Potomac Electric Power 10-K 8 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Entity Registrant Name	EXELON CORP
Entity Central Index Key	1,109,357
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
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		969,745,933
Entity Public Float			$ 41,118,095,431
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		127,021,331
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
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 & 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenues
Competitive businesses revenues			$ 19,168	$ 17,394	$ 16,330
Rate-regulated utility revenues			16,879	15,964	14,988
Electric operating revenues				0	0
Natural gas operating revenues				0	0
Revenues from alternative revenue programs			(62)	207	48
Operating revenues from affiliates				0	0
Total operating revenues			35,985	33,565	31,366
Operating expenses
Competitive businesses purchased power and fuel			11,679	9,668	8,817
Rate-regulated utility purchased power and fuel			4,991	4,367	3,823
Operating and maintenance			9,337	10,025	9,954
Depreciation and amortization			4,353	3,828	3,936
Taxes other than income			1,783	1,731	1,576
Total operating expenses			32,143	29,619	28,106
Gain (loss) on sales of assets and businesses			56	3	(48)
Bargain purchase gain			0	233	0
Gain on deconsolidation of business			0	213	0
Operating income (loss)			3,898	4,395	3,212
Other income and (deductions)
Interest expense, net			(1,529)	(1,524)	(1,495)
Interest expense to affiliates			(25)	(36)	(41)
Other, net			(112)	947	297
Total other income and (deductions)			(1,666)	(613)	(1,239)
Income (loss) before income taxes			2,232	3,782	1,973
Income taxes			120	(126)	753
Equity in losses of unconsolidated affiliates			(28)	(32)	(24)
Net income (loss)			2,084	3,876	1,196
Net income (loss) attributable to noncontrolling interests and/or preference stock dividends			74	90	75
Net income (loss) attributable to common shareholders			2,010	3,786	1,121
Other comprehensive income (loss), net of income taxes
Prior service benefit reclassified to periodic benefit cost			(66)	(56)	(48)
Actuarial loss reclassified to periodic cost			247	197	184
Pension and non-pension postretirement benefit plan valuation adjustment			(143)	10	(181)
Unrealized gain on cash flow hedges			12	3	2
Unrealized gain on marketable securities			0	6	1
Unrealized gain (loss) on investments in unconsolidated affiliates			2	4	(4)
Unrealized (loss) gain on foreign currency translation			(10)	7	10
Other comprehensive income (loss)			42	171	(36)
Comprehensive income (loss)			2,126	4,047	1,160
Comprehensive income attributable to noncontrolling interests and/or preference stock dividends			75	88	75
Comprehensive income (loss) attributable to common shareholders			$ 2,051	$ 3,959	$ 1,085
Average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic			967	947	924
Weighted Average Number of Shares Outstanding, Diluted			969	949	927
Earnings per average common share:
Earnings Per Share, Basic			$ 2.08	$ 4	$ 1.21
Earnings Per Share, Diluted			$ 2.07	$ 3.99	$ 1.21
Exelon Generation Co L L C [Member]
Operating revenues
Competitive businesses revenues			$ 19,169	$ 17,385	$ 16,318
Rate-regulated utility revenues				0	0
Electric operating revenues				0	0
Natural gas operating revenues				0	0
Revenues from alternative revenue programs				0	0
Operating revenues from affiliates			1,268	1,115	1,439
Total operating revenues			20,437	18,500	17,757
Operating expenses
Competitive businesses purchased power and fuel			11,679	9,671	8,818
Purchased power and/or fuel from affiliates			14	19	12
Operating and maintenance			4,803	5,602	5,000
Operating and maintenance from affiliates			661	697	663
Depreciation and amortization			1,797	1,457	1,879
Taxes other than income			556	555	506
Total operating expenses			19,510	18,001	16,878
Gain (loss) on sales of assets and businesses			48	2	(59)
Bargain purchase gain			0	233	0
Gain on deconsolidation of business			0	213	0
Operating income (loss)			975	947	820
Other income and (deductions)
Interest expense, net			(396)	(401)	(325)
Interest expense to affiliates			(36)	(39)	(39)
Other, net			(178)	948	401
Total other income and (deductions)			(610)	508	37
Income (loss) before income taxes			365	1,455	857
Income taxes			(108)	(1,376)	282
Equity in losses of unconsolidated affiliates			(30)	(33)	(25)
Net income (loss)			443	2,798	550
Net income (loss) attributable to noncontrolling interests			73	88	67
Net income (loss) attributable to membership interest			370	2,710	483
Other comprehensive income (loss), net of income taxes
Unrealized gain on cash flow hedges			12	3	2
Unrealized gain on marketable securities			0	1	1
Unrealized gain (loss) on investments in unconsolidated affiliates			1	4	(4)
Unrealized (loss) gain on foreign currency translation			(10)	7	10
Other comprehensive income (loss)			3	15	9
Comprehensive income (loss)			446	2,813	559
Comprehensive income attributable to noncontrolling interests and/or preference stock dividends			74	86	67
Comprehensive income (loss) attributable to common shareholders			372	2,727	492
Commonwealth Edison Co [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			5,884	5,478	5,263
Natural gas operating revenues				0	0
Revenues from alternative revenue programs			(29)	43	(24)
Operating revenues from affiliates			27	15	15
Total operating revenues			5,882	5,536	5,254
Operating expenses
Purchased power			1,626	1,533	1,411
Purchased power and/or fuel from affiliates			529	108	47
Operating and maintenance			1,068	1,157	1,303
Operating and maintenance from affiliates			267	270	227
Depreciation and amortization			940	850	775
Taxes other than income			311	296	293
Total operating expenses			4,741	4,214	4,056
Gain (loss) on sales of assets and businesses			5	1	7
Operating income (loss)			1,146	1,323	1,205
Other income and (deductions)
Interest expense, net			(334)	(348)	(448)
Interest expense to affiliates			(13)	(13)	(13)
Other, net			33	22	(65)
Total other income and (deductions)			(314)	(339)	(526)
Income (loss) before income taxes			832	984	679
Income taxes			168	417	301
Net income (loss)			664	567	378
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			664	567	378
PECO Energy Co [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			2,469	2,369	2,524
Natural gas operating revenues			568	494	462
Revenues from alternative revenue programs			(7)	0	0
Operating revenues from affiliates			8	7	8
Total operating revenues			3,038	2,870	2,994
Operating expenses
Purchased power			734	648	598
Purchased fuel			230	186	162
Purchased power and/or fuel from affiliates			126	135	287
Operating and maintenance			742	657	665
Operating and maintenance from affiliates			156	149	146
Depreciation and amortization			301	286	270
Taxes other than income			163	154	164
Total operating expenses			2,452	2,215	2,292
Gain (loss) on sales of assets and businesses			1	0	0
Operating income (loss)			587	655	702
Other income and (deductions)
Interest expense, net			(115)	(115)	(111)
Interest expense to affiliates			(14)	(11)	(12)
Other, net			8	9	8
Total other income and (deductions)			(121)	(117)	(115)
Income (loss) before income taxes			466	538	587
Income taxes			6	104	149
Net income (loss)			460	434	438
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			460	434	438
Baltimore Gas and Electric Company [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			2,428	2,384	2,531
Natural gas operating revenues			738	652	628
Revenues from alternative revenue programs			(26)	124	53
Operating revenues from affiliates			29	16	21
Total operating revenues			3,169	3,176	3,233
Operating expenses
Purchased power			671	566	528
Purchased fuel			254	183	162
Purchased power and/or fuel from affiliates			257	384	604
Operating and maintenance			615	563	605
Operating and maintenance from affiliates			162	153	132
Depreciation and amortization			483	473	423
Taxes other than income			254	240	229
Total operating expenses			2,696	2,562	2,683
Gain (loss) on sales of assets and businesses			1	0	0
Operating income (loss)			474	614	550
Other income and (deductions)
Interest expense, net			(106)	(95)	(87)
Interest expense to affiliates			0	(10)	(16)
Other, net			19	16	21
Total other income and (deductions)			(87)	(89)	(82)
Income (loss) before income taxes			387	525	468
Income taxes			74	218	174
Net income (loss)			313	307	294
Preference stock dividends			0	0	8
Net income (loss) attributable to common shareholders			313	307	286
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			313	307	294
Comprehensive income attributable to noncontrolling interests and/or preference stock dividends			0	0	8
Comprehensive income (loss) attributable to common shareholders			313	307	286
Pepco Holdings LLC [Member]
Operating revenues
Electric operating revenues			4,609	4,428
Natural gas operating revenues			181	161
Revenues from alternative revenue programs			0	40
Operating revenues from affiliates			15	50
Total operating revenues			4,805	4,679
Operating expenses
Purchased power			1,387	1,182
Purchased fuel			89	71
Purchased power and/or fuel from affiliates			355	463
Operating and maintenance			978	918
Operating and maintenance from affiliates			152	150
Depreciation and amortization			740	675
Taxes other than income			455	452
Total operating expenses			4,156	3,911
Gain (loss) on sales of assets and businesses			1	1
Operating income (loss)			650	769
Other income and (deductions)
Interest expense, net			(261)	(245)
Other, net			43	54
Total other income and (deductions)			(218)	(191)
Income (loss) before income taxes			432	578
Income taxes			35	217
Equity in losses of unconsolidated affiliates			1	1
Net income (loss)			398	362
Net income (loss) attributable to membership interest			398	362
Other comprehensive income (loss), net of income taxes
Actuarial loss reclassified to periodic cost			0	0
Other comprehensive income (loss)			0	0
Comprehensive income (loss) attributable to common shareholders			398	362
Pepco Holdings LLC [Member] | Predecessor [Member]
Operating revenues
Competitive businesses revenues	$ 0
Rate-regulated utility revenues	0
Electric operating revenues	1,122
Natural gas operating revenues	57
Revenues from alternative revenue programs	(26)
Operating revenues from affiliates	0
Total operating revenues	1,153
Operating expenses
Purchased power	471
Purchased fuel	26
Purchased power and/or fuel from affiliates	0
Operating and maintenance	294
Operating and maintenance from affiliates	0
Depreciation and amortization	152
Taxes other than income	105
Total operating expenses	1,048
Gain (loss) on sales of assets and businesses	0
Operating income (loss)	105
Other income and (deductions)
Interest expense, net	(65)
Other, net	(4)
Total other income and (deductions)	(69)
Income (loss) before income taxes	36
Income taxes	17
Equity in losses of unconsolidated affiliates	0
Net income (loss)	19
Net income (loss) attributable to membership interest	19
Other comprehensive income (loss), net of income taxes
Actuarial loss reclassified to periodic cost	1
Other comprehensive income (loss)	1
Comprehensive income (loss) attributable to common shareholders	$ 20
Pepco Holdings LLC [Member] | Successor [Member]
Operating revenues
Competitive businesses revenues		$ 0		0
Rate-regulated utility revenues		0		0
Electric operating revenues		3,463		4,428
Natural gas operating revenues		92		161
Revenues from alternative revenue programs		43		40
Operating revenues from affiliates		45	15	50
Total operating revenues		3,643		4,679
Operating expenses
Purchased power		925
Purchased fuel		36
Purchased power and/or fuel from affiliates		486
Operating and maintenance		1,144
Operating and maintenance from affiliates		89	152	150
Depreciation and amortization		515
Taxes other than income		354
Total operating expenses		3,549
Gain (loss) on sales of assets and businesses		(1)
Operating income (loss)		93
Other income and (deductions)
Interest expense, net		(195)
Other, net		44
Total other income and (deductions)		(151)
Income (loss) before income taxes		(58)
Income taxes		3
Equity in losses of unconsolidated affiliates		0
Net income (loss)		(61)
Net income (loss) attributable to membership interest		(61)
Other comprehensive income (loss), net of income taxes
Actuarial loss reclassified to periodic cost		0
Other comprehensive income (loss)		0
Comprehensive income (loss) attributable to common shareholders		$ (61)
Potomac Electric Power Company [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			2,233	2,126	2,167
Natural gas operating revenues				0	0
Revenues from alternative revenue programs			0	26	14
Operating revenues from affiliates			6	6	5
Total operating revenues			2,239	2,158	2,186
Operating expenses
Purchased power			448	359	411
Purchased power and/or fuel from affiliates			206	255	295
Operating and maintenance			275	396	607
Operating and maintenance from affiliates			226	58	35
Depreciation and amortization			385	321	295
Taxes other than income			379	371	377
Total operating expenses			1,919	1,760	2,020
Gain (loss) on sales of assets and businesses			0	1	8
Operating income (loss)			320	399	174
Other income and (deductions)
Interest expense, net			(128)	(121)	(127)
Other, net			31	32	36
Total other income and (deductions)			(97)	(89)	(91)
Income (loss) before income taxes			223	310	83
Income taxes			13	105	41
Net income (loss)			210	205	42
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			210	205	42
Delmarva Power & Light Company [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			1,139	1,125	1,128
Natural gas operating revenues			181	161	148
Revenues from alternative revenue programs			4	6	(6)
Operating revenues from affiliates			8	8	7
Total operating revenues			1,332	1,300	1,277
Operating expenses
Purchased power			352	282	369
Purchased fuel			89	71	60
Purchased power and/or fuel from affiliates			120	179	154
Operating and maintenance			182	283	422
Operating and maintenance from affiliates			162	32	19
Depreciation and amortization			182	167	157
Taxes other than income			56	57	55
Total operating expenses			1,143	1,071	1,236
Gain (loss) on sales of assets and businesses			1	0	9
Operating income (loss)			190	229	50
Other income and (deductions)
Interest expense, net			(58)	(51)	(50)
Other, net			10	14	13
Total other income and (deductions)			(48)	(37)	(37)
Income (loss) before income taxes			142	192	13
Income taxes			22	71	22
Net income (loss)			120	121	(9)
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			120	121	(9)
Atlantic City Electric Company [Member]
Operating revenues
Competitive businesses revenues				0	0
Rate-regulated utility revenues				0	0
Electric operating revenues			1,237	1,176	1,245
Natural gas operating revenues				0	0
Revenues from alternative revenue programs			(4)	8	9
Operating revenues from affiliates			3	2	3
Total operating revenues			1,236	1,186	1,257
Operating expenses
Purchased power			587	541	614
Purchased power and/or fuel from affiliates			29	29	37
Operating and maintenance			188	279	410
Operating and maintenance from affiliates			142	28	18
Depreciation and amortization			136	146	165
Taxes other than income			5	6	7
Total operating expenses			1,087	1,029	1,251
Gain (loss) on sales of assets and businesses			0	0	1
Operating income (loss)			149	157	7
Other income and (deductions)
Interest expense, net			(64)	(61)	(62)
Other, net			2	7	9
Total other income and (deductions)			(62)	(54)	(53)
Income (loss) before income taxes			87	103	(46)
Income taxes			12	26	(4)
Net income (loss)			75	77	(42)
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)			$ 75	$ 77	$ (42)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net Income (Loss)	$ 2,084	$ 3,876	$ 1,196
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	5,971	5,427	5,576
Impairment losses of long-lived assets, intangibles and regulatory assets	50	573	306
Gain on deconsolidation of business	0	(213)	0
(Gain) Loss on sales of assets and businesses	(56)	(3)	48
Bargain purchase gain	0	(233)	0
Deferred income taxes and amortization of investment tax credits	(106)	(362)	656
Net fair value changes related to derivatives	294	151	24
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	303	(616)	(229)
Other non-cash operating activities	1,124	721	1,333
Changes in assets and liabilities:
Accounts receivable	(565)	(470)	(432)
Inventories	(37)	(72)	7
Accounts payable and accrued expenses	551	(388)	771
Option premiums received (paid), net	(43)	28	(66)
Collateral (posted) received, net	82	(158)	931
Income taxes	340	299	576
Pension and non-pension postretirement benefit contributions	(383)	(405)	(397)
Deposit with IRS	0	0	(1,250)
Other assets and liabilities	(965)	(675)	(589)
Net cash flows provided by (used in) operating activities	8,644	7,480	8,461
Cash flows from investing activities
Capital expenditures	(7,594)	(7,584)	(8,553)
Proceeds from termination of direct financing lease investment	0	0	360
Proceeds from nuclear decommissioning trust fund sales	8,762	7,845	9,496
Investment in nuclear decommissioning trust funds	(8,997)	(8,113)	(9,738)
Reduction of restricted cash from deconsolidation of business	0	(87)	0
Acquisitions of businesses, net	(154)	(208)	(6,923)
Proceeds from sales of long-lived assets	91	219	61
Other investing activities	58	(43)	(153)
Net cash flows provided by (used in) investing activities	(7,834)	(7,971)	(15,450)
Cash flows from financing activities
Changes in short-term borrowings	(338)	(261)	(353)
Proceeds from short-term borrowings with maturities greater than 90 days	126	621	240
Repayments on short-term borrowings with maturities greater than 90 days	(1)	(700)	(462)
Issuance of long-term debt	3,115	3,470	4,716
Retirement of long-term debt	(1,786)	(2,490)	(1,936)
Retirement of long-term debt to financing trust	0	(250)	0
Common stock issued from treasury stock	0	1,150	0
Redemption of preference stock	0	0	(190)
Dividends paid on common stock	(1,332)	(1,236)	(1,166)
Proceeds from employee stock plans	105	150	55
Sale of noncontrolling interest	0	396	372
Other financing activities	(108)	(83)	(85)
Net cash flows provided by (used in) financing activities	(219)	767	1,191
Increase (Decrease) in cash, cash equivalents and restricted cash	591	276	(5,798)
Cash, cash equivalents, and restricted cash at beginning of period	1,190	914	6,712
Cash, cash equivalents, and restricted cash at end of period	1,781	1,190	914
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net Income (Loss)	443	2,798	550
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	3,415	3,056	3,519
Impairment losses of long-lived assets, intangibles and regulatory assets	50	510	243
Gain on deconsolidation of business	0	(213)	0
(Gain) Loss on sales of assets and businesses	(48)	(2)	59
Bargain purchase gain	0	(233)	0
Deferred income taxes and amortization of investment tax credits	(451)	(2,023)	(277)
Net fair value changes related to derivatives	307	167	40
Net realized and unrealized (gains) losses on nuclear decommissioning trust fund investments	303	(616)	(229)
Other non-cash operating activities	298	112	15
Changes in assets and liabilities:
Accounts receivable	(359)	(320)	(152)
Receivables from and payables to affiliates, net	8	(7)	(21)
Inventories	(12)	(29)	(4)
Accounts payable and accrued expenses	376	4	29
Option premiums received (paid), net	(43)	28	(66)
Collateral (posted) received, net	64	(129)	923
Income taxes	(193)	496	182
Pension and non-pension postretirement benefit contributions	(139)	(148)	(152)
Other assets and liabilities	(158)	(152)	(217)
Net cash flows provided by (used in) operating activities	3,861	3,299	4,442
Cash flows from investing activities
Capital expenditures	(2,242)	(2,259)	(3,078)
Proceeds from nuclear decommissioning trust fund sales	8,762	7,845	9,496
Investment in nuclear decommissioning trust funds	(8,997)	(8,113)	(9,738)
Reduction of restricted cash from deconsolidation of business	0	(87)	0
Acquisitions of businesses, net	(154)	(208)	(293)
Proceeds from sales of long-lived assets	90	218	37
Other investing activities	10	(58)	(240)
Net cash flows provided by (used in) investing activities	(2,531)	(2,662)	(3,816)
Cash flows from financing activities
Changes in short-term borrowings	0	(620)	620
Proceeds from short-term borrowings with maturities greater than 90 days	1	121	240
Repayments on short-term borrowings with maturities greater than 90 days	(1)	(200)	(162)
Issuance of long-term debt	15	1,645	388
Retirement of long-term debt	(141)	(1,261)	(202)
Changes in Exelon intercompany money pool	46	(1)	(1,191)
Distributions to member	(1,001)	(659)	(922)
Contributions from member	155	102	142
Sale of noncontrolling interest	0	396	372
Other financing activities	(55)	(54)	(19)
Net cash flows provided by (used in) financing activities	(981)	(531)	(734)
Increase (Decrease) in cash, cash equivalents and restricted cash	349	106	(108)
Cash, cash equivalents, and restricted cash at beginning of period	554	448	556
Cash, cash equivalents, and restricted cash at end of period	903	554	448
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net Income (Loss)	664	567	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	940	850	775
Deferred income taxes and amortization of investment tax credits	259	659	439
Other non-cash operating activities	242	164	215
Changes in assets and liabilities:
Accounts receivable	(136)	(59)	(25)
Receivables from and payables to affiliates, net	26	8	3
Inventories	1	4	1
Accounts payable and accrued expenses	70	(297)	339
Collateral (posted) received, net	11	(26)	7
Income taxes	62	(308)	306
Pension and non-pension postretirement benefit contributions	(42)	(41)	(38)
Other assets and liabilities	(348)	6	105
Net cash flows provided by (used in) operating activities	1,749	1,527	2,505
Cash flows from investing activities
Capital expenditures	(2,126)	(2,250)	(2,734)
Other investing activities	29	20	49
Net cash flows provided by (used in) investing activities	(2,097)	(2,230)	(2,685)
Cash flows from financing activities
Changes in short-term borrowings	0	0	(294)
Issuance of long-term debt	1,350	1,000	1,200
Retirement of long-term debt	(840)	(425)	(665)
Dividends paid on common stock	(459)	(422)	(369)
Contributions from parent	500	651	315
Other financing activities	(17)	(15)	(18)
Net cash flows provided by (used in) financing activities	534	789	169
Increase (Decrease) in cash, cash equivalents and restricted cash	186	86	(11)
Cash, cash equivalents, and restricted cash at beginning of period	144	58	69
Cash, cash equivalents, and restricted cash at end of period	330	144	58
PECO Energy Co [Member]
Cash flows from operating activities
Net Income (Loss)	460	434	438
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	301	286	270
Deferred income taxes and amortization of investment tax credits	(5)	19	78
Other non-cash operating activities	51	54	65
Changes in assets and liabilities:
Accounts receivable	(74)	(44)	(71)
Receivables from and payables to affiliates, net	7	(6)	6
Inventories	(14)	1	6
Accounts payable and accrued expenses	(3)	6	67
Income taxes	15	34	8
Pension and non-pension postretirement benefit contributions	(28)	(24)	(30)
Other assets and liabilities	29	(5)	(8)
Net cash flows provided by (used in) operating activities	739	755	829
Cash flows from investing activities
Capital expenditures	(849)	(732)	(686)
Changes in Exelon intercompany money pool	0	131	(131)
Other investing activities	9	4	20
Net cash flows provided by (used in) investing activities	(840)	(597)	(797)
Cash flows from financing activities
Issuance of long-term debt	700	325	300
Retirement of long-term debt	(500)	0	(300)
Dividends paid on common stock	(306)	(288)	(277)
Contributions from parent	89	16	18
Other financing activities	(22)	(3)	(4)
Net cash flows provided by (used in) financing activities	(39)	50	(263)
Increase (Decrease) in cash, cash equivalents and restricted cash	(140)	208	(231)
Cash, cash equivalents, and restricted cash at beginning of period	275	67	298
Cash, cash equivalents, and restricted cash at end of period	135	275	67
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net Income (Loss)	313	307	294
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	483	473	423
Impairment losses of long-lived assets, intangibles and regulatory assets	0	7	52
Deferred income taxes and amortization of investment tax credits	76	145	118
Other non-cash operating activities	58	65	88
Changes in assets and liabilities:
Accounts receivable	8	(5)	(98)
Receivables from and payables to affiliates, net	12	(4)	3
Inventories	2	(9)	1
Accounts payable and accrued expenses	(1)	(15)	138
Collateral (posted) received, net	4	0	0
Income taxes	(20)	60	18
Pension and non-pension postretirement benefit contributions	(54)	(53)	(49)
Other assets and liabilities	(92)	(150)	(43)
Net cash flows provided by (used in) operating activities	789	821	945
Cash flows from investing activities
Capital expenditures	(959)	(882)	(934)
Other investing activities	9	7	24
Net cash flows provided by (used in) investing activities	(950)	(875)	(910)
Cash flows from financing activities
Changes in short-term borrowings	(42)	32	(165)
Issuance of long-term debt	300	300	850
Retirement of long-term debt	0	(41)	(379)
Retirement of long-term debt to financing trust	0	(250)	0
Redemption of preference stock	0	0	(190)
Dividends paid on preferred securities	0	0	(8)
Dividends paid on common stock	(209)	(198)	(179)
Contributions from parent	109	184	61
Other financing activities	(2)	(5)	(11)
Net cash flows provided by (used in) financing activities	156	22	(21)
Increase (Decrease) in cash, cash equivalents and restricted cash	(5)	(32)	14
Cash, cash equivalents, and restricted cash at beginning of period	18	50	36
Cash, cash equivalents, and restricted cash at end of period	13	18	50
Pepco Holdings LLC [Member]
Cash flows from operating activities
Net Income (Loss)	398	362
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	740	675
Impairment losses of long-lived assets, intangibles and regulatory assets	0	52
Deferred income taxes and amortization of investment tax credits	32	252
Net fair value changes related to derivatives	0	0
Other non-cash operating activities	(143)	(58)
Changes in assets and liabilities:
Accounts receivable	2	26
Receivables from and payables to affiliates, net	8	(2)
Inventories	14	37
Accounts payable and accrued expenses	45	(106)
Income taxes	34	79
Pension and non-pension postretirement benefit contributions	74	99
Other assets and liabilities	178	258
Net cash flows provided by (used in) operating activities	1,132	950
Cash flows from investing activities
Capital expenditures	(1,375)	(1,396)
Purchases of investments	0	0
Other investing activities	4	(1)
Net cash flows provided by (used in) investing activities	(1,371)	(1,397)
Cash flows from financing activities
Changes in short-term borrowings	(296)	328
Proceeds from short-term borrowings with maturities greater than 90 days	125	0
Repayments on short-term borrowings with maturities greater than 90 days	0	(500)
Issuance of long-term debt	750	202
Retirement of long-term debt	(299)	(169)
Changes in Exelon intercompany money pool	0	0
Distributions to member	(326)	(311)
Proceeds from employee stock plans	0	0
Contributions from parent	385	758
Other financing activities	(9)	(2)
Net cash flows provided by (used in) financing activities	330	306
Increase (Decrease) in cash, cash equivalents and restricted cash	91	(141)
Cash, cash equivalents, and restricted cash at beginning of period	95	236
Cash, cash equivalents, and restricted cash at end of period	186	95	236
Pepco Holdings LLC [Member] | Predecessor [Member]
Cash flows from financing activities
Cash, cash equivalents, and restricted cash at beginning of period			58
Pepco Holdings LLC [Member] | Successor [Member]
Cash flows from financing activities
Cash, cash equivalents, and restricted cash at beginning of period		236
Cash, cash equivalents, and restricted cash at end of period			236
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net Income (Loss)	210	205	42
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	385	321	295
Impairment losses of long-lived assets, intangibles and regulatory assets	0	14	0
Deferred income taxes and amortization of investment tax credits	(18)	113	153
Other non-cash operating activities	60	(6)	175
Changes in assets and liabilities:
Accounts receivable	(5)	(20)	(41)
Receivables from and payables to affiliates, net	(17)	0	44
Inventories	(6)	(24)	1
Accounts payable and accrued expenses	59	(63)	32
Income taxes	(13)	81	110
Pension and non-pension postretirement benefit contributions	(17)	(72)	(32)
Other assets and liabilities	(164)	(142)	(128)
Net cash flows provided by (used in) operating activities	474	407	651
Cash flows from investing activities
Capital expenditures	(656)	(628)	(586)
Purchases of investments	0	0	(30)
Other investing activities	2	0	0
Net cash flows provided by (used in) investing activities	(654)	(628)	(616)
Cash flows from financing activities
Changes in short-term borrowings	14	3	(41)
Issuance of long-term debt	200	202	4
Retirement of long-term debt	(14)	(13)	(11)
Dividends paid on common stock	(169)	(133)	(136)
Contributions from parent	166	161	187
Other financing activities	(4)	(1)	(3)
Net cash flows provided by (used in) financing activities	193	219	0
Increase (Decrease) in cash, cash equivalents and restricted cash	13	(2)	35
Cash, cash equivalents, and restricted cash at beginning of period	40	42	7
Cash, cash equivalents, and restricted cash at end of period	53	40	42
Delmarva Power & Light Company [Member]
Cash flows from operating activities
Net Income (Loss)	120	121	(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	182	167	157
Impairment losses of long-lived assets, intangibles and regulatory assets	0	6	0
Deferred income taxes and amortization of investment tax credits	24	89	109
Other non-cash operating activities	24	9	114
Changes in assets and liabilities:
Accounts receivable	8	(22)	(5)
Receivables from and payables to affiliates, net	(9)	11	13
Inventories	(3)	(5)	0
Accounts payable and accrued expenses	11	(8)	(4)
Collateral (posted) received, net	0	0	1
Income taxes	2	26	28
Pension and non-pension postretirement benefit contributions	0	(2)	(22)
Other assets and liabilities	(7)	(71)	(72)
Net cash flows provided by (used in) operating activities	352	321	310
Cash flows from investing activities
Capital expenditures	(364)	(428)	(349)
Other investing activities	2	(1)	13
Net cash flows provided by (used in) investing activities	(362)	(429)	(336)
Cash flows from financing activities
Changes in short-term borrowings	(216)	216	(105)
Issuance of long-term debt	200	0	175
Retirement of long-term debt	(4)	(40)	(100)
Dividends paid on common stock	(96)	(112)	(54)
Contributions from parent	150	0	152
Other financing activities	(2)	0	(1)
Net cash flows provided by (used in) financing activities	32	64	67
Increase (Decrease) in cash, cash equivalents and restricted cash	22	(44)	41
Cash, cash equivalents, and restricted cash at beginning of period	2	46	5
Cash, cash equivalents, and restricted cash at end of period	24	2	46
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net Income (Loss)	75	77	(42)
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	136	146	165
Impairment losses of long-lived assets, intangibles and regulatory assets	0	7	0
Deferred income taxes and amortization of investment tax credits	25	32	22
Other non-cash operating activities	24	17	155
Changes in assets and liabilities:
Accounts receivable	(8)	14	(8)
Receivables from and payables to affiliates, net	1	0	13
Inventories	(4)	(7)	(1)
Accounts payable and accrued expenses	(7)	(2)	9
Income taxes	(2)	(11)	174
Pension and non-pension postretirement benefit contributions	(6)	(20)	(17)
Other assets and liabilities	(6)	(47)	(85)
Net cash flows provided by (used in) operating activities	228	206	385
Cash flows from investing activities
Capital expenditures	(335)	(312)	(311)
Other investing activities	1	(1)	4
Net cash flows provided by (used in) investing activities	(334)	(313)	(307)
Cash flows from financing activities
Changes in short-term borrowings	(94)	108	(5)
Proceeds from short-term borrowings with maturities greater than 90 days	125	0	0
Issuance of long-term debt	350	0	0
Retirement of long-term debt	(281)	(35)	(48)
Dividends paid on common stock	(59)	(68)	(63)
Contributions from parent	67	0	139
Other financing activities	(3)	0	(1)
Net cash flows provided by (used in) financing activities	105	5	22
Increase (Decrease) in cash, cash equivalents and restricted cash	(1)	(102)	100
Cash, cash equivalents, and restricted cash at beginning of period	31	133	33
Cash, cash equivalents, and restricted cash at end of period	$ 30	$ 31	$ 133

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents		$ 1,349	$ 898
Restricted cash and cash equivalents		247	207
Accounts receivable, net
Customer		4,607	4,445
Other		1,256	1,132
Mark-to-market derivative assets, current		804	976
Unamortized energy contract assets, current		48	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		334	340
Materials and supplies		1,351	1,311
Regulatory assets, current		1,222	1,267
Assets held for sale		904	0
Other		1,238	1,260
Total current assets		13,360	11,896
Property, plant and equipment, net		76,707	74,202
Deferred debits and other assets
Regulatory assets, noncurrent		8,237	8,021
Nuclear decommissioning trust funds		11,661	13,272
Investments		625	640
Goodwill		6,677	6,677
Mark-to-market derivative assets, noncurrent		452	337
Unamortized energy contract assets, noncurrent		372	395
Other		1,575	1,330
Total deferred debits and other assets		29,599	30,672
Total assets	[1]	119,666	116,770
Current liabilities
Short-term borrowings		714	929
Long-term debt due within one year		1,349	2,088
Accounts payable		3,800	3,532
Accrued expenses		2,112	1,837
Payables to affiliates, current		5	5
Regulatory Liability, Current		644	523
Mark-to-market derivative liabilities, current		475	232
Unamortized energy contract liabilities, current		149	231
Renewable energy credit obligation		344	352
Liabilities held for sale		777	0
Other		1,035	1,069
Total current liabilities		11,404	10,798
Long-term debt		34,075	32,176
Long-term debt to financing trusts		390	389
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		11,330	11,235
Asset retirement obligations, noncurrent		9,679	10,029
Pension obligations		3,988	3,736
Non-pension postretirement benefit obligations		1,928	2,093
Spent nuclear fuel obligation		1,171	1,147
Regulatory liabilities, noncurrent		9,559	9,865
Mark-to-market derivative liabilities, noncurrent		479	409
Unamortized energy contract liabilities, noncurrent		463	609
Other		2,130	2,097
Total deferred credits and other liabilities		40,727	41,220
Total liabilities	[1]	86,596	84,583
Commitments and Contingencies
Shareholders’ equity
Common stock		19,116	18,964
Treasury stock, at cost		(123)	(123)
Retained earnings		14,766	14,081
Accumulated other comprehensive income (loss), net		(2,995)	(3,026)
Total shareholders’ equity		30,764	29,896
Member’s equity
Noncontrolling interests		2,306	2,291
Total equity		33,070	32,187
Total liabilities and equity		119,666	116,770
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,667	9,597
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,548	3,618
Exelon Generation Co L L C [Member]
Current assets
Cash and cash equivalents		750	416
Restricted cash and cash equivalents		153	138
Accounts receivable, net
Customer		2,941	2,697
Other		562	321
Mark-to-market derivative assets, current		804	976
Receivables from affiliates, current		173	140
Unamortized energy contract assets, current		49	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		251	264
Materials and supplies		963	937
Assets held for sale		904	0
Other		883	933
Total current assets		8,433	6,882
Property, plant and equipment, net		23,981	24,906
Deferred debits and other assets
Nuclear decommissioning trust funds		11,661	13,272
Investments		414	433
Goodwill		47	47
Mark-to-market derivative assets, noncurrent		452	334
Prepaid pension asset		1,421	1,502
Unamortized energy contract assets, noncurrent		371	395
Deferred income taxes		21	16
Other		755	670
Total deferred debits and other assets		15,142	16,669
Total assets	[2]	47,556	48,457
Current liabilities
Short-term borrowings		0	2
Long-term debt due within one year		906	346
Accounts payable		1,847	1,773
Accrued expenses		898	1,022
Payables to affiliates, current		139	123
Borrowings from Exelon intercompany money pool		100	54
Mark-to-market derivative liabilities, current		449	211
Unamortized energy contract liabilities, current		31	43
Renewable energy credit obligation		343	352
Liabilities held for sale		777	0
Other		279	265
Total current liabilities		5,769	4,191
Long-term debt		6,989	7,734
Long-term debt to affiliates		898	910
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,383	3,811
Asset retirement obligations, noncurrent		9,450	9,844
Non-pension postretirement benefit obligations		900	916
Spent nuclear fuel obligation		1,171	1,147
Payables to affiliates, noncurrent		2,606	3,065
Mark-to-market derivative liabilities, noncurrent		252	174
Unamortized energy contract liabilities, noncurrent		20	48
Other		610	658
Total deferred credits and other liabilities		18,392	19,663
Total liabilities	[2]	32,048	32,498
Commitments and Contingencies
Shareholders’ equity
Retained earnings		3,724	4,349
Accumulated other comprehensive income (loss), net		(38)	(37)
Member’s equity
Membership interest		9,518	9,357
Total member’s equity		13,204	13,669
Noncontrolling interests		2,304	2,290
Total equity		15,508	15,959
Total liabilities and equity		47,556	48,457
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,634	9,556
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,480	3,516
Commonwealth Edison Co [Member]
Current assets
Cash and cash equivalents		135	76
Restricted cash and cash equivalents		29	5
Accounts receivable, net
Customer		539	559
Other		320	266
Receivables from affiliates, current		20	13
Inventories, net
Inventories, net		148	152
Regulatory assets, current		293	225
Other		86	68
Total current assets		1,570	1,364
Property, plant and equipment, net		22,058	20,723
Deferred debits and other assets
Regulatory assets, noncurrent		1,307	1,054
Investments		6	6
Goodwill		2,625	2,625
Receivable from affiliates, noncurrent		2,217	2,528
Prepaid pension asset		1,035	1,188
Other		395	238
Total deferred debits and other assets		7,585	7,639
Total assets		31,213	29,726
Current liabilities
Long-term debt due within one year		300	840
Accounts payable		607	568
Accrued expenses		373	327
Payables to affiliates, current		119	74
Regulatory Liability, Current		293	249
Mark-to-market derivative liabilities, current		26	21
Customer deposits		111	112
Other		96	103
Total current liabilities		1,925	2,294
Long-term debt		7,801	6,761
Long-term debt to financing trusts		205	205
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,813	3,469
Asset retirement obligations, noncurrent		118	111
Non-pension postretirement benefit obligations		201	219
Regulatory liabilities, noncurrent		6,050	6,328
Mark-to-market derivative liabilities, noncurrent		223	235
Other		630	562
Total deferred credits and other liabilities		11,035	10,924
Total liabilities		20,966	20,184
Commitments and Contingencies
Shareholders’ equity
Common stock		1,588	1,588
Other paid-in capital		7,322	6,822
Retained earnings (deficit) unappropriated		(1,639)	(1,639)
Retained earnings (deficit) appropriated		2,976	2,771
Total shareholders’ equity		10,247	9,542
Member’s equity
Total liabilities and equity		31,213	29,726
PECO Energy Co [Member]
Current assets
Cash and cash equivalents		130	271
Restricted cash and cash equivalents		5	4
Accounts receivable, net
Customer		321	327
Other		151	105
Inventories, net
Energy Related Inventory, Other Fossil Fuel		38	31
Materials and supplies		37	30
Regulatory assets, current		81	29
Prepaid utility taxes		0	8
Other		19	17
Total current assets		782	822
Property, plant and equipment, net		8,610	8,053
Deferred debits and other assets
Regulatory assets, noncurrent		460	381
Investments		25	25
Receivable from affiliates, noncurrent		389	537
Prepaid pension asset		349	340
Other		27	12
Total deferred debits and other assets		1,250	1,295
Total assets		10,642	10,170
Current liabilities
Long-term debt due within one year		0	500
Accounts payable		370	370
Accrued expenses		113	114
Payables to affiliates, current		59	53
Regulatory Liability, Current		175	141
Customer deposits		68	66
Other		24	23
Total current liabilities		809	1,267
Long-term debt		3,084	2,403
Long-term debt to financing trusts	[3]	184	184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,933	1,789
Asset retirement obligations, noncurrent		27	27
Non-pension postretirement benefit obligations		288	288
Regulatory liabilities, noncurrent		421	549
Other		76	86
Total deferred credits and other liabilities		2,745	2,739
Total liabilities		6,822	6,593
Commitments and Contingencies
Shareholders’ equity
Common stock		2,578	2,489
Retained earnings		1,242	1,087
Accumulated other comprehensive income (loss), net		0	1
Total shareholders’ equity		3,820	3,577
Member’s equity
Total liabilities and equity		10,642	10,170
Baltimore Gas and Electric Company [Member]
Current assets
Cash and cash equivalents		7	17
Restricted cash and cash equivalents		6	1
Accounts receivable, net
Customer		353	375
Other		90	94
Receivables from affiliates, current		1	1
Inventories, net
Materials and supplies		39	40
Gas Held in Storage		36	37
Regulatory assets, current		177	174
Prepaid utility taxes		74	69
Other		3	3
Total current assets		786	811
Property, plant and equipment, net		8,243	7,602
Deferred debits and other assets
Regulatory assets, noncurrent		398	397
Investments		5	5
Prepaid pension asset		279	285
Other		5	4
Total deferred debits and other assets		687	691
Total assets		9,716	9,104
Current liabilities
Short-term borrowings		35	77
Accounts payable		295	265
Accrued expenses		155	164
Payables to affiliates, current		65	52
Regulatory Liability, Current		77	62
Customer deposits		120	116
Other		27	24
Total current liabilities		774	760
Long-term debt		2,876	2,577
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,222	1,244
Asset retirement obligations, noncurrent		24	23
Non-pension postretirement benefit obligations		201	202
Regulatory liabilities, noncurrent		1,192	1,101
Other		73	56
Total deferred credits and other liabilities		2,712	2,626
Total liabilities		6,362	5,963
Commitments and Contingencies
Shareholders’ equity
Common stock		1,714	1,605
Retained earnings		1,640	1,536
Total shareholders’ equity		3,354	3,141
Member’s equity
Total liabilities and equity		9,716	9,104
Pepco Holdings LLC [Member]
Current assets
Cash and cash equivalents		124	30
Restricted cash and cash equivalents		43	42
Accounts receivable, net
Customer		453	486
Other		177	206
Inventories, net
Materials and supplies		163	151
Gas Held in Storage		9	7
Regulatory assets, current		489	554
Other		75	75
Total current assets		1,533	1,551
Property, plant and equipment, net		13,446	12,498
Deferred debits and other assets
Regulatory assets, noncurrent		2,312	2,493
Investments		130	132
Goodwill		4,005	4,005
Prepaid pension asset		486	490
Deferred income taxes		12	4
Long-term note receivable		0	4
Other		60	70
Total deferred debits and other assets		7,005	7,198
Total assets	[4]	21,984	21,247
Current liabilities
Short-term borrowings		179	350
Long-term debt due within one year		125	396
Accounts payable		496	348
Accrued expenses		256	261
Payables to affiliates, current		94	90
Regulatory Liability, Current		84	56
Unamortized energy contract liabilities, current		119	188
Customer deposits		116	119
Other		123	123
Total current liabilities		1,592	1,931
Long-term debt		6,134	5,478
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,146	2,070
Asset retirement obligations, noncurrent		52	16
Non-pension postretirement benefit obligations		103	105
Regulatory liabilities, noncurrent		1,864	1,872
Unamortized energy contract liabilities, noncurrent		442	561
Other		369	389
Total deferred credits and other liabilities		4,976	5,013
Total liabilities	[4]	12,702	12,422
Commitments and Contingencies
Shareholders’ equity
Retained earnings		62	(10)
Member’s equity
Membership interest		9,220	8,835
Total member’s equity		9,282	8,825
Total equity		9,282	8,825
Total liabilities and equity		21,984	21,247
Variable Interest Entity, Consolidated, Assets, Not Pledged		33	41
Variable Interest Entity, Consolidated, Liabilities, No Recourse		69	102
Potomac Electric Power Company [Member]
Current assets
Cash and cash equivalents		16	5
Restricted cash and cash equivalents		37	35
Accounts receivable, net
Customer		225	250
Other		81	87
Receivables from affiliates, current		1	0
Inventories, net
Inventories, net		93	87
Regulatory assets, current		270	213
Other		37	33
Total current assets		760	710
Property, plant and equipment, net		6,460	6,001
Deferred debits and other assets
Regulatory assets, noncurrent		643	678
Investments		105	102
Prepaid pension asset		316	322
Other		15	19
Total deferred debits and other assets		1,079	1,121
Total assets		8,299	7,832
Current liabilities
Short-term borrowings		40	26
Long-term debt due within one year		15	19
Accounts payable		214	139
Accrued expenses		126	137
Payables to affiliates, current		62	74
Regulatory Liability, Current		7	3
Customer deposits		54	54
Merger related obligation		38	42
Current portion of DC PLUG obligation		30	28
Other		42	28
Total current liabilities		628	550
Long-term debt		2,704	2,521
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,064	1,063
Non-pension postretirement benefit obligations		29	36
Regulatory liabilities, noncurrent		822	829
Other		312	300
Total deferred credits and other liabilities		2,227	2,228
Total liabilities		5,559	5,299
Commitments and Contingencies
Shareholders’ equity
Common stock		1,636	1,470
Retained earnings		1,104	1,063
Total shareholders’ equity		2,740	2,533
Member’s equity
Total liabilities and equity		8,299	7,832
Delmarva Power & Light Company [Member]
Current assets
Cash and cash equivalents		23	2
Restricted cash and cash equivalents		1	0
Accounts receivable, net
Customer		134	146
Other		46	38
Inventories, net
Materials and supplies		37	36
Gas Held in Storage		9	7
Regulatory assets, current		59	69
Other		27	27
Total current assets		336	325
Property, plant and equipment, net		3,821	3,579
Deferred debits and other assets
Regulatory assets, noncurrent		231	245
Investments		0	0
Goodwill		8	8
Prepaid pension asset		186	193
Other		6	7
Total deferred debits and other assets		431	453
Total assets		4,588	4,357
Current liabilities
Short-term borrowings		0	216
Long-term debt due within one year		91	83
Accounts payable		111	82
Accrued expenses		39	35
Payables to affiliates, current		33	46
Regulatory Liability, Current		59	42
Customer deposits		35	35
Other		7	8
Total current liabilities		375	547
Long-term debt		1,403	1,217
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		628	603
Non-pension postretirement benefit obligations		17	14
Regulatory liabilities, noncurrent		606	593
Other		50	48
Total deferred credits and other liabilities		1,301	1,258
Total liabilities		3,079	3,022
Commitments and Contingencies
Shareholders’ equity
Common stock		914	764
Retained earnings		595	571
Total shareholders’ equity		1,509	1,335
Member’s equity
Total liabilities and equity		4,588	4,357
Atlantic City Electric Company [Member]
Current assets
Cash and cash equivalents		7	2
Restricted cash and cash equivalents		4	6
Accounts receivable, net
Customer		95	92
Other		55	56
Receivables from affiliates, current		1	0
Inventories, net
Inventories, net		33	29
Regulatory assets, current		40	71
Other		5	2
Total current assets		240	258
Property, plant and equipment, net		2,966	2,706
Deferred debits and other assets
Regulatory assets, noncurrent		386	359
Investments		0	0
Prepaid pension asset		67	73
Long-term note receivable		0	4
Other		40	45
Total deferred debits and other assets		493	481
Total assets	[5]	3,699	3,445
Current liabilities
Short-term borrowings		139	108
Long-term debt due within one year		18	281
Accounts payable		154	118
Accrued expenses		35	33
Payables to affiliates, current		28	29
Regulatory Liability, Current		18	11
Customer deposits		26	31
Other		4	8
Total current liabilities		422	619
Long-term debt		1,170	840
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		535	493
Non-pension postretirement benefit obligations		17	14
Regulatory liabilities, noncurrent		402	411
Other		27	25
Total deferred credits and other liabilities		981	943
Total liabilities	[5]	2,573	2,402
Commitments and Contingencies
Shareholders’ equity
Common stock		979	912
Retained earnings		147	131
Total shareholders’ equity		1,126	1,043
Member’s equity
Total liabilities and equity		3,699	3,445
Variable Interest Entity, Consolidated, Assets, Not Pledged		23	29
Variable Interest Entity, Consolidated, Liabilities, No Recourse		$ 59	$ 90
[1]	Exelon’s consolidated assets include $9,667 million and $9,597 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,548 million and $3,618 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities for additional information.
[2]	Generation’s consolidated assets include $9,634 million and $9,556 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,480 million and $3,516 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities for additional information.
[3]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[4]	PHI’s consolidated total assets include $33 million and $41 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $69 million and $102 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities for additional information.
[5]	ACE’s consolidated assets include $23 million and $29 million at December 31, 2018 and 2017, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $59 million and $90 million at December 31, 2018 and 2017, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 - Variable Interest Entities for additional information.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares $ / shares in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares outstanding	968,187,955	963,335,888
Treasury stock, shares held	2,000,000	2,000,000

