy Co [Member] | Allowance for Doubtful Accounts, Noncurrent [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		8		23	8
Balance at End of Period			23	15	23		8
Baltimore Gas and Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		49		32	49		67
Charged to Costs and Expenses				8	1		15
Charged to Other Accounts				(3)	9		0
Deductions	[10]			13	27		33
Balance at End of Period			32	24	32		49
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		1	1		1
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			1	1	1		1
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Pepco Holdings LLC [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				10
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			52	80
Charged to Costs and Expenses			65	19
Charged to Other Accounts	[11]		5	6
Deductions	[12]		42	50
Balance at End of Period		52	80	55	80
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		56	52		56		40
Charged to Costs and Expenses		16					59
Charged to Other Accounts	[11]	2					5
Deductions	[12]	22					48
Balance at End of Period		52					56
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			63	10
Charged to Costs and Expenses			0	0
Charged to Other Accounts			(53)	3
Deductions			0	0
Balance at End of Period		63	10	13	10
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		63	63		63		61
Charged to Costs and Expenses		0					0
Charged to Other Accounts		0					2
Deductions		0					0
Balance at End of Period		63					63
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			0	2
Charged to Costs and Expenses			1	2
Charged to Other Accounts			0	0
Deductions			(1)	2
Balance at End of Period		0	2	2	2
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	0		0		0
Charged to Costs and Expenses		0					0
Charged to Other Accounts		0					0
Deductions		0					0
Balance at End of Period		0					0
Potomac Electric Power Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				6
Potomac Electric Power Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		29	17		16
Charged to Costs and Expenses				8	29		20
Charged to Other Accounts	[13]			2	3		1
Deductions	[14]			18	20		20
Balance at End of Period			29	21	29		17
Potomac Electric Power Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Potomac Electric Power Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		1	0		0
Charged to Costs and Expenses				1	3		0
Charged to Other Accounts				0	0		0
Deductions				1	2		0
Balance at End of Period			1	1	1		0
Delmarva Power and Light Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				4
Delmarva Power and Light Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		24	17		11
Charged to Costs and Expenses				3	23		20
Charged to Other Accounts	[15]			2	2		2
Deductions	[16]			13	18		16
Balance at End of Period			24	16	24		17
Delmarva Power and Light Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Delmarva Power and Light Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				1	1		0
Charged to Other Accounts				0	0		0
Deductions				1	1		0
Balance at End of Period			0	0	0		0
Atlantic City Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		27	17		9
Charged to Costs and Expenses				8	32		18
Charged to Other Accounts	[17]			2	2		2
Deductions	[18]			19	24		12
Balance at End of Period			27	18	27		17
Atlantic City Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Atlantic City Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 0		1	0		0
Charged to Costs and Expenses				0	1		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			$ 1	$ 1	$ 1		$ 0
[1]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million, $23 million, and $8 million for the years ended December 31, 2017, 2016, and 2015, respectively.
[2]	Includes charges for late payments and non-service receivables.
[3]	Primarily represents the addition of PHI's results as of March 23, 2016, the date of the merger
[4]	Write-off of individual accounts receivable.
[5]	Primarily charges for late payments and non-service receivables.
[6]	Write-off of individual accounts receivable.
[7]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million, $23 million, and $8 million for the years ended December 31, 2017, 2016, and 2015, respectively.
[8]	Primarily charges for late payments.
[9]	Write-off of individual accounts receivable.
[10]	Write-off of individual accounts receivable.
[11]	Primarily charges for late payments.
[12]	Write-off of individual accounts receivable.
[13]	Primarily charges for late payments.
[14]	Write-off of individual accounts receivable.
[15]	Primarily charges for late payments.
[16]	Write-off of individual accounts receivable.
[17]	Primarily charges for late payments.
[18]	Write-off of individual accounts receivable.

Uncategorized Items - exc-20171

Label	Element	Value
Pepco Holdings LLC [Member] | Successor [Member]
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	$ 888,000,000
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	21,000,000
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	(3,000,000)
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	(515,000,000)
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	(22,000,000)
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	19,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(1,030,000,000)
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	1,008,000,000
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	0
Increase (Decrease) in Due to Affiliates	us-gaap_IncreaseDecreaseInDueToAffiliates	(6,000,000)
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	(514,000,000)
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	338,000,000
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	0
Repayments of Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfDebtMaturingInMoreThanThreeMonths	300,000,000
Proceeds from Sale of Property Held-for-sale	us-gaap_ProceedsFromSaleOfPropertyHeldForSale	24,000,000
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	0
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	42,000,000
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	(5,000,000)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax	0
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	(7,000,000)
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	295,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	9,000,000
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	311,000,000
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	0
Increase (Decrease) in Restricted Cash	us-gaap_IncreaseDecreaseInRestrictedCash	37,000,000
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	179,000,000
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	(149,000,000)
Proceeds from Issuance of Preferred Stock and Preference Stock	us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	264,000,000
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	28,000,000
Proceeds from Contributions from Parent	us-gaap_ProceedsFromContributionsFromParent	0
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	4,000,000
Payments of Ordinary Dividends, Common Stock	us-gaap_PaymentsOfDividendsCommonStock	0
Proceeds from (Repayments of) Short-term Debt	us-gaap_ProceedsFromRepaymentsOfShortTermDebt	(121,000,000)
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	12,000,000
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	42,000,000
Cash and Cash Equivalents, at Carrying Value	us-gaap_CashAndCashEquivalentsAtCarryingValue	319,000,000
Cash and Cash Equivalents, at Carrying Value	us-gaap_CashAndCashEquivalentsAtCarryingValue	319,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(343,000,000)
Impairment of Long-Lived Assets Held-for-use	us-gaap_ImpairmentOfLongLivedAssetsHeldForUse	0
Payments to Acquire Property, Plant, and Equipment	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment	273,000,000
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	500,000,000
Increase (Decrease) in Due to Affiliates	us-gaap_IncreaseDecreaseInDueToAffiliates	0
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	(46,000,000)
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	11,000,000
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	68,000,000
Repayments of Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfDebtMaturingInMoreThanThreeMonths	0
Proceeds from Sale of Property Held-for-sale	us-gaap_ProceedsFromSaleOfPropertyHeldForSale	0
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	(18,000,000)
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	0
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	2,000,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax	0
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	372,000,000
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	19,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	5,000,000
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	8,000,000
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	2,000,000
Increase (Decrease) in Restricted Cash	us-gaap_IncreaseDecreaseInRestrictedCash	(3,000,000)
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	0
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	293,000,000
Proceeds from Issuance of Preferred Stock and Preference Stock	us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0
Payments of Distributions to Affiliates	us-gaap_PaymentsOfDistributionsToAffiliates	0
AOCI Attributable to Parent [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	0
Undistributed Earnings [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	0
Membership Interest [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest	$ 7,200,000,000