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders Equity - USD ($) shares in Thousands, $ in Millions		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]Membership Interest [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]	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]	[4]	Pepco Holdings LLC [Member]Deferred Compensation, Share-based Payments [Member]Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Common Stock [Member]	[1]	Pepco Holdings LLC [Member]Retained Earnings [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]Pepco Holdings LLC [Member]	[4]	Pepco Holdings LLC [Member]Undistributed Earnings [Member]	Pepco Holdings LLC [Member]Accumulated Other Comprehensive Income (Loss) [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 & Light Company [Member]	Delmarva Power & Light Company [Member]Common Stock [Member]	Delmarva Power & 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]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,330			$ 18,676	$ (2,327)	$ 12,104	$ (2,624)		$ 1,308	$ 193
Other Additional Capital | Successor [Member]																																																$ 3,829
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		$ 8,243	$ 1,588	$ 5,677	$ (1,639)	$ 2,617	$ 3,236	$ 2,455	$ 780	$ 1		$ 2,877		$ 1,367		$ 1,320	$ 2,687		$ 190														$ 2,240	$ 1,122	$ 1,118	$ 1,237	$ 612	$ 625	$ 1,000	$ 773	$ 227
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				$ 4,413				$ 3,832		$ 617					$ (36)
Beginning Balance at Dec. 31, 2015												$ 12,978	$ 8,997	$ 2,737	$ (63)		$ 1,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Predecessor [Member]																																				19						19
Employee stock purchase plan issuances | Predecessor [Member]																																				3				3
Tax benefit on stock compensation | Predecessor [Member]																																				(1)
Other comprehensive income (loss), net of income taxes | Predecessor [Member]																																				1											1
Ending Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439				3,838		636					(35)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Predecessor [Member]																																				3				3
Beginning Balance (in shares) at Dec. 31, 2015		954,668
Beginning Balance at Dec. 31, 2015																		8,243	1,588	5,677	(1,639)	2,617	3,236	2,455	780	1		2,877		1,367		1,320	2,687		190														2,240	1,122	1,118	1,237	612	625	1,000	773	227
Beginning Balance (Predecessor [Member]) at Dec. 31, 2015																																				4,413				3,832		617					(36)
Beginning Balance at Dec. 31, 2015												12,978	8,997	2,737	(63)		1,307
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		$ 1,196	$ (66)				1,121			67	8	550		483			67	378			378		438		438			294				294	294																42		42	(9)		(9)	(42)	0	(42)
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,868
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 85			85	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,242
Employee stock purchase plan issuances		$ 55			55	0	0	0		0	0
Tax benefit on stock compensation		(18)			(18)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		5								5
Sale of noncontrolling interests		239			(4)					243		239	(4)				243
Noncontrolling Interest, Change in Redemption Value		157								157		157					157
Noncontrolling Interest, Period Increase (Decrease)												5					5
Common stock dividends		(1,172)					(1,172)											(369)				(369)	(277)		(277)			(179)				(179)	(179)																(169)		(169)	(54)		(54)	(63)	0	(63)
Preferred and preference stock dividends		(8)									(8)																	(8)				(8)	(8)
Stock Redeemed or Called During Period, Value		(193)									(193)																	(190)							(190)
Adjustments to Additional Paid in Capital, Other												268	268					315		315								61	$ (7)	61	$ (7)		61	$ (7)															187	187		152	152		139	139
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(922)		(922)
Income Tax Effects Allocated Directly to Equity, Other																							18	18		0
Other comprehensive income (loss), net of income taxes		$ (36)					0	(36)				9			9
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							$ 8,077			$ (61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Additional Capital | Successor [Member]																																																3,835
Common stock | Successor [Member]																																																$ 3
Beginning Balance (Predecessor [Member]) at Mar. 23, 2016																																				4,439				$ 3,838		$ 636					(35)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Successor [Member]																																				(61)
Other comprehensive income (loss), net of income taxes | Successor [Member]																																				0
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							8,077			(61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]				$ 33
Stockholders' Equity, Other																																							$ 29
Common stock | Successor [Member]																																				165
Business Combination, Contingent Consideration, Asset | Successor [Member]																																				235
Business Combination, Contingent Consideration, Asset		$ 235										163
Beginning Balance (Successor [Member]) at Mar. 24, 2016	[2]																																			7,200							7,200			0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) | Successor [Member]																																				(61)										(61)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid | Successor [Member]																																				53							53
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared | Successor [Member]	[3]																																			(400)							(400)
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions | Successor [Member]																																				1,251							1,251
Ending Balance (in shares) at Dec. 31, 2016		958,778
Ending Balance at Dec. 31, 2016																		8,725	1,588	6,150	(1,639)	2,626	3,415	2,473	941	1		2,848		1,421		1,427	2,848		0														2,300	1,309	991	1,326	764	562	1,034	912	122
Ending Balance (Successor [Member]) at Dec. 31, 2016																																				8,016							8,077			(61)	0
Ending Balance at Dec. 31, 2016												13,284	9,261	2,298	(54)		1,779
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Other | Successor [Member]																																				35	$ (62)						35	$ (62)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 27,640			18,794	(2,327)	12,053	(2,660)	[5]	1,780	0				(54)	[5]										1	[5]
Other Additional Capital																		158		158
Retained Earnings, Appropriated																					(378)	378
Net income (loss)		$ 3,876	364				3,786			90	0	2,798		2,710			88	567			567		434		434			307				307	307			362										362			205		205	121		121	77	0	77
Stock Issued During Period, Shares, Share-based Compensation, Gross		5,066
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 56			56	0	0			0	0
Employee stock purchase plan issuances, shares		1,324
Employee stock purchase plan issuances		$ 150			150	0	0			0	0
Stock Issued During Period, Shares, New Issues		0
Stock Issued During Period, Value, New Issues		$ 0			0
Stock Issued During Period, Value, Treasury Stock Reissued		(1,150)				2,204	(1,054)
Tax benefit on stock compensation					0
Sale of noncontrolling interests		407			(36)					443		407	(36)				443
Noncontrolling Interest, Change in Redemption Value		(20)								(20)
Noncontrolling Interest, Period Increase (Decrease)												(18)					(18)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Paid												33	33
Common stock dividends		(1,243)					(1,243)											(422)				(422)	(288)		(288)			(198)				(198)	(198)																(133)		(133)	(112)		(112)	(68)	0	(68)
Adjustments to Additional Paid in Capital, Other		0										99	99					651		651								184		184			184		0														161	161
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(659)		(659)																						(311)										(311)
Income Tax Effects Allocated Directly to Equity, Other		0																					16	16
Other comprehensive income (loss), net of income taxes		$ 171					0	173	[5]	(2)		15			17	[5]	(2)									0	[5]									0
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions																																				758							758
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard							539	(539)
Ending Balance (in shares) at Dec. 31, 2017		965,168
Ending Balance at Dec. 31, 2017		$ 29,896																9,542	1,588	6,822	(1,639)	2,771	3,577	2,489	1,087	1		3,141		1,605		1,536	3,141		0														2,533	1,470	1,063	1,335	764	571	1,043	912	131
Ending Balance at Dec. 31, 2017												15,959	9,357	4,349	(37)		2,290																			8,825							8,835			(10)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		32,187			18,964	(123)	14,081	(3,026)	[5]	2,291	0				(37)	[5]										1	[5]
Other Additional Capital																		21		21
Retained Earnings, Appropriated																		2,771			(567)	567
Additional Paid in Capital																		6,822
Common stock		18,964																1,588					2,489					1,605																					1,470			764			912
Net income (loss)		$ 2,084	$ 453				2,010			74	0	443		370			73	664			664		460		460			313				313	313			398										398			210		210	120		120	75	0	75
Stock Issued During Period, Shares, Share-based Compensation, Gross		3,534
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 41			41	0	0	0		0	0
Employee stock purchase plan issuances, shares		1,318
Employee stock purchase plan issuances		$ 105			105	0	0	0		0	0
Sale of noncontrolling interests		6			6			0		0	0	6	6	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(60)			0					(60)		(60)					(60)
Common stock dividends		(1,339)					(1,339)											(459)				(459)	(306)		(306)			(209)				(209)	(209)																(169)		(169)	(96)		(96)	(59)	0	(59)
Adjustments to Additional Paid in Capital, Other												155	155					500		500								109		109		0	109		0														166	166		150	150		67	67
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared												(1,001)		(1,001)																						(326)										(326)
Income Tax Effects Allocated Directly to Equity, Other		0																					89	89
Other comprehensive income (loss), net of income taxes		42					0	41	[5]	1		3			2	[5]	1									0	[5]									0
Members Equity Including Portion Attributable To Noncontrolling Interest Acquisitions																																				385							385
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard		$ 4					14	(10)				3		6	(3)
Ending Balance (in shares) at Dec. 31, 2018		970,020
Ending Balance at Dec. 31, 2018		$ 30,764																10,247	$ 1,588	$ 7,322	(1,639)	2,976	3,820	$ 2,578	$ 1,242	0		3,354		$ 1,714		$ 1,640	$ 3,354		$ 0														2,740	$ 1,636	$ 1,104	1,509	$ 914	$ 595	1,126	$ 979	$ 147
Ending Balance at Dec. 31, 2018												$ 15,508	$ 9,518	$ 3,724	(38)		$ 2,304																			$ 9,282							$ 9,220			$ 62	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		33,070			$ 19,116	$ (123)	$ 14,766	$ (2,995)	[5]	$ 2,306	$ 0				$ (38)	[5]										$ 0	[5]
Retained Earnings, Appropriated																		2,976			$ (664)	$ 664
Additional Paid in Capital																		7,322
Common stock		$ 19,116																$ 1,588					$ 2,578					$ 1,714																					$ 1,636			$ 914			$ 979
[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]	The March 24, 2016, beginning balance differs from the PHI Merger total purchase price by $59 million related to an acquisition accounting adjustment recorded at Exelon Corporate to reflect unitary state income tax consequences of the merger.
[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.
[4]	he liabilities assumed include $29 million for PHI stock-based compensation awards and $33 million for a merger related obligation, each assumed by PHI from Exelon. See Note 5 — Mergers, Acquisitions and Dispositions.
[5]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Shareholders Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 1.38	$ 1.31	$ 1.26

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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 in the generation, delivery and marketing of energy through Generation and the energy distribution and transmission businesses through ComEd, PECO, BGE, Pepco, DPL and ACE. On March 23, 2016 , Exelon completed the merger with PHI, which became 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. See Note 5 — Mergers, Acquisitions and Dispositions for additional 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 merger with 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 it has pushed-down to the consolidated financial statements of PHI such that the assets and liabilities of PHI are 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 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. PHI also has a business services subsidiary, PHISCO, which provides a variety of support services at cost, including legal, accounting, engineering, customer operations, distribution and transmission planning, asset management, system operations, and power procurement, to PHI operating companies. The costs of BSC and PHISCO are directly charged or allocated to the applicable subsidiaries. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. Exelon owns 100% of Generation, PECO, BGE and PHI and more than 99% of ComEd. PHI owns 100% of Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and EGRP, 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 additional information 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. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or accounting for investments in equity securities without readily determinable fair value 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 and PECO. 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 accounting for investments in equity securities without readily determinable fair values if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under accounting for investments in equity securities without readily determinable fair values, the Registrants report their investments at cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. 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. Prior Period Adjustments and Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Incom e, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. See New Accounting Standards below for additional information. Accounting for the Effects of Regulation (Exelon and the Utility Registrants) For their regulated electric and gas operations, Exelon and the Utility Registrants reflect the effects of cost-based rate regulation in their financial statements, which is required 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's regulatory assets and liabilities as of the balance sheet date are probable of being recovered or settled in future rates. 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 financial statements. See Note 4 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, Exelon and the Utility 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 in Exelon's and the Utility Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. Exelon and the Utility 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. The Registrants’ operating revenues generally consist of revenues from contracts with customers involving the sale and delivery of energy commodities and related products and services, utility revenues from alternative revenue programs (ARP), and realized and unrealized revenues recognized under mark-to-market energy commodity derivative contracts. The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers in an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and natural gas tariff sales, distribution and transmission services. 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 ARP revenue for its best estimate of the electric distribution, energy efficiency, and transmission revenue impacts resulting from future changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE, Pepco and DPL record ARP revenue for their best estimate of the electric and natural gas distribution revenue impacts resulting from future changes in rates that they believe are probable of approval by the MDPSC and/or DCPSC in accordance with their revenue decoupling mechanisms. PECO, BGE, Pepco, DPL and ACE record ARP revenue for their best estimate of the transmission revenue impacts resulting from future changes in rates that they believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 4 — Regulatory Matters and Note 23 — Supplemental Financial Information for additional information. 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. 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 in its Consolidated Balance Sheets. See Note 4 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information. Taxes Directly Imposed on Revenue-Producing Transactions. 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. Se e Note 23 — 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. 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 in the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. 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 in their Consolidated Statements of Operations and Comprehensive Income. 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 additional information. 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, 2018 and 2017 , the Registrants' restricted cash and cash equivalents primarily represented the following items: Registrant Description Exelon Payment of medical, dental, vision and long-term disability benefits, in addition to the items listed for Generation and the Utility Registrants. Generation Project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities. ComEd Collateral held from suppliers associated with energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site. PECO Proceeds from the sales of assets that were subject to PECO’s mortgage indenture. BGE Proceeds from the loan program for the completion of certain energy efficiency measures and collateral held from energy suppliers. PHI Payment of merger commitments, collateral held from its energy suppliers associated with procurement contracts and repayment of transition bonds. Pepco Payment of merger commitments and collateral held from energy suppliers. DPL Collateral held from energy suppliers. ACE Repayment of transition bonds and collateral held from energy suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2018 and 2017 , the Registrants' noncurrent restricted cash and cash equivalents primarily represented ComEd’s over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site, and ACE’s repayment of transition bonds. See Note 23 — Supplemental Financial Information for additional information. 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. Utility Registrants estimate the allowance by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Utility Registrants' customer accounts are written off consistent with approved regulatory requirements. See Note 4 — 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 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, • 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, materials and supplies, and emissions allowances are generally included in inventory when purchased. Fossil fuel and emissions allowances are expensed to purchased power and fuel expense when used or sold. Materials and supplies generally includes transmission, distribution and generating plant materials and are expensed to operating and maintenance or capitalized to property, plant and equipment, as appropriate, when installed or used. Debt and Equity Security Investments (Exelon and Generation ) Debt Security Investments. Debt securities are reported at fair value and classified as available-for-sale securities. Unrealized gains and losses, net of tax, are reported in OCI. Equity Security Investments without Readily Determinable Fair Values. Exelon has certain equity securities without readily determinable fair values. Exelon has elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity Security Investments with Readily Determinable Fair Values. Equity securities held in the NDT funds are classified as equity securities with readily determinable fair values. 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. Exelon's and Generation's NDT funds are classified as current or noncurrent assets, depending on the timing of the decommissioning activities and income taxes on trust earnings. See Note 4 — 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 additional 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 the Utility Registrants. 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, net. 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. Capitalized Software. Certain costs, such as design, coding, and testing 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. Capitalized Interest and AFUDC. 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. AFUDC 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 an allowance 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. See Note 6 — Property, Plant and Equipment , Note 9 — Jointly Owned Electric Utility Plant and Note 23 — 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. Any potential future SNF disposal fees will be expensed through fuel expense. Additionally, 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 22 — Commitments and Contingencies for additional information regarding the cost of SNF storage and disposal. 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. 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 Registrants are based on a combination of depreciation studies, historical retirements, site licenses and management estimates of operating costs and expected future energy market conditions. See Note 8 — Early Plant Retirements for additional information on the impacts of expected and potential early plant retirements. See Note 6 — Property, Plant and Equipment for additional 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 Utility Registrants’ Consolidated Statements of Operations and Comprehensive Income. Amortization of ComEd’s electric distribution and energy efficiency formula rate regulatory assets and the Utility Registrants' transmission formula rate regulatory assets is recorded to Operating revenues. Amortization of income tax related regulatory assets and liabilities is 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 4 — Regulatory Matters and Note 23 — Supplemental Financial Information for additional information regarding Generation’s nuclear fuel and ARC, and the amortization of the Utility Registrants' regulatory assets. Asset Retirement Obligations (All Registrants) Generation estimates and recognizes a liability for its legal obligation to perform asset retirement activities even though the timing and/or methods of settlement may be conditional on future events. Generation generally updates its nuclear decommissioning ARO annually, unless circumstances warrant more frequent updates, based on its annual evaluation of cost escalation factors and probabilities assigned to the multiple outcome scenarios within its probability-weighted discounted cash flow models. Generation’s multiple outcome scenarios are generally based on decommissioning cost studies which are updated, on a rotational basis, for each of Generation’s nuclear units at least every five years, unless circumstances warrant more frequent updates. 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. 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 22 — Commitments and Contingencies for additional information. Asset Impairments Long-Lived Assets (All Registrants). The Registrants e

Variable Interest Entities (All

Variable Interest Entities (All Registrants)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , Exelon, Generation, PHI and ACE collectively consolidated five VIEs or VIE groups for which the applicable Registrant was the primary beneficiary (see Consolidated Variable Interest Entities below). As of December 31, 2018 and 2017 , Exelon and Generation collectively had significant interests in seven other VIEs 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, 2018 and 2017 are as follows: December 31, 2018 Exelon (a) Generation PHI (a) ACE Current assets $ 938 $ 931 $ 7 4 Noncurrent assets 9,071 9,045 26 19 Total assets $ 10,009 $ 9,976 $ 33 $ 23 Current liabilities $ 274 $ 252 $ 22 19 Noncurrent liabilities 3,280 3,233 47 40 Total liabilities $ 3,554 $ 3,485 $ 69 $ 59 December 31, 2017 Exelon (a) Generation PHI (a) ACE Current assets $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,317 9,286 31 23 Total assets $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,316 3,250 66 58 Total liabilities $ 3,624 $ 3,522 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE 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, 2018 and 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 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 sold a 49% interest in EGRP to an outside investor for $400 million of cash plus immaterial working capital and other customary post-closing adjustments. EGRP meets the definition of a VIE because the EGRP 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; therefore, Generation will continue to consolidate EGRP. EGRP is a collection of wind and solar project entities and some of these project entities are VIEs that are consolidated by EGRP. 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 EGRP. While Generation or EGRP 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 EGRP owns 100% of the majority of the wind entities, four 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 EGRP's current economic interests in three 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 EGRP 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. 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 and was subsequently contributed to EGRP in 2017. 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. In 2017, Generation’s interests in EGRP were contributed to and are pledged for the ExGen Renewables IV non-recourse debt project financing structure. Refer to Note 13 — Debt and Credit Agreements for additional information on ExGen Renewables IV and ITEM 2. PROPERTIES for additional details on the specific projects included within EGRP. 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 $34 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: • 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 RSSA, through the end of March 31, 2017. With the expiration of the RSSA, the PPA was reinstated beginning April 1, 2017. (see Note 4 — Regulatory Matters for additional details), • Generation provided a $400 million loan to CENG. As of December 31, 2018 , the remaining obligation is $196 million , including accrued interest. The remaining balance was fully paid by CENG in January 2019. • 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 22 — Commitments and Contingencies for more details), • Generation and EDF share in the $688 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, 2018 and 2017 , Exelon's, PHI'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, 2018 , 2017 and 2016 , ACE transferred $30 million , $48 million and $60 million to ATF, respectively. As of December 31, 2018 and 2017 , ComEd, PECO, BGE, 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, 2018 and 2017 , these assets and liabilities primarily consisted of the following: December 31, 2018 Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 66 62 4 4 Accounts receivable, net Customer 146 146 — — Other 23 23 — — Inventory Materials and supplies 212 212 — — Other current assets 52 49 3 — Total current assets 913 906 7 4 Property, plant and equipment, net 6,145 6,145 — — Nuclear decommissioning trust funds 2,351 2,351 — — Other noncurrent assets 258 232 26 19 Total noncurrent assets 8,754 8,728 26 19 Total assets $ 9,667 $ 9,634 $ 33 $ 23 Long-term debt due within one year $ 87 $ 66 $ 21 $ 18 Accounts payable 96 96 — — Accrued expenses 72 72 1 1 Unamortized energy contract liabilities 15 15 — — Other current liabilities 3 3 — — Total current liabilities 273 252 22 19 Long-term debt 1,072 1,025 47 40 Asset retirement obligations 2,160 2,160 — — Unamortized energy contract liabilities 1 1 — — Other noncurrent liabilities 42 42 — — Total noncurrent liabilities 3,275 3,228 47 40 Total liabilities $ 3,548 $ 3,480 $ 69 $ 59 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. December 31, 2017 Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 126 $ 126 $ — $ — Restricted cash and cash equivalents 64 58 6 6 Accounts receivable, net Customer 170 170 — — Other 25 25 — — Inventory Materials and supplies 205 205 — — Other current assets 45 41 4 — Total current assets 635 625 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 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 102 $ 67 $ 35 $ 31 Accounts payable 114 114 — — Accrued expenses 67 66 1 1 Unamortized energy contract liabilities 18 18 — — Other current liabilities 7 7 — — Total current liabilities 308 272 36 32 Long-term debt 1,154 1,088 66 58 Asset retirement obligations 2,035 2,035 — — Other noncurrent liabilities 121 121 — — Total noncurrent liabilities 3,310 3,244 66 58 Total liabilities $ 3,618 $ 3,516 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. 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 in 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, 2018 and 2017 , Exelon and Generation had significant unconsolidated variable interests in seven VIEs 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, Exelon and Generation have several individually immaterial VIEs that in aggregate represent a total investment of $15 million and $13 million , respectively, as of December 31, 2018 . These immaterial VIEs are equity and debt securities in energy development companies. As of December 31, 2018 , the maximum exposure to loss related to these securities included in Investments in Exelon's and Generation's Consolidated Balance Sheets is limited to the $15 million and $13 million , respectively. The following tables present summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 597 $ 472 $ 1,069 Total liabilities (a) 37 222 259 Exelon's ownership interest in VIE (a) — 223 223 Other ownership interests in VIE (a) 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 223 223 Contract intangible asset 7 — 7 Net assets pledged for Zion Station decommissioning (b) — — — 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 Net assets pledged for Zion Station decommissioning (b) 2 — 2 __________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not in 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 in 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 $9 million and $39 million as of December 31, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions LLC of $9 million and $37 million as of December 31, 2018 and December 31, 2017 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. For each of the unconsolidated VIEs, Exelon and Generation have 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 material agreements with, or commitments by, third parties that would materially affect the fair value or risk of their variable interests in these VIEs. As of December 31, 2018 and 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. ComEd and PECO 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. See Note 13 — Debt and Credit Agreements for additional information.

Revenue Recognition Revenue Rec

Revenue Recognition Revenue Recognition (All Registrants)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer (All Registrants) [Abstract]
Revenue from Contract with Customer [Text Block]	3. Revenue from Contracts with Customers (All Registrants) The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers at an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and gas tariff sales, distribution and transmission services. The performance obligations associated with these sources of revenue are further discussed below. Unless otherwise noted, for each of the significant revenue categories and related performance obligations described below, the Registrants have the right to consideration from the customer in an amount that corresponds directly with the value transferred to the customer for the performance completed to date. Therefore, the Registrant's have elected to use the right to invoice practical expedient for the contracts within these revenue categories and generally recognize revenue in the amount for which they have the right to invoice the customer. As a result, there are generally no significant judgments used in determining or allocating the transaction price. Competitive Power Sales (Exelon and Generation) Generation sells power and other energy-related commodities to both wholesale and retail customers across multiple geographic regions through its customer-facing business, Constellation. Power sale contracts generally contain various performance obligations including the delivery of power and other energy-related commodities such as capacity, ZECs, RECs or other ancillary services. Certain performance obligations such as power and capacity are generally delivered over time whereas other performance obligations such as RECs and ZECs are generally delivered at a point in time. In either case, revenues related to all of the performance obligations in such bundled power sale contracts are generally recognized concurrently as the power is generated. Except as noted in the paragraph below, there are no significant judgments in allocating the transaction price since all performance obligations are satisfied simultaneously upon the generation of power. Payment terms generally require that the customers pay for the power or the energy-related commodity within the month following delivery to the customer and there are generally no significant financing components. Certain contracts may contain limits on the total amount of revenue we are able to collect over the entire term of the contract. In such cases, the Registrants estimate the total consideration expected to be received over the term of the contract net of the constraint and allocate the expected consideration to the performance obligations in the contract such that revenue is recognized ratably over the term of the entire contract as the performance obligations are satisfied. Competitive Natural Gas Sales (Exelon and Generation) Generation sells natural gas on a full requirements basis or for an agreed upon volume to both commercial and residential customers. The primary performance obligation associated with natural gas sale contracts is the delivery of the natural gas to the customer. Revenues related to the sale of natural gas are recognized over time as the natural gas is delivered to and consumed by the customer. Payment from customers is typically due within the month following delivery of the natural gas to the customer and there are generally no significant financing components. Other Competitive Products and Services (Exelon and Generation) Generation also sells other energy-related products and services such as long-term construction and installation of energy efficiency assets and new power generating facilities, primarily to commercial and industrial customers. These contracts generally contain a single performance obligation, which is the construction and/or installation of the asset for the customer. The average contract term for these projects is approximately 18 months. Revenues, and associated costs, are recognized throughout the contract term using an input method to measure progress towards completion. The method recognizes revenue based on the various inputs used to satisfy the performance obligation, such as costs incurred and total labor hours expended. The total amount of revenue that will be recognized is based on the agreed upon contractually-stated amount. Payments from customers are typically due within 30 or 45 days from the date the invoice is generated and sent to the customer. Regulated Electric and Gas Tariff Sales (Exelon and the Utility Registrants) The Utility Registrants sell electricity and electricity distribution services to residential, commercial, industrial and governmental customers through regulated tariff rates approved by their state regulatory commissions. PECO, BGE and DPL also sell natural gas and gas distribution services to residential, commercial, and industrial customers through regulated tariff rates approved by their state regulatory commissions. The performance obligation associated with these tariff sale contracts is the delivery of electricity and/or natural gas. Tariff sales are generally considered daily contracts given that customers can discontinue service at any time. Revenues are generally recognized over time (each day) as the electricity and/or natural gas is delivered to customers. Payment terms generally require that customers pay for the services within the month following delivery of the electricity or natural gas to the customer and there are generally no significant financing components or variable consideration. Electric and natural gas utility customers have the choice to purchase electricity or natural gas from competitive electric generation and natural gas suppliers. While the Utility Registrants are required under state legislation to bill their customers for the supply and distribution of electricity and/or natural gas, they recognize revenue related only to the distribution services when customers purchase their electricity or natural gas from competitive suppliers. Regulated Transmission Services (Exelon and the Utility Registrants) Under FERC’s open access transmission policy, the Utility Registrants, as owners of transmission facilities, are required to provide open access to their transmission facilities under filed tariffs at cost-based rates approved by FERC. The Utility Registrants are members of PJM, the regional transmission organization designated by FERC to coordinate the movement of wholesale electricity in PJM’s region, which includes portions of the mid-Atlantic and Midwest. In accordance with FERC-approved rules, the Utility Registrants and other transmission owners in the PJM region make their transmission facilities available to PJM, which directs and controls the operation of these transmission facilities and accordingly compensates the Utility Registrants and other transmission owners. The performance obligations associated with the Utility Registrants’ contract with PJM include (i) Network Integration Transmission Services (NITS), (ii) scheduling, system control and dispatch services, and (iii) access to the wholesale grid. These performance obligations are satisfied over time, and Utility Registrants utilize output methods to measure the progress towards their completion. Passage of time is used for NITS and access to the wholesale grid and MWhs of energy transported over the wholesale grid is used for scheduling, system control and dispatch services. PJM pays the Utility Registrants for these services on a weekly basis and there are no financing components or variable consideration. Costs to Obtain or Fulfill a Contract with a Customer (Exelon and Generation) Generation incurs incremental costs in order to execute certain retail power and gas sales contracts. These costs primarily relate to retail broker fees and sales commissions. Generation has capitalized such contract acquisition costs in the amount of $32 million and $26 million as of December 31, 2018 and December 31, 2017 , respectively, within Other current assets and Other deferred debits in Exelon’s and Generation’s Consolidated Balance Sheets. These costs are capitalized when incurred and amortized using the straight-line method over the average length of such retail contracts, which is approximately 2 years. Exelon and Generation recognized amortization expense associated with these costs in the amount of $22 million and $30 million for the twelve months ended December 31, 2018 , and December 31, 2017 , respectively, within Operating and maintenance expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Generation does not incur material costs to fulfill contracts with customers that are not already capitalized under existing guidance. In addition, the Utility Registrants do not incur any material costs to obtain or fulfill contracts with customers. Contract Balances (All Registrants) Contract Assets Generation records contract assets for the revenue recognized on the construction and installation of energy efficiency assets and new power generating facilities before Generation has an unconditional right to bill for and receive the consideration from the customer. These contract assets are subsequently reclassified to receivables when the right to payment becomes unconditional. Generation records contract assets and contract receivables within Other current assets and Accounts receivable, net - Customer, respectively, within Exelon’s and Generation’s Consolidated Balance Sheets. The following table provides a rollforward of the contract assets reflected in Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to December 31, 2018 : Contract Assets Exelon and Generation Balance as of January 1, 2018 $ 283 Increases as a result of changes in the estimate of the stage of completion 50 Amounts reclassified to receivables (146 ) Balance at December 31, 2018 $ 187 The Utility Registrants do not have any contract assets. Contract Liabilities Generation records contract liabilities when consideration is received or due prior to the satisfaction of the performance obligations. These contract liabilities primarily relate to upfront consideration received or due for equipment service plans, solar panel leases and the Illinois ZEC program that introduces a cap on the total consideration to be received by Generation. The Generation contract liability related to the Illinois ZEC program includes certain amounts with ComEd that are eliminated in consolidation in Exelon’s Consolidated Statements of Operations and Consolidated Balance Sheets. Generation records contract liabilities within Other current liabilities and Other noncurrent liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. The following table provides a rollforward of the contract liabilities reflected in Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to December 31, 2018 : Contract Liabilities Exelon Generation Balance as of January 1, 2018 $ 35 $ 35 Increases as a result of additional cash received or due 179 465 Amounts recognized into revenues (187 ) (458 ) Balance at December 31, 2018 $ 27 $ 42 The Utility Registrants also record contract liabilities when consideration is received prior to the satisfaction of the performance obligations. As of December 31, 2018 and December 31, 2017 , the Utility Registrants' contract liabilities were immaterial. Transaction Price Allocated to Remaining Performance Obligations (All Registrants) The following table shows the amounts of future revenues expected to be recorded in each year for performance obligations that are unsatisfied or partially unsatisfied as of December 31, 2018 . Generation has elected the exemption which permits the exclusion from this disclosure of certain variable contract consideration. As such, the majority of Generation’s power and gas sales contracts are excluded from this disclosure as they contain variable volumes and/or variable pricing. Thus, this disclosure only includes contracts for which the total consideration is fixed and determinable at contract inception. The average contract term varies by customer type and commodity but ranges from one month to several years. The majority of the Utility Registrants’ tariff sale contracts are generally day-to-day contracts and, therefore, do not contain any future, unsatisfied performance obligations to be included in this disclosure. Further, the Utility Registrants have elected the exemption to not disclose the transaction price allocation to remaining performance obligations for contracts with an original expected duration of one year or less. As such, gas and electric tariff sales contracts and transmission revenue contracts are excluded from this disclosure. 2019 2020 2021 2022 2023 and thereafter Total Exelon $ 631 $ 329 $ 119 $ 47 $ 138 $ 1,264 Generation 631 329 119 47 138 1,264 Revenue Disaggregation (All Registrants) The Registrants disaggregate revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. See Note 24 — Segment Information for the presentation of the Registrant's revenue disaggregation.

Regulatory Matters (All Registr

Regulatory Matters (All Registrants)	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Regulatory Matters (All Registrants)	Regulatory Matters (All Registrants) The following matters below discuss the status of material regulatory and legislative proceedings of the Registrants. Utility Regulatory Matters (Exelon and the Utility Registrants) Distribution Base Rate Case Proceedings The following tables show the completed and pending distribution base rate case proceedings in 2018. Completed Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase (Decrease) Approved Revenue Requirement Increase (Decrease) Approved ROE Approval Date Rate Effective Date ComEd - Illinois (Electric) (b) April 16, 2018 $ (23 ) (a) $ (24 ) (a) 8.69 % December 4, 2018 January 1, 2019 PECO - Pennsylvania (Electric) (c) March 29, 2018 $ 82 (a) $ 25 (a) N/A December 20, 2018 January 1, 2019 BGE - Maryland (Natural Gas) June 8, 2018 (amended August 24, 2018 and October 12, 2018) $ 61 $ 43 9.8 % January 4, 2019 January 4, 2019 Pepco - Maryland (Electric) January 2, 2018 (amended February 5, 2018) $ 3 (a) $ (15 ) (a) 9.5 % May 31, 2018 June 1, 2018 Pepco - District of Columbia (Electric) (d) December 19, 2017 (amended February 9, 2018) $ 66 $ (24 ) (a) 9.525 % August 9, 2018 August 13, 2018 DPL - Maryland (Electric) (e) July 14, 2017 (amended November 16, 2017) $ 19 $ 13 9.5 % February 9, 2018 February 9, 2018 DPL - Delaware (Electric) August 17, 2017 (amended February 9, 2018) $ 12 (a) $ (7 ) (a) 9.7 % August 21, 2018 March 17, 2018 DPL - Delaware (Natural Gas) August 17, 2017 (amended February 9, 2018) $ 4 (a) $ (4 ) (a) 9.7 % November 8, 2018 March 17, 2018 __________ (a) Includes the annual ongoing TCJA tax savings further discussed below. (b) Pursuant to EIMA and FEJA, ComEd’s electric distribution rates are established through a performance-based formula, which sunsets at the end of 2022. ComEd is required to file an annual update to its electric distribution formula rate on or before May 1 st , with resulting rates effective in January of the following year. ComEd’s annual electric distribution formula rate update is based on prior year actual costs and current year projected capital additions (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred from the year (annual reconciliation). ComEd’s 2018 approved revenue requirement above reflects a decrease of $58 million for the initial year revenue requirement for 2018 and an increase of $34 million related to the annual reconciliation for 2017. The revenue requirement for 2018 and the annual reconciliation for 2017 provides for a weighted average debt and equity return on distribution rate base of 6.52% inclusive of an allowed ROE of 8.69% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its electric distribution formula rate. During the first quarter of 2018, ComEd revised its electric distribution formula rate to implement revenue decoupling provisions provided for under FEJA. As a result of this revision, ComEd’s electric distribution formula rate revenues are not impacted by abnormal weather, usage per customer or numbers of customers. ComEd began reflecting the impacts of this change in its Operating revenues and electric distribution formula rate regulatory asset in the first quarter of 2017. (c) The PECO base rate case proceeding was resolved through a settlement agreement, which did not specify an approved ROE. (d) On September 7, 2018, Pepco submitted an updated filing for an increase of $4 million to the customer base rate credit established in connection with the merger between Exelon and PHI for residential customers, representing the TCJA benefits for the period January 1, 2018 through August 12, 2018. (e) The DPL Maryland base rate case proceeding was resolved through a settlement agreement, which did not specify an overall ROE. The settlement agreement included an ROE of 9.5% solely for purposes of calculating AFUDC and regulatory asset carrying costs. In the second quarter of 2018, DPL discovered a rate design issue in Maryland such that the current rates were not sufficient to collect the full amount of the $13 million revenue increase agreed to by the parties in the recent settlement. On September 5, 2018, the MDPSC approved DPL’s proposed revisions to resolve the rate design issue on a prospective basis, effective September 5, 2018. Pending Distribution Base Rate Case Proceedings Registrant/Jurisdiction Filing Date Requested Revenue Requirement Increase Requested ROE Expected Approval Timing ACE - New Jersey (Electric) August 21, 2018 (amended November 19, 2018) $ 122 (a) 10.1 % Third quarter of 2019 (b) Pepco - Maryland (Electric) January 15, 2019 $ 30 10.3 % Third quarter of 2019 __________ (a) Requested increase is before New Jersey sales and use tax and includes $40 million of higher depreciation expense related to its updated depreciation study and the annual ongoing TCJA tax savings further discussed below. (b) ACE plans to put interim rates in effect on or around May 21, 2019, subject to refund, as allowed by the regulation. Transmission Formula Rates Transmission Formula Rate (Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE). ComEd’s, BGE’s, Pepco's, DPL's and ACE's transmission rates are each established based on a FERC-approved formula. ComEd, BGE, Pepco, DPL and ACE are required to file an annual update to the FERC-approved formula on or before May 15, with the resulting rates effective on June 1 of the same year. The annual formula rate update is based on prior year actual costs and current year projected capital additions (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect beginning June 1 of the prior year and actual costs incurred for that year (annual reconciliation). For 2018, the following total increases/(decreases) were included in ComEd’s, BGE’s, Pepco's, DPL's and ACE's electric transmission formula rate filings: Registrant Initial Revenue Requirement (Decrease) Increase (b) Annual Reconciliation Increase/(Decrease) Total Revenue Requirement (Decrease) Increase Allowed Return on Rate Base (d) Allowed ROE (e) ComEd (a) $ (44 ) $ 18 $ (26 ) 8.32 % 11.50 % BGE (a) 10 4 26 (c) 7.61 % 10.50 % Pepco 6 2 8 7.82 % 10.50 % DPL 14 13 27 7.29 % 10.50 % ACE (a) 4 (4 ) — 8.02 % 10.50 % __________ (a) The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted. (b) The initial revenue requirement changes reflect the annual benefit of lower income tax rates effective January 1, 2018 resulting from the enactment of the TCJA of $69 million , $18 million , $13 million , $12 million and $11 million for ComEd, BGE, Pepco, DPL and ACE, respectively. They do not reflect the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. See further discussion below. (c) The change in BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $12 million to recover the costs of providing transmission service to specifically designated load by BGE. (d) Represents 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. Pending Transmission Formula Rate (Exelon and PECO). On May 1, 2017, PECO filed a request with FERC seeking approval to update its transmission rates and change the manner in which PECO’s transmission rate is determined from a fixed rate to a formula rate. The formula rate will be updated annually to ensure that under this rate customers pay the actual costs of providing transmission services. The formula rate filing includes a requested increase of $22 million to PECO’s annual transmission revenues and a requested rate of return on common equity of 11% , inclusive of a 50 basis point adder for being a member of a regional transmission organization. PECO requested that the new transmission rate be effective as of July 2017. On June 27, 2017, FERC issued an Order accepting the filing and suspending the proposed rates until December 1, 2017, subject to refund, and set the matter for hearing and settlement judge procedures. On May 4, 2018, the Chief Administrative Law Judge terminated settlement judge procedures and designated a new presiding judge. PECO cannot predict the outcome of this proceeding, or the transmission formula FERC may approve. On May 11, 2018, pursuant to the transmission formula rate request discussed above, PECO made its first annual formula rate update, which included a revenue decrease of $6 million. The revenue decrease of $6 million included an approximately $20 million reduction as a result of the tax savings associated with the TCJA. The updated transmission rate was effective June 1, 2018, subject to refund. Tax Cuts and Jobs Act The Utility Registrants have made filings with their state regulatory commissions to pass back tax savings related to TCJA to their distribution customers, which are detailed below. The tax savings include the benefit of lower federal income tax rates and the settlement of a portion of the deferred income tax regulatory liabilities established upon the enactment of the TCJA. The ongoing annual TCJA tax savings in the table below represent the annual savings for distribution customers reflected in the initial customers rates approved after the TCJA. Subsequent annual TCJA tax savings will be approved as part of the annual update to the electric distribution formula rate for ComEd or base rate case proceedings for PECO, BGE, Pepco, DPL and ACE. Ongoing TCJA Tax Savings Stub Period Bill Credit from TCJA Tax Savings Registrant/Jurisdiction Amount Approval Date Rate Effective Date Stub Period Approval Date Refund Amount/Period ComEd - Illinois (Electric) $ 201 January 18, 2018 February 1, 2018 Not applicable PECO - Pennsylvania (Electric) $ 71 December 20, 2018 January 1, 2019 January 1, 2018 - December 31, 2018 December 20, 2018 $67 / 2019 (majority in January) PECO - Pennsylvania (Natural Gas) $ 4 (a) July 1, 2018 Not applicable BGE - Maryland (Electric) $ 72 January 31, 2018 February 1, 2018 January 1, 2018 - January 31, 2018 To be addressed in next electric distribution base rate case BGE - Maryland (Natural Gas) $ 31 January 31, 2018 February 1, 2018 January 1, 2018 - January 31, 2018 January 4, 2019 $2 / Q1 2019 Pepco - Maryland (Electric) $ 31 May 31, 2018 June 1, 2018 January 1, 2018 - June 1, 2018 May 31, 2018 $10 / July 2018 Pepco - District of Columbia (Electric) $ 39 August 9, 2018 August 13, 2018 January 1, 2018 - August 12, 2018 September 7, 2018 $20 / September 2018 DPL - Maryland (Electric) $ 14 April 18, 2018 April 20, 2018 January 1, 2018 - March 31, 2018 April 18, 2018 $2 / June 2018 DPL - Delaware (Electric) $ 19 August 21, 2018 March 17, 2018 February 1, 2018 - March 17, 2018 August 21, 2018 $3 / Q4 2018 DPL - Delaware (Natural Gas) $ 7 November 8, 2018 March 17, 2018 February 1, 2018 - March 17, 2018 November 8, 2018 $1 / Q4 2018 ACE - New Jersey (Electric) $ 23 August 29, 2018 September 8, 2018 January 1, 2018 - June 30, 2018 August 29, 2018 $6 / Q4 2018 __________ (a) On May 17, 2018, the PAPUC issued an order directing Pennsylvania utility companies without an existing base rate case, including PECO’s gas distribution business, to start passing back the savings from January 1, 2018 onward through a negative surcharge mechanism to be effective on July 1, 2018. Pursuant to that order, PECO filed a negative surcharge mechanism and began on July 1, 2018, to return the estimated annual 2018 tax savings above to its natural gas distribution customers. As discussed above, ComEd’s, BGE’s, Pepco’s, DPL’s and ACE’s transmission formula rates currently do not provide for the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. On December 13, 2016 (as amended on March 13, 2017) and on February 23, 2018 (as amended on July 9, 2018), BGE and ComEd, Pepco, DPL and ACE, respectively, each filed with FERC to revise their transmission formula rate mechanisms to provide for pass back and recovery of transmission-related income tax-related regulatory liabilities and assets, including those established upon enactment of the TCJA. See discussion below for additional information regarding these filings. See Note 14 - Income Taxes for additional information on Corporate Tax Reform. Other State Regulatory Matters Illinois Regulatory Matters Energy Efficiency Formula Rate (Exelon and ComEd). 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 st each year, with resulting rates effective in January of the following year. The annual update is 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 (initial year revenue requirement). The update also reconciles any differences between the revenue requirement in effect for the prior year and actual costs incurred from the year (annual reconciliation). The approved energy efficiency formula rate also provides for revenue decoupling provisions similar to those in ComEd’s electric distribution formula rate. During 2018, the ICC approved the following total increases in ComEd's requested energy efficiency revenue requirement: Filing Date Requested Revenue Requirement Increase Approved Revenue Requirement Increase Approved ROE Approval Date Rate Effective Date June 1, 2018 $ 39 $ 42 (a) 8.69 % December 4, 2018 January 1, 2019 _________ (a) ComEd’s 2018 approved revenue requirement above reflects an increase of $41 million for the initial year revenue requirement for 2018 and 2019 and an increase of $1 million related to the annual reconciliation for 2017. The revenue requirement for 2018 and 2019 and the annual reconciliation for 2017 provides for a weighted average debt and equity return on distribution rate base of 6.52% inclusive of an allowed ROE of 8.69% , reflecting the average rate on 30-year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its energy efficiency formula rate. Maryland Regulatory Matters Cash Working Capital Order (Exelon and BGE). On November 17, 2016, the MDPSC rendered a decision in the proceeding to review BGE’s request to recover its cash working capital (CWC) requirement for its Provider of Last Resort service, also known as Standard Offer Service (SOS), as well as other components that make up the Administrative Charge, the mechanism that enables BGE to recover its SOS-related costs. The Administrative Charge is comprised of five components: CWC, uncollectibles, incremental costs, return, and an administrative adjustment, which acts as a proxy for retail suppliers’ costs. The Commission accepted BGE's positions on recovery of CWC and pass-through recovery of BGE’s actual uncollectibles and incremental costs. The order also grants BGE a return on the SOS. The Commission ruled that the level of the administrative adjustment will be determined in BGE’s next rate case. Subsequently, the MDPSC Staff and residential consumer advocate sought clarification and appealed the amount of return awarded to BGE on the SOS. The appeal currently resides with the Maryland Court of Special Appeals. BGE cannot predict the outcome of this appeal. Smart Meter and Smart Grid Investments (Exelon and BGE). In August 2010, the MDPSC approved a comprehensive smart grid initiative for BGE that included the planned installation of 2 million residential and commercial electric and natural gas smart meters at an expected total cost of $480 million of which $200 million was funded by SGIG. The MDPSC’s approval ordered BGE to defer the associated incremental costs, depreciation and amortization, and an appropriate return, in a regulatory asset until such time as a cost-effective advanced metering system is implemented. See AMI programs in the Regulatory Assets and Liabilities section below for additional information. As part of the 2015 electric and natural gas distribution rate case filed on November 6, 2015, BGE sought recovery of its smart grid initiative costs, supported by evidence demonstrating that BGE had, in fact, implemented a cost-beneficial advanced metering system. On June 3, 2016, the MDPSC issued an order concluding that the smart grid initiative overall is cost beneficial to its customers. However, the June 3 rd order contained several cost disallowances and adjustments including disallowances of certain program and meter installation costs and denial of recovery of any return on unrecovered costs for non-AMI meters replaced under the program. BGE and the residential consumer advocate subsequently both filed a petition for rehearing of the June 3 rd order. On July 29, 2016, the MDPSC issued an order on the petitions for rehearing that reversed certain of its prior cost disallowances and adjustments related to the smart grid initiative. As a combined result of the MDPSC orders in BGE's 2015 electric and natural gas distribution base rate case, BGE recorded a $52 million charge in June 2016 to Operating and maintenance expense in Exelon’s and BGE’s Consolidated Statements of Operations and Comprehensive Income reducing certain regulatory assets and other long-lived assets and reclassified $56 million of legacy meter costs from Property, plant and equipment, net to Regulatory assets in Exelon's and BGE's Consolidated Balance Sheets. In BGE’s 2018 natural gas distribution base rate case, the MDPSC allowed BGE to recover the gas portion of the post-test year regulatory asset, including a return thereon, over three years. The electric portion of the same regulatory asset will be addressed in BGE’s next electric distribution base rate case. The Maryland Strategic Infrastructure Development and Enhancement Program (Exelon and BGE). In 2013, legislation in Maryland was signed into law to establish a mechanism, separate from base rate proceedings, for gas companies to promptly recover reasonable and prudent costs of eligible infrastructure replacement projects incurred after June 1, 2013. The monthly surcharge and infrastructure replacement costs must be approved by the MDPSC and are subject to a cap and require an annual true-up of the surcharge revenues against actual expenditures. Investment levels in excess of the cap would be recoverable in a subsequent gas base rate proceeding at which time all costs for the infrastructure replacement projects would be rolled into gas distribution base rates. Irrespective of the cap, BGE is required to file a gas rate case every five years under this legislation. On December 1, 2017 (as amended on January 22, 2018), BGE filed an application with the MDPSC seeking approval for a new gas infrastructure replacement plan and associated surcharge, effective for the five-year period from 2019 through 2023. On May 30, 2018, the MDPSC approved with modifications a new infrastructure plan and associated surcharge, subject to BGE's acceptance of the Order. On June 1, 2018, BGE accepted the MDPSC Order and the associated surcharge will be effective in rates beginning in January 2019. The new five-year plan calls for capital expenditures over the 2019-2023 timeframe of $732 million, with an associated revenue requirement of $200 million. District of Columbia Regulatory Matters District of Columbia Power Line Undergrounding Initiative (Exelon, PHI and Pepco). The District of Columbia government enacted on a permanent basis (effective July 11, 2017) legislation to amend the Electric Company Infrastructure Improvement Financing Act of 2014 (as amended) (the Infrastructure Improvement Financing Act) to authorize the District of Columbia Power Line Undergrounding (DC PLUG) initiative, a projected six year, $500 million project to place underground some of the District of Columbia’s most outage-prone power lines with $250 million of the project costs funded by Pepco and $250 million funded by the District of Columbia. The $250 million of project costs funded by Pepco will earn a return and be recovered through a volumetric surcharge on the electric bill of Pepco's customers in the District of Columbia. The $250 million of project costs funded by the District of Columbia will come from two sources. Project costs of $187.5 million will be funded through a charge assessed on Pepco by the District of Columbia; Pepco will recover this charge from customers through a volumetric distribution rider. The remaining costs up to $62.5 million are to be funded by the existing capital projects program of the District Department of Transportation (DDOT). Ownership and responsibility for the operation and maintenance of assets funded by the District of Columbia will be transferred to Pepco for a nominal amount upon completion, and Pepco will not recover or earn a return on the cost of these assets. In accordance with the Infrastructure Improvement Financing Act, Pepco filed an application for approval of the first two-year plan in the DC PLUG initiative (the First Biennial Plan) on July 3, 2017. Pepco will then be required to make two additional applications. On November 9, 2017, the DCPSC issued an order approving the First Biennial Plan and the application for a financing order. Pursuant to that order, Pepco is obligated to pay $187.5 million to the District of Columbia over the six-year project term, of which it expects to pay $30 million in 2019. Pepco recorded an obligation and offsetting regulatory asset in November. Rates for the DC PLUG initiative went into effect on February 7, 2018. New Jersey Regulatory Matters ACE Infrastructure Investment Program Filing (Exelon, PHI and ACE). On February 28, 2018, ACE filed with the NJBPU the company’s Infrastructure Investment Program (IIP) proposing to seek recovery of a series of investments through a new rider mechanism, totaling $338 million , between 2019-2022 to provide safe and reliable service for its customers. The IIP will allow for more timely recovery of investments made to modernize and enhance ACE’s electric system. ACE currently expects a decision in this matter in the second quarter of 2019 but cannot predict if the NJBPU will approve the application as filed. New Jersey Consolidated Tax Adjustment (Exelon, PHI and ACE). The Consolidated Tax Adjustment (CTA) is a ratemaking policy that requires utilities that are part of a consolidated tax group to share with customers the tax benefits that came from losses at unregulated affiliates through a reduction in rate base. After opening a generic proceeding to review the policy, in 2014, the NJBPU issued a decision which retained the CTA, but in a modified format that significantly reduced the impact of the CTA to ACE. On September 18, 2017, the Appellate Division of the Superior Court of New Jersey reversed the NJBPU’s decision in adopting the revised CTA policy and held that NJBPU’s actions related to the CTA constituted a rulemaking that should have been undertaken pursuant to the requirements of the Administrative Procedures Act. The Court did not address the merits of the CTA methodology itself. The NJBPU issued a proposed rule for comment, consistent with the requirements of the Administrative Procedures Act. On January 17, 2019, the NJBPU adopted the proposed CTA regulations, which do not have a material impact on ACE. The CTA regulations will be sent to the Office of Administrative Law for publication in the New Jersey Register, which is expected on or before March 4, 2019. New Jersey Clean Energy Legislation (Exelon and ACE). On May 23, 2018, the Governor of New Jersey signed new legislation, effective immediately, that established and modified New Jersey’s clean energy and energy efficiency programs and solar and renewable energy portfolio standards. The new legislation expands the state's renewable portfolio standard to require that 50% of electric generation sold be from renewable energy sources by 2030; modifies the New Jersey solar renewable energy portfolio standard to require that 5.1% of electric generation sold in New Jersey be from solar electric power by 2021; lowers the solar alternative compliance payment amount starting in 2019 and requires the NJBPU to adopt rules to replace the current solar renewable energy credit program; and requires the NJBPU to increase its offshore wind energy credit program to 3,500 MW. The new legislation further imposes an energy efficiency standard that each electric public utility will be required to reduce annual usage by 2% and provides for utilities to annually file for recovery of the costs of the programs, including the revenue impact of sales losses resulting from the programs. The NJBPU is required to initiate a study to determine the savings targets for each public utility, to adopt other rules regarding the programs, and to approve energy efficiency and peak demand reduction programs for each utility. The new legislation also requires the NJBPU to conduct an energy storage analysis including the potential costs and benefits and to initiate a proceeding to establish a goal of achieving 2,000 MW of energy storage by 2030; requires the utilities to conduct a study on voltage optimization on their distribution system; and requires the NJBPU to establish a community solar program to permit customers to participate in a solar project that is not located on the customer’s property which the NJBPU issued regulations on January 17, 2019. On the same day, the Governor of New Jersey also signed new legislation, effective immediately, that will establish a ZEC program providing compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. Electric distribution utilities in New Jersey, including ACE, will be authorized to collect from retail distribution customers through a non-bypassable charge all costs associated with the utility’s procurement of the ZECs. See Generation Regulatory Matters below for additional information. Other Federal Regulatory Matters Transmission-Related Income Tax Regulatory Assets (Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE). On December 13, 2016 (as amended on March 13, 2017), BGE filed with FERC to begin recovering certain existing and future transmission-related income tax regulatory assets through its transmission formula rate. BGE’s existing regulatory assets included (1) amounts that, if BGE’s transmission formula rate provided for recovery, would have been previously amortized and (2) amounts that would be amortized and recovered prospectively. ComEd, Pepco, DPL and ACE had similar transmission-related income tax regulatory liabilities and assets also requiring FERC approval. On November 16, 2017, FERC issued an order rejecting BGE’s proposed revisions to its transmission formula rate to recover these transmission-related income tax regulatory assets. FERC’s rejection order focused on the lack of timeliness of BGE’s request to recover amounts that would have been previously amortized but indicated that ongoing recovery of certain transmission-related income tax regulatory assets would provide for a more accurate revenue requirement. Based on FERC’s order, management of each company concluded that the portion of the total transmission-related income tax regulatory assets that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery was no longer probable of recovery. 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 of 2017, reducing their associated transmission-related income tax regulatory assets. Similar regulatory assets and liabilities at PECO are not subject to the same FERC transmission rate recovery formula and, thus, are not impacted by BGE’s November 16, 2017 FERC order. See above for additional information regarding PECO's transmission formula rate filing. For the year ended December 31, 2017 Exelon $ 35 ComEd 3 BGE 5 PHI 27 Pepco 14 DPL 6 ACE 7 On December 18, 2017, BGE filed for clarification and rehearing of FERC’s order, still seeking full recovery of its existing transmission-related income tax regulatory asset amounts, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. On February 27, 2018 (and updated on March 26, 2018), BGE submitted a letter to FERC advising that the lower federal corporate income tax rate effective January 1, 2018 provided for in the TCJA will be reflected in BGE’s annual formula rate update effective June 1, 2018, but that the deferred income tax benefits will not be passed back to customers unless BGE’s formula rate is revised to provide for pass back and recovery of transmission-related income tax-related regulatory liabilities and assets. On February 23, 2018 (as amended on July 9, 2018), ComEd, Pepco, DPL, and ACE each filed with FERC to revise their transmission formula rate mechanisms to facilitate passing back to customers ongoing annual TCJA tax savings and to permit recovery of transmission-related income tax regulatory assets, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. On September 7, 2018, FERC issued orders rejecting BGE’s December 18, 2017 request for rehearing and clarification and ComEd's, Pepco's, DPL's and ACE's February 23, 2018 (as amended on July 9, 2018) filings, again citing the lack of timeliness of the requests to recover amounts that would have been previously amortized, but indicating that ongoing recovery of certain transmission-related income tax regulatory assets would provide for a more accurate revenue requirement. The orders did not address the remittance of TCJA transmission-related income tax regulatory liabilities, but rather referenced FERC’s separate Notice of Inquiry of such amounts issued on March 15, 2018. On October 1, 2018, ComEd, BGE, Pepco, DPL, and ACE submitted new filings to recover ongoing non-TCJA amortization amounts and refund TCJA transmission-related income tax regulatory liabilities for the prospective period starting on October 1, 2018. FERC issued deficiency letters requesting additional information on November 21, 2018 and January 28, 2019. ComEd, BGE, Pepco, DPL, and ACE responded to the November 21, 2018 deficiency letter on November 29, 2018 but cannot predict the outcome of these FERC proceedings. If FERC ultimately rules that the future, ongoing non-TCJA amortization amounts are not recoverable, Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE woul

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (All Registrants)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Mergers, Acquisitions and Dispositions (Exelon, Generation and PHI) Acquisition of FirstEnergy Solutions Load Business (Exelon and Generation) On July 9, 2018, Generation entered into an Asset Purchase Agreement (the Purchase Agreement) with FirstEnergy Solutions Corporation (FirstEnergy). Pursuant to the Purchase Agreement, FirstEnergy agreed to assign all of its retail electricity and wholesale load serving contracts and certain other related commodity contracts to Generation for an all cash purchase price of $140 million . The closing of the transaction was subject to certain conditions including the approval of the Purchase Agreement by the United States Bankruptcy Court for the Northern District of Ohio (Bankruptcy Court). At FirstEnergy's request, Bankruptcy Court's review of the transaction was delayed on six occasions, and Generation disputed these delays with the Bankruptcy Court. On January 23, 2019 the Bankruptcy Court approved an order that stipulated FirstEnergy's termination of the Purchase Agreement, effective January 22, 2019. The termination order provided for Generation to receive a refund of its escrow deposit, payment of a termination fee and reimbursement of transaction expenses, all of which were immaterial. 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 shutdown 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. 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. An after-tax bargain purchase gain of $233 million was included within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income which primarily reflects differences in strategies between Generation and Entergy for the intended use and ultimate decommissioning of the plant. 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: 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 22 - Commitments and Contingencies for additional information regarding SNF obligations to the DOE. Exelon and Generation incurred $57 million of merger and integration related costs to FitzPatrick for the year ended December 31, 2017 which are included within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. Exelon and Generation did not incur any merger and integration costs related to FitzPatrick for the year ended December 31, 2018 . 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 purchase price of $257 million 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. 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), for a total purchase price consideration of approximately $7.1 billion . As a result of the 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. Total nominal cost of commitments was $513 million excluding renewable generation commitments (approximately $444 million on a net present value basis amount, excluding renewable generation commitments and charitable contributions). During the fourth quarter of 2018, Exelon finalized the application of $5 million funding for residential and non-residential customers in the DPL Maryland service territory. This resulted in an adjustment to merger commitment costs recorded at Exelon Corporate and DPL. Exelon Corporate recorded a decrease of $5 million and DPL recorded an increase of $5 million 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 merger date: Expected Payment Period Successor Description Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 259 $ 264 $ 91 $ 72 $ 101 Energy efficiency 2016 - 2021 117 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 508 $ 320 $ 120 $ 89 $ 111 Remaining commitments as of December 31, 2018 $ 128 $ 92 $ 73 $ 12 $ 7 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 solar generation in Maryland, District of Columbia and Delaware, at an estimated cost of approximately $127 million , which will generate future earnings at Exelon and Generation. Investment costs, which are expected to be primarily capital in nature, will be recognized as incurred and recorded on Exelon's and Generation's financial statements. As of December 31, 2018, 27 MWs were developed and Exelon and Generation have incurred costs of $83 million . Exelon has also committed to purchase 100 MWs of wind energy in PJM. DPL has committed to conducting three RFPs to procure up to a total of 120 MWs of wind RECs for the purpose of meeting Delaware's renewable portfolio standards. DPL has conducted two of the three wind REC RFPs. The first 40 MW wind REC tranche was conducted in 2017 and did not result in a purchase agreement. The second 40 MW wind REC tranche was conducted in 2018 and resulted in a proposed REC purchase agreement that is pending review and approval with the DPSC. The third and final 40 MW wind REC tranche will be conducted in 2022. 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 Maryland Court of Appeals, which is the highest court in Maryland. On August 29, 2018, the Maryland Court of Appeals affirmed the MDPSC's May 2015 Order approving the merger of Exelon and PHI. 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 for the PHI merger was approximately $7.1 billion . The excess of the purchase price over the estimated fair value of the assets acquired and the liabilities assumed totaled $4 billion , which was recognized as goodwill by PHI and Exelon at the merger 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. None of this goodwill is expected to be tax deductible. For purposes of future required impairment assessments, the goodwill has been assigned to PHI's reportable units Pepco, DPL and ACE. See Note 10 - Intangible Assets for additional information. Immediately following closing of the merger, $235 million of net assets associated with PHI's unregulated business interests were distributed by PHI to Exelon. Exelon contributed $163 million of such net assets to Generation. 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, in Exelon's Consolidated Statements of Operations and Comprehensive Income includes Operating revenues and Net Income (Loss) as follows: For the Years Ended December 31, 2018 2017 2016 Operating Revenues 4,670 4,829 3,785 Net Income (Loss) 453 364 (66 ) For the periods ended December 31, 2018 , 2017 and 2016 , the Registrants have recognized costs to achieve the PHI merger as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2018 2017 2016 Exelon $ 7 $ 16 $ 143 Generation 5 22 37 ComEd (b) — 1 (6 ) PECO 1 4 5 BGE (b) 1 4 (1 ) Pepco (b) — (6 ) 28 DPL (b) — (7 ) 20 ACE (b) — (6 ) 19 Successor Predecessor For the Year Ended December 31, March 24, 2016 to December 31, 2016 January 1, 2016 to Acquisition, Integration and Financing Costs (a) 2018 2017 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 as regulatory assets of $24 million , $8 million , $8 million , and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $8 million , $6 million , $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional 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 PHI merger 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 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 . Disposition of Oyster Creek (Exelon and Generation) On July 31, 2018, Generation entered into an agreement with Holtec International (Holtec) and its indirect wholly owned subsidiary, Oyster Creek Environmental Protection, LLC (OCEP), for the sale and decommissioning of the Oyster Creek Generating Station (Oyster Creek) located in Forked River, New Jersey. On September 17, 2018, Oyster Creek permanently ceased generation operations. Under the terms of the transaction, Generation will transfer to OCEP substantially all the assets associated with Oyster Creek, including assets held in NDT funds, along with the assumption of liability for all responsibility for the site, including full decommissioning and ongoing management of spent fuel until the spent fuel is moved offsite. In addition to the assumption of liability for the full decommissioning and ongoing management of spent fuel, other consideration to be received in the transaction is contingent on several factors, including a requirement that Generation deliver a minimum NDT fund balance at closing, subject to adjustment for specific terms that include income taxes that would be imposed on any net unrealized built-in gains and certain decommissioning activities to be performed during the pre-close period after the unit shuts down in the fall of 2018 and prior to the anticipated close of the transaction. The terms of the transaction also include various forms of performance assurance for the obligations of OCEP to timely complete the required decommissioning, including a parental guaranty from Holtec for all performance and payment obligations of OCEP, and a requirement for Holtec to deliver a letter of credit to Generation upon the occurrence of specified events. As a result of the transaction, in 2018, Exelon and Generation reclassified certain Oyster Creek assets and liabilities in Exelon’s and Generation’s Consolidated Balance Sheets as held for sale at their respective fair values. At December 31, 2018 Generation has $897 million and $777 million of Assets held for sale and Liabilities held for sale, respectively, for Oyster Creek. Upon remeasurement of the Oyster Creek ARO in 2018, Exelon and Generation recognized an $84 million pre-tax charge to Operating and maintenance expense. See Note 15 - Asset Retirement Obligations for additional information. Completion of the transaction contemplated by the sale agreement is subject to the satisfaction of several closing conditions, including approval of the license transfer from the NRC and other regulatory approvals, and the receipt of a private letter ruling from the IRS. Generation currently anticipates satisfaction of the closing conditions to occur in the second half of 2019. Disposition of EGTP and Acquisition of Handley Generating Station (Exelon and Generation) 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 was an indirect wholly owned subsidiary of Exelon and Generation. 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 additional information. On November 7, 2017, EGTP and all of 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, which resulted in Exelon and Generation deconsolidating EGTP's assets and liabilities from their consolidated financial statements in the fourth quarter of 2017 that resulted 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, 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 closed on April 4, 2018 for a purchase price of $62 million . The Chapter 11 bankruptcy proceedings were finalized on April 17, 2018, resulting in the ownership of EGTP assets (other than the Handley Generating Station) being transferred to EGTP's lenders. Other Asset Dispositions (Exelon, Generation, DPL and Pepco) In December 2017, Generation entered into an 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. As a result, as of December 31, 2017, certain assets and liabilities were classified as held for sale and included in the Other current assets and Other current liabilities balances in Exelon's and Generation's Consolidated Balance Sheet. On February 28, 2018, Generation completed the sale of its interest for $87 million , resulting in a pre-tax gain which is included within Gain on sales of assets and businesses in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. In June 2018, additional proceeds were received, and a pre-tax gain was recorded within Gain on sales of assets and businesses in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. During the fourth quarter of 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 sales of assets and businesses 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. 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 additional 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 and businesses in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

Property, Plant and Equipment (

Property, Plant and Equipment (All Registrants)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-90 $ 53,090 $ 49,506 Electric—generation 1-56 29,170 29,019 Gas—transportation and distribution 5-90 5,530 5,050 Common—electric and gas 5-75 1,627 1,447 Nuclear fuel (a) 1-8 5,957 6,420 Construction work in progress N/A 3,377 2,825 Other property, plant and equipment (b) 1-50 858 999 Total property, plant and equipment 99,609 95,266 Less: accumulated depreciation (c) 22,902 21,064 Property, plant and equipment, net $ 76,707 $ 74,202 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017 , respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017 , and total accumulated amortization was $42 million and $40 million , as of December 31, 2018 and 2017 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 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, 2018 and 2017 . Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $39 million , $19 million , $25 million , $61 million , $17 million and $28 million , respectively, at December 31, 2018 . (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,969 million and $3,159 million as of December 31, 2018 and 2017 , 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 2018 2017 2016 Electric—transmission and distribution 2.73 % 2.75 % 2.73 % Electric—generation (a) 5.37 % 4.36 % 5.94 % Gas 2.07 % 2.10 % 2.17 % Common—electric and gas 6.98 % 7.05 % 7.41 % __________ (a) See Note 8 — Early Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI. Generation The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—generation 1-56 $ 29,170 $ 29,019 Nuclear fuel (a) 1-8 5,957 6,420 Construction work in progress N/A 997 838 Other property, plant and equipment (b) 1-8 63 57 Total property, plant and equipment 36,187 36,334 Less: accumulated depreciation (c) 12,206 11,428 Property, plant and equipment, net $ 23,981 $ 24,906 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017 , respectively. (b) Includes buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017 , respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017 , and total accumulated amortization was $42 million and $40 million , as of December 31, 2018 and 2017 , respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million and $3,159 million as of December 31, 2018 and 2017 , respectively. The annual depreciation provisions as a percentage of average service life for electric generation assets were 5.37% , 4.36% and 5.94% for the years ended December 31, 2018 , 2017 and 2016 , respectively. See Note 8 — Early Plant Retirements for additional information on the accelerated depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI. License Renewals Depreciation provisions are based on the estimated useful lives of the stations, which reflect the actual renewal of the operating licenses for all of Generation's operating nuclear generating stations except for TMI and Clinton. As a result, the receipt of license renewals has no material impact in the Consolidated Statements of Operations and Comprehensive Income. Beginning in 2017, TMI and Oyster Creek depreciation provisions were based on their 2019 expected shutdown dates. Beginning February 2018, Oyster Creek depreciation provisions were based on its announced shutdown date of September 2018. Clinton depreciation provisions are based on an estimated useful life through 2027 which is the last year of the Illinois Zero Emissions Standard. See Note 4 — Regulatory Matters for additional information regarding license renewals and the Illinois ZECs and Note 8 — Early 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, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-80 $ 25,991 $ 24,423 Construction work in progress N/A 705 517 Other property, plant and equipment (a), (b) 35-50 46 52 Total property, plant and equipment 26,742 24,992 Less: accumulated depreciation 4,684 4,269 Property, plant and equipment, net $ 22,058 $ 20,723 __________ (a) Includes buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 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, 2018 and 2017 . (b) Represents 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 2.95% , 2.99% and 3.03% for the years ended December 31, 2018 , 2017 and 2016 , respectively. PECO The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-65 $ 8,359 $ 7,975 Gas—transportation and distribution 5-70 2,694 2,504 Common—electric and gas 5-50 756 710 Construction work in progress N/A 343 254 Other property, plant and equipment (a) 50 19 21 Total property, plant and equipment 12,171 11,464 Less: accumulated depreciation 3,561 3,411 Property, plant and equipment, net $ 8,610 $ 8,053 __________ (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 2018 2017 2016 Electric—transmission and distribution 2.35 % 2.37 % 2.32 % Gas 1.90 % 1.89 % 1.82 % Common—electric and gas 5.44 % 5.47 % 5.11 % BGE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-90 $ 7,951 $ 7,464 Gas—distribution 5-90 2,630 2,379 Common—electric and gas 5-40 860 771 Construction work in progress N/A 410 367 Other property, plant and equipment (a) 20 25 26 Total property, plant and equipment 11,876 11,007 Less: accumulated depreciation 3,633 3,405 Property, plant and equipment, net $ 8,243 $ 7,602 __________ (a) Represents plant 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 2018 2017 2016 Electric—transmission and distribution 2.61 % 2.58 % 2.56 % Gas 2.36 % 2.33 % 2.45 % Common—electric and gas 8.50 % 8.64 % 9.45 % PHI The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average 2018 2017 Asset Category Electric—transmission and distribution 5-75 $ 12,664 $ 11,517 Gas—distribution 5-75 486 449 Common—electric and gas 5-75 126 82 Construction work in progress N/A 912 835 Other property, plant and equipment (a) 3-43 99 102 Total property, plant and equipment 14,287 12,985 Less: accumulated depreciation 841 487 Property, plant and equipment, net $ 13,446 $ 12,498 __________ (a) Represents plant 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 2018 2017 2016 Electric—transmission and distribution 2.61 % 2.63 % 2.52 % Gas 1.59 % 2.07 % 2.57 % Common—electric and gas 6.30 % 6.50 % 8.12 % Pepco The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-75 $ 9,217 $ 8,646 Construction work in progress N/A 536 473 Other property, plant and equipment (a) 25-33 61 59 Total property, plant and equipment 9,814 9,178 Less: accumulated depreciation 3,354 3,177 Property, plant and equipment, net $ 6,460 $ 6,001 __________ (a) Represents plant 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 2.40% , 2.35% and 2.17% for the years ended December 31, 2018 , 2017 and 2016 , respectively. DPL The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-70 $ 4,195 $ 3,875 Gas—distribution 5-75 651 614 Common—electric and gas 5-75 136 117 Construction work in progress N/A 151 205 Other property, plant and equipment (a) 10-43 17 15 Total property, plant and equipment 5,150 4,826 Less: accumulated depreciation 1,329 1,247 Property, plant and equipment, net $ 3,821 $ 3,579 __________ (a) Represents plant 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 2018 2017 2016 Electric—transmission and distribution 2.77 % 2.75 % 2.49 % Gas 1.59 % 2.07 % 2.57 % Common—electric and gas 3.70 % 4.14 % 4.99 % ACE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-60 $ 3,866 $ 3,607 Construction work in progress N/A 209 138 Other property, plant and equipment (a) 13-15 28 27 Total property, plant and equipment 4,103 3,772 Less: accumulated depreciation 1,137 1,066 Property, plant and equipment, net $ 2,966 $ 2,706 __________ (a) Represents plant 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 2.45% , 2.46% and 2.45% for the years ended December 31, 2018 , 2017 and 2016 , respectively. Capitalized Software Costs (All Registrants) The following tables presents net unamortized capitalized software costs and amortization of capitalized software costs by year. Net unamortized software costs Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 810 $ 164 $ 206 $ 98 $ 166 $ 165 $ 26 $ 21 $ 14 December 31, 2017 834 173 227 111 179 133 2 1 1 Amortization of capitalized software costs Exelon Generation ComEd PECO BGE Pepco DPL ACE 2018 $ 282 $ 78 $ 79 $ 37 $ 48 $ 2 $ 2 $ 1 2017 270 73 73 39 46 — — — 2016 255 72 62 33 44 — — — Successor Predecessor PHI For the year ended December 31, 2018 For the year ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Amortization of capitalized software costs $ 33 $ 34 $ 29 $ 8 Capitalized Interest and AFUDC (All Registrants) The following table summarizes total incurred interest, capitalized interest and credits to AFUDC by year: Exelon Generation ComEd PECO BGE Pepco DPL ACE 2018 Total incurred interest (a) $ 1,695 $ 464 $ 377 $ 141 $ 130 $ 162 $ 62 $ 68 Capitalized interest 31 31 — — — — — — Credits to AFUDC debt and equity 109 — 30 12 24 34 4 4 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 Successor Predecessor PHI For the year ended December 31, 2018 For the year ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Total incurred interest (a) $ 305 $ 263 $ 207 $ 68 Credits to AFUDC debt and equity 44 54 35 10 __________ (a) Includes interest expense to affiliates. See Note 1 — Significant Accounting Policies for additional information regarding property, plant and equipment policies. See Note 13 — Debt and Credit Agreements for additional 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, 2018
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. In the second quarter of 2018, 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 its 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, long-lived merchant wind assets held and used with a net carrying amount of $41 million were fully impaired and a pre-tax impairment charge of $41 million was recorded during 2018 within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. During the first quarter of 2018, Mystic Unit 9 did not clear in the ISO-NE capacity auction for the 2021 - 2022 planning year. On March 29, 2018, Generation notified ISO-NE of the early retirement of its Mystic Generating Station's Units 7, 8, 9 and the Mystic Jet Unit (Mystic Generating Station assets) absent regulatory reforms. These events suggested that the carrying value of its New England asset group may be impaired. As a result, Generation completed a comprehensive review of the estimated undiscounted future cash flows of the New England asset group and no impairment charge was required. Further developments such as the failure of ISO-NE to adopt long-term solutions for reliability and fuel security could potentially result in future impairments of the New England asset group, which could be material. See Note 8 — Early Plant Retirements for additional 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. 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 in 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 5 — 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. In 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 5 — Mergers, Acquisitions and Dispositions for additional information. 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 Plant Retirements Early P

Early Plant Retirements Early Plant Retirements (Exelon, Generation)	12 Months Ended
	Dec. 31, 2018
Implications of Potential Early Plant Retirements [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	Early Plant Retirements (Exelon and Generation) Exelon and Generation continuously evaluate factors that affect the current and expected economic value of Generation’s plants, including, but not limited to: market power prices, results of capacity auctions, potential legislative and regulatory solutions to ensure plants are fairly compensated for the benefits they provide through their carbon-free emissions, reliability, or fuel security, and the impact of potential 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 plant, and the resulting financial statement impacts, may be affected by many 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 NDT fund requirements for nuclear plants, 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, and where applicable, just prior to its next scheduled nuclear refueling outage. Nuclear Generation In 2015 and 2016, Generation identified the Clinton and Quad Cities nuclear plants in Illinois, Ginna and Nine Mile Point nuclear plants in New York and Three Mile Island nuclear plant in Pennsylvania as having the greatest risk of early retirement based on economic valuation and other factors. On June 2, 2016, Generation announced it would shutdown the Clinton and Quad Cities nuclear plants on June 1, 2017 and June 1, 2018, respectively, given a lack of progress on Illinois energy legislation and MISO market reforms, and capacity auctions results that failed to cover cash operating costs and a risk-adjusted rate of return to shareholders. On December 7, 2016, Illinois FEJA was signed into law by the Governor of Illinois and included a ZES that now provides compensation to Clinton and Quad Cities for the carbon-free attributes of their production through 2027. With the passage of the Illinois ZES in December 2016, Generation reversed its June 2016 decision to permanently cease generation operations at the Clinton and Quad Cities nuclear generating plants. Clinton and Quad Cities are currently licensed to operate through 2026 and 2032, respectively. See Note 4 - Regulatory Matters for additional information on the Illinois FEJA and the ZES. In New York, the Ginna and Nine Mile Point nuclear plants faced similar economic challenges and on August 1, 2016, the NYPSC issued an order adopting the CES, which now provides payments to Ginna and Nine Mile Point, as well as FitzPatrick, for the environmental attributes of their production through 2029. Ginna and Nine Mile Point Unit 1 are currently licensed to operate through 2029, and Nine Mile Point Unit 2 through 2046. See Note 4 - Regulatory Matters for additional information on the New York CES. Assuming the continued effectiveness of both the Illinois ZES and the New York CES, 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 financial statements. In Pennsylvania, the TMI nuclear plant failed to clear in the May 2017 PJM capacity auction for the 2020-2021 planning year, the third consecutive year that TMI failed to clear in the PJM base residual capacity auction and 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. TMI is currently committed to operate through May 2019 and is licensed to operate through 2034. Generation has filed the required market and regulatory notifications to shutdown the plant. PJM has subsequently notified Generation that it has not identified any reliability issues and has approved the deactivation of TMI as proposed. 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 continued to face rising operating costs amid a historically low wholesale power price environment. On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at the Oyster Creek nuclear plant at the end of its current operating cycle and permanently ceased generation operations in September 2018. As a result of these early nuclear 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 information on changes to the nuclear decommissioning ARO balance. The total annual impact of these charges by year are summarized in the table below. Income statement expense (pre-tax) 2018 (a) 2017 (b) 2016 (c) Depreciation and Amortization Accelerated depreciation (d) $ 539 $ 250 $ 712 Accelerated nuclear fuel amortization 57 12 60 Operating and Maintenance One-time charges (e,f) 32 77 26 Change in ARO accretion, net of any contractual offset (g) — — 2 Contractual offset for ARC depreciation (g) — — (86 ) Total $ 628 $ 339 $ 714 _________ (a) Reflects incremental accelerated depreciation for TMI and Oyster Creek. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 2018. (b) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (c) 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. (d) Reflects incremental accelerated depreciation of plant assets, including any ARC. (e) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Excludes the charge to Operating and maintenance expense from the ARO remeasurement due to the announced sale of Oyster Creek. See Note 5 — Mergers, Acquisitions and Dispositions for additional information. (f) 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. (g) For Quad Cities based on the regulatory agreement with the ICC, 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. In 2017, PSEG made public similar financial challenges facing its New Jersey nuclear plants, including Salem, of which Generation owns a 42.59% ownership interest. PSEG is the operator of Salem and also has the decision making authority to retire Salem. On May 23, 2018, New Jersey enacted legislation that established a ZEC program, similar to that in Illinois and New York, that will provide compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. The NJBPU must complete its processes for determining eligibility for, and participation in, the ZEC program by April 18, 2019. On December 19, 2018, PSEG submitted its application for Salem. Assuming the successful implementation of the New Jersey ZEC program and the selection of Salem as one of the qualifying facilities, the New Jersey ZEC program has the potential to mitigate the heightened risk of earlier retirement for Salem. See Note 4 - Regulatory Matters for additional information. The following table provides the balance sheet amounts as of December 31, 2018 for Generation’s ownership share of the significant assets and liabilities associated with Salem that would potentially be impacted by a decision to permanently cease generation operations. December 31, 2018 Asset Balances Materials and supplies inventory $ 45 Nuclear fuel inventory, net 118 Completed plant, net 538 Construction work in progress 44 Liability Balances Asset retirement obligation (395 ) NRC License Renewal Term 2036 (unit 1) 2040 (unit 2) Generation’s Dresden, Byron, and Braidwood nuclear plants in Illinois are also showing increased signs of economic distress, which could lead to an early retirement, in a market that does not currently compensate them for their unique contribution to grid resiliency and their ability to produce large amounts of energy without carbon and air pollution. The May 2018 PJM capacity auction for the 2021-2022 planning year resulted in the largest volume of nuclear capacity ever not selected in the auction, including all of Dresden, and portions of Byron and Braidwood. Exelon continues to work with stakeholders on state policy solutions, while also advocating for broader market reforms at the regional and federal level. Other Generation On March 29, 2018, Generation notified grid operator ISO-NE of its plans to early retire its Mystic Generating Station assets absent regulatory reforms on June 1, 2022, at the end of the current capacity commitment for Mystic Units 7 and 8. Mystic Unit 9 is currently committed through May 2021. The ISO-NE announced that it would take a three-step approach to fuel security. • First, on May 1, 2018, ISO-NE made a filing with FERC requesting waiver of certain tariff provisions to allow it to retain Mystic Units 8 and 9 for fuel security for the 2022 - 2024 capacity commitment periods. FERC denied the waiver request on procedural grounds on July 2, 2018 and ordered ISO-NE to (i) make a filing within 60 days providing for the filing of a short-term cost-of-service agreement to address fuel security concerns and (ii) make a filing by July 1, 2019 proposing permanent tariff revisions that would improve its market design to better address regional fuel security concerns. • Second, in accordance with FERC's July 2, 2018 order, on August 31, 2018, ISO-NE made a filing with FERC proposing short-term tariff changes to permit it to retain a resource for fuel security reliability reasons, which FERC accepted on December 3, 2018. • Third, ISO-NE stated its intention to work with stakeholders to develop long-term market rule changes to address system resiliency considering significant reliability risks identified in ISO-NE’s January 2018 fuel security report. Changes to market rules are necessary because critical units to the region, such as Mystic Units 8 and 9, cannot recover future operating costs, including the cost of procuring fuel. In its July 2, 2018 order, FERC ordered ISO-NE to make a filing by July 1, 2019 proposing permanent tariff revisions that would improve its market design to better address regional fuel security concerns. In January 2019, ISO-NE has indicated that it intends to seek an extension of the deadline for this filing to November 15, 2019. On May 16, 2018, Generation made a filing with FERC to establish cost-of-service compensation and terms and conditions of service for Mystic Units 8 and 9 for the period between June 1, 2022 - May 31, 2024. Among the costs included in the filing are costs associated with the Everett Marine Terminal. On December 20, 2018, FERC issued an order accepting the cost of service agreement reflecting a number of adjustments to the annual fixed revenue requirement and allowing for recovery of a substantial portion of the costs associated with the Everett Marine Terminal. FERC also directed a paper hearing on ROE using a new methodology. Initial and reply briefs on ROE will be due on April 18, 2019 and July 18, 2019. These will be reflected in a compliance filing due February 18, 2019. On January 4, 2019, Generation notified ISO-NE that it will participate in the Forward Capacity Market auction for the 2022 - 2023 capacity commitment period. In addition, on January 22, 2019, Exelon and several other parties filed requests for rehearing of certain findings of the December 20, 2018 order. The request for rehearing does not alter Generation's commitment to participate in the Forward Capacity Auction for the 2022-2023 capacity commitment period. The following table provides the balance sheet amounts as of December 31, 2018 for Generation’s significant assets and liabilities associated with the Mystic Units 8 and 9 and Everett Marine Terminal assets that would potentially be impacted by a decision to permanently cease generation operations. December 31, 2018 Asset Balances Materials and supplies inventory $ 30 Fuel inventory 20 Completed plant, net 901 Construction work in progress 9 Liability Balances Asset retirement obligation (1 ) To ensure the continued reliable supply of fuel to Mystic Units 8 and 9 while they remain operating, on October 1, 2018, Generation acquired the Everett Marine Terminal in Massachusetts for a purchase price of $81 million , with the majority of the fair value allocated to Property, plant and equipment and no goodwill recorded. Generation also settled its existing long-term gas supply agreement, resulting in a pre-tax gain of $75 million , which is included within Purchased power and fuel expense in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

Jointly Owned Electric Utility

Jointly Owned Electric Utility Plant (Exelon, Generation, PECO, BGE, PHI, Pepco, DPL and ACE)	12 Months Ended
	Dec. 31, 2018
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, Pepco's, DPL's and ACE's undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2018 and 2017 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, 2018: Plant (e) $ 1,131 $ 1,451 $ 648 $ 910 $ 4 $ 28 $ 103 $ 15 Accumulated depreciation (e) 587 523 227 126 3 16 53 13 Construction work in progress 13 15 44 56 — 1 — — 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 — — — — __________ (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, 2018 and 2017 . (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 of the Salem generating plant substation. 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 substation. (d) Generation, DPL and ACE own a 44.24% , 11.91% and 4.83% 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 and general plant. 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 in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income and in Operating and maintenance expenses in PECO's, BGE's, Pepco's, 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, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets (All Registrants)	Intangible Assets (Exelon, Generation, ComEd, PECO, PHI, Pepco, DPL and ACE) Goodwill Exelon’s, ComEd’s and PHI's gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2018 and 2017 were as follows: Balance at January 1, 2017 Impairment losses Balance at December 31, 2017 Impairment losses Balance at December 31, 2018 Exelon Gross amount $ 8,660 $ — $ 8,660 $ — $ 8,660 Accumulated impairment loss 1,983 — 1,983 — 1,983 Carrying amount 6,677 — 6,677 — 6,677 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 PHI (b) Gross amount 4,005 — 4,005 — 4,005 Carrying amount 4,005 — 4,005 — 4,005 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom merger (predecessor parent company of ComEd). (b) Reflects goodwill recorded in 2016 from the PHI 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 ComEd's and PHI's reporting units below their carrying amounts. 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. ComEd has a single operating segment. PHI's operating segments are Pepco, DPL and ACE. See Note 24 — 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. PHI identified an error related to the allocation of goodwill to its reporting units in 2016 while performing the 2018 annual impairment assessment. As revised in 2018, Exelon's and PHI's $4 billion of goodwill has been assigned to the Pepco, DPL and ACE reporting units in the amounts of $2.1 billion , $1.4 billion and $0.5 billion , respectively, an increase (decrease) of $0.4 billion , $0.3 billion , and $(0.7) billion for Pepco, DPL and ACE, respectively, from the originally reported amounts. This error did not result in a change to the total amount of goodwill recorded at PHI nor would it have resulted in an impairment of PHI's goodwill in 2016 or 2017. Therefore, management has concluded that the error is not material to the previously issued financial statements. 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, ComEd's and PHI'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 authoritative 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 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. 2018 and 2017 Goodwill Impairment Assessment. ComEd and PHI qualitatively determined that it was more likely than not that the fair values of their reporting units exceeded their carrying values and, therefore, did not perform quantitative assessments as of November 1, 2018 and 2017 for ComEd and as of November 1, 2017 for PHI. As part of their qualitative assessments, ComEd and PHI 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 as of November 1, 2016. As a result of the reallocation of goodwill to PHI’s reporting units as discussed above, as of November 1, 2018, PHI performed a quantitative test for its 2018 annual goodwill impairment assessment. The first step of the test comparing the estimated fair values of the Pepco, DPL and ACE reporting units to their carrying values, including goodwill, indicated no impairments of goodwill; therefore, no second step was 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 Exelon's, ComEd's and PHI’s goodwill, which could be material. Based on the results of the annual goodwill test performed as of November 1, 2016 and November 1, 2018 for ComEd and PHI, respectively, the estimated fair values of the ComEd, Pepco, DPL and ACE reporting units would have needed to decrease by more than 30% , 30% , 20% and 30% , respectively, for ComEd and PHI to fail the first step of their respective impairment tests. 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, 2018 and 2017 : December 31, 2018 December 31, 2017 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Generation Unamortized Energy Contracts (b) 1,957 (1,588 ) 369 1,938 (1,574 ) 364 Customer Relationships 325 (162 ) 163 305 (133 ) 172 Trade Name 243 (171 ) 72 243 (148 ) 95 ComEd Chicago Settlement Agreements (c) 162 (148 ) 14 162 (141 ) 21 PHI Unamortized Energy Contracts (b) (1,515 ) 954 (561 ) (1,515 ) 766 (749 ) Exelon Corporate Software License (a) 95 (34 ) 61 95 (25 ) 70 Exelon $ 1,267 $ (1,149 ) $ 118 $ 1,228 $ (1,255 ) $ (27 ) __________ (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 in 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. The following table summarizes the estimated future amortization expense related to intangible assets and liabilities as of December 31, 2018 : For the Years Ending December 31, Exelon Generation ComEd PHI 2019 $ (32 ) $ 70 $ 7 $ (119 ) 2020 (20 ) 78 7 (115 ) 2021 (4 ) 78 — (92 ) 2022 (23 ) 56 — (89 ) 2023 (21 ) 50 — (81 ) The following table summarizes the amortization expense related to intangible assets and liabilities for each of the years ended December 31, 2018 , 2017 and 2016 : For the Years Ended December 31, Exelon (a)(b) Generation (a) ComEd PHI (b) 2018 $ (109 ) $ 63 $ 7 $ (188 ) 2017 (237 ) 83 7 (336 ) 2016 (336 ) 79 7 (430 ) __________ (a) At Exelon and Generation, amortization of unamortized energy contracts totaling $14 million , $35 million and $35 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, was recorded in Operating revenues or Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income. (b) At Exelon and PHI, amortization of 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 in their Consolidated Statements of Operations and Comprehensive Income. Acquired Intangible Assets and Liabilities Business combinations require 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 authoritative 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 authoritative guidance. Key assumptions include the customer attrition rate and the discount rate. The authoritative 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. 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 authoritative 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, PECO's, PHI's, DPL's and ACE's other intangible assets, included in Other current assets and Other deferred debits and other assets in the Consolidated Balance Sheets, include RECs (Exelon, Generation, 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 sold to a counterparty under a contract that specifically identifies a power plant is recognized at a point in time when the power is produced. This includes both bundled and unbundled REC sales. Otherwise, the revenue is recognized upon physical transfer of the REC to the customer. The following table summarizes the current and noncurrent Renewable and Alternative Energy Credits as of December 31, 2018 and 2017 : As of December 31, 2018 Exelon Generation PECO PHI DPL ACE Current AEC's $ 2 $ — $ 2 $ — $ — $ — Current REC's 279 270 — 9 8 1 Noncurrent REC's 52 52 — — — — As of December 31, 2017 Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Current REC's 321 312 — 9 8 1 Noncurrent REC's 27 27 — — — —

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	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, 2018 and 2017 : Exelon December 31, 2018 Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 714 $ — $ 714 $ — $ 714 Long-term debt (including amounts due within one year) (a) 35,424 — 33,711 2,158 35,869 Long-term debt to financing trusts (b) 390 — — 400 400 SNF obligation 1,171 — 949 — 949 December 31, 2017 Carrying Amount 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 Generation December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,793 $ — $ 7,467 $ 1,443 $ 8,910 SNF obligation 1,171 — 949 — 949 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 ComEd December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,101 $ — $ 8,390 $ — $ 8,390 Long-term debt to financing trusts (b) 205 — — 209 209 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 PECO December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,157 $ 50 $ 3,207 Long-term debt to financing trusts 184 — — 191 191 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 BGE December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 35 $ — $ 35 $ — $ 35 Long-term debt (including amounts due within one year) (a) 2,876 — 2,950 — 2,950 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 PHI December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 179 $ — $ 179 $ — $ 179 Long-term debt (including amounts due within one year) (a) 6,259 — 5,436 665 6,101 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 Pepco December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 40 $ — $ 40 $ — $ 40 Long-term debt (including amounts due within one year) (a) 2,719 — 2,901 196 3,097 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 DPL December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,494 $ — $ 1,303 $ 193 $ 1,496 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 ACE December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 139 $ — $ 139 $ — $ 139 Long-term debt (including amounts due within one year) (a) 1,188 — 987 275 1,262 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 __________ (a) Includes unamortized debt issuance costs which are not fair valued of $216 million , $51 million , $63 million , $23 million , $18 million , $14 million , $34 million , $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2018 . 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 . (b) Includes unamortized debt issuance costs which are not fair valued of $0 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018 . 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 . 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 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 $119 million and $114 million as of December 31, 2018 and 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 5 - 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. 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 in Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2018 and 2017 : Generation Exelon As of December 31, 2018 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) $ 581 $ — $ — $ — $ 581 $ 1,243 $ — $ — $ — $ 1,243 NDT fund investments Cash equivalents (b) 252 86 — — 338 252 86 — — 338 Equities 2,918 1,591 — 1,381 5,890 2,918 1,591 — 1,381 5,890 Fixed income Corporate debt — 1,593 230 — 1,823 — 1,593 230 — 1,823 U.S. Treasury and agencies 2,081 99 — — 2,180 2,081 99 — — 2,180 Foreign governments — 50 — — 50 — 50 — — 50 State and municipal debt — 149 — — 149 — 149 — — 149 Other (c) — 30 — 846 876 — 30 — 846 876 Fixed income subtotal 2,081 1,921 230 846 5,078 2,081 1,921 230 846 5,078 Middle market lending — — 313 367 680 — — 313 367 680 Private equity — — — 329 329 — — — 329 329 Real estate — — — 510 510 — — — 510 510 NDT fund investments subtotal (d) 5,251 3,598 543 3,433 12,825 5,251 3,598 543 3,433 12,825 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Pledged assets for Zion Station decommissioning Cash equivalents 9 — — — 9 9 — — — 9 Equities — — — — — — — — — — Middle market lending — — — — — — — — — — Pledged assets for Zion Station decommissioning subtotal 9 — — — 9 9 — — — 9 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 24 — — — 24 72 — — — 72 Fixed income — — — — — — 15 — — 15 Life insurance contracts — 22 — — 22 — 70 38 — 108 Rabbi trust investments subtotal (f) 29 22 — — 51 120 85 38 — 243 Commodity derivative assets Economic hedges 541 2,760 1,470 — 4,771 541 2,760 1,470 — 4,771 Proprietary trading — 69 77 — 146 — 69 77 — 146 Effect of netting and allocation of (e) (582 ) (2,357 ) (732 ) — (3,671 ) (582 ) (2,357 ) (732 ) — (3,671 ) Commodity derivative assets subtotal (41 ) 472 815 — 1,246 (41 ) 472 815 — 1,246 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — — — — — Economic hedges — 13 — — 13 — 13 — — 13 Effect of netting and allocation of collateral — (3 ) — — (3 ) — (3 ) — — (3 ) Interest rate and foreign currency derivative assets subtotal — 10 — — 10 — 10 — — 10 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,829 4,102 1,400 3,433 14,764 6,582 4,165 1,438 3,433 15,618 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,027 ) — (4,632 ) (642 ) (2,963 ) (1,276 ) — (4,881 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (240 ) — (698 ) (3 ) (455 ) (489 ) — (947 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Economic hedges — (6 ) — — (6 ) — (6 ) — — (6 ) Effect of netting and allocation of collateral — 3 — — 3 — 3 — — 3 Interest rate and foreign currency derivative liabilities subtotal — (3 ) — — (3 ) — (7 ) — — (7 ) Deferred compensation obligation — (35 ) — — (35 ) — (137 ) — — (137 ) Total liabilities (3 ) (493 ) (240 ) — (736 ) (3 ) (599 ) (489 ) — (1,091 ) Total net assets $ 5,826 $ 3,609 $ 1,160 $ 3,433 $ 14,028 $ 6,579 $ 3,566 $ 949 $ 3,433 $ 14,527 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 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 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 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 (f) 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) (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 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 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 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) 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 __________ (a) Generation excludes cash of $283 million and $259 million at December 31, 2018 and 2017 and restricted cash of $39 million and $127 million at December 31, 2018 and 2017 . Exelon excludes cash of $458 million and $389 million at December 31, 2018 and 2017 and restricted cash of $80 million and $145 million at December 31, 2018 and 2017 and includes long-term restricted cash of $185 million and $85 million at December 31, 2018 and 2017 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) Includes $50 million and $77 million of cash received from outstanding repurchase agreements at December 31, 2018 and 2017 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $44 million and less than $1 million , which have a total notional amount of $1,432 million and $811 million at December 31, 2018 and 2017 , 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 $130 million and $82 million at December 31, 2018 and 2017 , 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) Excludes net assets of less than $1 million at December 31, 2018 and 2017 . These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases. (f) The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the years ended December 31, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the years ended December 31, 2018 and 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $57 million , $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018 . 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 . (h) Of the collateral posted/(received), $(94) million and $(117) million represents variation margin on the exchanges as of December 31, 2018 and 2017 , respectively. Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $72 million as of December 31, 2018 . Changes were immaterial in fair value, cumulative adjustments and impairments for the year ended December 31, 2018 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value in 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, 2018 and 2017 : ComEd PECO BGE As of December 31, 2018 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) $ 209 $ — $ — $ 209 $ 111 $ — $ — $ 111 $ 4 $ — $ — $ 4 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 10 — 10 — — — — Rabbi trust investments subtotal (b) — — — — 7 10 — 17 6 — — 6 Total assets 209 — — 209 118 10 — 128 10 — — 10 Liabilities Deferred compensation obligation — (6 ) — (6 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (249 ) (249 ) — — — — — — — — Total liabilities — (6 ) (249 ) (255 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 209 $ (6 ) $ (249 ) $ (46 ) $ 118 $ — $ — $ 118 $ 10 $ (5 ) $ — $ 5 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 (b) — — — — 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 (c) — — (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 __________ (a) ComEd excludes cash of $93 million and $45 million at December 31, 2018 and 2017 and restricted cash of $28 million at December 31, 2018 and includes long-term restricted cash of $166 million and $62 million at December 31, 2018 and December 31, 2017 , which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $24 million and $47 million at December 31, 2018 and 2017 . BGE excludes cash of $7 million and $17 million at December 31, 2018 and 2017 and restricted cash of $2 million and $1 million at December 31, 2018 and December 31, 2017 . (b) The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the years ended December 31, 2018 and December 31, 2017 . (c) The Level 3 balance consists of the current and noncurrent liability of $26 million and $223 million , respectively, at December 31, 2018 , and $21 million and $235 million , respectively, at December 31, 2017 , 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 in 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, 2018 and 2017 : As of December 31, 2018 As of December 31, 2017 PHI Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Cash equivalents (a) $ 147 $ — $ — $ 147 $ 83 $ — $ — $ 83 Rabbi trust investments Cash equivalents 42 — — 42 72 — — 72 Mutual Funds 13 — — 13 — — — — Fixed income — 15 — 15 — 12 — 12 Life insurance contracts — 22 38 60 — 23 22 45 Rabbi trust investments subtotal (b) 55 37 38 130 72 35 22 129 Total assets 202 37 38 277 155 35 22 212 Liabilities Deferred compensation obligation — (21 ) — (21 ) — (25 ) — (25 ) Mark-to-market derivative liabilities — — — — (1 ) — — (1 ) Effect of netting and allocation of collateral — — — — 1 — — 1 Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (21 ) — (21 ) — (25 ) — (25 ) Total net assets $ 202 $ 16 $ 38 $ 256 $ 155 $ 10 $ 22 $ 187 Pepco DPL ACE As of December 31, 2018 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) $ 38 $ — $ — $ 38 $ 16 $ — $ — $ 16 $ 23 $ — $ — $ 23 Rabbi trust investments Cash equivalents 41 — — 41 — — — — — — — — Fixed income — 5 — 5 — — — — — — — — Life insurance contracts — 22 37 59 — — — — — — — — Rabbi trust investments subtotal (b) 41 27 37 105 — — — — — — — — Total assets 79 27 37 143 16 — — 16 23 — — 23 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 79 $ 24 $ 37 $ 140 $ 16 $ (1 ) $ — $ 15 $ 23 $ — $ — $ 23 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 (b) 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 — — — — (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 __________ (a) PHI excludes cash of $39 million and $12 million at December 31, 2018 and 2017 and includes long term restricted cash of $19 million and $23 million at December 31, 2018 and 2017 which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $15 million and $4 million at December 31, 2018 and 2017 . DPL excludes cash of $8 million and $2 million at December 31, 2018 and 2017 . ACE excludes cash of $7 million and $2 million at December 31, 2018 and 2017 and includes long-term restricted cash of $19 million and $23 million at December 31, 2018 and 2017 at December 31, 2018 and 2017 which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) The amount of unrealized gains/(losses) at PHI totaled $1 million for the years ended December 31, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for the years ended December 31, 2018 and 2017 , respectively. 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, 2018 and 2017 : Generation ComEd PHI Exelon For the year ended December 31, 2018 NDT Fund Investments Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of January 1, 2018 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 Total realized / unrealized gains (losses) Included in net income — — (105 ) (a) 3 (102 ) — 4 — (98 ) Included in noncurrent payables to affiliates (1 ) — — — (1 ) — — 1 — Included in payable for Zion Station decommissioning — 7 — — 7 — — — 7 Included in regulatory assets/liabilities — — — — — 7 (b) — (1 ) 6 Change in collateral — — (5 ) — (5 ) — — — (5 ) Purchases, sales, issuances and settlements Purchases 36 1 190 (e) 4 231 — — — 231 Sales — (20 ) (4 ) — (24 ) — — — (24 ) Issuances — — — — — — — — — Settlements (140 ) — 5 — (135 ) — 12 — (123 ) Transfers into Level 3 — — (22 ) (d) — (22 ) — — — (22 ) Transfers out of Level 3 — — (36 ) (d) (2 ) (38 ) — — — (38 ) Other miscellaneous — — — — — — — — Balance as of December 31, 2018 $ 543 $ — $ 575 $ 42 $ 1,160 $ (249 ) $ 38 $ — $ 949 The amount of total (losses) gains included in income attributed to the change in unrealized (losses) gains related to assets and liabilities held as of December 31, 2018 $ (5 ) $ — $ 165 $ 3 $ 163 $ — $ — $ — $ 163 Generation ComEd PHI Exelon For the year ended December 31, 2017 NDT Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) 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 ) — (110 ) — — — (110 ) Transfers into Level 3 — — (6 ) (d) — (6 ) — — — (6 ) Transfers out of Level 3 — — (50 ) (d) (11 ) (61 ) — — — (61 ) Other miscellaneous $ — $ — $ 31 $ (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 held as of December 31, 2017 $ 1 $ — $ 254 $ 3 $ 258 $ — $ 3 $ — $ 261 __________ (a) Includes a reduction for the reclassification of $265 million and $352 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2018 and 2017 , respectively. (b) Includes $24 million of decreases in fair value and an increase for realized losses due to settlements of $17 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2018 . 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 . (c) The amounts represented are life insurance contracts at Pepco. (d) Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts. (e) Includes $(19) million of fair value from contracts acquired as a result of the Everett Marine Terminal acquisition 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, 2018 and 2017 : Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Operating and Operating Revenues Purchased Power an

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments (All Registrants)	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 amount of energy Generation produces differs from the amount of energy 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 purchase normal sale (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 Combined Notes to 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 margin on exchange positions, is aggregated in the collateral and netting column. As of December 31, 2018 , $2 million of cash collateral posted with external counterparties and an additional $12 million of cash collateral posted with ComEd, and as of December 31, 2017 , $4 million of cash collateral held, 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 PECO and BGE must be deposited in an unaffiliated 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, 2018 : Generation ComEd Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 3,505 $ 105 $ (2,809 ) $ 801 $ — $ 801 Mark-to-market derivative assets (noncurrent assets) 1,266 41 (862 ) 445 — 445 Total mark-to-market derivative assets 4,771 146 (3,671 ) 1,246 — 1,246 Mark-to-market derivative liabilities (current liabilities) (3,429 ) (74 ) 3,056 (447 ) (26 ) (473 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,203 ) (20 ) 972 (251 ) (223 ) (474 ) Total mark-to-market derivative liabilities (4,632 ) (94 ) 4,028 (698 ) (249 ) (947 ) Total mark-to-market derivative net assets (liabilities) $ 139 $ 52 $ 357 $ 548 $ (249 ) $ 299 __________ (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 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 $121 million and $51 million , respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(94) 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, 2017 : Generation ComEd Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) 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 ) (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 ) (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ 667 __________ (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 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 $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) Of the collateral posted/(received), $(117) 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, 2018 , 2017 and 2016 , 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" in the Consolidated Statements of Cash Flows. For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain (Loss) Operating revenues $ (270 ) $ (126 ) $ (490 ) Purchased power and fuel (47 ) (43 ) 459 Total Exelon and Generation $ (317 ) $ (169 ) $ (31 ) In general, increases and decreases in forward market prices have a positive and negative impact, respectively, on Generation’s owned and contracted generation positions that have not been hedged. Generation hedges commodity price risk on a ratable basis over three-year periods. As of December 31, 2018 , the percentage of expected generation hedged for the Mid-Atlantic, Midwest, New York and ERCOT reportable segments is 89% - 92% , 56% - 59% and 32% - 35% for 2019 , 2020 and 2021 , respectively. On December 17, 2010, ComEd executed 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 4 — Regulatory Matters for additional information. 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 2018 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 2018 and previous PGC settlements, 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 executed 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, 2018 , 2017 and 2016 , 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" in the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain Operating revenues $ 17 $ 6 $ 2 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 also utilize interest rate swaps, which are treated as economic hedges, to manage their interest rate exposure. 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, 2018 : Generation Exelon Corporate Exelon Description Economic Hedges Collateral and Netting (a) Subtotal Economic Total Mark-to-market derivative assets (current assets) $ 5 $ (2 ) $ 3 $ — $ 3 Mark-to-market derivative assets (noncurrent assets) 8 (1 ) 7 — 7 Total mark-to-market derivative assets 13 (3 ) 10 — 10 Mark-to-market derivative liabilities (current liabilities) (4 ) 2 (2 ) — (2 ) Mark-to-market derivative liabilities (noncurrent liabilities) (2 ) 1 (1 ) (4 ) (5 ) Total mark-to-market derivative liabilities (6 ) 3 (3 ) (4 ) (7 ) Total mark-to-market derivative net assets (liabilities) $ 7 $ — $ 7 $ (4 ) $ 3 __________ (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, 2017 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges 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. Economic Hedges (Interest Rate and Foreign Exchange Risk) Exelon and Generation execute 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. On July 1, 2018, Exelon de-designated its fair value hedges related to interest rate risk and Generation de-designated its cash flow hedges related to interest rate risk. The amount deferred in AOCI associated with the previously designated cash flow hedges will be reclassified into earnings as the underlying forecasted transaction occurs. The result of this de-designation is that all economic hedges for interest rate swaps will be recorded at fair value through earnings going forward, referred to as economic hedges in the following tables. The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2018 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 268 $ — $ 268 Interest rate swaps 620 800 1,420 Total $ 888 $ 800 $ 1,688 The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 94 $ — $ 94 Interest rate swaps (a) 1 — 1 Total $ 95 $ — $ 95 __________ (a) On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017. For the years ended December 31, 2018 , 2017 and 2016 , 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, 2018 2017 2016 Income Statement Location Gain (Loss) Generation Operating Revenues $ 7 $ (6 ) $ (10 ) Generation Purchased Power and Fuel (9 ) — — Generation Interest Expense (7 ) (3 ) — Total Generation $ (9 ) $ (9 ) $ (10 ) For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain (Loss) Exelon Operating Revenues $ 7 $ (6 ) $ (10 ) Exelon Purchased Power and Fuel (9 ) — — Exelon Interest Expense (4 ) (3 ) — Total Exelon $ (6 ) $ (9 ) $ (10 ) 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 had no fixed-to-floating swaps designated as fair value hedges as of December 31, 2018 and had $800 million notional amounts designated as fair value hedges as of December 31, 2017 . 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 2018 2017 2016 2018 2017 2016 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (11 ) $ (13 ) $ (9 ) $ 20 $ 28 $ 23 During the years ended December 31, 2018 , 2017 and 2016 , the impact on the results of operations due to ineffectiveness from fair value hedges were gains of $9 million , $15 million and $14 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. Exelon and Generation have no floating-to-fixed swaps designated as cash flow hedges as of December 31, 2018 , and had $636 million notional amounts designated as cash flow hedges as of December 31, 2017 . The tables below provide the activity of OCI related to cash flow hedges for the years ended December 31, 2018 and 2017 , 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, 2018 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Effective portion of changes in fair value 11 11 Reclassifications from AOCI to net income Interest expense 1 1 AOCI derivative loss at December 31, 2018 $ (4 ) $ (2 ) 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 ) __________ (a) Amount is net of related income tax expense of $1 million for the year ended December 31, 2017 . During the years ended December 31, 2018 , 2017 and 2016 , the impact on the results of operations as a result of ineffectiveness from cash flow hedges 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. 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 commodity positions. 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 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, 2018 , 2017 and 2016 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses). For the Years Ended December 31, 2018 2017 2016 Income Statement Location Loss Operating revenues $ — $ (1 ) $ (1 ) Credit Risk, Collateral and Contingent-Related Features (All Registrants) The Registrants would be exposed to credit-related losses in the event of non-performance by counterparties on executed derivative instruments. The credit exposure of derivative contracts, before collateral, is represented by the fair value of contracts at the reporting date. For commodity derivatives, Generation enters into enabling agreements that allow for payment netting with its counterparties, which reduces Generation’s exposure to counterparty risk by providing for the offset of amounts payable to the counterparty against amounts receivable from the counterparty. Typically, each enabling agreement is for a specific commodity and so, with respect to each individual counterparty, netting is limited to transactions involving that specific commodity product, except where master netting agreements exist with a counterparty that allow for cross product netting. In addition to payment netting language in the enabling agreement, Generation’s credit department establishes credit limits, margining thresholds and collateral requirements for each counterparty, which are defined in the derivative contracts. Counterparty credit limits are based on an internal credit review process that considers a variety of factors, including the results of a s

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt and Credit Agreements (All Registrants)	Debt and Credit Agreements (All Registrants) Short-Term Borrowings Exelon Corporate, ComEd, BGE, Pepco, DPL and ACE 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 Exelon intercompany money pool. PHI Corporate meets its short-term liquidity requirements primarily through the issuance of short-term notes and the Exelon intercompany money pool. 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, 2018 and 2017 : 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 2018 (a)(b)(c) 2017 (a)(b)(c) 2018 2017 2018 2017 Exelon Corporate $ 600 $ 600 $ — $ — 1.93 % 1.16 % Generation 5,300 5,300 — — 1.96 % 1.23 % ComEd 1,000 1,000 — — 2.14 % 1.24 % PECO 600 600 — — 2.24 % 1.13 % BGE 600 600 35 77 2.18 % 1.28 % Pepco 300 500 40 26 2.24 % 1.06 % DPL 300 500 — 216 2.07 % 1.48 % ACE 300 350 14 108 2.21 % 1.43 % Total $ 9,000 $ 9,450 $ 89 $ 427 __________ (a) Excludes $545 million and $480 million in bilateral credit facilities at December 31, 2018 and 2017 , respectively, and $159 million and $179 million in credit facilities for project finance at December 31, 2018 and 2017 , respectively. These credit facilities do not back Generation's commercial paper program. (b) At December 31, 2018, excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million and $5 million , respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. At December 31, 2017, excludes $128 million of credit facility agreements arranged at minority and community banks at 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. (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, 2018 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2018 Borrower Facility Type Aggregate Bank (a) Facility Draws Outstanding Letters of Credit Actual To Support Additional Commercial (b) Exelon Corporate Syndicated Revolver $ 600 $ — $ 9 $ 591 $ 591 Generation Syndicated Revolver 5,300 — 1,203 4,097 4,097 Generation Bilaterals 545 — 353 192 — Generation Project Finance 159 — 119 40 — ComEd Syndicated Revolver 1,000 — 2 998 998 PECO Syndicated Revolver 600 — — 600 600 BGE Syndicated Revolver 600 — 1 599 564 Pepco Syndicated Revolver 300 — 8 292 252 DPL Syndicated Revolver 300 — 1 299 299 ACE Syndicated Revolver 300 — — 300 286 Total $ 9,704 $ — $ 1,696 $ 8,008 $ 7,687 __________ (a) Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million and $5 million , respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively. The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2018 , 2017 and 2016 . Exelon 2018 2017 2016 Average borrowings $ 531 $ 823 $ 1,125 Maximum borrowings outstanding 1,237 2,147 3,076 Average interest rates, computed on a daily basis 2.21 % 1.32 % 0.88 % Average interest rates, at December 31 2.15 % 1.24 % 1.12 % Generation 2018 2017 2016 Average borrowings $ 37 $ 405 $ 536 Maximum borrowings outstanding 583 1,455 1,735 Average interest rates, computed on a daily basis 1.96 % 1.23 % 0.94 % Average interest rates, at December 31 1.96 % 1.23 % 1.14 % ComEd 2018 2017 2016 Average borrowings $ 154 $ 200 $ 256 Maximum borrowings outstanding 520 470 755 Average interest rates, computed on a daily basis 2.14 % 1.24 % 0.77 % Average interest rates, at December 31 2.14 % 1.24 % N/A PECO 2018 2017 2016 Average borrowings $ 68 $ 2 $ — Maximum borrowings outstanding 350 60 — Average interest rates, computed on a daily basis 2.24 % 1.13 % N/A Average interest rates, at December 31 2.24 % 1.13 % N/A BGE 2018 2017 2016 Average borrowings $ 65 $ 54 $ 143 Maximum borrowings outstanding 239 165 369 Average interest rates, computed on a daily basis 2.18 % 1.28 % 0.77 % Average interest rates, computed at December 31 2.18 % 1.28 % 0.95 % PHI Corporate 2018 2017 2016 Average borrowings N/A N/A $ 153 Maximum borrowings outstanding N/A N/A 559 Average interest rates, computed on a daily basis N/A N/A 1.03 % Average interest rates, computed at December 31 N/A N/A N/A Pepco 2018 2017 2016 Average borrowings $ 22 $ 51 $ 4 Maximum borrowings outstanding 90 197 73 Average interest rates, computed on a daily basis 2.24 % 1.06 % 0.71 % Average interest rates, computed at December 31 2.24 % 1.06 % 0.90 % DPL 2018 2017 2016 Average borrowings $ 87 $ 40 $ 33 Maximum borrowings outstanding 245 216 116 Average interest rates, computed on a daily basis 2.07 % 1.48 % 0.68 % Average interest rates, computed at December 31 2.07 % 1.48 % N/A ACE 2018 2017 2016 Average borrowings $ 95 $ 30 $ — Maximum borrowings outstanding 210 133 5 Average interest rates, computed on a daily basis 2.21 % 1.43 % 0.65 % Average interest rates, computed at December 31 2.21 % 1.43 % N/A Short-Term Loan Agreements 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 expired on March 22, 2018. The loan agreement was renewed on March 22, 2018 and will expire on March 21, 2019. 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 May 23, 2018, ACE entered into two term loan agreements in the aggregate amount of $ 125 million , which expire on May 22, 2019. Pursuant to the term loan agreements, loans made thereunder bear interest at a variable rate equal to LIBOR plus 0.55% and all indebtedness thereunder is unsecured. Credit Agreements On January 5, 2016, Generation entered into a credit agreement establishing a $150 million bilateral credit facility. On January 4, 2019, the credit agreement was amended to extend its maturity from January 2019 to April 2021. 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 , scheduled to mature in October of 2019. 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, 2018, each of the Registrants' respective syndicated revolving credit facilities had their maturity dates extended to May 26, 2023. 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 . On January 4, 2019, the credit agreement was amended to extend its maturity from January 2019 to March 2021. This facility will solely be used by Generation to issue letters of credit. On March 15, 2018, the credit agreement for a Generation bilateral credit facility of $30 million was amended to increase the overall facility size to $95 million , scheduled to mature in March of 2020. 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 — — 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, 2018 : 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, 2018 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Pepco DPL ACE Interest coverage ratio 7.34 10.99 7.34 8.14 9.77 5.98 7.03 5.06 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 both December 31, 2018 and December 31, 2017 , $79 million in variable rate demand bonds issued by DPL were outstanding and are included in the Long-term debt due within one year in 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, 2018 and 2017 : Exelon Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.70 % - 7.90 % 2019 - 2048 16,496 15,197 Senior unsecured notes 2.45 % - 7.60 % 2019 - 2046 11,285 11,285 Unsecured notes 2.40 % - 6.35 % 2021 - 2048 2,900 2,600 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % 2020 39 82 Notes payable and other (b)(c) 2.85 % - 8.88 % 2019 - 2053 188 405 Junior subordinated notes 3.50 % 2022 1,150 1,150 Long-term software licensing agreement 3.95 % 2024 73 79 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % — 2024 - 2031 112 112 Medium-Terms Notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Transition bonds 5.55 % 2023 59 90 Loan Agreement 2.00 % 2023 50 — Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,253 1,331 Variable rates (f) 5.81 % 2019 - 2024 849 865 Total long-term debt 34,911 33,657 Unamortized debt discount and premium, net (66 ) (57 ) Unamortized debt issuance costs (216 ) (201 ) Fair value adjustment 795 865 Long-term debt due within one year (e) (1,349 ) (2,088 ) Long-term debt $ 34,075 $ 32,176 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 % - 7.50 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Total long-term debt to financing trusts 390 390 Unamortized debt issuance costs — (1 ) Long-term debt to financing trusts $ 390 $ 389 __________ (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 $36 million and $53 million at December 31, 2018 and 2017 , respectively. Lease payments of $21 million , $5 million , $1 million , $1 million , less than $1 million, and $8 million will be made in 2019 , 2020 , 2021 , 2022 , 2023 , 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. (d) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. (e) In January 2019, $300 million of ComEd long-term debt due within one year was paid in full. (f) Excludes interest on CEU Upstream nonrecourse debt, see discussion below. Generation Maturity Date December 31, Rates 2018 2017 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2019 - 2042 $ 6,019 $ 6,019 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % 2020 39 82 Notes payable and other (a)(b) 2.85 % - 7.83 % 2019 - 2024 164 223 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,253 1,331 Variable rates (c) 5.81 % 2019 - 2024 849 865 Total long-term debt 8,759 8,955 Unamortized debt discount and premium, net (6 ) (8 ) Unamortized debt issuance costs (51 ) (60 ) Fair value adjustment 91 103 Long-term debt due within one year (906 ) (346 ) Long-term debt $ 7,887 $ 8,644 __________ (a) Includes Generation’s capital lease obligations of $14 million and $18 million at December 31, 2018 and 2017 , respectively. Generation will make lease payments of $7 million , $5 million , $1 million , and $1 million in 2019 , 2020 , 2021 , and 2022 , respectively. Lease payments of less than $1 million annually will be made from 2023 through expiration of the final capital lease in 2024. (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. (c) Excludes interest on CEU Upstream nonrecourse debt, see discussion below. ComEd Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 2.15 % - 6.45 % 2019 - 2048 $ 8,179 $ 7,529 Notes payable and other (b) 7.49 % 2053 8 147 Total long-term debt 8,187 7,676 Unamortized debt discount and premium, net (23 ) (23 ) Unamortized debt issuance costs (63 ) (52 ) Long-term debt due within one year (d) (300 ) (840 ) Long-term debt $ 7,801 $ 6,761 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, 2018 and 2017 , respectively. Lease payments of less than $1 million annually will be made from 2019 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. (d) In January 2019, the $300 million balance was paid in full. PECO Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2021 - 2048 $ 3,075 $ 2,925 Loan Agreement 2.00 % 2023 50 0 Total long-term debt 3,125 2,925 Unamortized debt discount and premium, net (18 ) (5 ) Unamortized debt issuance costs (23 ) (17 ) Long-term debt due within one year — (500 ) Long-term debt $ 3,084 $ 2,403 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 7.38 % - 7.50 % 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 2018 2017 Long-term debt Unsecured notes 2.40 % - 6.35 % 2021 - 2048 2,900 2,600 Total long-term debt 2,900 2,600 Unamortized debt discount and premium, net (6 ) (6 ) Unamortized debt issuance costs (18 ) (17 ) Long-term debt $ 2,876 $ 2,577 PHI Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.81 % - 7.90 % 2021 - 2048 $ 5,242 $ 4,743 Senior unsecured notes 7.45 % 2032 185 185 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Transition bonds (b) 5.55 % 2023 59 90 Notes payable and other (c) 7.28 % - 8.88 % 2019 - 2022 16 33 Total long-term debt 5,636 5,189 Unamortized debt discount and premium, net 4 5 Unamortized debt issuance costs (14 ) (6 ) Fair value adjustment 633 686 Long-term debt due within one year (125 ) (396 ) Long-term debt $ 6,134 $ 5,478 __________ (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 $14 million and $27 million at December 31, 2018 and 2017 , respectively. Pepco Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2048 $ 2,735 $ 2,535 Notes payable and other (b) 7.28 % - 8.88 % 2019 - 2022 16 35 Total long-term debt 2,751 2,570 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (34 ) (32 ) Long-term debt due within one year (15 ) (19 ) Long-term debt $ 2,704 $ 2,521 __________ (a) Substantially all of Pepco's assets are subject to the lien of its respective mortgage indenture. (b) Includes capital lease obligations of $14 million and $27 million at December 31, 2018 and 2017 , respectively. Lease payments of $14 million will be made in 2019 . DPL Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.81 % - 4.27 % 2023 - 2048 $ 1,370 $ 1,171 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Total long-term debt 1,504 1,309 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (12 ) (11 ) Long-term debt due within one year (91 ) (83 ) Long-term debt $ 1,403 $ 1,217 __________ (a) Substantially all of DPL's assets are subject to the lien of its respective mortgage indenture. ACE Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 3.38 % - 6.80 % 2021 - 2036 $ 1,137 $ 1,037 Transition bonds (b) 5.55 % 2023 59 90 Total long-term debt 1,196 1,127 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (7 ) (5 ) Long-term debt due within one year (18 ) (281 ) Long-term debt $ 1,170 $ 840 __________ (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, 2018 are $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 2019 through 2023 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 1,349 $ 906 $ 300 $ — $ — $ 125 $ 15 $ 91 $ 18 2020 3,528 2,108 500 — — 20 — — 20 2021 1,511 1 350 300 300 261 1 — 260 2022 3,084 1,024 — 350 250 310 310 — — 2023 850 — — 50 300 500 — 500 — Thereafter 24,979 (a) 4,720 7,243 (b) 2,609 (c) 2,050 4,420 2,425 913 898 Total $ 35,301 $ 8,759 $ 8,393 $ 3,309 $ 2,900 $ 5,636 $ 2,751 $ 1,504 $ 1,196 __________ (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 20 — Earnings Per Share for additional information on the issuance of common stock. Nonrecourse Debt Exelon and Generation have issued nonrecourse debt financing, in which approximately $2.9 billion of generating assets have been pledged as collateral at December 31, 2018 . 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, 2018 , $ 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, 2018 , the outstanding debt balance of $15 million was classified within Long term debt due within one year in Exelon’s and Generation’s Consolidated Balance Sheets. See Note 5 — 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, 2018 , $8 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 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, 2018 , $508 million was outstanding. In addition, Generation has issued letters of credit to support its equity investment in the project. As of December 31, 2018 , Generation had $38 million in letters of credit outstanding related to the project. In 2017, Generation’s interests in Antelope Valley were also contributed to and are pledged as collateral for the EGR IV financing structure referenced below. 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, 2018 , $479 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, 2018 , the Continental Wind letter of credit facility had $114 million in letters of credit outstanding related to the project. In 2017, Generation’s interests in Continental Wind were contributed to EGRP. Refer to Note 2 - Variable Interest Entities for additional information on EGRP. ExGen Texas Power. In September 2014, EGTP, an indirect subsidiary of Exelon and Generation, issued $675 million aggregate principal amount of a nonrecourse senior secured term loan. The net proceeds were distributed to Generation for general business purposes. The loan was scheduled to mature on September 18, 2021. In addition to the financing, EGTP entered into various interest rate swaps with an initial notional amount of approximately $505 million at an interest rate of 2.34% to hedge a portion of the interest rate exposure in connection with this financing, as required by the debt covenants. 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, which permitted EGTP to draw on its revolving credit facility and initiate an orderly sales process of its assets. On November 7, 2017, 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. As a result, Exelon and Generation deconsolidated the nonrecourse senior secured term loan, the revolving credit facility, and the interest rate swaps from their consolidated financial stat

Income Taxes (All Registrants)

Income Taxes (All Registrants)	12 Months Ended
	Dec. 31, 2018
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 are determined by the Utility Registrants’ respective rate regulators, subject to certain IRS “normalization” rules. See Note 4 — Regulatory Matters for additional information regarding settlements for passing back of TCJA income tax savings benefits to customers. The Registrants assessed the applicable provisions in the TCJA and recorded the associated impacts as of December 31, 2017. The Registrants recorded provisional income tax amounts as of December 31, 2017, as allowed under SAB 118 issued by the SEC in December 2017, for changes pursuant to the TCJA related to depreciation because the impacts could not be finalized upon issuance of the Registrants’ financial statements, but for which reasonable estimates could be determined. On August 3, 2018, the U.S. Department of Treasury, in conjunction with the IRS, released proposed regulations clarifying the immediate expensing provisions enacted by the TCJA, specifically that regulated utility property acquired after September 27, 2017, and placed in service by December 31, 2017, qualifies for 100% expensing. Until the proposed regulations are finalized, taxpayers may rely on the proposed regulations for tax years ending after September 28, 2017. The Registrants recorded the impact of these proposed regulations and the adjustment was immaterial. While the Registrants have recorded the impacts of the TCJA based on their interpretation of the provisions as enacted, it is expected the U.S. Department of Treasury and the IRS will issue additional interpretative guidance in the future that could result in changes to previously finalized provisions. At this time, many of the states in which Exelon does business have issued guidance regarding TCJA and the impact was not material. 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 remained in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. 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 was 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. 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. See Note 4 - Regulatory Matters for additional information. 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, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 226 $ 337 $ (63 ) $ 11 $ (5 ) $ (4 ) $ 28 $ (3 ) $ (14 ) Deferred (98 ) (347 ) 145 10 47 24 (21 ) 13 18 Investment tax credit amortization (24 ) (21 ) (2 ) — — (1 ) — — — State Current (1 ) 6 (29 ) 1 — 7 — — — Deferred 17 (83 ) 117 (16 ) 32 9 6 12 8 Total $ 120 $ (108 ) $ 168 $ 6 $ 74 $ 35 $ 13 $ 22 $ 12 For the Year Ended December 31, 2017 (a) 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 (471 ) (2,005 ) 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 162 1 136 (9 ) 49 32 13 13 4 Total $ (126 ) $ (1,376 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26 Successor Predecessor For the Year Ended December 31, 2016 (a) 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 600 (254 ) 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 78 (2 ) 63 5 31 16 12 — 13 7 Total $ 753 $ 282 $ 301 $ 149 $ 174 $ 41 $ 22 $ (4 ) $ 3 $ 17 __________ (a) Exelon retrospectively adopted the new standard Revenue from Contracts with Customers. The standard was adopted as of January 1, 2018. Components of income tax expense or benefit are recast to reflect the impact of the new standard. 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, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 0.6 (16.6 ) 8.3 (2.6 ) 6.6 3.0 2.2 6.7 7.4 Qualified NDT fund income (1.9 ) (11.8 ) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (6.5 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.3 ) (0.4 ) Plant basis differences (3.5 ) — (0.2 ) (14.1 ) (1.3 ) (1.6 ) (2.7 ) (0.3 ) (0.5 ) Production tax credits and other credits (2.2 ) (13.5 ) — — — — — — — Noncontrolling interests (1.0 ) (6.1 ) — — — — — — — Excess deferred tax amortization (8.3 ) — (9.1 ) (3.2 ) (8.0 ) (14.5 ) (14.8 ) (12.0 ) (14.9 ) Tax Cuts and Jobs Act of 2017 0.9 2.7 (0.1 ) — — 0.1 — — — Other 1.0 1.3 0.5 0.3 0.9 0.3 0.2 0.4 1.2 Effective income tax rate 5.4 % (29.5 )% 20.2 % 1.3 % 19.1 % 8.1 % 5.8 % 15.5 % 13.8 % For the Year Ended December 31, 2017 (a) 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 2.9 5.7 0.6 5.4 4.8 3.2 5.4 5.6 Qualified NDT fund income 3.8 9.9 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.1 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (b) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.7 ) — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.6 ) (1.2 ) — — — (9.5 ) (6.3 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.6 ) — — — — — — — Tax Cuts and Jobs Act of 2017 (c) (33.1 ) (128.3 ) 0.1 (2.3 ) 0.9 6.4 2.7 2.5 1.6 Other 0.1 (0.5 ) 0.2 (0.1 ) 0.2 (0.1 ) (0.2 ) 0.1 (0.4 ) Effective income tax rate (3.3 )% (94.6 )% 42.4 % 19.3 % 41.5 % 37.5 % 33.9 % 37.0 % 25.2 % Successor Predecessor For the Year Ended December 31, 2016 (a) March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL (d) ACE (d) PHI (d) 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 (e) 3.3 3.2 5.6 1.3 5.0 15.7 52.7 6.2 5.8 11.9 Qualified NDT fund income 3.4 7.9 — — — — — — — — 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 (4.9 ) — (0.6 ) (9.6 ) (2.7 ) (22.8 ) (25.5 ) 10.3 39.0 (13.5 ) Production tax credits and other credits (3.6 ) (8.3 ) — — — — — — — — Noncontrolling interests (0.2 ) (0.6 ) — — — — — — — — Statute of limitations expiration (0.4 ) (1.7 ) — — — — — — — — Penalties 1.9 — 4.5 — — — — — (0.7 ) — Merger Expenses 5.6 1.1 — — — 23.5 112.9 (44.9 ) (89.0 ) 11.1 Other (f) (0.7 ) (1.4 ) 0.1 (1.2 ) — (1.8 ) (2.2 ) 1.3 3.3 3.6 Effective income tax rate 38.2 % 32.9 % 44.3 % 25.4 % 37.2 % 49.4 % 169.2 % 8.7 % (5.2 )% 47.2 % __________ (a) Exelon retrospectively adopted the new standard Revenue from Contracts with Customers. The standard was adopted as of January 1, 2018. The effective income tax rates are recast to reflect the impact of the new standard. (b) 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 Note 4 - Regulatory Matters for additional information. (c) Included are impacts for TCJA 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. (d) 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. (e) Includes a remeasurement of uncertain state income tax positions for Pepco and DPL. (f) 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. 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, 2018 and 2017 are presented below: As of December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,533 ) $ (2,495 ) $ (4,059 ) $ (1,862 ) $ (1,399 ) $ (2,577 ) $ (1,148 ) $ (743 ) $ (645 ) Accrual based contracts 117 (44 ) — — — 161 — — — Derivatives and other financial instruments 89 35 69 — — 3 — — — Deferred pension and postretirement obligation 1,435 (188 ) (255 ) (26 ) (26 ) (102 ) (78 ) (46 ) (14 ) Nuclear decommissioning activities (351 ) (351 ) — — — — — — — Deferred debt refinancing costs 234 23 (7 ) — (3 ) 187 (4 ) (2 ) (1 ) Regulatory assets and liabilities (749 ) — 300 (129 ) 172 (90 ) 58 96 83 Tax loss carryforward 237 78 — 18 25 96 12 52 26 Tax credit carryforward 811 816 — — — — — — — Investment in partnerships (797 ) (775 ) — — — — — — — Other, net 934 239 151 67 12 196 98 17 19 Deferred income tax liabilities (net) $ (10,573 ) $ (2,662 ) $ (3,801 ) $ (1,932 ) $ (1,219 ) $ (2,126 ) $ (1,062 ) $ (626 ) $ (532 ) Unamortized investment tax credits (724 ) (700 ) (12 ) (1 ) (3 ) (8 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,297 ) $ (3,362 ) $ (3,813 ) $ (1,933 ) $ (1,222 ) $ (2,134 ) $ (1,064 ) $ (628 ) $ (535 ) 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. The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2018 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Federal Federal general business credits carryforwards 811 (a) 816 — — — — — — — State State net operating losses 4,103 (b) 1,544 (b) — 224 (c) 395 (d) 1,492 (e) 192 (f) 772 (g) 365 (h) Deferred taxes on state tax attributes (net) 272 104 — 18 26 102 12 52 26 Valuation allowance on state tax attributes 35 26 — — 1 6 — — — __________ (a) Exelon’s federal general business credit carryforwards will begin expiring in 2033. (b) Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2019. (c) PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031. (d) BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026. (e) PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036. (f) Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2033. (g) DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2030. (h) 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, 2018 , 2017 and 2016 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2018 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Change to positions that only affect timing 15 15 — — — — — — — Increases based on tax positions prior to 2018 30 21 — — — 8 7 1 — Decreases based on tax positions prior to 2018 (251 ) (36 ) — — (120 ) (88 ) (66 ) (22 ) — Decrease from settlements with taxing authorities (53 ) (53 ) — — — — — — — Decreases from expiration of statute of limitations (7 ) (7 ) — — — — — — — Unrecognized tax benefits at December 31, 2018 $ 477 $ 408 $ 2 $ — $ — $ 45 $ — $ — $ 14 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 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 ) — — — — — — — Unrecognized tax benefits at December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Exelon 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 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 ) — — — — — — — Decreases from settlements with taxing authorities (27 ) (27 ) — — — — — — — Unrecognized tax benefits at December 31, 2016 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22 As a result of a court decision issued in July 2018 to an unrelated taxpayer, Exelon's and Generation’s unrecognized federal and state tax benefits increased in the third quarter of 2018 by approximately $71 million . Approximately $20 million of this increase impacted Exelon's and Generation’s effective tax rate and resulted in a charge to earnings in the third quarter of 2018. Exelon’s and Generation’s unrecognized federal and state tax benefits decreased in the fourth quarter of 2018 by approximately $90 million due to the settlement of a federal audit issue with IRS Appeals. The recognition of these tax benefits decreased the effective tax rate at Exelon and Generation resulting in an income tax benefit of approximately $9 million . In the fourth quarter of 2018, Exelon, Generation, BGE, PHI, Pepco, and DPL decreased their unrecognized state tax benefits by $241 million , $33 million , $120 million , $88 million , $66 million , and $22 million , respectively, due to the receipt of favorable guidance with respect to the deductibility of certain depreciable fixed assets. The recognition of these tax benefits decreased the effective tax rate at Exelon and Generation resulting in an income tax benefit of approximately $26 million . The recognition of the tax benefits related to BGE, PHI, Pepco, and DPL was offset by corresponding regulatory liabilities and that portion had no immediate impact to their effective tax rate. 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. Unrecognized tax benefits that if recognized would affect the effective tax rate Exelon, Generation, ComEd and PHI have $463 million , $408 million , $2 million and $31 million , respectively, of unrecognized tax benefits at December 31, 2018 that, if recognized, would decrease the effective tax rate. PHI has $21 million of unrecognized state tax benefits at December 31, 2018 that, if recognized, $14 million would be in the form of a net operating loss carryforward, which is expected to require a full valuation allowance based on present circumstances. PHI and ACE have $14 million of unrecognized tax benefits at December 31, 2018 that, if recognized, may be included in future base rates and that portion would have no impact to the effective tax rate. Exelon, Generation, ComEd and PHI had $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. Unrecognized tax benefits that if recognized would affect only the timing of tax payments There are no unrecognized tax benefits as of December 31, 2018 that affect only the timing of tax payments. Exelon and Generation had $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. 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. 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, 2018 , Exelon and ComEd have approximately $33 million and $ 2 million , respectively, of unrecognized federal and state income tax benefits related to the like-kind exchange litigation described further below. If Exelon does not appeal the October 2018 U.S. Court of Appeals for the Seventh Circuit's decision to the U.S. Supreme Court, Exelon's and ComEd's unrecognized tax benefits will decrease in the first quarter of 2019. See below for further details. Settlement of Income Tax Audits, Refund Claims, and Litigation As of December 31, 2018 , Exelon, Generation, PHI and ACE have approximately $425 million , $411 million , $14 million , and $ 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 $411 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefit related to PHI 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. Net interest receivable (payable) as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 236 $ (2 ) $ 4 $ — $ — $ 1 $ — $ — $ — December 31, 2017 233 (3 ) 4 — — 2 — — — Net penalties payable as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ (17 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2017 (17 ) — — — — — — — — 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, 2018 $ (3 ) $ — $ — $ — $ — $ — $ — $ — December 31, 2017 37 (1 ) 11 — — — — — December 31, 2016 165 (13 ) 117 — — 6 — (1 ) Net penalty expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2018 $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2017 (2 ) — — — — — — — December 31, 2016 106 — 86 — — — — — Successor Predecessor PHI December 31, 2018 December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Net interest expense $ — $ — $ (2 ) $ — Description of tax years open to assessment by major jurisdiction Taxpayer Open Years Exelon (and predecessors) and subsidiaries consolidated federal income tax returns 1999, 2001-2017 PHI Holdings and subsidiaries consolidated federal income tax returns 2013, 2015-2016 Exelon and subsidiaries Illinois unitary income tax returns 2010-2017 Constellation combined New York corporate income tax returns 2010-March 2012 Exelon combined New York corporate income tax returns 2011-2017 Exelon New Jersey corporate income tax returns 2013-2017 Exelon Pennsylvania corporate net income tax returns 2011-2017 PECO Pennsylvania separate company returns 2015-2017 DPL Delaware separate company returns Same as federal ACE New Jersey separate company returns 2014-2017 Exelon and subsidiaries District of Columbia corporate income tax returns 2015-2017 PHI Holdings and subsidiaries District of Columbia corporate income tax returns 2015-2016 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. As previously disclosed, Exelon terminated its investment in one of the leases in 2014 and the remaining two leases were terminated in 2016. The IRS asserted that the Exelon purchase and leaseback transaction was substantially similar to a leasing transaction, known as a SILO, which is a listed transaction that the IRS has identified as a potentially abusive tax shelter. Thus, they disagreed with Exelon's position and asserted that the entire gain of approximately $1.2 billion was taxable in 1999. In 2013, the IRS issued a notice of deficiency to Exelon and Exelon filed a petition to initiate litigation in the United States Tax Court. In 2016, the Tax Court held that Exelon was not entitled to defer gain on the transaction. In addition to the tax and interest related to the gain deferral, the Tax Court also ruled that Exelon was liable for $90 million in penalties and interest on the penalties. Exelon has fully paid the amounts assessed resulting from the Tax Court decision. In September 2017, Exelon appealed the Tax Court decision to the U.S. Court of Appeals for the Seventh Circuit. In October 2018, the U.S. Court of Appeals for the Seventh Circuit affirmed the Tax Court’s decision. Exelon filed a petition seeking rehearing of the Seventh Circuit’s decision, but the Seventh Circuit denied that petition in December 2018. Exelon has until March 5, 2019 to seek a further review by the U.S. Supreme Court. State Income Tax Law Changes On April 24, 2018, Maryland enacted companion bills, House Bill 1794 and Senate Bill 1090, providing for a phase in of a single sales factor apportionment formula from the current three factor formula for determining an entity's Maryland state income taxes. The single sales factor will be fully phased in by 2022. In the second quarter of 2018, Exelon, Generation, PHI, Pepco and DPL recorded a one-time increase to deferred income taxes of approximately $16 million , $5 million , $17 million , $16 million and $1 million , respectively. At PHI, Pepco and DPL, the increase to the Maryland deferred income tax liability was offset by regulatory assets. Further, the change in tax law is not expected to have a material ongoing impact to Exelon's, Generation's, PHI's, Pepco's or DPL's future results of operations. Long-Term Marginal State Income Tax Rate (Exelon, Generation, PHI and Pepco) In the third quarter of 2018, Exelon reviewed and updated its marginal state income tax rates based on 2017 state apportionment rates. As a result of the rate changes, in the third quarter of 2018, Exelon, Generation, PHI and DPL recorded a one-time decrease to deferred income taxes of approximately $50 million , $53 million , $4 million and $2 million respectively. Pepco recorded a one-time increase to deferred income taxes of approximately $1 million . Exelon, PHI and DPL recorded a corresponding regulatory liability of approximately $1 million , $1 million and $2 million respectively. Pepco recorded a corresponding regulatory asset of approximately $1 million . Further, Exelon, Generation and PHI recorded a decrease to income tax expense (net of federal taxes) of approximately $50 million , $53 million and $3 million . Allocation of Tax Benefits (All Registrants) Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE are all party to an agreement with Exelon and other subsidiaries of Exelon that provides for the allocation of consolidated tax liabilities and benefits (Tax Sharing Agreement). The Tax Sharing Agreement provides that each party is allo

Asset Retirement Obligations (A

Asset Retirement Obligations (All Registrants)	12 Months Ended
	Dec. 31, 2018
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 in Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2017 to December 31, 2018 : Nuclear decommissioning ARO at January 1, 2017 $ 8,734 Accretion expense 458 Acquisition of FitzPatrick 444 Net increase due to 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 Accretion expense 478 Net decrease due to changes in, and timing of, estimated future cash flows (77 ) Costs incurred related to decommissioning plants (58 ) Nuclear decommissioning ARO at December 31, 2018 (a) (b) $ 10,005 __________ (a) Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. (b) Includes $772 million of ARO related to Oyster Creek which is classified as Liabilities held for sale in Exelon's and Generation's Consolidated Balance Sheets at December 31, 2018 . See Note 5 — Mergers, Acquisitions and Dispositions for additional information. The net $77 million decrease in the ARO during 2018 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 $203 million decrease primarily due to lower estimated costs for the construction of interim spent fuel storage at TMI and a net decrease in estimated costs to decommission Calvert Cliffs, FitzPatrick, Limerick, and Salem nuclear units resulting from the completion of updated cost studies. These adjustments also include a decrease due to changes in decommissioning scenarios and their probabilities. These decreases were partially offset by a $116 million increase for the impact of the early retirement and the announced pending sale of Oyster Creek and a $122 million increase for estimated cost escalation rates, primarily for labor, energy and waste burial costs. See Note 5 — Mergers, Acquisitions and Dispositions and Note 8 — Early Plant Retirements for additional information regarding Oyster Creek. 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 TMI's ARO liability incorporates the early shutdown date, increases in the probabilities of longer term decommissioning scenarios, and an increase in the estimated costs to decommission based on an updated decommissioning cost study. See Note 8 — Early 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. NDT Funds 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 with the PAPUC proposing an annual recovery from customers of approximately $4 million . This amount reflects a decrease from the previously 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 NDT 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, 2018 and 2017 , Exelon and Generation had NDT funds totaling $12,695 million and $ 13,349 million , respectively. Included within the December 31, 2018 balance is the $890 million reclassification of Oyster Creek NDT as Assets held for sale in Exelon's and Generation's Consolidated Balance Sheets. See Note 5 — Mergers, Acquisitions and Dispositions for additional information regarding the announced pending sale of Oyster Creek. The NDT funds include $144 million and $77 million for the current portion of the NDT at December 31, 2018 and 2017 , respectively, which are included in Other current assets in Exelon's and Generation's Consolidated Balance Sheets. See Note 11 — Fair Value of Financial Assets and Liabilities for additional information related to the NDT funds. The following table provides unrealized (losses) gains on NDT funds of Exelon and Generation for the years ended 2018 , 2017 and 2016 : 2018 2017 2016 Net unrealized (losses) gains on NDT funds—Regulatory Agreement Units (a) $ (715 ) $ 455 $ 216 Net unrealized (losses) gains on NDT funds—Non-Regulatory Agreement Units (b) (483 ) 521 194 __________ (a) Net unrealized (losses) gains related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities in Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates in Generation’s Consolidated Balance Sheets. (b) Net unrealized (losses) gains 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. Realized earnings, including interest and dividends on the NDT funds, for the non-Regulatory Agreement Units investments are recognized when earned and are included in Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income whereas the Regulatory Agreement Units are eliminated within Other, net. Accounting Implications of the Regulatory Agreements with ComEd and PECO Based on the regulatory agreements with the ICC and PAPUC that dictate 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 and the former PECO units in total, 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. For the former ComEd units, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income as long as the NDT funds are expected to exceed the total estimated decommissioning obligation. For the former PECO units, decommissioning-related activities are generally offset within Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income regardless of whether the NDT funds are expected to exceed or fall short of the total estimated decommissioning obligation. 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. ComEd and PECO have 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 financial statements could be material. As of December 31, 2018 , 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. 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 financial statements 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. See Note 4 — Regulatory Matters and Note 25 — Related Party Transactions for additional 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 In 2010, Generation completed an Asset Sale Agreement (ASA) under which ZionSolutions assumed responsibility for decommissioning Zion Station and Generation transferred to ZionSolutions substantially all the Zion Station’s assets, including the related NDT funds. Pursuant to the ASA, ZionSolutions will periodically request reimbursement, subject to certain restrictions, from the Zion Station-related NDT funds for costs incurred related to its decommissioning efforts at Zion Station. As the transfer of the Zion Station assets did not qualify for asset sale accounting treatment, the related NDT funds were reclassified as pledged assets for Zion Station decommissioning, which are recorded within Other current assets 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, and the transferred ARO for decommissioning was replaced with a payable for Zion Station decommissioning, which is recorded in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets. Changes in the value of the Zion Station NDT fund assets, net of applicable taxes, are 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 $120 million , which is included within the nuclear decommissioning ARO at December 31, 2018 . 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 Exelon's and Generation's pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2018 and 2017 : 2018 2017 Carrying value of Zion Station pledged assets $ 9 $ 39 Current payable to ZionSolutions (a) 9 37 Cumulative withdrawals by ZionSolutions to pay decommissioning costs (b) 965 942 _______ (a) Included in Other current liabilities within Exelon's and Generation's Consolidated Balance Sheets. Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized gains and losses associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized. (b) 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 $45 million in May 2018 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 in 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, 2018 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 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, 2018 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 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 5.0% to 6.2% (as compared to a historical 5-year annual average pre-tax return of approximately 4.9% ). 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 30, 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. See NDT Funds section above for additional information. On March 28, 2018, Generation submitted its annual decommissioning funding status report with the NRC for shutdown reactors, reactors within five years of shutdown except for Zion Station which is included in a separate report to the NRC submitted by EnergySolutions (see Zion Station Decommissioning above), and reactor involved in an acquisition. This report reflected the status of decommissioning funding assurance as of December 31, 2017 and included an update for the acquisition of FitzPatrick on March 31, 2017, the early retirement of TMI announced on May 30, 2017, an adjustment for the February 2, 2018 announced retirement date of Oyster Creek and the updated status of Peach Bottom Unit 1 based on the new collections rate described above. As of December 31, 2017, Generation provided adequate decommissioning funding assurance for all of its shutdown reactors, reactors within five years of shutdown, and reactor involved in an acquisition. Generation will file its next decommissioning funding status report for all units with the NRC by March 31, 2019. This report will reflect the status of decommissioning funding assurance as of December 31, 2018. A shortfall at any unit could necessitate that Generation address the shortfall by, among other things, obtaining a parental guarantee for Generation's share of the funding assurance. However, the amount of any guarantee or other assurance will ultimately depend on the decommissioning approach, 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. 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 in the Registrants’ Consolidated Balance Sheets from January 1, 2017 to December 31, 2018 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Non-nuclear AROs at January 1, 2017 $ 393 $ 199 $ 121 $ 28 $ 24 $ 14 $ 2 $ 9 $ 3 Net (decrease) increase due to changes in, and timing of, estimated future cash flows (11 ) (1 ) (13 ) (1 ) 2 2 1 1 — Development projects 1 1 — — — — — — — Accretion expense (a) 18 10 7 1 — — — — — Deconsolidation of EGTP (7 ) (7 ) — — — — — — — Payments (10 ) (5 ) (2 ) (1 ) (2 ) — — — — Non-nuclear AROs at December 31, 2017 384 197 113 27 24 16 3 10 3 Net increase due to changes in, and timing of, estimated future cash flows (b) 80 35 7 — 2 36 34 1 1 Accretion expense (a) 16 10 4 1 1 — — — — Asset divestitures (3 ) (3 ) — — — — — — — Payments (6 ) (1 ) (3 ) — (2 ) — — — — Non-nuclear AROs at December 31, 2018 $ 471 $ 238 $ 121 $ 28 $ 25 $ 52 $ 37 $ 11 $ 4 __________ (a) For ComEd and PECO, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (b) In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	12 Months Ended
	Dec. 31, 2018
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, non-craft, 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, non-craft, employees are not eligible for OPEB benefits and employees represented by Local 614 are not eligible for retiree health care benefits. Effective January 1, 2019, Exelon is merging the Exelon Corporation Cash Balance Pension Plan (CBPP) into the Exelon Corporation Retirement Program (ECRP). The merging of the plans is not changing the benefits offered to the plan participants and, thus, has no impact on Exelon's pension obligation. However, beginning in 2019, actuarial losses and gains related to the CBPP and ECRP will be amortized over participants’ average remaining service period of the merged ECRP rather than each individual plan. The table below shows the pension and other postretirement benefit plans in which employees of each operating company participated at December 31, 2018 : 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 X X Exelon Corporation Cash Balance Pension Plan (a) X X X X 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 X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X 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 X X X X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X 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 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 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 X X X X Exelon Corporation Health Care Program (a) X X X 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 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 2018, Exelon received an updated valuation of its pension and OPEB to reflect actual census data as of January 1, 2018. This valuation resulted in an increase to the pension and OPEB obligations of $23 million and $14 million, respectively. Additionally, accumulated other comprehensive loss decreased by $18 million (after-tax) and regulatory assets and liabilities increased by $61 million and $1 million, respectively. In connection with the acquisition of FitzPatrick in 2017, Exelon recorded pension and OPEB obligations for FitzPatrick employees of $16 million and $17 million , respectively. See Note 5 — Mergers, Acquisitions and Dispositions for additional information 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 2018 2017 2018 2017 Change in benefit obligation: Net benefit obligation at beginning of year $ 22,337 $ 21,060 $ 4,856 $ 4,457 Service cost 405 387 112 106 Interest cost 802 842 175 182 Plan participants’ contributions — — 45 53 Actuarial (gain) loss (a) (1,561 ) 1,182 (540 ) 350 Plan amendments (4 ) 9 — — Acquisitions (b) — 16 — 17 Settlements (48 ) (34 ) (4 ) — Gross benefits paid (1,239 ) (1,125 ) (275 ) (309 ) Net benefit obligation at end of year $ 20,692 $ 22,337 $ 4,369 $ 4,856 Pension Benefits Other Postretirement Benefits Exelon 2018 2017 2018 2017 Change in plan assets: Fair value of net plan assets at beginning of year $ 18,573 $ 16,791 $ 2,732 $ 2,578 Actual return on plan assets (945 ) 2,600 (136 ) 346 Employer contributions 337 341 46 64 Plan participants’ contributions — — 45 53 Gross benefits paid (1,239 ) (1,125 ) (275 ) (309 ) Settlements (48 ) (34 ) (4 ) — Fair value of net plan assets at end of year $ 16,678 $ 18,573 $ 2,408 $ 2,732 __________ (a) The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience. The pension and OPEB actuarial losses in 2017 primarily reflect a decrease in the discount rate. (b) Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017. Exelon presents its benefit obligations and plan assets net on its balance sheet within the following line items: Pension Benefits Other Postretirement Benefits Exelon 2018 2017 2018 2017 Other current liabilities $ 26 $ 28 $ 33 $ 31 Pension obligations 3,988 3,736 — — Non-pension postretirement benefit obligations — — 1,928 2,093 Unfunded status (net benefit obligation less plan assets) $ 4,014 $ 3,764 $ 1,961 $ 2,124 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 2018 2017 Projected benefit obligation $ 20,692 $ 22,337 Fair value of net plan assets 16,678 18,573 ABO in excess of plan assets Exelon 2018 2017 Projected benefit obligation $ 20,692 $ 22,337 Accumulated benefit obligation 19,656 21,153 Fair value of net plan assets 16,678 18,573 On a PBO basis, the Exelon plans were funded at 81% and 83% at December 31, 2018 and 2017 , respectively. On an ABO basis, the Exelon plans were funded at 85% and 88% at December 31, 2018 and 2017 , 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 2018 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 3.62% . The majority of the 2018 other postretirement benefit cost is calculated using an expected long-term rate of return on plan assets of 6.60% for funded plans and a discount rate of 3.61% . 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, 2018 , 2017 and 2016 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 2018 2017 (a) 2016 (b) 2018 2017 (a) 2016 (b) Components of net periodic benefit cost: Service cost $ 405 $ 387 $ 354 $ 112 $ 106 $ 107 Interest cost 802 842 830 175 182 185 Expected return on assets (1,252 ) (1,196 ) (1,141 ) (173 ) (162 ) (162 ) Amortization of: Prior service cost (credit) 2 1 14 (186 ) (188 ) (185 ) Actuarial loss 629 607 554 66 61 63 Settlement and other charges (c) 3 3 2 1 — — Net periodic benefit cost $ 589 $ 644 $ 613 $ (5 ) $ (1 ) $ 8 __________ (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 January 1, 2016 to March 23, 2016 Components of net periodic benefit cost: Service cost $ 12 $ 1 Interest cost 26 6 Expected return on assets (30 ) (5 ) Amortization of: Prior service cost (credit) — (3 ) Actuarial loss 14 2 Net periodic benefit cost $ 22 $ 1 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, 2018 , 2017 and 2016 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 2018 2017 2016 (a) 2018 2017 2016 (a) Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ 635 $ (222 ) $ 644 $ (232 ) $ 166 $ (101 ) Amortization of actuarial loss (629 ) (607 ) (554 ) (66 ) (61 ) (63 ) Current year prior service cost (credit) (4 ) 9 (60 ) — — — Amortization of prior service (cost) credit (2 ) (1 ) (14 ) 186 188 185 Settlements (3 ) (3 ) — — — — Acquisitions — — 994 — — 94 Total recognized in AOCI and regulatory assets (liabilities) $ (3 ) $ (824 ) $ 1,010 $ (112 ) $ 293 $ 115 Total recognized in AOCI $ 3 $ (401 ) $ 51 $ (55 ) $ 168 $ 20 Total recognized in regulatory assets (liabilities) $ (6 ) $ (423 ) $ 959 $ (57 ) $ 125 $ 95 Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Changes in plan assets and benefit Current year actuarial loss (gain) $ — $ — Amortization of actuarial loss (14 ) (2 ) Amortization of prior service (cost) credit — 3 Total recognized in AOCI and regulatory assets (liabilities) $ (14 ) $ 1 Total recognized in AOCI $ (1 ) $ — Total recognized in regulatory assets (liabilities) $ (13 ) $ 1 __________ (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, 2018 and 2017 , respectively, for all plans combined: Exelon Exelon Pension Benefits Other Postretirement Benefits 2018 2017 2018 2017 Prior service (credit) cost $ (29 ) $ (24 ) $ (337 ) $ (522 ) Actuarial loss 7,558 7,556 531 829 Total $ 7,529 $ 7,532 $ 194 $ 307 Total included in AOCI $ 3,899 $ 3,896 $ 70 $ 125 Total included in regulatory assets (liabilities) $ 3,630 $ 3,636 $ 124 $ 182 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 12.0 years, 11.8 years and 11.9 years for the years ended December 31, 2018 , 2017 and 2016 , respectively. 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 8.8 years, 8.8 years and 9.0 years for the years ended December 31, 2018 , 2017 and 2016 , respectively. The average remaining service period of postretirement benefit plan participants related to expected retirement was 9.5 years, 9.6 years and 9.7 years for the years ended December 31, 2018 , 2017 and 2016 , respectively. 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 . The mortality assumption is composed of a base table that represents the current expectation of life expectancy of the population adjusted by an improvement scale that attempts to anticipate future improvements in life expectancy. Exelon’s mortality assumption is supported by an actuarial experience study of Exelon's plan participants and utilizes the IRS's RP–2000 base table projected to 2012 with improvement scale AA and projected thereafter with generational improvement scale BB two-dimensional adjusted to a 0.75% long-term rate reached in 2027. There were no changes to the mortality assumption in 2016 , 2017 or 2018 . The following assumptions were used to determine the benefit obligations for the plans at December 31, 2018 , 2017 and 2016 . 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 2018 2017 2016 (f) 2018 2017 2016 (f) Discount rate 4.31 % (a) 3.62 % (b) 4.04 % (c) 4.30 % (a) 3.61 % (b) 4.04 % (c) Investment Crediting Rate 4.46 % 4.00 % 4.46 % N/A N/A N/A Rate of compensation increase (d) (d) (e) (d) (d) (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 5.00% __________ (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, 2018 . Certain benefit plans used individual rates ranging from 4.13% - 4.36% and 4.27% - 4.38% 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, 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. (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, 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. (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 for the PHI predecessor for the period from January 1, 2016, to March 23, 2016. The following assumptions were used to determine the net periodic benefit costs for the plans for the years ended December 31, 2018 , 2017 and 2016 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Pension Benefits Other Postretirement Benefits Exelon 2018 2017 2016 2018 2017 2016 Discount rate 3.62 % (a) 4.04 % (b) 4.29 % (c) 3.61 % (a) 4.04 % (b) 4.29 % (c) Investment Crediting Rate 4.00 % 4.46 % 5.31 % N/A N/A N/A Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.00 % (d) 6.60 % (d) 6.58 % (d) 6.71 % (d) Rate of compensation increase (f) (f) (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% 5.50% Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Discount rate 4.65%/4.55% (g) 4.55 % Investment crediting rate 2.89 % N/A Expected return on plan assets (h) 6.50 % 6.75 % 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 decreasing to ultimate trend of 5.00% in 2020 __________ (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, 2018 . 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 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. (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, 2016 . Certain benefit plans used the individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) 3.25% through 2019 and 3.75% thereafter. (f) 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. (g) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively. (h) Expected return on other postretirement benefit plan assets is pre-tax. Contributions The following tables provide contributions to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2018 (a) 2017 (a) 2016 (a) 2018 2017 2016 Exelon $ 337 $ 341 $ 347 $ 46 $ 64 $ 50 Generation 128 137 140 11 11 12 ComEd 38 36 33 4 5 5 PECO 28 24 30 — — — BGE 40 39 31 14 14 18 BSC (b) 41 38 39 5 2 3 Pepco 6 62 24 11 10 8 DPL — — 22 — 2 — ACE 6 — 15 — 20 2 PHISCO (c) 50 5 17 1 — 2 Pension Benefits Other Postretirement Benefits Successor Predecessor Successor Predecessor 2018 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 2018 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI $ 62 $ 67 $ 74 $ 4 $ 12 $ 32 $ 12 $ — __________ (a) Exelon's and Generation's pension contributions include $21 million and $25 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 and 2016 , respectively. There were no pension contributions for the year ended December 31, 2018 . (b) Includes $2 million , $4 million , and $6 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2018 , 2017 , and 2016 , 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 until all the qualified plans are fully funded on an ABO basis, and (2) the minimum amounts under ERISA to meet minimum contribution requirement and/or 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 2019: Qualified Pension Plans Non-Qualified Pension Plans Other Exelon $ 301 $ 25 $ 44 Generation 135 7 13 ComEd 65 1 2 PECO 25 1 — BGE 34 1 15 BSC 41 7 2 PHI 1 8 12 Pepco — 2 10 DPL — 1 — ACE — — 1 PHISCO 1 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, 2018 were: Pension Benefits Other Postretirement Benefits 2019 $ 1,196 $ 255 2020 1,221 263 2021 1,258 269 2022 1,284 274 2023 1,302 282 2024 through 2028 6,770 1,483 Total estimated future benefit payments through 2028 $ 13,031 $ 2,826 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 represent the Registrants’ as well as BSC's and PHISCO's pension and OPEB costs. As a result of new pension guidance effective on January 1, 2018, certain balances have been reclassified on Exelon’s Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2017 and 2016. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment, net, for the years ended December 31, 2018, 2017 and 2016, while the non–service cost components are included in Other, net and Regulatory assets for year ended December 31, 2018 and in Other, net and Property, plant and equipment, net, for the years ended December 31, 2017 and 2016. For Generation and the Utility Registrants, the service cost and non–service cost components are included in Operating and maintenance expense and Property, plant and equipment, net on their consolidated financial statements for the years ended December 31, 2018 , 2017 and 2016 . For the Years Ended December 31, Exelon Generation (a) ComEd PECO BGE BSC (b) Pepco (c) DPL (c) ACE (c) PHISCO (c)(d) 2018 $ 583 $ 204 $ 177 $ 18 $ 60 $ 57 $ 15 $ 6 $ 12 $ 34 2017 643 227 176 29 64 53 25 13 13 43 2016 621 218 166 33 68 48 31 18 15 47 Successor Predecessor PHI For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Pension and Other Postretirement Benefit Costs $ 67 $ 94 $ 88 $ 23 __________ (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 above. (c) 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 . (d) 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. Plan Assets Investment Strategy. On a regular basis, Exelon evaluates its investment strategy to ensure that plan assets will be sufficient to pay plan benefits when due. As part of this ongoing evaluation, Exelon may make changes to its targeted asset allocation and investment strategy. Exelon has developed and implemented a liability hedging investment strategy for its qualified pension plans that has reduced the volatility of its pension assets relative to its pension liabilities. Exelon is likely to continue to gradually increase the liability hedging portfolio as the funded status of its plans improves. The overall objective is to achieve attractive risk-adjusted returns that will balance the liquidity requirements of the plans’ liabilities while striving to minimize the risk of significant losses. Trust assets for Exelon’s other postretirement plans are managed in a diversified investment strategy that prioritizes maximizing liquidity and returns while minimizing asset volatility. Actual asset returns have an impact on the costs reported for the Exelon-sponsored pension and other postretirement benefit plans. The actual asset returns across Exelon’s pension and other postretirement benefit plans for the year ended December 31, 2018 were (4.86)% and (4.66)% , respectively, compared to an expected long-term return assumption of 7.00% and 6.60% , respectively. Exelon used an EROA

Severance (All Registrants)

Severance (All Registrants)	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
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. Severance Liability Amounts included in the table below represent the severance liability recorded for employees of each Registrant. Exelon's severance liability includes amounts related to BSC that are billed through intercompany allocations . Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2016 $ 88 $ 36 $ 3 $ — $ — $ 29 $ — $ — $ — Severance costs (a) 35 31 2 — — 3 — — — Payments (29 ) (9 ) (2 ) — — (12 ) — — — Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — Severance costs (a) 35 9 1 — 1 5 1 — — Payments (52 ) (20 ) (2 ) — — (18 ) (1 ) — — Balance at December 31, 2018 $ 77 $ 47 $ 2 $ — $ 1 $ 7 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits. 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 years ended December 31, 2018 and 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: Severance Benefits Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 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. PHI, Pepco, DPL and ACE recorded regulatory assets for merger related integration costs which include a portion of these severance costs. These regulatory assets are either currently being recovered in rates or are deemed probable of recovery in future rates. See Note 4 — Regulatory Matters for additional information.

Shareholder Equity (All Registr

Shareholder Equity (All Registrants)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	Shareholders' Equity (Exelon, ComEd, PECO, BGE, Pepco, DPL and ACE) The following table presents common stock authorized and outstanding as of December 31, 2018 and 2017 : December 31, 2018 2017 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 968,187,955 963,335,888 ComEd $ 12.50 250,000,000 127,021,331 127,021,246 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 60,285 and 60,584 warrants outstanding to purchase ComEd common stock at December 31, 2018 and 2017 , 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, 2018 and 2017 , 20,095 and 20,195 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 additional 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 shares of common stock were held as treasury stock with a historical cost of $123 million at December 31, 2018 and 2017 . 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 2018 , 2017 , and 2016 Exelon had no common stock repurchases. Preferred and Preference Securities of Subsidiaries At December 31, 2018 and 2017 , Exelon was authorized to issue up to 100,000,000 shares of preferred securities, none of which were outstanding. At December 31, 2018 and 2017 , 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, 2018
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, 2018 , there were approximately 11 million shares authorized for issuance under the LTIP. For the years ended December 31, 2018 , 2017 and 2016 , 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, 2018 , 2017 and 2016 , 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, 2018 , 2017 and 2016 and PHI's predecessor period January 1, 2016 to March 23, 2016 : Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2018 2017 2016 (a) Performance share awards $ 143 $ 107 $ 93 Restricted stock units 57 77 75 Stock options — — — Other stock-based awards 8 7 7 Total stock-based compensation expense included in operating and maintenance expense 208 191 175 Income tax benefit (54 ) (74 ) (68 ) Total after-tax stock-based compensation expense $ 154 $ 117 $ 107 __________ (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, Components of Stock-Based Compensation Expense 2016 Time-based restricted stock units $ 2 Performance-based restricted stock units 1 Time-based restricted stock awards — Total stock-based compensation expense included in operating and maintenance expense 3 Income tax benefit (1 ) Total after-tax stock-based compensation expense $ 2 The following tables present the Registrants' stock-based compensation expense (pre-tax) for the years ended December 31, 2018 , 2017 and 2016 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Year Ended December 31, Subsidiaries 2018 2017 2016 Exelon $ 208 $ 191 $ 175 Generation 77 88 78 ComEd 8 7 8 PECO 5 3 3 BGE 3 1 1 BSC (a) 111 88 81 PHI Successor (b)(c) 4 4 4 Predecessor January 1 to 2016 PHI $ 3 __________ (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, 2018 and 2017 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, 2018 , 2017 and 2016 for Exelon or PHI, or for PHI during the predecessor period January 1, 2016 to March 23, 2016 . Exelon receives 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 recognizes the tax benefit related to compensation costs. The following tables present information regarding Exelon’s tax benefits for the years ended December 31, 2018 , 2017 and 2016 . Exelon Year Ended December 31, 2018 2017 2016 Realized tax benefit when exercised/distributed: Restricted stock units 28 35 27 Performance share awards 16 29 18 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 2018 , 2017 and 2016 . 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, 2018 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2017 6,723,611 $ 47.69 2.65 $ 7 Options exercised (1,522,952 ) 36.54 Options forfeited — — Options expired (1,173,007 ) 74.99 Balance of shares outstanding at December 31, 2018 4,027,652 $ 43.95 2.90 $ 14 Exercisable at December 31, 2018 (a) 4,027,652 $ 43.95 2.90 $ 14 __________ (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, 2018 , 2017 and 2016 : Year Ended 2018 2017 2016 Intrinsic value (a) $ 12 $ 15 $ 11 Cash received for exercise price 56 107 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, 2018 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, 2018 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2017 (a) 3,389,503 $ 32.24 Granted 1,321,988 38.60 Vested (1,845,300 ) 32.03 Forfeited (65,046 ) 32.96 Undistributed vested awards (b) (507,804 ) 36.76 Nonvested at December 31, 2018 (a) 2,293,341 $ 35.06 __________ (a) Excludes 1,131,487 and 1,488,383 of restricted stock units issued to retirement-eligible employees as of December 31, 2018 and 2017 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2018 . For Exelon, the weighted average grant date fair value (per share) of restricted stock units granted for the years ended December 31, 2018 , 2017 and 2016 was $38.60 , $34.98 and $28.14 , respectively. At December 31, 2018 and 2017 , Exelon had obligations related to outstanding restricted stock units not yet settled of $83 million and $108 million , respectively, which are included in common stock in Exelon’s Consolidated Balance Sheets. For the years ended December 31, 2018 , 2017 and 2016 , Exelon settled restricted stock units with fair value totaling $106 million , $88 million and $68 million , respectively. At December 31, 2018 , $38 million of total unrecognized compensation costs related to nonvested restricted stock units are expected to be recognized over the remaining weighted-average period of 2.5 years. 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, 2018 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2017 (a) 2,956,966 $ 32.65 Granted 1,637,542 38.15 Change in performance 1,348,029 30.66 Vested (848,574 ) 36.26 Forfeited (50,467 ) 36.24 Undistributed vested awards (b) (1,640,268 ) 33.38 Nonvested at December 31, 2018 (a) 3,403,228 $ 33.13 __________ (a) Excludes 3,586,259 and 2,723,440 of performance share awards issued to retirement-eligible employees as of December 31, 2018 and 2017 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2018 . 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, 2018 , 2017 and 2016 : Year Ended 2018 (a) 2017 2016 Weighted average grant date fair value (per share) $ 38.15 $ 35.00 $ 28.85 Fair value of performance shares settled 61 72 45 Fair value of performance shares settled in cash 49 56 28 __________ (a) As of December 31, 2018 , $33 million of total unrecognized compensation costs related to nonvested performance shares 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 performance-based restricted stock awards was $26.10 for the year ended December 31, 2016 . There were no time-based restricted stock awards granted for the year ended December 31, 2016 . There were no time-based share settlements or performance-based share settlements for the year-ended December 31, 2016 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, 2018 2017 Current liabilities (a) $ 135 $ 57 Deferred credits and other liabilities (b) 109 100 Common stock 26 26 Total $ 270 $ 183 __________ (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, 2018
Earnings Per Share [Abstract]
Earnings Per Share (Exelon)	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, 2018 2017 2016 Net income attributable to common shareholders $ 2,010 $ 3,786 $ 1,121 Weighted average common shares outstanding — basic 967 947 924 Assumed exercise and/or distributions of stock-based awards 2 2 3 Weighted average common shares outstanding — diluted 969 949 927 The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 3 million in 2018 , 8 million in 2017 , and 12 million in 2016 . 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, 2018 , 2017 , and 2016 . See Note 18 — Shareholders' Equity for additional 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. See Note 18 — Shareholders' Equity for additional information regarding share repurchases.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon, Generation, and PECO)	12 Months Ended
	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income [Abstract]
Changes in Accumulated Other Comprehensive Income (Exelon, Generation, and PECO)	Changes in Accumulated Other Comprehensive Income (Exelon, Generation and PECO) The following tables present changes in accumulated other comprehensive income (loss) (AOCI) by component for the years ended December 31, 2018 and 2017 : For the Year Ended December 31, 2018 Gains and Unrealized Pension and Foreign AOCI of Investments Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 11 — (143 ) (10 ) 1 (141 ) Amounts reclassified from AOCI (b) 1 — 181 — — 182 Net current-period OCI 12 — 38 (10 ) 1 41 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (10 ) — — — (10 ) Ending balance $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 11 — — (10 ) — 1 Amounts reclassified from AOCI (b) 1 — — — — 1 Net current-period OCI 12 — — (10 ) — 2 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (3 ) — — — (3 ) Ending balance $ (4 ) $ — $ — $ (33 ) $ (1 ) $ (38 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (1 ) — — — (1 ) Ending balance $ — $ — $ — $ — $ — $ — For the Year Ended December 31, 2017 Gains and Unrealized Pension and Foreign AOCI of Investments 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 Impact of adoption of Reclassification of Certain Tax Effects from AOCI (d) — — (539 ) — — (539 ) Ending balance $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) 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 __________ (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) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Financial Liabilities. The standard was adopted as of January 1, 2018, which resulted in an increase to Retained earnings and Accumulated other comprehensive loss of $10 million , $3 million and $1 million for Exelon, Generation and PECO, respectively. The amounts reclassified related to Rabbi Trusts. See Note 1 — Significant Accounting Policies for additional information. (d) Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million , primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 1 — Significant Accounting Policies for additional information. ComEd, PECO, BGE, PHI, Pepco, DPL and ACE did not have any reclassifications out of AOCI to Net income during the years ended December 31, 2018 and 2017 . The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the years ended December 31, 2018 and 2017 : For the Year Ended December 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (1 ) $ (1 ) Interest expense (1 ) (1 ) Total before tax — — Tax benefit $ (1 ) $ (1 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 90 $ — Actuarial losses (b) (333 ) — (243 ) — Total before tax 62 — Tax benefit $ (181 ) $ — Net of tax Total Reclassifications $ (182 ) $ (1 ) Net of tax 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 (Losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense (5 ) (5 ) Total before tax 1 1 Tax benefit $ (4 ) $ (4 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 92 $ — Actuarial losses (b) (324 ) — (232 ) — Total before tax 92 — Tax benefit $ (140 ) $ — Net of tax Total Reclassifications $ (144 ) $ (4 ) Net of tax __________ (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 information. The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2018 , 2017 and 2016 : For the Year Ended December 31, 2018 2017 2016 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 24 $ 36 $ 30 Actuarial loss reclassified to periodic benefit cost (86 ) (128 ) (118 ) Pension and non-pension postretirement benefit plans valuation adjustment 50 13 115 Change in unrealized gains on cash flow hedges (5 ) (7 ) — Change in unrealized gains (losses) on investments in unconsolidated affiliates — (3 ) 3 Change in unrealized gains on marketable securities — (1 ) — Total $ (17 ) $ (90 ) $ 30 Generation Change in unrealized gains on cash flow hedges $ (4 ) $ (6 ) $ (2 ) Change in unrealized gains (losses) on investments in unconsolidated affiliates (1 ) (3 ) 3 Change in unrealized gains on marketable securities — (1 ) — Total $ (5 ) $ (10 ) $ 1

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (All Registrants)	Commitments and Contingencies (All Registrants) Commitments Constellation Merger Commitments (Exelon and Generation). 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 included 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 in leasehold improvements totaled approximately $90 million . In addition, Generation entered into a 20 -year operating lease as the primary lessee of the building. The direct investment commitment also included $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 after the merger. The MDPSC order contemplated 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 $458 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 is expected to 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. The remaining commitment is to be paid on or before January 15, 2023 unless the period is extended by consent of Exelon and the State of Maryland. As of December 31, 2018 and 2017 , Exelon's and Generation's Consolidated Balance Sheets include a $50 million liability within Deferred credits and other liabilities for this remaining commitment. Commercial Commitments (All Registrants). Exelon’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 1,703 $ 1,394 $ 308 $ 1 $ — $ — $ — Surety bonds (a) 1,402 1,331 33 38 — — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (b) 24 3 3 2 3 3 10 Total commercial commitments $ 3,507 $ 2,728 $ 344 $ 41 $ 3 $ 3 $ 388 __________ (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 $61 million , $19 million of which is a guarantee by Pepco, $26 million by DPL and $16 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, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 1,680 $ 1,380 $ 299 $ 1 $ — $ — $ — Surety bonds (a) 1,220 1,201 19 — — — — Total commercial commitments $ 2,900 $ 2,581 $ 318 $ 1 $ — $ — $ — __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. ComEd’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (a) 12 10 — 2 — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 214 $ 12 $ — $ 2 $ — $ — $ 200 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PECO’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 9 $ 9 $ — $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 9 $ — $ — $ — $ — $ 178 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. BGE’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 3 $ 2 $ 1 $ — $ — $ — $ — Surety bonds (a) 17 3 14 — — — — Total commercial commitments $ 20 $ 5 $ 15 $ — $ — $ — $ — __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PHI commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 8 $ — $ 8 $ — $ — $ — $ — Surety bonds (a) $ 41 $ 41 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 24 3 3 2 3 3 10 Total commercial commitments $ 73 $ 44 $ 11 $ 2 $ 3 $ 3 $ 10 __________ (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 $61 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, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 8 $ — $ 8 $ — $ — $ — $ — Surety bonds (a) $ 33 $ 33 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 8 1 1 1 1 1 3 Total commercial commitments $ 49 $ 34 $ 9 $ 1 $ 1 $ 1 $ 3 __________ (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 $19 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 Pepco believes the likelihood of payments being required under the guarantees is remote. DPL commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 5 $ 5 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 10 1 1 1 1 1 5 Total commercial commitments $ 15 $ 6 $ 1 $ 1 $ 1 $ 1 $ 5 __________ (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 $26 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 DPL believes the likelihood of payments being required under the guarantees is remote. ACE commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 3 $ 3 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 6 1 1 — 1 1 2 Total commercial commitments $ 9 $ 4 $ 1 $ — $ 1 $ 1 $ 2 __________ (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 ACE believes the likelihood of payments being required under the guarantees is remote. Leases (All Registrants) 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, 2018 were: Exelon (a)(b) Generation (a)(b) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2019 $ 140 $ 33 $ 7 $ 5 $ 35 $ 48 $ 11 $ 14 $ 7 2020 149 46 5 5 35 46 10 13 6 2021 143 46 4 5 33 43 9 12 5 2022 126 47 4 5 18 42 8 12 5 2023 97 46 3 5 3 39 8 10 4 Remaining years 723 545 — — 19 159 40 35 5 Total minimum future lease payments $ 1,378 $ 763 $ 23 $ 25 $ 143 $ 377 $ 86 $ 96 $ 32 __________ (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 2019 - 2023 , was $3 million , $5 million , $1 million and $1 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 $26 million , $28 million , $28 million and $14 million related to years 2019 - 2022 , respectively. The following table presents the Registrants’ rental expense under operating leases for the years ended December 31, 2018, 2017 and 2016: For the Year Ended December 31, Exelon Generation (a) ComEd PECO BGE Pepco DPL ACE 2018 $ 670 $ 558 $ 7 $ 10 $ 35 $ 10 $ 13 $ 8 2017 709 578 9 9 32 11 16 14 2016 777 667 15 7 22 8 15 13 Successor Predecessor For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI Rental expense under operating leases $ 48 $ 63 $ 49 $ 12 __________ (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 $493 million , $508 million and $604 million during 2018 , 2017 and 2016 , 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 (Exelon and Generation) 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, 2018 , the current liability limit per incident is $14.1 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 November 1, 2018. 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 $13.6 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 $3.1 billion , however any amounts payable under this secondary layer would be capped at $454 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 $14.1 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 annual distribution declared by NEIL is estimated to be $58 million for 2018 , and was $60 million and $21 million for 2017 and 2016 , respectively. In addition, in March 2018, NEIL declared a supplemental distribution. Generation's portion of the supplemental distribution declared by NEIL was $31 million . 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 $345 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 statements. Spent Nuclear Fuel Obligation (Exelon and Generation) 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 years ended December 31, 2018 , 2017 and 2016 , 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) $ 1,274 $ 1,100 __________ (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, 2018 and 2017 , 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, 2018 December 31, 2017 DOE receivable - current (a) $ 124 $ 94 DOE receivable - noncurrent (b) 15 15 Amounts owed to co-owners (a)(c) (17 ) (11 ) __________ (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 , with interest to the date of payment, 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, 2018 and 2017 , the SNF liability for the one-time fee with interest was $1,171 million and $1,147 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, 2018 was 2.351% for the deferred amount transferred from ComEd and 2.217% for the deferred FitzPatrick amount. 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 (All Registrants). 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 statements. MGP Sites (Exelon and the Utility Registrants). ComEd, PECO, BGE and DPL have identified sites where former MGP or gas purification 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, 21 of which have been remediated and approved by the Illinois EPA or the U.S. EPA and 21 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 2023. • 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 sites, 9 of which have been remediated and approved by the MDE and 4 that require some level of remediation and/or ongoing activity. BGE expects the majority of the remediation at these sites to continue through at least 2019. • 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 4 — 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. During the third quarter of 2018, the Utility Registrants completed a study of their future estimated environmental remediation requirements. The study resulted in a $48 million increase to the environmental liability and related regulatory asset for ComEd. The increase was primarily due to a revised closure strategy at one site, which resulted in an increase in the excavation area and depth of impacted soils from the site. The study did not result in a material change to the environmental liability for PECO, BGE, Pepco, DPL, and ACE. As of December 31, 2018 and 2017 , 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, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 496 $ 356 Generation 108 — ComEd 329 327 PECO 27 25 BGE 5 4 PHI 27 — Pepco 25 — DPL 1 — ACE 1 — 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 — Cotter Corporation (Exelon and Generation). 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 remed

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 and 2016 . For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 919 $ 114 $ 243 $ 131 $ 94 $ 337 $ 316 $ 21 $ — Property 557 273 30 15 143 94 58 32 3 Payroll 247 130 27 16 17 24 5 3 2 Other 60 39 11 1 — — — — — Total taxes other than income $ 1,783 $ 556 $ 311 $ 163 $ 254 $ 455 $ 379 $ 56 $ 5 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 __________ (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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 506 $ 506 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 302 302 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (715 ) (715 ) — — — — — — — Non-regulatory agreement units (483 ) (483 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (8 ) (8 ) — — — — — — — Regulatory offset to NDT fund-related activities (b) 171 171 — — — — — — — Total decommissioning-related activities (227 ) (227 ) — — — — — — — Investment income 43 32 — 1 1 4 2 1 — Interest income related to uncertain income tax positions 5 1 — — — — — — — AFUDC—Equity 69 — 19 7 18 25 22 2 1 Non-service net periodic benefit cost (47 ) — — — — — — — — Other 45 16 14 — — 14 7 7 1 Other, net $ (112 ) $ (178 ) $ 33 $ 8 $ 19 $ 43 $ 31 $ 10 $ 2 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 NDT funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on NDT 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 NDT 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 ) — — — — — — — Benefit related to uncertain income tax positions (c) 2 — — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Non-service net periodic benefit cost (109 ) — — — — — — — — Other 31 4 10 — — 16 8 7 1 Other, net $ 947 $ 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 NDT funds (a) Regulatory agreement units $ 237 $ 237 $ — $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 126 126 — — — — — — — — Net unrealized gains on NDT 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 NDT 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 Non-service net periodic benefit cost (116 ) — — — — — — — — — Loss on debt extinguishment (3 ) (2 ) — — — — — — — — Other 24 (5 ) 7 1 — 15 8 2 21 (11 ) Other, net $ 297 $ 401 $ (65 ) $ 8 $ 21 $ 36 $ 13 $ 9 $ 44 $ (4 ) __________ (a) Includes investment income and realized gains and losses on sales of investments within the NDT funds. (b) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of net 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. (c) See Note 14 — Income Taxes for additional information on the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position. Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2018 , 2017 and 2016 . For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment $ 3,740 $ 1,748 $ 820 $ 274 $ 335 $ 480 $ 218 $ 131 $ 94 Regulatory assets 555 — 120 27 148 260 167 51 42 Amortization of intangible assets, net 58 49 — — — — — — — Amortization of energy contract assets and liabilities (a) 14 14 — — — — — — — Nuclear fuel (b) 1,115 1,115 — — — — — — — ARO accretion (c) 489 489 — — — — — — — Total depreciation, amortization and accretion $ 5,971 $ 3,415 $ 940 $ 301 $ 483 $ 740 $ 385 $ 182 $ 136 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 __________ (a) Included in Operating revenues or Purchased power and fuel in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 1,421 $ 369 $ 332 $ 125 $ 94 $ 250 $ 123 $ 56 $ 61 Income taxes (net of refunds) 95 746 (153 ) (2 ) 14 (32 ) 41 (6 ) (12 ) Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 583 $ 204 $ 177 $ 18 $ 59 $ 67 $ 15 $ 6 $ 12 Loss (gain) from equity method investments 28 30 — — — (1 ) — — — Provision for uncollectible accounts 159 48 40 33 10 28 11 6 11 Provision for excess and obsolete inventory 24 20 3 — — — — — — Stock-based compensation costs 75 — — — — — — — — Other decommissioning-related activity (a) (2 ) (2 ) — — — — — — — Energy-related options (b) 10 10 — — — — — — — Amortization of regulatory asset related to debt costs 8 — 3 1 — 4 2 1 1 Amortization of rate stabilization deferral 14 — — — — 14 14 — — Amortization of debt fair value adjustment (15 ) (12 ) — — — (3 ) — — — Merger-related commitments (c) — — — — — 5 — 5 — Severance costs 35 9 — — — — — — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Amortization of debt costs 36 14 5 2 1 3 2 — 1 Discrete impacts from EIMA and FEJA (d) 28 — 28 — — — — — — Long-term incentive plan 140 — — — — — — — — Other (19 ) (23 ) (14 ) (3 ) (12 ) 6 (6 ) 7 — Total other non-cash operating activities $ 1,124 $ 298 $ 242 $ 51 $ 58 $ 143 $ 60 $ 24 $ 24 Non-cash investing and financing activities: Change in capital expenditures not paid $ (69 ) $ (199 ) $ 11 $ (12 ) $ 50 $ 93 $ 20 $ 22 $ 46 Change in PPE related to ARO update (107 ) (130 ) 7 — 1 15 12 2 1 Dividends on stock compensation 6 — — — — — — — — Acquisition of land 3 — — — — 3 — — 3 __________ (a) Includes the elimination of decommissioning-related activities 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 5 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 4 — Regulatory Matters for additional information. 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 ) (28 ) (13 ) (7 ) (6 ) Total other non-cash operating activities $ 721 $ 112 $ 164 $ 54 $ 65 $ 58 $ (6 ) $ 9 $ 17 Non-cash investing and financing activities: Change 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 decommissioning-related activities 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 5 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 4 — Regulatory Matters for additional 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 additional information on 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 ) (3 ) (14 ) (6 ) (11 ) (3 ) Total other non-cash operating activities $ 1,333 $ 15 $ 215 $ 65 $ 88 $ 175 $ 114 $ 155 $ 515 $ 46 Non-cash investing and financing activities: Change 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, net of cash (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 5 - Mergers, Acquisitions and Dispositions for additional 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 4 — Regulatory Matters for additional 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 additional information on 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 5 - Mergers, Acquisitions and Dispositions for additional information. The following tables provide a reconciliation of cash, cash equivalents and restricted cash reported within the Registrants' Consolidated Balance Sheets that sum to the total of the same amounts in their Consolidated Statements of Cash Flows. Successor December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,349 $ 750 $ 135 $ 130 $ 7 $ 124 $ 16 $ 23 $ 7 Restricted cash 247 153 29 5 6 43 37 1 4 Restricted cash included in other long-term assets 185 — 166 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,781 $ 903 $ 330 $ 135 $ 13 $ 186 $ 53 $ 24 $ 30 Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 898 $ 416 $ 76 $ 271 $ 17 $ 30 $ 5 $ 2 $ 2 Restricted cash 207 138 5 4 1 42 35 — 6 Restricted cash included in other long-term assets 85 — 63 — — 23 — — 23 Total cash, cash equivalents and restricted cash $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 Successor Predecessor December 31, 2016 December 31, 2016 March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 9 $ 46 $ 101 $ 170 $ 319 Restricted cash 253 158 2 4 24 33 — 9 43 11 Restricted cash included in other long-term assets 26 — — — 3 — — 23 23 18 Total cash, cash equivalents and restricted cash $ 914 $ 448 $ 58 $ 67 $ 50 $ 42 $ 46 $ 133 $ 236 $ 348 Predecessor December 31, 2015 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 6,502 $ 431 $ 67 $ 295 $ 9 $ 26 $ 5 $ 5 $ 3 Restricted cash 205 123 2 3 24 14 2 — 12 Restricted cash included in other long-term assets 5 2 — — 3 18 — — 18 Total cash, cash equivalents and restricted cash $ 6,712 $ 556 $ 69 $ 298 $ 36 $ 58 $ 7 $ 5 $ 33 Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues (a) $ 1,656 $ 965 $ 223 $ 114 $ 168 $ 186 $ 97 $ 59 $ 30 Allowance for uncollectible accounts (b) (319 ) (104 ) (81 ) (61 ) (20 ) (53 ) (21 ) (13 ) (19 ) December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues (a) $ 1,858 $ 1,017 $ 242 $ 162 $ 205 $ 232 $ 133 $ 68 $ 31 Allowance for uncollectible (b) (322 ) (114 ) (73 ) (56 ) (24 ) (55 ) (21 ) (16 ) (18 ) __________ (a) Represents unbilled portion of receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable. The Utility Registrants are required, under separate legislation and regulations in Illinois, Pennsylvania, Maryland, District of Columbia and New Jersey, to purchase certain receivables from alternative retail electric and, as applicable, natural gas suppliers that participate in the utilities' consolidated billing. ComEd, BGE, Pepco and DPL purchase receivables at a discount to recover primarily uncollectible accounts expense from the suppliers. PECO and ACE purchase receivables at face value and recover uncollectible accounts expense, including those from alternative retail electric and natural gas supplies, through base distribution rates and a rate rider, respectively. Exelon and the Utility Registrants do not record unbilled commodity receivables under their POR programs. Purchased billed receivables are recorded on a net basis in Exelon’s and the Utility Registrant's Consolidated Statements of Operations and Comprehensive Income and are classified in Other accounts receivable, net in their Consolidated Balance Sheets. The following tables provide information about the purchased receivables of those companies as of December 31, 2018 and 2017 . December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 313 $ 94 $ 74 $ 61 $ 84 $ 57 $ 8 $ 19 Allowance for uncollectible accounts (a) (34 ) (17 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 279 $ 77 $ 69 $ 58 $ 75 $ 52 $ 7 $ 16 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 __________ (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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate. The following tables provide additional information about Registrants' investments at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 14 $ — $ 6 $ 8 $ — $ — $ — $ — $ — Bloom 180 180 — — — — — — — NET Power 70 70 — — — — — — — Other equity method investments 3 1 — — — — — — — Total equity method investments 267 251 6 8 — — — — — Other investments: Employee benefit trusts and investments (b) 244 49 — 17 5 130 105 — — Equity investments without readily determinable fair values 72 72 — — — — — — — Other available for sale debt security investments 40 40 — — — — — — — Other 2 2 — — — — — — — Total investments $ 625 $ 414 $ 6 $ 25 $ 5 $ 130 $ 105 $ — $ — 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 — — Equity investments without readily determinable fair values 62 62 — — — — — — — Other available for sale debt security investments 37 37 — — — — — — — Total investments $ 640 $ 433 $ 6 $ 25 $ 5 $ 132 $ 102 $ — $ — __________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments in the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) The Registrants’ debt and equity security investments are recorded at fair market value. The following tables provide additional information about liabilities of the Registrants at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 1,191 $ 479 $ 187 $ 49 $ 68 $ 99 $ 29 $ 19 $ 12 Taxes accrued 412 226 71 28 46 74 58 4 5 Interest accrued 334 77 105 33 39 50 25 8 12 Severance accrued 44 26 2 — — 5 — — — Other accrued expenses 131 90 8 3 2 28 14 8 6 Total accrued expenses $ 2,112 $ 898 $ 373 $ 113 $ 155 $ 256 $ 126 $ 39 $ 35 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 100 63 5 2 1 29 17 6 5 Total accrued expenses $ 1,837 $ 1,022 $ 327 $ 114 $ 164 $ 261 $ 137 $ 35 $ 33 __________ (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, 2018
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. Exelon has twelve reportable segments, which include 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” and ComEd, PECO, BGE, PHI's three reportable segments consisting of Pepco, DPL, and ACE. 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. 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 and the United States footprint of MISO, excluding MISO’s Southern Region. • New England represents operations within ISO-NE. • New York represents operations within ISO-NY. • ERCOT represents operations within Electric Reliability Council of Texas. • Other Power Regions : • South represents operations in the FRCC, MISO’s Southern Region, the remaining portions of the SERC not included within MISO or PJM. • West represents operations in the WECC, including California ISO. • 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 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. During the first quarter of 2019, due to a change in economics in our New England region, Generation is changing the way that information is reviewed by the CODM. The New England region will no longer be regularly reviewed as a separate region by the CODM nor will it be presented separately in any external information presented to third parties. Information for the New England region will be reviewed by the CODM as part of Other Power Regions. As a result, beginning in the first quarter of 2019, Generation will disclose five reportable segments consisting of Mid-Atlantic, Midwest, New York, ERCOT and Other Power Regions. Beginning in the first quarter of 2019, Other Power Regions will include: • South represents operations in the FRCC, MISO’s Southern Region, the remaining portions of the SERC not included within MISO or PJM. • West represents operations in the WECC, including California ISO. • Canada represents operations across the entire country of Canada and includes AESO, OIESO and the Canadian portion of MISO. • New England represents operations within ISO-NE. 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, 2018 , 2017 , and 2016 is as follows: Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 17,411 $ — $ — $ — $ — $ — $ (1,256 ) $ 16,155 Competitive businesses natural gas revenues 2,718 — — — — — (8 ) 2,710 Competitive businesses other revenues 308 — — — — — (5 ) 303 Rate-regulated electric revenues — 5,882 2,470 2,428 4,609 — (45 ) 15,344 Rate-regulated natural gas revenues — — 568 741 181 — (20 ) 1,470 Shared service and other revenues — — — — 15 1,948 (1,960 ) 3 Total operating revenues $ 20,437 $ 5,882 $ 3,038 $ 3,169 $ 4,805 $ 1,948 $ (3,294 ) $ 35,985 2017 Competitive businesses electric revenues $ 15,332 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,227 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 593 — — — — — (1 ) 592 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 ) — Total operating revenues $ 18,500 $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 1,831 $ (3,025 ) $ 33,567 Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon 2016 Competitive businesses electric revenues $ 15,400 $ — $ — $ — $ — $ — $ (1,430 ) $ 13,970 Competitive businesses natural gas revenues 2,146 — — — — — — 2,146 Competitive businesses other revenues 211 — — — — — (4 ) 207 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 Total operating revenues $ 17,757 $ 5,254 $ 2,994 $ 3,233 $ 3,643 $ 1,648 $ (3,164 ) $ 31,365 Intersegment revenues (d) : 2018 $ 1,269 $ 27 $ 8 $ 29 $ 15 $ 1,942 $ (3,289 ) $ 1 2017 1,110 15 7 16 50 1,824 (3,020 ) 2 2016 1,428 15 8 21 45 1,647 (3,159 ) 5 Depreciation and amortization: 2018 $ 1,797 $ 940 $ 301 $ 483 $ 740 $ 92 $ — $ 4,353 2017 1,457 850 286 473 675 87 — 3,828 2016 1,879 775 270 423 515 74 — 3,936 Operating expenses (c) : 2018 $ 19,510 $ 4,741 $ 2,452 $ 2,696 $ 4,156 $ 1,929 $ (3,341 ) $ 32,143 2017 18,001 4,214 2,215 2,562 3,911 1,742 (3,026 ) 29,619 2016 16,878 4,056 2,292 2,683 3,549 1,812 (3,164 ) 28,106 Interest expense, net: 2018 $ 432 $ 347 $ 129 $ 106 $ 261 $ 279 $ — $ 1,554 2017 440 361 126 105 245 283 — 1,560 2016 364 461 123 103 195 290 — 1,536 Income (loss) before income taxes: 2018 $ 365 $ 832 $ 466 $ 387 $ 432 $ (249 ) $ (1 ) $ 2,232 2017 1,455 984 538 525 578 (296 ) (2 ) 3,782 2016 857 679 587 468 (58 ) (555 ) (5 ) 1,973 Income taxes: 2018 $ (108 ) $ 168 $ 6 $ 74 $ 35 $ (55 ) $ — $ 120 2017 (1,376 ) 417 104 218 217 294 — (126 ) 2016 282 301 149 174 3 (156 ) — 753 Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Net income (loss): 2018 $ 443 $ 664 $ 460 $ 313 $ 398 $ (193 ) $ (1 ) $ 2,084 2017 2,798 567 434 307 362 (590 ) (2 ) 3,876 2016 550 378 438 294 (61 ) (398 ) (5 ) 1,196 Capital expenditures: 2018 $ 2,242 $ 2,126 $ 849 $ 959 $ 1,375 $ 43 $ — $ 7,594 2017 $ 2,259 $ 2,250 $ 732 $ 882 $ 1,396 $ 65 $ — $ 7,584 2016 $ 3,078 $ 2,734 $ 686 $ 934 $ 1,008 $ 113 $ — $ 8,553 Total assets: 2018 $ 47,556 $ 31,213 $ 10,642 $ 9,716 $ 21,984 $ 8,355 $ (9,800 ) $ 119,666 2017 48,457 29,726 10,170 9,104 21,247 8,618 (10,552 ) 116,770 __________ (a) See Note 25 — Related Party Transactions for additional information on intersegment revenues. (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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes. (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 authoritative 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, 2018 . Successor and Predecessor PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : December 31, 2018 - Successor Rate-regulated electric revenues $ 2,239 $ 1,151 $ 1,236 $ — $ (17 ) $ 4,609 Rate-regulated natural gas revenues — 181 — — — 181 Shared service and other revenues — — — 435 (420 ) 15 Total operating revenues $ 2,239 $ 1,332 $ 1,236 $ 435 $ (437 ) $ 4,805 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 Total operating revenues $ 2,158 $ 1,300 $ 1,186 $ 52 $ (17 ) $ 4,679 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 Total operating revenues $ 1,675 $ 942 $ 989 $ 50 $ (13 ) $ 3,643 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 — — — — — — Total operating revenues $ 511 $ 335 $ 268 $ 43 $ (4 ) $ 1,153 Intersegment revenues: December 31, 2018 - Successor $ 6 $ 8 $ 3 $ 435 $ (437 ) $ 15 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 ) — Depreciation and amortization: December 31, 2018 - Successor $ 385 $ 182 $ 136 $ 37 $ — $ 740 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 Operating expenses: December 31, 2018 - Successor $ 1,919 $ 1,143 $ 1,087 $ 442 $ (435 ) $ 4,156 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 Pepco DPL ACE Other (b) Intersegment PHI Interest expense, net: December 31, 2018 - Successor $ 128 $ 58 $ 64 $ 11 $ — $ 261 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 Income (loss) before income taxes: December 31, 2018 - Successor $ 223 $ 142 $ 87 $ 388 $ (408 ) $ 432 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 Income taxes: December 31, 2018 - Successor $ 13 $ 22 $ 12 $ (10 ) $ (2 ) $ 35 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 Net income (loss): December 31, 2018 - Successor $ 210 $ 120 $ 75 $ (22 ) $ 15 $ 398 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 Capital expenditures: December 31, 2018 - Successor $ 656 $ 364 $ 335 $ 20 $ — $ 1,375 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 Total assets: December 31, 2018 - Successor $ 8,299 $ 4,588 $ 3,699 $ 10,819 $ (5,421 ) $ 21,984 December 31, 2017 - Successor 7,832 4,357 3,445 10,600 (4,987 ) 21,247 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes. (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. The following tables disaggregate the Registrants' revenue recognized from contracts with customers into categories that depict how the nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factors. For Generation, the disaggregation of revenues reflects Generation's two primary products of power sales and natural gas sales, with further disaggregation of power sales provided by geographic region. For the Utility Registrants, the disaggregation of revenues reflects the two primary utility services of rate-regulated electric sales and rate-regulated natural gas sales (where applicable), with further disaggregation of these tariff sales provided by major customer groups. Exelon's disaggregated revenues are consistent with Generation and the Utility Registrants but exclude any intercompany revenues. Competitive Business Revenues (Generation): 2018 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,241 $ 233 $ 5,474 $ 13 $ 5,487 Midwest 4,527 190 4,717 (11 ) 4,706 New England 2,660 185 2,845 (4 ) 2,841 New York 1,723 (36 ) 1,687 — 1,687 ERCOT 572 560 1,132 1 1,133 Other Power Regions 870 686 1,556 (62 ) 1,494 Total Competitive Businesses Electric Revenues 15,593 1,818 17,411 (63 ) 17,348 Competitive Businesses Natural Gas Revenues 1,524 1,194 2,718 62 2,780 Competitive Businesses Other Revenues (c) 510 (202 ) 308 1 309 Total Generation Consolidated Operating Revenues 17,627 2,810 $ 20,437 $ — $ 20,437 2017 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,523 $ (8 ) $ 5,515 $ 25 $ 5,540 Midwest 3,923 283 4,206 (25 ) 4,181 New England 2,064 (54 ) 2,010 (8 ) 2,002 New York 1,605 (38 ) 1,567 (17 ) 1,550 ERCOT 641 317 958 4 962 Other Power Regions 594 482 1,076 (27 ) 1,049 Total Competitive Businesses Electric Revenues 14,350 982 15,332 (48 ) 15,284 Competitive Businesses Natural Gas Revenues 1,658 917 2,575 53 2,628 Competitive Businesses Other Revenues (c) 744 (151 ) 593 (5 ) 588 Total Generation Consolidated Operating Revenues $ 16,752 $ 1,748 $ 18,500 $ — $ 18,500 2016 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 6,182 $ 30 $ 6,212 $ (33 ) $ 6,179 Midwest 4,007 395 4,402 10 4,412 New England 1,953 (175 ) 1,778 (9 ) 1,769 New York 1,198 10 1,208 (42 ) 1,166 ERCOT 810 21 831 6 837 Other Power Regions 670 299 969 (62 ) 907 Total Competitive Businesses Electric Revenues 14,820 580 15,400 (130 ) 15,270 Competitive Businesses Natural Gas Revenues 1,953 193 2,146 135 2,281 Competitive Businesses Other Revenues (c) 756 (545 ) 211 (5 ) 206 Total Generation Consolidated Operating Revenues $ 17,529 $ 228 $ 17,757 $ — $ 17,757 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Includes revenues from derivatives and leases. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $38 million and $52 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 and 2016 , respectively, unrealized mark-to-market losses of $262 million , $131 million , and $500 million in 2018 , 2017 , and 2016 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): 2018 2017 2016 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 3,022 $ 51 $ 3,073 $ 3,105 $ 109 $ 3,214 $ 3,282 $ 35 $ 3,317 Midwest 3,112 23 3,135 2,810 10 2,820 2,969 2 2,971 New England 368 (14 ) 354 538 (24 ) 514 467 (29 ) 438 New York 1,112 10 1,122 1,007 1 1,008 771 (19 ) 752 ERCOT 501 (243 ) 258 575 (243 ) 332 412 (131 ) 281 Other Power Regions 515 (140 ) 375 476 (171 ) 305 483 (147 ) 336 Total Revenues net of purchased power and fuel for Reportable Segments $ 8,630 $ (313 ) $ 8,317 $ 8,511 $ (318 ) $ 8,193 $ 8,384 $ (289 ) $ 8,095 Other (b) 114 313 427 299 318 617 543 289 832 Total Generation Revenues net of purchased power and fuel expense $ 8,744 $ — $ 8,744 $ 8,810 $ — $ 8,810 $ 8,927 $ — $ 8,927 __________ (a) Includes purchases and sales from/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. Includes a $54 million and $57 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 and 2016 , respectively, unrealized mark-to-market losses of $319 million , $175 million , and $41 million in 2018 , 2017 , and 2016 , respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $57 million , $12 million and $60 million for the year ended December 31, 2018 , 2017 , and 2016 and the elimination of intersegment RNF. Electric and Gas Revenue by Customer Class (Utility Registrants): 2018 Successor Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,942 $ 1,566 $ 1,382 $ 2,351 $ 1,021 $ 669 $ 661 Small commercial & industrial 1,487 404 257 488 140 186 162 Large commercial & industrial 538 223 429 1,124 846 100 178 Public authorities & electric railroads 47 28 28 58 32 14 12 Other (a) 867 243 327 593 193 175 227 Total rate-regulated electric revenues (b) 5,881 2,464 2,423 4,614 2,232 1,144 1,240 Rate-regulated natural gas revenues Residential — 395 491 99 — 99 — Small commercial & industrial — 143 77 44 — 44 — Large commercial & industrial — 1 124 8 — 8 — Transportation — 23 — 16 — 16 — Other (c) — 6 63 13 — 13 — Total rate-regulated natural gas revenues (d) — 568 755 180 — 180 — Total rate-regulated revenues from contracts with customers 5,881 3,032 3,178 4,794 2,232 1,324 1,240 Other revenues Revenues from alternative revenue programs (29 ) (7 ) (26 ) — — 4 (4 ) Other rate-regulated electric revenues (e) 30 12 13 10 7 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Total other revenues 1 6 (9 ) 11 7 8 (4 ) Total rate-regulated revenues for reportable segments $ 5,882 $ 3,038 $ 3,169 $ 4,805 $ 2,239 $ 1,332 $ 1,236 2017 Successor Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,715 $ 1,505 $ 1,365 $ 2,246 $ 964 $ 663 $ 619 Small commercial & industrial 1,363 401 254 490 137 187 166 Large commercial & industrial 455 223 427 1,086 794 103 189 Public authorities & electric railroads 44 30 31 60 33 14 13 Other (a) 886 204 299 541 199 163 191 Total rate-regulated electric revenues (b) 5,463 2,363 2,376 4,423 2,127 1,130 1,178 Rate-regulated natural gas revenues Residential — 331 437 90 — 90 — Small commercial & industrial — 131 75 38 — 38 — Large commercial & industrial — 1 119 8 — 8 — Transportation — 23 — 15 — 15 — Other (c) — 8 28 9 — 9 — Total rate-regulated natural gas revenues (d) — 494 659 160 — 160 — Total rate-regulated revenues from contracts with customers 5,463 2,857 3,035 4,583 2,127 1,290 1,178 Other revenues Revenues from alternative revenue programs 43 — 124 40 26 6 8 Other rate-regulated electric revenues (e) 30 12 13 8 5 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Other revenues (f) — — — 47 — — — Total other revenues 73 13 141 96 31 10 8 Total rate-regulated revenues for reportable segments $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 2,158 $ 1,300 $ 1,186 Successor Predecessor 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Revenues from contracts with customers ComEd PECO BGE Pepco DPL ACE PHI PHI Rate-regulated electric revenues Residential $ 2,603 $ 1,631 $ 1,504 $ 1,004 $ 672 $ 664 $ 1,779 $ 561 Small commercial & industrial 1,318 430 276 150 188 183 400 121 Large commercial & industrial 462 234 434 790 99 201 835 255 Public authorities & electric railroads 45 32 35 32 13 13 45 13 Other (a) 820 192 276 190 160 187 400 169 Total rate-regulated electric revenues (b) 5,248 2,519 2,525 2,166 1,132 1,248 3,459 1,119 Rate-regulated natural gas revenues Residential — 309 432 — 86 — 50 36 Small commercial & industrial — 121 66 — 35 — 21 14 Large commercial & industrial — — 114 — 6 — 4 2 Transportation — 24 — — 13 — 10 3 Other (c) — 9 28 — 8 — 7 2 Total rate-regulated natural gas revenues (d) — 463 640 — 148 — 92 57 Total rate-regulated revenues from contracts with customers 5,248 2,982 3,165 2,166 1,280 1,248 3,551 1,176 Other revenues Revenues from alternative revenue programs (24 ) — 53 14 (6 ) 9 43 (26 ) Other rate-regulated electric revenues (e) 30 12 13 6 3 — 6 3 Other rate-regulated natural gas revenues (e) — — 2 — — — — — Other revenues (f) — — — — — — 43 — Total other revenues 6 12 68 20 (3 ) 9 92 (23 ) Total rate-regulated revenues for reportable segments $ 5,254 $ 2,994 $ 3,233 $ 2,186 $ 1,277 $ 1,257 $ 3,643 $ 1,153 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $ 27 million , $7 million , $8 million , $15 million , $6 million , $8 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018 , $15 million , $6 million , $5 million , $3 million , $6 million , $8 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, in 2017 , and $15 million , $7 million , $7 million , $2 million , $5 million , $7 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2016 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of $1 million and $21 million at PECO and BGE, respectively, in 2018 , $1 million and $11 million at PECO and BGE, respectively, in 2017 , and $1 million and $14 million at PECO and BGE, respectively, in 2016 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $47 million and $43 million at PHI in 2017 and 2016 , respectively.

Related Party Transactions (All

Related Party Transactions (All Registrants)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 Operating revenues from affiliates: Generation (a) (2 ) — PECO (a) — 1 1 BGE (a) — 4 4 ACE (a) — — — Other 1 2 5 Total operating revenues from affiliates $ (1 ) $ 7 $ 10 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 14 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II — 10 16 Total interest expense to affiliates, net $ 25 $ 36 $ 41 Earnings (losses) in equity method investments: Qualifying facilities and domestic power projects $ (29 ) $ (33 ) $ (25 ) Other 1 1 1 Total losses in equity method investments $ (28 ) $ (32 ) $ (24 ) December 31, 2018 2017 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 Total payables to affiliates (current) $ 5 $ 5 Long-term debt to financing trusts: ComEd Financing III $ 206 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 390 $ 389 __________ (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 authoritative guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 4 — 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, 2018 2017 2016 Operating revenues from affiliates: ComEd (a) $ 523 $ 121 $ 47 PECO (b) 128 138 290 BGE (c) 260 388 608 Pepco (d) 206 255 295 DPL (e) 120 179 154 ACE (f) 29 29 37 BSC 2 1 2 Other — 4 6 Total operating revenues from affiliates $ 1,268 $ 1,115 $ 1,439 Purchased power and fuel from affiliates: ComEd $ (6 ) $ 13 $ — BGE 20 9 12 Other — (3 ) — Total purchased power and fuel from affiliates $ 14 $ 19 $ 12 Operating and maintenance from affiliates: ComEd (g) $ 7 $ 7 $ 7 PECO (g) 2 1 3 BGE (g) 2 1 1 Pepco 1 — 1 PHISCO 1 1 1 BSC (h) 652 689 650 Other (4 ) (2 ) — Total operating and maintenance from affiliates $ 661 $ 697 $ 663 Interest expense to affiliates, net: Exelon Corporate (i) $ 36 $ 37 $ 39 PCI — 1 — PECO — 1 — Total interest expense to affiliates, net: $ 36 $ 39 $ 39 Earnings (losses) in equity method investments Qualifying facilities and domestic power projects $ (30 ) $ (33 ) $ (25 ) Capitalized costs BSC (h) $ 67 $ 98 $ 98 Cash distributions paid to member $ 1,001 $ 659 $ 922 Contributions from member $ 155 $ 102 $ 142 December 31, 2018 2017 Receivables from affiliates (current): ComEd (a) $ 69 $ 28 PECO (b) 30 26 BGE (c) 24 24 Pepco (d) 28 36 DPL (e) 7 12 ACE (f) 5 6 PHISCO (h) — 1 Other 10 7 Total receivables from affiliates (current) $ 173 $ 140 Intercompany money pool (current): Exelon Corporate $ 100 $ — PCI — 54 Total intercompany money pool (current) $ 100 $ 54 Payables to affiliates (current): Exelon Corporate (i) $ 17 $ 21 BSC (h) 95 74 ComEd 19 12 PECO (b) — 4 Other 8 12 Total payables to affiliates (current) $ 139 $ 123 Other liabilities to affiliates (current): ComEd (a) $ 14 $ — Long-term debt to affiliates (noncurrent): Exelon Corporate (k) $ 898 $ 910 Payables to affiliates (noncurrent): ComEd (j) $ 2,217 $ 2,528 PECO (j) 389 537 Total payables to affiliates (noncurrent) $ 2,606 $ 3,065 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs and ZECs to ComEd. (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. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. (d) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. (e) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. (f) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. (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 for additional information. (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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in 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, 2018 2017 2016 Operating revenues from affiliates Generation $ 9 $ 9 $ 7 BSC 7 6 6 PECO 10 — 1 BGE 1 — 1 Total operating revenues from affiliates $ 27 $ 15 $ 15 Purchased power from affiliates Generation (a) $ 529 $ 108 $ 47 Operating and maintenance from affiliates BSC (b) $ 265 $ 270 $ 225 PECO 1 — 1 BGE 1 — 1 Total operating and maintenance from affiliates $ 267 $ 270 $ 227 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 135 $ 118 $ 112 Cash dividends paid to parent $ 459 $ 422 $ 369 Contributions from parent $ 500 $ 651 $ 315 December 31, 2018 2017 Prepaid voluntary employee beneficiary association trust (c) $ 5 $ 2 Receivables from affiliates (current): Voluntary employee beneficiary association trust $ 1 $ 1 Generation 19 12 Total receivables from affiliates (current) $ 20 $ 13 Receivables from affiliates (noncurrent): Generation (d) $ 2,217 $ 2,528 Payables to affiliates (current): Generation (a) $ 55 $ 28 BSC (b) 56 39 ComEd Financing III 4 4 Exelon Corporate 4 3 Total payables to affiliates (current) $ 119 $ 74 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 and ZECs from Generation. (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) 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, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 2 $ 1 $ 3 BSC 3 5 3 ComEd 1 — 1 BGE 1 1 1 ACE 1 — — Total operating revenues from affiliates $ 8 $ 7 $ 8 Purchased power from affiliates Generation (b) $ 126 $ 135 $ 287 Operating and maintenance from affiliates: BSC (c) $ 146 $ 146 $ 142 Generation 2 2 2 ComEd 7 — 1 BGE 1 1 1 Total operating and maintenance from affiliates $ 156 $ 149 $ 146 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Exelon Corporate 2 — — Generation — (1 ) — Total interest expense to affiliates, net: $ 14 $ 11 $ 12 Capitalized costs BSC (c) $ 64 $ 59 $ 57 Cash dividends paid to parent $ 306 $ 288 $ 277 Contributions from parent $ 89 $ 16 $ 18 December 31, 2018 2017 Prepaid voluntary employee beneficiary association trust (d) $ 1 $ — Receivables from affiliates (noncurrent): Generation (e) $ 389 $ 537 Payables to affiliates (current): Generation (b) $ 30 $ 22 BSC (c) 26 29 Exelon Corporate 2 1 PECO Trust III 1 1 Total payables to affiliates (current) $ 59 $ 53 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. (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, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 22 $ 10 $ 13 BSC 5 5 6 ComEd 1 — 1 PECO 1 1 1 Total operating revenues from affiliates $ 29 $ 16 $ 21 Purchased power from affiliates Generation (b) $ 257 $ 384 $ 604 Operating and maintenance from affiliates: BSC (c) $ 157 $ 152 $ 130 Generation 3 — — ComEd 1 — 1 PECO 1 1 1 Total operating and maintenance from affiliates $ 162 $ 153 $ 132 Interest expense to affiliates, net: BGE Capital Trust II $ — $ 10 $ 16 Capitalized costs BSC (c) $ 79 $ 54 $ 36 Cash dividends paid to parent $ 209 $ 198 $ 179 Contributions from parent $ 109 $ 184 $ 61 December 31, 2018 2017 Receivables from affiliates (current): Other $ 1 $ 1 Payables to affiliates (current): Generation (b) $ 24 $ 24 BSC (c) 38 25 Exelon Corporate 2 1 Other 1 2 Total payables to affiliates (current) $ 65 $ 52 __________ (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. (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, For the Year Ended December 31, March 24, 2016 to December 31, 2018 2017 2016 Operating revenues from affiliates: BSC $ 12 $ 48 $ 44 PHISCO 1 2 — Generation 2 — 1 Total operating revenues from affiliates $ 15 $ 50 $ 45 Purchased power from affiliates Generation $ 355 $ 463 $ 486 Operating and maintenance from affiliates: BSC (a) $ 147 $ 145 $ 86 Other 5 5 3 Total operating and maintenance from affiliates $ 152 $ 150 $ 89 Earnings (losses) in equity method investments: Other $ 1 $ — $ — Capitalized costs: BSC (a) $ 102 $ — $ — PHISCO (a) 79 — — Total capitalized costs $ 181 $ — $ — Cash dividends paid to parent $ 326 $ 311 $ 273 Contributions from parent $ 385 $ 758 $ 1,251 December 31, 2018 2017 Payables to affiliates (current): Generation $ 40 $ 54 BGE — 1 BSC (a) 41 24 Exelon Corporate 6 6 Other 7 5 Total payables to affiliates (current) $ 94 $ 90 __________ (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, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 1 $ — $ 1 BSC 1 — — PHISCO 4 6 4 Total operating revenues from affiliates $ 6 $ 6 $ 5 Purchased power from affiliates Generation (b) $ 206 $ 255 $ 295 Operating and maintenance: PHISCO (c), (e) $ — $ 219 $ 263 PES (d) — 29 39 Total operating and maintenance $ — $ 248 $ 302 Operating and maintenance from affiliates: BSC (c) $ 89 $ 53 $ 31 PHISCO (c), (e) 137 5 4 Total operating and maintenance from affiliates $ 226 $ 58 $ 35 Capitalized costs: BSC (c) $ 40 $ — $ — PHISCO (c) 32 — — Total capitalized costs $ 72 $ — $ — Cash dividends paid to parent $ 169 $ 133 $ 136 Contributions from parent $ 166 $ 161 $ 187 December 31, 2018 2017 Receivables from affiliates (current): DPL $ 1 $ — Payables to affiliates (current): Exelon Corporation $ 1 $ — Generation (b) 28 36 BSC (c) 19 11 PHISCO (c) 14 27 Total payables to affiliates (current) $ 62 $ 74 __________ (a) Pepco provides energy to Generation for Generation’s own use. (b) Pepco procures a portion of its electricity supply requirements from Generation under its MDPSC and DCPSC approved market based SOS commodity programs. (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 performed underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco. (e) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018. DPL The financial statements of DPL include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: BSC $ 1 $ — $ — PHISCO 4 6 5 ComEd 1 — — ACE 1 — — Other 1 2 2 Total operating revenues from affiliates $ 8 $ 8 $ 7 Purchased power from affiliates Generation (a) $ 120 $ 179 $ 154 Operating and maintenance: PHISCO (b), (d) $ — $ 165 $ 194 PES (c) — 9 8 Total operating and maintenance $ — $ 174 $ 202 Operating and maintenance from affiliates: BSC (b) $ 51 $ 31 $ 18 PHISCO (b), (d) 111 — — Other — 1 1 Total operating and maintenance from affiliates $ 162 $ 32 $ 19 Capitalized costs: BSC (b) $ 28 $ — $ — PHISCO (b) 25 — — Total capitalized costs $ 53 $ — $ — Cash dividends paid to parent $ 96 $ 112 $ 54 Contributions from parent $ 150 $ — $ 152 December 31, 2018 2017 Payables to affiliates (current): Exelon Corporate $ 1 $ — Generation (a) 7 12 BSC (b) 11 7 PHISCO (b) 12 27 Pepco 1 — ACE 1 — Total payables to affiliates (current) $ 33 $ 46 __________ (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. (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 performed underground transmission construction services, including services that are treated as capital costs, for DPL. (d) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018. ACE The financial statements of ACE include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: PHISCO $ 2 $ 1 $ 2 Other 1 1 1 Total operating revenues from affiliates $ 3 $ 2 $ 3 Purchased power from affiliates Generation (a) $ 29 $ 29 $ 37 Operating and maintenance: PHISCO (b), (c) $ — $ 135 $ 155 Operating and maintenance from affiliates: BSC (b) $ 42 $ 25 $ 15 PHISCO (b), (c) 98 — — Other 2 3 3 Total operating and maintenance from affiliates $ 142 $ 28 $ 18 Capitalized costs: BSC (b) $ 20 $ — $ — PHISCO (b) 21 — — Total capitalized costs $ 41 $ — $ — Cash dividends paid to parent $ 59 $ 68 $ 63 Contributions from parent $ 67 $ — $ 139 December 31, 2018 2017 Receivable from affiliate (current): DPL $ 1 $ — Payables to affiliates (current): Generation (a) $ 5 $ 6 BSC (b) 8 5 PHISCO (b) 13 18 Other 2 — Total payables to affiliates (current) $ 28 $ 29 __________ (a) ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. (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. (c) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.

Quarterly Data (Unaudited) (All

Quarterly Data (Unaudited) (All Registrants)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Quarterly Data (Unaudited) (All Registrants)	Quarterly Data (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 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 9,693 $ 8,747 $ 1,101 $ 1,308 $ 585 $ 990 June 30 8,076 7,665 942 300 539 95 September 30 9,403 8,768 1,146 1,499 733 823 December 31 8,814 8,384 708 1,288 152 1,880 Net Income Net Income 2018 2017 2018 2017 Quarter ended: March 31 $ 0.61 $ 1.07 $ 0.60 $ 1.06 June 30 0.56 0.10 0.56 0.10 September 30 0.76 0.86 0.76 0.85 December 31 0.16 1.95 0.16 1.94 Generation The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 5,512 $ 4,878 $ 347 $ 373 $ 136 $ 418 June 30 4,579 4,216 282 (427 ) 178 (235 ) September 30 5,278 4,750 311 497 234 304 December 31 5,069 4,657 35 504 (178 ) 2,224 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 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 1,512 $ 1,298 $ 292 $ 314 $ 165 $ 141 June 30 1,398 1,357 288 319 164 118 September 30 1,598 1,571 323 404 193 189 December 31 1,373 1,309 242 286 141 120 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 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 866 $ 796 $ 142 $ 192 $ 113 $ 127 June 30 653 630 127 137 96 88 September 30 757 715 154 169 126 112 December 31 765 729 165 157 124 107 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 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 977 $ 951 $ 177 $ 228 $ 128 $ 125 June 30 662 674 85 98 51 45 September 30 731 738 103 124 63 62 December 31 799 813 109 163 71 76 PHI The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Membership Interest 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 1,251 $ 1,175 $ 126 $ 180 $ 65 $ 140 June 30 1,076 1,074 153 148 84 66 September 30 1,361 1,310 245 285 187 153 December 31 1,117 1,121 126 159 62 4 Pepco The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 557 $ 530 $ 56 $ 79 $ 31 $ 58 June 30 523 514 85 84 54 43 September 30 628 604 112 149 89 87 December 31 531 510 65 87 36 17 DPL The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 384 $ 362 $ 49 $ 78 $ 31 $ 57 June 30 289 282 42 41 26 19 September 30 328 327 51 59 33 31 December 31 331 330 48 52 30 14 ACE The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 310 $ 275 $ 23 $ 25 $ 7 $ 28 June 30 265 270 25 25 8 8 September 30 406 370 84 79 61 41 December 31 254 271 14 28 (1 ) —

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Exelon and Generation)	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events (Exelon and Generation) Generation’s Antelope Valley, a 242 MW solar facility in Lancaster, CA, sells all of its output to Pacific Gas and Electric Company (PG&E) through a PPA. As of December 31, 2018, Generation had approximately $750 million and $510 million of net long-lived assets and nonrecourse debt outstanding, respectively, related to Antelope Valley. The nonrecourse debt is guaranteed by the DOE Loan Programs Office. Neither the guarantor nor the lender have recourse against Exelon or Generation in the event of default. On January 29, 2019, PG&E filed for protection under Chapter 11 of the U.S. Bankruptcy Code. PG&E’s bankruptcy creates an event of default for Antelope Valley’s nonrecourse debt. As such, Antelope Valley is currently in discussions with the DOE Loan Programs Office, and the debt has not yet been accelerated. Given that the event of default did not occur until January 2019, the debt continued to be classified as non-current on Exelon’s and Generation’s Consolidated Balance Sheets as of December 31, 2018, and may be reclassified to current in 2019. Generation has also assessed and determined that Antelope Valley’s long-lived assets are not impaired as of December 31, 2018. Changes in assumptions such as the likelihood of the PPA being rejected as part of the bankruptcy proceedings could potentially result in future impairments of Antelope Valley. The impairment loss could be substantially all of the net long-lived assets if Antelope Valley was valued without the PPA. Generation is monitoring the bankruptcy proceedings for any changes in circumstances that would indicate the carrying amount of the net long-lived assets of Antelope Valley may not be recoverable. Antelope Valley is a wholly owned indirect subsidiary of EGR IV, which had approximately $1,990 million and $830 million of additional net long-lived assets and nonrecourse debt outstanding, respectively, as of December 31, 2018. EGR IV is a wholly owned indirect subsidiary of Exelon and Generation and includes Generation's interest in EGRP and other projects with non-controlling interests. EGR IV is currently not in default, however, an acceleration of Antelope Valley’s debt could impact EGR IV. The lenders do not have recourse against Exelon or Generation in the event of default by EGR IV. See Note 2 - Variable Interest Entities for additional details on EGRP and Note 13 — Debt and Credit Agreements for additional details on Generation's nonrecourse project financings .

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Parent (Exelon Corporate)	12 Months Ended
	Dec. 31, 2018
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) 2018 2017 2016 Operating expenses Operating and maintenance $ (5 ) $ 10 $ 221 Operating and maintenance from affiliates 9 25 51 Other 4 4 4 Total operating expenses 8 39 276 Operating loss (8 ) (39 ) (276 ) Other income and (deductions) Interest expense, net (312 ) (315 ) (312 ) Equity in earnings of investments 2,188 4,414 1,508 Interest income from affiliates, net 42 40 39 Other, net 3 1 7 Total other income 1,921 4,140 1,242 Income before income taxes 1,913 4,101 966 Income taxes (97 ) 315 (155 ) Net income $ 2,010 $ 3,786 $ 1,121 Other comprehensive income (loss) Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic costs $ (66 ) $ (56 ) $ (48 ) Actuarial loss reclassified to periodic cost 247 197 184 Pension and non-pension postretirement benefit plan valuation adjustment (143 ) 10 (181 ) Unrealized gain on cash flow hedges 12 3 2 Unrealized gain on marketable securities — 6 1 Unrealized gain (loss) on equity investments 1 6 (4 ) Unrealized (loss) gain on foreign currency translation (10 ) 7 10 Other comprehensive income (loss) 41 173 (36 ) Comprehensive income $ 2,051 $ 3,959 $ 1,085 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) 2018 2017 2016 Net cash flows provided by operating activities $ 2,581 $ 1,921 $ 1,029 Cash flows from investing activities Changes in Exelon intercompany money pool 1 (129 ) 1,390 Investment in affiliates (1,236 ) (1,717 ) (1,757 ) Acquisition of business — — (6,962 ) Other investing activities — (5 ) 5 Net cash flows used in investing activities (1,235 ) (1,851 ) (7,324 ) Cash flows from financing activities Issuance of long-term debt — — 1,800 Proceeds from short-term borrowings with maturities greater than 90 days — 500 — Retirement of long-term debt — (569 ) (46 ) Common stock issued from treasury stock — 1,150 — Dividends paid on common stock (1,332 ) (1,236 ) (1,166 ) Proceeds from employee stock plans 105 150 55 Other financing activities (4 ) (9 ) (20 ) Net cash flows (used in) provided by financing activities (1,231 ) (14 ) 623 Increase (Decrease) in cash, cash equivalents and restricted cash 115 56 (5,672 ) Cash, cash equivalents and restricted cash at beginning of period 74 18 5,690 Cash, cash equivalents and restricted cash at end of period $ 189 $ 74 $ 18 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2018 2017 ASSETS Current assets Cash and cash equivalents $ 189 $ 74 Accounts receivable, net Other accounts receivable 48 431 Accounts receivable from affiliates 44 33 Notes receivable from affiliates 216 217 Regulatory assets 182 284 Other 4 4 Total current assets 683 1,043 Property, plant and equipment, net 48 50 Deferred debits and other assets Regulatory assets 3,742 3,697 Investments in affiliates 40,448 39,311 Deferred income taxes 1,455 1,431 Notes receivable from affiliates 898 910 Other 235 234 Total deferred debits and other assets 46,778 45,583 Total assets $ 47,509 $ 46,676 Exelon Corporation and Subsidiary Companies Schedule I – Condensed Financial Information of Parent (Exelon Corporate) Condensed Balance Sheets December 31, (In millions) 2018 2017 LIABILITIES AND SHAREHOLDERS’ EQUITY Current liabilities Short-term borrowings $ 500 $ 500 Accounts payable 1 2 Accrued expenses 184 99 Payables to affiliates 360 360 Regulatory liabilities 15 16 Pension obligations 63 65 Other 14 46 Total current liabilities 1,137 1,088 Long-term debt 7,147 7,161 Deferred credits and other liabilities Regulatory liabilities 32 15 Pension obligations 7,795 7,792 Non-pension postretirement benefit obligations 199 322 Deferred income taxes 233 220 Other 202 180 Total deferred credits and other liabilities 8,461 8,529 Total liabilities 16,745 16,778 Commitments and contingencies Shareholders’ equity Common stock (No par value, 2,000 shares authorized, 968 shares and 963 shares outstanding at December 31, 2018 and 2017, respectively) 19,116 18,966 Treasury stock, at cost (2 shares at December 31, 2018 and 2017) (123 ) (123 ) Retained earnings 14,766 14,081 Accumulated other comprehensive loss, net (2,995 ) (3,026 ) Total shareholders’ equity 30,764 29,898 Total liabilities and shareholders’ equity $ 47,509 $ 46,676 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 5 — 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, 2018 and December 31, 2017 . Short-Term Loan Agreements On March 23, 2017, Exelon Corporate entered into a $500 million term loan agreement which expired on March 22, 2018. The loan agreement was renewed on March 22, 2018 and will expire on March 21, 2019. 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 its syndicated revolving credit facility with aggregate bank commitments of $600 million through May 26, 2021. On May 26, 2018, Exelon Corporate had its maturity date extended to May 26, 2023. As of December 31, 2018 , Exelon Corporation had available capacity under those commitments of $591 million . See Note 13 — Debt and Credit Agreements of the Combined Notes to Consolidated Financial Statements for additional 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, 2018 and December 31, 2017 : Maturity Date December 31, Rates 2018 2017 Long-term debt Junior subordinated notes 3.50 % 2022 $ 1,150 $ 1,150 Senior unsecured notes (a) 2.45 % 7.60 % 2020 - 2046 5,889 5,889 Total long-term debt 7,039 7,039 Unamortized debt discount and premium, net (7 ) (8 ) Unamortized debt issuance costs (47 ) (49 ) Fair value adjustment of consolidated subsidiary 162 179 Long-term debt $ 7,147 $ 7,161 __________ (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 2019 , 2020 , 2021 , 2022 , 2023 and thereafter are as follows: 2019 $ — 2020 1,450 2021 300 2022 1,150 2023 — Remaining years 4,139 Total long-term debt $ 7,039 Commitments and Contingencies See Note 22 — 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) 2018 2017 2016 Operating and maintenance from affiliates: BSC (a) $ 11 $ 23 $ 51 Other (2 ) 2 — Total operating and maintenance from affiliates: $ 9 $ 25 $ 51 Interest income from affiliates, net: Generation $ 36 $ 37 $ 39 BSC 4 3 — Exelon Energy Delivery Company, LLC (b) $ 2 $ — $ — Total interest income from affiliates, net: $ 42 $ 40 $ 39 Equity in earnings (losses) of investments: Exelon Energy Delivery Company, LLC (b) $ 1,835 $ 1,670 $ 1,041 PCI (17 ) 1 6 BSC — 1 1 UII, LLC — 41 (9 ) Exelon Transmission Company, LLC 1 (10 ) (13 ) Exelon Enterprise — 1 (1 ) Generation 369 2,710 483 Total equity in earnings of investments: $ 2,188 $ 4,414 $ 1,508 Cash contributions received from affiliates $ 2,302 $ 1,879 $ 1,912 December 31, (in millions) 2018 2017 Accounts receivable from affiliates (current): BSC (a) $ 13 $ 1 Generation 17 21 ComEd 4 3 PECO 2 1 BGE 2 1 PHISCO 6 6 Total accounts receivable from affiliates (current): $ 44 $ 33 Notes receivable from affiliates (current): BSC (a) $ 116 $ 217 Generation (c) 100 — Total notes receivable from affiliates (current): $ 216 $ 217 Investments in affiliates: BSC (a) $ 197 $ 196 Exelon Energy Delivery Company, LLC (b) 26,702 25,082 PCI 61 78 UII, LLC 268 268 Exelon Transmission Company, LLC 1 1 Voluntary Employee Beneficiary Association trust (1 ) (4 ) Exelon Enterprises 22 22 Generation 13,204 13,674 Other (6 ) (6 ) Total investments in affiliates: $ 40,448 $ 39,311 Notes receivable from affiliates (non-current): Generation (c) $ 898 $ 910 Accounts payable to affiliates (current): UII, LLC $ 360 $ 360 __________ (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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in Exelon’s Consolidated Balance Sheets.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
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, 2018 Allowance for uncollectible accounts (a) $ 322 $ 159 $ 35 (c) $ 197 (e) $ 319 Deferred tax valuation allowance 37 — 5 7 35 Reserve for obsolete materials 174 25 (31 ) (d) 12 156 For the year ended December 31, 2017 Allowance for uncollectible accounts (a) $ 334 $ 126 $ 27 (c) $ 165 (e) $ 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 (e) $ 334 Deferred tax valuation allowance 13 — 10 (b) 3 20 Reserve for obsolete materials 105 12 1 (b) 5 113 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million , $15 million , and $23 million for the years ended December 31, 2018 , 2017 and 2016 , 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) Primarily reflects the reclassification of assets as held for sale. (e) Write-off of individual accounts receivable. Exelon Generation Company, LLC and Subsidiary Companies (2) Generation (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 114 $ 44 $ 4 $ 58 $ 104 Deferred tax valuation allowance 23 — 3 — 26 Reserve for obsolete materials 166 20 (32 ) (a) 9 145 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 __________ (a) Primarily reflects the reclassification of assets as held for sale. Commonwealth Edison Company and Subsidiary Companies (3) ComEd (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Shareholders’ Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 73 $ 44 $ 23 (a) $ 59 (b) $ 81 Reserve for obsolete materials 5 3 1 3 6 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 __________ (a) Primarily charges for late payments and non-service receivables. (b) Write-off of individual accounts receivable. PECO Energy Company and Subsidiary Companies (4) PECO (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts (a) $ 56 $ 33 $ 3 (b) $ 31 (c) $ 61 Reserve for obsolete materials 2 — — — 2 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 __________ (a) Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million , $15 million , and $23 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. (b) Primarily charges for late payments. (c) Write-off of individual accounts receivable. Baltimore Gas and Electric Company and Subsidiary Companies (5) BGE (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 24 $ 10 $ (2 ) $ 12 (a) $ 20 Deferred tax valuation allowance 1 — — — 1 Reserve for obsolete materials — 1 — — 1 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 — — — — — __________ (a) Write-off of individual accounts receivable. Pepco Holdings LLC and Subsidiary Companies (6) PHI (i) Successor Company Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income (Loss) for the Years Ended December 31, 2018 and 2017 and for the Period March 24, 2016 to December 31, 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018 and 2017 and for the Period March 24, 2016 to December 31, 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Equity for the Years Ended December 31, 2018 and 2017 and for the Period March 24, 2016 to December 31, 2016 Notes to Consolidated Financial Statements (ii) Predecessor Company Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 13, 2017 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income for the Period January 1, 2016 to March 23, 2016 Consolidated Statements of Cash Flows for the Period January 1, 2016 to March 23, 2016 Consolidated Statements of Changes in Equity for the Period January 1, 2016 to March 23, 2016 Notes to Consolidated Financial Statements (iii) Successor Financial Statement Schedule: Schedule II – Valuation and Qualifying Accounts - For the Years Ended December 31, 2018 and 2017 and the Period March 24, 2016 to December 31, 2016 (iv) Predecessor Financial Statement Schedule: Schedule II – Valuation and Qualifying Accounts - For the Period January 1, 2016 to March 23, 2016 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, 2018 (Successor) Allowance for uncollectible accounts $ 55 $ 28 $ 7 (a) $ 37 (b) $ 53 Deferred tax valuation allowance 13 — 2 7 8 Reserve for obsolete materials 2 — — — 2 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 — — — — — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Potomac Electric Power Company (7) Pepco (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income for the Years Ended December 31, 2018, 2017 and 2016 Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Balance Sheets at December 31, 2018 and 2017 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 21 $ 11 $ 3 (a) $ 14 (b) $ 21 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 29 $ 8 $ 2 (a) $ 18 (b) $ 21 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 Reserve for obsolete materials — 3 — 2 1 __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Delmarva Power & Light Company (8) DPL (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Statements of Operations and Comprehensive Income (Loss) for the Years Ended December 31, 2018, 2017 and 2016 Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Balance Sheets at December 31, 2018 and 2017 Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 16 $ 6 $ 2 (a) $ 11 (b) $ 13 Reserve for obsolete materials — — — — — For the year ended December 31, 2017 Allowance for uncollectible accounts $ 24 $ 3 $ 2 (a) $ 13 (b) $ 16 Reserve for obsolete materials — 1 — 1 — For the year ended December 31, 2016 Allowance for uncollectible accounts $ 17 $ 23 $ 2 (a) $ 18 (b) $ 24 Reserve for obsolete materials — 1 — 1 — __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable. Atlantic City Electric Company and Subsidiary Company (9) ACE (i) Financial Statements (Item 8): Report of Independent Registered Public Accounting Firm dated February 8, 2019 of PricewaterhouseCoopers LLP Consolidated Statements of Operations and Comprehensive Income (Loss) for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Statements of Cash Flows for the Years Ended December 31, 2018, 2017 and 2016 Consolidated Balance Sheets at December 31, 2018 and 2017 Consolidated Statements of Changes in Shareholder's Equity for the Years Ended December 31, 2018, 2017 and 2016 Notes to Consolidated Financial Statements (ii) Financial Statement Schedule: Schedule II—Valuation and Qualifying Accounts for the Years Ended December 31, 2018, 2017 and 2016 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, 2018 Allowance for uncollectible accounts $ 18 $ 11 $ 2 (a) $ 12 (b) $ 19 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2017 Allowance for uncollectible accounts $ 27 $ 8 $ 2 (a) $ 19 (b) $ 18 Reserve for obsolete materials 1 — — — 1 For the year ended December 31, 2016 Allowance for uncollectible accounts $ 17 $ 32 $ 2 (a) $ 24 (b) $ 27 Reserve for obsolete materials — 1 — — 1 __________ (a) Primarily charges for late payments. (b) Write-off of individual accounts receivable.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Description of Business (All Registrants)	Description of Business (All Registrants) Exelon is a utility services holding company engaged in the generation, delivery and marketing of energy through Generation and the energy distribution and transmission businesses through ComEd, PECO, BGE, Pepco, DPL and ACE. On March 23, 2016 , Exelon completed the merger with PHI, which became 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. See Note 5 — Mergers, Acquisitions and Dispositions for additional 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 merger with 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 it has pushed-down to the consolidated financial statements of PHI such that the assets and liabilities of PHI are 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 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. PHI also has a business services subsidiary, PHISCO, which provides a variety of support services at cost, including legal, accounting, engineering, customer operations, distribution and transmission planning, asset management, system operations, and power procurement, to PHI operating companies. The costs of BSC and PHISCO are directly charged or allocated to the applicable subsidiaries. The results of Exelon’s corporate operations are presented as “Other” within the consolidated financial statements and include intercompany eliminations unless otherwise disclosed. Exelon owns 100% of Generation, PECO, BGE and PHI and more than 99% of ComEd. PHI owns 100% of Pepco, DPL and ACE. Generation owns 100% of its significant consolidated subsidiaries, either directly or indirectly, except for certain consolidated VIEs, including CENG and EGRP, 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 additional information 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. Where the Registrants do not have a controlling financial interest in an entity, proportionate consolidation, equity method accounting or accounting for investments in equity securities without readily determinable fair value 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 and PECO. 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 accounting for investments in equity securities without readily determinable fair values if they lack significant influence, which generally results when they hold less than 20% of the common stock of an entity. Under accounting for investments in equity securities without readily determinable fair values, the Registrants report their investments at cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. 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)	Prior Period Adjustments and Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Incom e, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. See New Accounting Standards below for additional information.
Accounting for the Effects of Regulation (Exelon, ComEd, PECO and BGE)	Accounting for the Effects of Regulation (Exelon and the Utility Registrants) For their regulated electric and gas operations, Exelon and the Utility Registrants reflect the effects of cost-based rate regulation in their financial statements, which is required 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's regulatory assets and liabilities as of the balance sheet date are probable of being recovered or settled in future rates. 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 financial statements. See Note 4 — Regulatory Matters for additional information. With the exception of income tax-related regulatory assets and liabilities, Exelon and the Utility 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 in Exelon's and the Utility Registrants’ Consolidated Balance Sheets to align with the classification of the related deferred income tax balances. Exelon and the Utility 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. The Registrants’ operating revenues generally consist of revenues from contracts with customers involving the sale and delivery of energy commodities and related products and services, utility revenues from alternative revenue programs (ARP), and realized and unrealized revenues recognized under mark-to-market energy commodity derivative contracts. The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers in an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and natural gas tariff sales, distribution and transmission services. 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 ARP revenue for its best estimate of the electric distribution, energy efficiency, and transmission revenue impacts resulting from future changes in rates that ComEd believes are probable of approval by the ICC and FERC in accordance with its formula rate mechanisms. BGE, Pepco and DPL record ARP revenue for their best estimate of the electric and natural gas distribution revenue impacts resulting from future changes in rates that they believe are probable of approval by the MDPSC and/or DCPSC in accordance with their revenue decoupling mechanisms. PECO, BGE, Pepco, DPL and ACE record ARP revenue for their best estimate of the transmission revenue impacts resulting from future changes in rates that they believe are probable of approval by FERC in accordance with their formula rate mechanisms. See Note 4 — Regulatory Matters and Note 23 — Supplemental Financial Information for additional information. 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. 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 in its Consolidated Balance Sheets. See Note 4 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information.
Revenue, Transaction Price Measurement, Tax Exclusion [Policy Text Block]	Taxes Directly Imposed on Revenue-Producing Transactions. 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. Se e Note 23 — 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.
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 in the Registrants’ Consolidated Balance Sheets and are recognized in book income over the life of the related property. 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 in their Consolidated Statements of Operations and Comprehensive Income. 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 additional information.
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, 2018 and 2017 , the Registrants' restricted cash and cash equivalents primarily represented the following items: Registrant Description Exelon Payment of medical, dental, vision and long-term disability benefits, in addition to the items listed for Generation and the Utility Registrants. Generation Project-specific nonrecourse financing structures for debt service and financing of operations of the underlying entities. ComEd Collateral held from suppliers associated with energy and REC procurement contracts, any over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site. PECO Proceeds from the sales of assets that were subject to PECO’s mortgage indenture. BGE Proceeds from the loan program for the completion of certain energy efficiency measures and collateral held from energy suppliers. PHI Payment of merger commitments, collateral held from its energy suppliers associated with procurement contracts and repayment of transition bonds. Pepco Payment of merger commitments and collateral held from energy suppliers. DPL Collateral held from energy suppliers. ACE Repayment of transition bonds and collateral held from energy suppliers. Restricted cash and cash equivalents not available to satisfy current liabilities are classified as noncurrent assets. As of December 31, 2018 and 2017 , the Registrants' noncurrent restricted cash and cash equivalents primarily represented ComEd’s over-recovered RPS costs and alternative compliance payments received from RES pursuant to FEJA and costs for the remediation of an MGP site, and ACE’s repayment of transition bonds.
Allowance for Uncollectible Accounts (All Registrants)	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. Utility Registrants estimate the allowance by applying loss rates developed specifically for each company to the outstanding receivable balance by customer risk segment. Utility Registrants' customer accounts are written off consistent with approved regulatory requirements.
Variable Interest Entities (All Registrants)	Variable Interest Entities (All Registrants) Exelon accounts for its investments in and arrangements with VIEs based on 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, • 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.
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, materials and supplies, and emissions allowances are generally included in inventory when purchased. Fossil fuel and emissions allowances are expensed to purchased power and fuel expense when used or sold. Materials and supplies generally includes transmission, distribution and generating plant materials and are expensed to operating and maintenance or capitalized to property, plant and equipment, as appropriate, when installed or used.
Marketable Securities (All Registrants)	Debt and Equity Security Investments (Exelon and Generation ) Debt Security Investments. Debt securities are reported at fair value and classified as available-for-sale securities. Unrealized gains and losses, net of tax, are reported in OCI. Equity Security Investments without Readily Determinable Fair Values. Exelon has certain equity securities without readily determinable fair values. Exelon has elected to use the practicability exception to measure these investments, defined as cost adjusted for changes from observable transactions for identical or similar investments of the same issuer, less impairment. Changes in measurement are reported in earnings. Equity Security Investments with Readily Determinable Fair Values. Equity securities held in the NDT funds are classified as equity securities with readily determinable fair values. 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. Exelon's and Generation's NDT funds are classified as current or noncurrent assets, depending on the timing of the decommissioning activities and income taxes on trust earnings.
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 the Utility Registrants. 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, net. 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. Capitalized Software. Certain costs, such as design, coding, and testing 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. Capitalized Interest and AFUDC. 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. AFUDC 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 an allowance 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.
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. Any potential future SNF disposal fees will be expensed through fuel expense. Additionally, 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.
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.
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 Registrants are based on a combination of depreciation studies, historical retirements, site licenses and management estimates of operating costs and expected future energy market conditions. See Note 8 — Early Plant Retirements for additional information on the impacts of expected and potential early plant retirements. See Note 6 — Property, Plant and Equipment for additional 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 Utility Registrants’ Consolidated Statements of Operations and Comprehensive Income. Amortization of ComEd’s electric distribution and energy efficiency formula rate regulatory assets and the Utility Registrants' transmission formula rate regulatory assets is recorded to Operating revenues. Amortization of income tax related regulatory assets and liabilities is 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.
Asset Retirement Obligations (All Registrants)	Asset Retirement Obligations (All Registrants) Generation estimates and recognizes a liability for its legal obligation to perform asset retirement activities even though the timing and/or methods of settlement may be conditional on future events. Generation generally updates its nuclear decommissioning ARO annually, unless circumstances warrant more frequent updates, based on its annual evaluation of cost escalation factors and probabilities assigned to the multiple outcome scenarios within its probability-weighted discounted cash flow models. Generation’s multiple outcome scenarios are generally based on decommissioning cost studies which are updated, on a rotational basis, for each of Generation’s nuclear units at least every five years, unless circumstances warrant more frequent updates. 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.
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.
Long-lived Assets (All Registrants)	Long-Lived Assets (All Registrants). 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.
Goodwill (All Registrants)	Goodwill (Exelon, ComEd and PHI). 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 on 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.
Equity Method Investments (All Registrants)	Equity Method Investments (Exelon and Generation). 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.
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. For derivatives intended to serve as economic hedges, changes in fair value are recognized in earnings each period. Amounts classified in earnings are included in Operating revenue, Purchased power and fuel, Interest expense or Other, net in the Consolidated Statements of Operations and Comprehensive Income based on the activity the transaction is economically hedging. While the majority of the derivatives serve as economic hedges, there are also derivatives entered into for proprietary trading purposes, subject to Exelon’s Risk Management Policy, and changes in the fair value of those derivatives are recorded in revenue in the Consolidated Statements of Operations and Comprehensive Income. At the Utility Registrants, 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. 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. On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. See Note 4 — Regulatory Matters and Note 12 — Derivative Financial Instruments for additional information. 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.
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 assumptions, and accounting elections. 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.
Investment, Policy [Policy Text Block]	Debt Security Investments (Exelon and Generation). Declines in the fair value of debt security investments below the cost basis are reviewed to determine if such decline is other-than-temporary. If the decline is determined to be other-than-temporary, the amount of the impairment loss is included in earnings. Equity Security Investments (Exelon and Generation). Equity investments with readily determinable fair values are measured and recorded at fair value with any changes in fair value recorded through earnings. Investments in equity securities without readily determinable fair values are qualitatively assessed for impairment each reporting period. If it is determined that the equity security is impaired on the basis of the qualitative assessment, an impairment loss will be recognized in earnings to the amount by which the security’s carrying amount exceeds its fair value.
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	Prior Period Adjustments and Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Incom e, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. See New Accounting Standards below for additional information.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Standards Adopted in 2018: In 2018, the Registrants adopted the following new authoritative accounting guidance issued by the FASB. Defined Benefit Plan Disclosures (Issued August 2018). Eliminates existing disclosure requirements related to amounts in Accumulated other comprehensive income expected to be recognized in Net periodic benefit cost over the next year and the effects of a one-percentage-point change in the assumed health care cost trend rates. In addition, new disclosures were added such as the weighted-average interest crediting rates for cash balance plans and an explanation for the reasons for significant gains and losses related to changes in the benefit obligation. The standard is effective January 1, 2021, with early adoption permitted, and must be applied retrospectively. Exelon early adopted this standard in the fourth quarter of 2018. See Note 16 — Retirement Benefits for additional information. Fair Value Measurement Disclosures (Issued August 2018). Updates the disclosure requirements for fair value measurements to improve the usefulness of information for financial statement users. The guidance removes the requirements to disclose (1) the amount of and reasons for transfers between Level 1 and Level 2, (2) the policy for timing of transfers between levels, and (3) the valuation processes for Level 3 fair value measurements and adds a requirement to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. The standard is effective January 1, 2020, with early adoption permitted. The amendments to remove disclosures must be applied retrospectively and can be early adopted, while the amendments to add disclosures must be applied prospectively and adoption can be delayed until the effective date. The Registrants early adopted, in the fourth quarter of 2018, the amendments to remove disclosures and will adopt the amendments to add disclosures in the first quarter of 2020. The impact of the new disclosures is not expected to be material to the Registrants’ consolidated financial statements. See Note 11 — Fair Value of Financial Assets and Liabilities for additional information. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income (Issued February 2018). Provides an election for a reclassification from AOCI to Retained earnings to eliminate the stranded tax effects resulting from the TCJA. This standard is effective January 1, 2019, with early adoption permitted, and may be applied either in the period of adoption or retrospective to each period in which the effects of the TCJA were recognized. Exelon early adopted this standard and elected to apply the guidance retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million in its Consolidated Balance Sheet and Consolidated Statement of Changes in Shareholders' Equity related to deferred income taxes associated with Exelon’s pension and OPEB obligations. There was no impact for Generation or the Utility Registrants. Exelon's accounting policy is to release the stranded tax effects from AOCI related to its pension and OPEB plans under a portfolio (or aggregate) approach as an entire pension or OPEB plan is liquidated or terminated. See Note 21 — Changes in Accumulated Other Comprehensive Income for additional information. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (Issued March 2017). Changes the accounting and presentation of pension and OPEB costs at the plan sponsor (i.e., Exelon) level. The guidance requires plan sponsors to report the service cost and other non-service cost components of net periodic pension cost and net periodic OPEB cost (together, net benefit cost) separately. Under the new guidance, service cost is presented as part of income from operations and the other non-service cost components are classified outside of income from operations in the Consolidated Statements of Operations and Comprehensive Income. Additionally, service cost is the only component eligible for capitalization on a prospective basis beginning on January 1, 2018. Under prior GAAP, the total amount of net benefit cost was recorded as part of income from operations and all components were eligible for capitalization. Exelon applied the presentation of the service component and the other non-service cost components of net benefit costs retrospectively and, accordingly, have recasted those amounts, which were not material, in its Consolidated Statement of Operations and Comprehensive Income in prior periods presented. Exelon elected the practical expedient that permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan note for the comparative periods as the estimation basis for applying the retrospective presentation requirements. In Exelon’s consolidated financial statements, non-service cost components of pension and OPEB cost capitalizable under a regulatory framework were prospectively reported as regulatory assets (previously, they were capitalizable under pension and OPEB accounting guidance and reported as PP&E). These regulatory assets are amortized outside of operating income. See Note 16 — Retirement Benefits for additional information. Generation, ComEd, PECO, BGE, BSC, PHI, Pepco, DPL, ACE and PHISCO participate in Exelon’s single employer pension and OPEB plans and apply multi-employer accounting. Multi-employer accounting was not impacted by this standard; therefore, Exelon's subsidiary financial statements did not change upon its adoption. Statement of Cash Flows: Classification of Restricted Cash (Issued November 2016). The standard states that amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows (instead of being presented as cash flow activities). The Registrants applied the new guidance using the full retrospective method and, accordingly, have recasted the presentation of restricted cash in their Consolidated Statements of Cash Flows in the prior periods presented. See Note 23 — Supplemental Financial Information for additional information. Recognition and Measurement of Financial Assets and Financial Liabilities (Issued January 2016). Eliminates the available-for-sale and cost method 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 and, for equity investments without a readily determinable fair value, provides a measurement alternative of cost less impairment plus or minus adjustments for observable price changes in identical or similar assets. In addition, equity investments 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 net income immediately in the period in which it is identified. The guidance does not impact the classification or measurement of investments in debt securities. The guidance also amends several disclosure requirements, including requiring i) financial assets and financial liabilities to be presented separately in the balance sheet or note, grouped by measurement category and form, ii) disclosure of the methods and significant assumptions used to estimate fair value or a description of the changes in the methods and assumptions used to estimate fair value, and iii) for financial assets and liabilities measured at amortized cost, disclosure of the fair value of the amount that would be received to sell the asset or paid to transfer the liability. The guidance was applied using a modified retrospective transition approach with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of adoption. The Registrants recorded an insignificant adjustment to opening retained earnings as of January 1, 2018 related to unrealized gains/losses on available for sale equity securities. See Note 21 — Changes in Accumulated Other Comprehensive Income for additional information. Revenue from Contracts with Customers (Issued May 2014 and subsequently amended to address implementation questions). Changes the criteria for recognizing revenue from a contract with a customer. The new standard replaces existing guidance on revenue recognition, including most industry specific guidance, with a five-step model for recognizing and measuring revenue from contracts with customers. The objective of the new standard is to provide a single, comprehensive revenue recognition model for all contracts with customers to improve comparability within industries, across industries, and across capital markets. The underlying principle is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. The guidance also requires a number of disclosures regarding the nature, amount, timing, and uncertainty of revenue and the related cash flows. The guidance can be applied retrospectively to each prior reporting period presented (full retrospective method) or retrospectively with a cumulative effect adjustment to retained earnings for initial application of the guidance at the date of initial adoption (modified retrospective method). The Registrants applied the new guidance using the full retrospective method and, accordingly, have recasted certain amounts in their Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows, Consolidated Balance Sheets, Consolidated Statements of Changes in Shareholders' Equity and Combined Notes to Consolidated Financial Statements in the prior periods presented. The amounts recasted in the Registrants' 2017 and 2016 Consolidated Statements of Operations and Comprehensive Income are shown in the table below. The amounts recasted in the Registrants’ Consolidated Statements of Cash Flows, Consolidated Balance Sheets, Consolidated Statements of Changes in Shareholders' Equity and Combined Notes to Consolidated Financi al Statements were not material. See Note 3 — Revenue from Contracts with Customers for additional information. Successor For the year ended December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 17,360 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 16,171 — — — — — — — — Operating revenues — 17,351 — — — — — — — Electric operating revenues — — 5,521 2,369 2,484 4,468 2,152 1,131 1,184 Natural gas operating revenues — — — 494 676 161 — 161 — Operating revenues from affiliates — 1,115 15 7 16 50 6 8 2 Total operating revenues $ 33,531 $ 18,466 $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 2,158 $ 1,300 $ 1,186 Operating Revenues - Adjustments Competitive business revenues $ 34 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (207 ) — — — — — — — — Operating revenues — 34 — — — — — — — Electric operating revenues — — (43 ) — (100 ) (40 ) (26 ) (6 ) (8 ) Natural gas operating revenues — — — — (24 ) — — — — Revenues from alternative revenue programs 207 — 43 — 124 40 26 6 8 Operating revenues from affiliates — — — — — — — — Total operating revenues $ 34 $ 34 $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 17,394 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 15,964 — — — — — — — — Operating revenues — 17,385 — — — — — — — Electric operating revenues — — 5,478 2,369 2,384 4,428 2,126 1,125 1,176 Natural gas operating revenues — — — 494 652 161 — 161 — Revenues from alternative revenue programs 207 — 43 — 124 40 26 6 8 Operating revenues from affiliates — 1,115 15 7 16 50 6 8 2 Total operating revenues $ 33,565 $ 18,500 $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 2,158 $ 1,300 $ 1,186 Successor Predecessor March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 For the year ended December 31, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Operating Revenues - As reported Competitive business revenues $ 16,324 $ — $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 15,036 — — — — — — — — — Operating revenues — 16,312 — — — — — — — — Electric operating revenues — — 5,239 2,524 2,603 2,181 1,122 1,254 3,506 1,096 Natural gas operating revenues — — — 462 609 — 148 — 92 57 Operating revenues from affiliates — 1,439 15 8 21 5 7 3 45 — Total operating revenues $ 31,360 $ 17,751 $ 5,254 $ 2,994 $ 3,233 $ 2,186 $ 1,277 $ 1,257 $ 3,643 $ 1,153 Operating Revenues - Adjustments Competitive business revenues $ 6 $ — $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (48 ) — — — — — — — — — Operating revenues — 6 — — — — — — — — Electric operating revenues — — 24 — (72 ) (14 ) 6 (9 ) (43 ) 26 Natural gas operating revenues — — — — 19 — — — — — Revenues from alternative revenue programs 48 — (24 ) — 53 14 (6 ) 9 43 (26 ) Operating revenues from affiliates — — — — — — — — — — Total operating revenues $ 6 $ 6 $ — $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 16,330 $ — $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 14,988 — — — — — — — — — Operating revenues — 16,318 — — — — — — — — Electric operating revenues — — 5,263 2,524 2,531 2,167 1,128 1,245 3,463 1,122 Natural gas operating revenues — — — 462 628 — 148 — 92 57 Revenues from alternative revenue programs 48 — (24 ) — 53 14 (6 ) 9 43 (26 ) Operating revenues from affiliates — 1,439 15 8 21 5 7 3 45 — Total operating revenues $ 31,366 $ 17,757 $ 5,254 $ 2,994 $ 3,233 $ 2,186 $ 1,277 $ 1,257 $ 3,643 $ 1,153 New Accounting Standards Adopted as of January 1, 2019: The following new authoritative accounting guidance issued by the FASB was adopted as of January 1, 2019 and will be reflected by the Registrants in their consolidated financial statements beginning in the first quarter of 2019. Cloud Computing Arrangements (Issued August 2018). Aligns the requirements for capitalizing costs incurred to implement a cloud computing arrangement with the internal-use software guidance. As a result, certain implementation costs incurred in a cloud computing arrangement that are currently expensed as incurred will be deferred and amortized over the non-cancellable term of the arrangement plus any reasonably certain renewal periods. The standard is effective January 1, 2020, with early adoption permitted, and can be applied using either a prospective or retrospective transition approach. A retrospective approach requires a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants early adopted this standard using a prospective approach as of January 1, 2019. The new guidance is not expected to have a material impact on the Registrants’ financial statements. Leases (Issued February 2016). Increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. The Registrants adopted the standard on January 1, 2019. The new standard requires lessees to recognize both the right-of-use assets and lease liabilities in the balance sheet for most leases, whereas under previous GAAP only finance lease liabilities (referred to as capital leases) were recognized in the balance sheet. In addition, the definition of a lease has been revised which may result in changes to the classification of an arrangement as a lease. Under the new standard, an arrangement that conveys the right to control the use of an identified asset by obtaining substantially all of its economic benefits and directing how it is used is a lease, whereas the previous definition focuses on the ability to control the use of the asset or to obtain its output. Quantitative and qualitative disclosures related to the amount, timing and judgments of an entity’s accounting for leases and the related cash flows are expanded. Disclosure requirements apply to both lessees and lessors, whereas previous disclosures related only to lessees. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from previous GAAP. Lessor accounting is also largely unchanged. The new standard provides a number of transition practical expedients, which the Registrants have elected, including: • a "package of three" expedients that must be taken together and allow entities to (1) not reassess whether existing contracts contain leases, (2) carryforward the existing lease classification, and (3) not reassess initial direct costs associated with existing leases, • an implementation expedient which allows the requirements of the standard in the period of adoption with no restatement of prior periods, and • a land easement expedient which allows entities to not evaluate land easements under the new standard at adoption if they were not previously accounted for as leases. The Registrants have assessed the lease standard and executed a detailed implementation plan in preparation for adoption, which included the following key activities: • Developed a complete lease inventory and abstracted the required data attributes into a lease accounting system that supports the Registrants' lease portfolios and integrates with existing systems. • Evaluated the transition practical expedients available under the standard. • Identified, assessed and documented technical accounting issues, policy considerations and financial reporting implications. • Identified and implemented changes to processes and controls to ensure all impacts of the new standard are effectively addressed. The adoption of the new standard is expected to result in right of use assets and lease obligations for operating leases recorded in the Registrants’ Consolidated Balance Sheets on January 1, 2019 of approximately: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE ROU Assets $1,400-$1,500 $1,000-$1,100 $5-$10 $1-$5 $100-$120 $250-$270 $60-$65 $70-$75 $20-$25 Lease Liabilities $1,600-$1,700 $1,200-$1,300 $5-$10 $1-$5 $100-$120 $300-$320 $60-$65 $75-$80 $20-$25 The impact of adopting the new standard on retained earnings as of January 1, 2019 is expected to be immaterial. New Accounting Standards Issued and Not Yet Adopted as of December 31, 2018: The following new authoritative accounting guidance issued by the FASB has not yet been adopted and reflected by the Registrants in their consolidated financial statements as of December 31, 2018. Unless otherwise indicated, the Registrants are currently assessing the impacts such guidance may have (which could be material) in their Consolidated Balance Sheets, Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows and disclosures, as well as the potential to early adopt where applicable. The Registrants have assessed other FASB issuances of new standards which are not listed below given the current expectation that such standards will not significantly impact the Registrants' financial reporting. Goodwill Impairment (Issued January 2017). Simplifies the accounting for goodwill impairment by removing Step 2 of the current test, which requires calculation of a hypothetical purchase price allocation. Under the revised guidance, goodwill impairment will be measured as the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill (currently Step 1 of the two-step impairment test). Entities will continue to have the option to perform a qualitative assessment to determine if a quantitative impairment test is necessary. Exelon, Generation, ComEd, PHI and DPL have goodwill as of December 31, 2018. This updated guidance is not currently expected to impact the Registrants’ financial reporting. The standard is effective January 1, 2020, with early adoption permitted, and must be applied on a prospective basis. Impairment of Financial Instruments (Issued June 2016). Provides for a new Current Expected Credit Loss (CECL) impairment model for specified financial instruments including loans, trade receivables, debt securities classified as held-to-maturity investments and net investments in leases recognized by a lessor. Under the new guidance, on initial recognition and at each reporting period, an entity is required to recognize an allowance that reflects the entity’s current estimate of credit losses expected to be incurred over the life of the financial instrument. The standard does not make changes to the existing impairment models for non-financial assets such as fixed assets, intangibles and goodwill. The standard will be effective January 1, 2020 (with early adoption as of January 1, 2019 permitted) and requires a modified retrospective transition approach through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants are currently assessing the impacts of this standard.

Earnings Per Share Earnings Per

Earnings Per Share Earnings Per Share (Policies)	12 Months Ended
	Dec. 31, 2018
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 Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cumulative Effect of New Accounting Pronouncement Adoption Revenue from Contract with Customer [Table Text Block]	.	.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2018
Variable Interest Entity [Abstract]
Schedule of 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, 2018 and 2017 are as follows: December 31, 2018 Exelon (a) Generation PHI (a) ACE Current assets $ 938 $ 931 $ 7 4 Noncurrent assets 9,071 9,045 26 19 Total assets $ 10,009 $ 9,976 $ 33 $ 23 Current liabilities $ 274 $ 252 $ 22 19 Noncurrent liabilities 3,280 3,233 47 40 Total liabilities $ 3,554 $ 3,485 $ 69 $ 59 December 31, 2017 Exelon (a) Generation PHI (a) ACE Current assets $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,317 9,286 31 23 Total assets $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,316 3,250 66 58 Total liabilities $ 3,624 $ 3,522 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. The following tables present summary information about Exelon and Generation’s significant unconsolidated VIE entities: December 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 597 $ 472 $ 1,069 Total liabilities (a) 37 222 259 Exelon's ownership interest in VIE (a) — 223 223 Other ownership interests in VIE (a) 560 27 587 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 223 223 Contract intangible asset 7 — 7 Net assets pledged for Zion Station decommissioning (b) — — — 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 Net assets pledged for Zion Station decommissioning (b) 2 — 2 __________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not in 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 in 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 $9 million and $39 million as of December 31, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions LLC of $9 million and $37 million as of December 31, 2018 and December 31, 2017 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. As of December 31, 2018 and 2017 , these assets and liabilities primarily consisted of the following: December 31, 2018 Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 414 $ 414 $ — $ — Restricted cash and cash equivalents 66 62 4 4 Accounts receivable, net Customer 146 146 — — Other 23 23 — — Inventory Materials and supplies 212 212 — — Other current assets 52 49 3 — Total current assets 913 906 7 4 Property, plant and equipment, net 6,145 6,145 — — Nuclear decommissioning trust funds 2,351 2,351 — — Other noncurrent assets 258 232 26 19 Total noncurrent assets 8,754 8,728 26 19 Total assets $ 9,667 $ 9,634 $ 33 $ 23 Long-term debt due within one year $ 87 $ 66 $ 21 $ 18 Accounts payable 96 96 — — Accrued expenses 72 72 1 1 Unamortized energy contract liabilities 15 15 — — Other current liabilities 3 3 — — Total current liabilities 273 252 22 19 Long-term debt 1,072 1,025 47 40 Asset retirement obligations 2,160 2,160 — — Unamortized energy contract liabilities 1 1 — — Other noncurrent liabilities 42 42 — — Total noncurrent liabilities 3,275 3,228 47 40 Total liabilities $ 3,548 $ 3,480 $ 69 $ 59 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. December 31, 2017 Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 126 $ 126 $ — $ — Restricted cash and cash equivalents 64 58 6 6 Accounts receivable, net Customer 170 170 — — Other 25 25 — — Inventory Materials and supplies 205 205 — — Other current assets 45 41 4 — Total current assets 635 625 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 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 102 $ 67 $ 35 $ 31 Accounts payable 114 114 — — Accrued expenses 67 66 1 1 Unamortized energy contract liabilities 18 18 — — Other current liabilities 7 7 — — Total current liabilities 308 272 36 32 Long-term debt 1,154 1,088 66 58 Asset retirement obligations 2,035 2,035 — — Other noncurrent liabilities 121 121 — — Total noncurrent liabilities 3,310 3,244 66 58 Total liabilities $ 3,618 $ 3,516 $ 102 $ 90 __________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

Revenue Recognition Revenue R_2

Revenue Recognition Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer (All Registrants) [Abstract]
Contract with Customer, Asset and Liability [Table Text Block]	he following table provides a rollforward of the contract assets reflected in Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to December 31, 2018 : Contract Assets Exelon and Generation Balance as of January 1, 2018 $ 283 Increases as a result of changes in the estimate of the stage of completion 50 Amounts reclassified to receivables (146 ) Balance at December 31, 2018 $ 187 The Utility Registrants do not have any contract assets. The following table provides a rollforward of the contract liabilities reflected in Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to December 31, 2018 : Contract Liabilities Exelon Generation Balance as of January 1, 2018 $ 35 $ 35 Increases as a result of additional cash received or due 179 465 Amounts recognized into revenues (187 ) (458 ) Balance at December 31, 2018 $ 27 $ 42
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	2019 2020 2021 2022 2023 and thereafter Total Exelon $ 631 $ 329 $ 119 $ 47 $ 138 $ 1,264 Generation 631 329 119 47 138 1,264

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE December 31, 2018 $ 65 $ 8 $ — $ 49 $ 8 $ 5 $ 3 $ — December 31, 2017 $ 69 $ 6 $ — $ 53 $ 10 $ 6 $ 4 $ — __________ (a) Reflects ComEd's unrecognized equity returns earned for ratemaking purposes on its electric distribution formula rate 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 Regulatory Asset Impairments [Table Text Block]	For the year ended December 31, 2017 Exelon $ 35 ComEd 3 BGE 5 PHI 27 Pepco 14 DPL 6 ACE 7 On December 18, 2017, BGE filed for clarification and rehearing of FERC’s order, still seeking full recovery of its existing transmission-related income tax regulatory asset amounts, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. On February 27, 2018 (and updated on March 26, 2018), BGE submitted a letter to FERC advising that the lower federal corporate income tax rate effective January 1, 2018 provided for in the TCJA will be reflected in BGE’s annual formula rate update effective June 1, 2018, but that the deferred income tax benefits will not be passed back to customers unless BGE’s formula rate is revised to provide for pass back and recovery of transmission-related income tax-related regulatory liabilities and assets. On February 23, 2018 (as amended on July 9, 2018), ComEd, Pepco, DPL, and ACE each filed with FERC to revise their transmission formula rate mechanisms to facilitate passing back to customers ongoing annual TCJA tax savings and to permit recovery of transmission-related income tax regulatory assets, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. On September 7, 2018, FERC issued orders rejecting BGE’s December 18, 2017 request for rehearing and clarification and ComEd's, Pepco's, DPL's and ACE's February 23, 2018 (as amended on July 9, 2018) filings, again citing the lack of timeliness of the requests to recover amounts that would have been previously amortized, but indicating that ongoing recovery of certain transmission-related income tax regulatory assets would provide for a more accurate revenue requirement. The orders did not address the remittance of TCJA transmission-related income tax regulatory liabilities, but rather referenced FERC’s separate Notice of Inquiry of such amounts issued on March 15, 2018. On October 1, 2018, ComEd, BGE, Pepco, DPL, and ACE submitted new filings to recover ongoing non-TCJA amortization amounts and refund TCJA transmission-related income tax regulatory liabilities for the prospective period starting on October 1, 2018. FERC issued deficiency letters requesting additional information on November 21, 2018 and January 28, 2019. ComEd, BGE, Pepco, DPL, and ACE responded to the November 21, 2018 deficiency letter on November 29, 2018 but cannot predict the outcome of these FERC proceedings. If FERC ultimately rules that the future, ongoing non-TCJA amortization amounts are not recoverable, Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE would record additional charges to Income tax expense, which could be up to approximately $76 million , $51 million , $15 million , $10 million , $3 million , $5 million and $2 million , respectively, as of December 31, 2018. On October 9, 2018, ComEd, Pepco, DPL, and ACE sought rehearing of FERC's September 7, 2018 order, still seeking full recovery of their existing transmission-related income tax regulatory asset amounts, including those amounts that would have been previously amortized and recovered through rates had the transmission formula rate provided for such recovery. ComEd, Pepco, DPL, and ACE cannot predict the outcome of this rehearing request. On November 2, 2018, BGE filed an appeal of FERC’s September 7, 2018 order to the Court of Appeals for the D.C. Circuit. PJM Transmission Rate Design (All Registrants). On June 15, 2016, several parties, including the Utility Registrants, filed a proposed settlement with FERC to resolve outstanding issues related to cost responsibility for charges to transmission customers for certain transmission facilities that operate at or above 500 kV. The settlement included provisions for monthly credits or charges related to the periods prior to January 1, 2016 that are expected to be refunded or recovered through PJM wholesale transmission rates through December 2025. On May 31, 2018, FERC issued an order approving the settlement and directed PJM to adjust wholesale transmission rates within 30 days. Pursuant to the order, similar charges for the period January 1, 2016 through June 30, 2018 will also be refunded or recovered through PJM wholesale transmission rates over the subsequent 12-month period. PJM commenced billing the refunds and charges associated with this settlement in August 2018. The Utility Registrants expect to refund or recover these settlement amounts through prospective electric distribution customer rates. On July 2, 2018, several parties filed petitions for rehearing or clarification. Pursuant to the FERC approval of the settlement and the expected refund or recovery of the associated amounts from electric distribution customers, in the second quarter of 2018 and as adjusted in the third quarter of 2018, the Utility Registrants recorded the following payables to/receivables from PJM and related regulatory assets/liabilities. Generation recorded a $41 million net payable to PJM and a pre-tax charge within Purchased power and fuel expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. PJM Receivable PJM Payable Regulatory Asset Regulatory Liability Exelon $ 220 $ 176 $ 136 $ 221 Generation (a) — 41 — — ComEd 122 — — 122 PECO 85 — — 85 BGE — 51 51 — PHI 13 84 85 14 Pepco — 84 84 — DPL 10 — — 10 ACE 3 — 1 4 __________ (a)
Schedule of Regulatory Assets	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, 2018 and December 31, 2017 : December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,553 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,266 — — — — — — — Deferred income taxes 414 — 404 — 10 10 — — AMI programs - Deployment Costs 202 — — 113 89 50 39 — AMI programs - Legacy Meters 328 136 24 48 120 90 30 — AMI programs - Post-test year costs 32 — — 32 — — — — Electric distribution formula rate annual reconciliations 158 158 — — — — — — Electric distribution formula rate significant one-time events 81 81 — — — — — — Energy efficiency costs 472 472 — — — — — — Fair value of long-term debt 702 — — — 569 — — — Fair value of PHI's unamortized energy contracts 561 — — — 561 — — — Asset retirement obligations 118 79 22 16 1 1 — — MGP remediation costs 326 309 17 — — — — — Renewable energy 249 249 — — — — — — Electric Energy and Natural Gas Costs 193 — 49 51 93 84 — 9 Transmission formula rate annual reconciliations 41 6 — 4 31 10 14 7 Energy efficiency and demand response programs 545 — 1 289 255 188 67 — Merger integration costs 42 — — 3 39 18 11 10 Under-recovered revenue decoupling 59 — — 2 57 57 — — Securitized stranded costs 50 — — — 50 — — 50 Removal costs 564 — — — 564 158 97 309 DC PLUG charge 159 — — — 159 159 — — Deferred storm costs 41 — — — 41 9 4 28 Other 303 110 24 17 162 79 28 13 Total regulatory assets 9,459 1,600 541 575 2,801 913 290 426 Less: current portion 1,222 293 81 177 489 270 59 40 Total noncurrent regulatory assets $ 8,237 $ 1,307 $ 460 $ 398 $ 2,312 $ 643 $ 231 $ 386 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits $ 2,455 $ — $ — $ — $ — $ — $ — $ — Pension and other postretirement benefits - Merger related 1,393 — — — — — — — Deferred income taxes 306 — 297 — 9 9 — — AMI programs - Deployment costs 385 — — 129 101 58 43 — AMI programs - Legacy meters 223 155 36 53 134 100 34 — AMI programs - Post-test year costs 32 — — 32 — — — — Electric distribution formula rate annual reconciliations 186 186 — — — — — — Electric distribution formula rate significant one-time events 58 58 — — — — — — Energy efficiency costs 166 166 — — — — — — 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 — — — — — Renewable energy 258 256 — — 2 — 1 1 Electric energy and natural gas costs 47 — 1 16 30 8 7 15 Transmission formula rate annual reconciliations 35 6 — 7 22 3 8 11 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 — Securitized stranded costs 79 — — — 79 — — 79 Removal costs 529 — — — 529 150 93 286 DC PLUG charge 190 — — — 190 190 — — Deferred storm costs 27 — — — 27 7 5 15 Other 311 106 31 15 165 79 29 14 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 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities 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 — Electric Energy and Natural Gas Costs 111 47 60 — 4 — 1 3 Other 399 185 94 26 64 3 14 8 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
Schedule of Regulatory Liabilities	December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities 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 — Electric Energy and Natural Gas Costs 111 47 60 — 4 — 1 3 Other 399 185 94 26 64 3 14 8 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 December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Deferred income taxes $ 5,228 $ 2,394 $ — $ 1,132 $ 1,702 $ 798 $ 510 $ 394 Nuclear decommissioning 2,606 2,217 389 — — — — — Removal costs 1,547 1,368 — 52 127 20 107 — Electric Energy and Natural Gas Costs 294 137 132 6 19 — 18 1 Other 528 227 75 79 100 11 30 25 Total regulatory liabilities 10,203 6,343 596 1,269 1,948 829 665 420 Less: current portion 644 293 175 77 84 7 59 18 Total noncurrent regulatory liabilities $ 9,559 $ 6,050 $ 421 $ 1,192 $ 1,864 $ 822 $ 606 $ 402

Mergers, Acquisitions and Dis_2

Mergers, Acquisitions and Dispositions (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Business Combinations [Abstract]
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: 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 22 - Commitments and Contingencies for additional information regarding SNF obligations to the DOE.
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 merger date: Expected Payment Period Successor Description Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 259 $ 264 $ 91 $ 72 $ 101 Energy efficiency 2016 - 2021 117 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 508 $ 320 $ 120 $ 89 $ 111 Remaining commitments as of December 31, 2018 $ 128 $ 92 $ 73 $ 12 $ 7
Business Acquisition, Pro Forma Information [Table Text Block]	The current impact of PHI, including its unregulated businesses, in Exelon's Consolidated Statements of Operations and Comprehensive Income includes Operating revenues and Net Income (Loss) as follows: For the Years Ended December 31, 2018 2017 2016 Operating Revenues 4,670 4,829 3,785 Net Income (Loss) 453 364 (66 )
Restructuring and Related Costs [Table Text Block]	For the periods ended December 31, 2018 , 2017 and 2016 , the Registrants have recognized costs to achieve the PHI merger as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2018 2017 2016 Exelon $ 7 $ 16 $ 143 Generation 5 22 37 ComEd (b) — 1 (6 ) PECO 1 4 5 BGE (b) 1 4 (1 ) Pepco (b) — (6 ) 28 DPL (b) — (7 ) 20 ACE (b) — (6 ) 19 Successor Predecessor For the Year Ended December 31, March 24, 2016 to December 31, 2016 January 1, 2016 to Acquisition, Integration and Financing Costs (a) 2018 2017 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 as regulatory assets of $24 million , $8 million , $8 million , and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $8 million , $6 million , $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.	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: Severance Benefits Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 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.
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 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 .

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	Exelon The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-90 $ 53,090 $ 49,506 Electric—generation 1-56 29,170 29,019 Gas—transportation and distribution 5-90 5,530 5,050 Common—electric and gas 5-75 1,627 1,447 Nuclear fuel (a) 1-8 5,957 6,420 Construction work in progress N/A 3,377 2,825 Other property, plant and equipment (b) 1-50 858 999 Total property, plant and equipment 99,609 95,266 Less: accumulated depreciation (c) 22,902 21,064 Property, plant and equipment, net $ 76,707 $ 74,202 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017 , respectively. (b) Includes Generation’s buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017 , respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017 , and total accumulated amortization was $42 million and $40 million , as of December 31, 2018 and 2017 , respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 , 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, 2018 and 2017 . Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $39 million , $19 million , $25 million , $61 million , $17 million and $28 million , respectively, at December 31, 2018 . (c) Includes accumulated amortization of nuclear fuel in the reactor core at Generation of $2,969 million and $3,159 million as of December 31, 2018 and 2017 , respectively. Generation The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—generation 1-56 $ 29,170 $ 29,019 Nuclear fuel (a) 1-8 5,957 6,420 Construction work in progress N/A 997 838 Other property, plant and equipment (b) 1-8 63 57 Total property, plant and equipment 36,187 36,334 Less: accumulated depreciation (c) 12,206 11,428 Property, plant and equipment, net $ 23,981 $ 24,906 __________ (a) Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017 , respectively. (b) Includes buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017 , respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017 , and total accumulated amortization was $42 million and $40 million , as of December 31, 2018 and 2017 , respectively. (c) Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million and $3,159 million as of December 31, 2018 and 2017 , respectively. ComEd The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-80 $ 25,991 $ 24,423 Construction work in progress N/A 705 517 Other property, plant and equipment (a), (b) 35-50 46 52 Total property, plant and equipment 26,742 24,992 Less: accumulated depreciation 4,684 4,269 Property, plant and equipment, net $ 22,058 $ 20,723 __________ (a) Includes buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 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, 2018 and 2017 . (b) Represents land held for future use and non-utility property. PECO The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-65 $ 8,359 $ 7,975 Gas—transportation and distribution 5-70 2,694 2,504 Common—electric and gas 5-50 756 710 Construction work in progress N/A 343 254 Other property, plant and equipment (a) 50 19 21 Total property, plant and equipment 12,171 11,464 Less: accumulated depreciation 3,561 3,411 Property, plant and equipment, net $ 8,610 $ 8,053 __________ (a) Represents land held for future use and non-utility property. BGE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-90 $ 7,951 $ 7,464 Gas—distribution 5-90 2,630 2,379 Common—electric and gas 5-40 860 771 Construction work in progress N/A 410 367 Other property, plant and equipment (a) 20 25 26 Total property, plant and equipment 11,876 11,007 Less: accumulated depreciation 3,633 3,405 Property, plant and equipment, net $ 8,243 $ 7,602 __________ (a) Represents plant held for future use and non-utility property. PHI The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average 2018 2017 Asset Category Electric—transmission and distribution 5-75 $ 12,664 $ 11,517 Gas—distribution 5-75 486 449 Common—electric and gas 5-75 126 82 Construction work in progress N/A 912 835 Other property, plant and equipment (a) 3-43 99 102 Total property, plant and equipment 14,287 12,985 Less: accumulated depreciation 841 487 Property, plant and equipment, net $ 13,446 $ 12,498 __________ (a) Represents plant held for future use and non-utility property. Pepco The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-75 $ 9,217 $ 8,646 Construction work in progress N/A 536 473 Other property, plant and equipment (a) 25-33 61 59 Total property, plant and equipment 9,814 9,178 Less: accumulated depreciation 3,354 3,177 Property, plant and equipment, net $ 6,460 $ 6,001 __________ (a) Represents plant held for future use and non-utility property. DPL The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-70 $ 4,195 $ 3,875 Gas—distribution 5-75 651 614 Common—electric and gas 5-75 136 117 Construction work in progress N/A 151 205 Other property, plant and equipment (a) 10-43 17 15 Total property, plant and equipment 5,150 4,826 Less: accumulated depreciation 1,329 1,247 Property, plant and equipment, net $ 3,821 $ 3,579 __________ (a) Represents plant held for future use and non-utility property. ACE The following table presents a summary of property, plant and equipment by asset category as of December 31, 2018 and 2017 : Average Service Life (years) 2018 2017 Asset Category Electric—transmission and distribution 5-60 $ 3,866 $ 3,607 Construction work in progress N/A 209 138 Other property, plant and equipment (a) 13-15 28 27 Total property, plant and equipment 4,103 3,772 Less: accumulated depreciation 1,137 1,066 Property, plant and equipment, net $ 2,966 $ 2,706 __________ (a) Represents plant held for future use and non-utility property.
Property Plant And Equipment Average Service Life Percentage By Asset Category Table	Exelon 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 2018 2017 2016 Electric—transmission and distribution 2.73 % 2.75 % 2.73 % Electric—generation (a) 5.37 % 4.36 % 5.94 % Gas 2.07 % 2.10 % 2.17 % Common—electric and gas 6.98 % 7.05 % 7.41 % __________ (a) See Note 8 — Early Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI. PECO 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 2018 2017 2016 Electric—transmission and distribution 2.35 % 2.37 % 2.32 % Gas 1.90 % 1.89 % 1.82 % Common—electric and gas 5.44 % 5.47 % 5.11 % BGE 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 2018 2017 2016 Electric—transmission and distribution 2.61 % 2.58 % 2.56 % Gas 2.36 % 2.33 % 2.45 % Common—electric and gas 8.50 % 8.64 % 9.45 % PHI 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 2018 2017 2016 Electric—transmission and distribution 2.61 % 2.63 % 2.52 % Gas 1.59 % 2.07 % 2.57 % Common—electric and gas 6.30 % 6.50 % 8.12 % DPL 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 2018 2017 2016 Electric—transmission and distribution 2.77 % 2.75 % 2.49 % Gas 1.59 % 2.07 % 2.57 % Common—electric and gas 3.70 % 4.14 % 4.99 %
Schedule Of Capitalized Software	Capitalized Software Costs (All Registrants) The following tables presents net unamortized capitalized software costs and amortization of capitalized software costs by year. Net unamortized software costs Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 810 $ 164 $ 206 $ 98 $ 166 $ 165 $ 26 $ 21 $ 14 December 31, 2017 834 173 227 111 179 133 2 1 1 Amortization of capitalized software costs Exelon Generation ComEd PECO BGE Pepco DPL ACE 2018 $ 282 $ 78 $ 79 $ 37 $ 48 $ 2 $ 2 $ 1 2017 270 73 73 39 46 — — — 2016 255 72 62 33 44 — — — Successor Predecessor PHI For the year ended December 31, 2018 For the year ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Amortization of capitalized software costs $ 33 $ 34 $ 29 $ 8
Schedule Of Capitalized Interest And AFUDC	Capitalized Interest and AFUDC (All Registrants) The following table summarizes total incurred interest, capitalized interest and credits to AFUDC by year: Exelon Generation ComEd PECO BGE Pepco DPL ACE 2018 Total incurred interest (a) $ 1,695 $ 464 $ 377 $ 141 $ 130 $ 162 $ 62 $ 68 Capitalized interest 31 31 — — — — — — Credits to AFUDC debt and equity 109 — 30 12 24 34 4 4 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 Successor Predecessor PHI For the year ended December 31, 2018 For the year ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Total incurred interest (a) $ 305 $ 263 $ 207 $ 68 Credits to AFUDC debt and equity 44 54 35 10 __________ (a) Includes interest expense to affiliates.

Early Plant Retirements Early_2

Early Plant Retirements Early Plant Retirements (Tables)	12 Months Ended
	Dec. 31, 2018
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) 2018 (a) 2017 (b) 2016 (c) Depreciation and Amortization Accelerated depreciation (d) $ 539 $ 250 $ 712 Accelerated nuclear fuel amortization 57 12 60 Operating and Maintenance One-time charges (e,f) 32 77 26 Change in ARO accretion, net of any contractual offset (g) — — 2 Contractual offset for ARC depreciation (g) — — (86 ) Total $ 628 $ 339 $ 714 _________ (a) Reflects incremental accelerated depreciation for TMI and Oyster Creek. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 2018. (b) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (c) 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. (d) Reflects incremental accelerated depreciation of plant assets, including any ARC. (e) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Excludes the charge to Operating and maintenance expense from the ARO remeasurement due to the announced sale of Oyster Creek. See Note 5 — Mergers, Acquisitions and Dispositions for additional information. (f) 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. (g) For Quad Cities based on the regulatory agreement with the ICC, 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.
Implications of Potential Early Plant Retirement on Balance Sheet [Table Text Block]	The following table provides the balance sheet amounts as of December 31, 2018 for Generation’s significant assets and liabilities associated with the Mystic Units 8 and 9 and Everett Marine Terminal assets that would potentially be impacted by a decision to permanently cease generation operations. December 31, 2018 Asset Balances Materials and supplies inventory $ 30 Fuel inventory 20 Completed plant, net 901 Construction work in progress 9 Liability Balances Asset retirement obligation (1 ) December 31, 2018 Asset Balances Materials and supplies inventory $ 45 Nuclear fuel inventory, net 118 Completed plant, net 538 Construction work in progress 44 Liability Balances Asset retirement obligation (395 ) NRC License Renewal Term 2036 (unit 1) 2040 (unit 2)

Jointly Owned Electric Utilit_2

Jointly Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2018
Public Utilities, Property, Plant and Equipment [Abstract]
Schedule of Jointly Owned Utility Plants	Exelon's, Generation's, PECO's, BGE's, Pepco's, DPL's and ACE's undivided ownership interests in jointly owned electric plants and transmission facilities at December 31, 2018 and 2017 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, 2018: Plant (e) $ 1,131 $ 1,451 $ 648 $ 910 $ 4 $ 28 $ 103 $ 15 Accumulated depreciation (e) 587 523 227 126 3 16 53 13 Construction work in progress 13 15 44 56 — 1 — — 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 — — — — __________ (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, 2018 and 2017 . (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 of the Salem generating plant substation. 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 substation. (d) Generation, DPL and ACE own a 44.24% , 11.91% and 4.83% 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 and general plant.

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Schedule Of Goodwill	Exelon’s, ComEd’s and PHI's gross amount of goodwill, accumulated impairment losses and carrying amount of goodwill for the years ended December 31, 2018 and 2017 were as follows: Balance at January 1, 2017 Impairment losses Balance at December 31, 2017 Impairment losses Balance at December 31, 2018 Exelon Gross amount $ 8,660 $ — $ 8,660 $ — $ 8,660 Accumulated impairment loss 1,983 — 1,983 — 1,983 Carrying amount 6,677 — 6,677 — 6,677 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 PHI (b) Gross amount 4,005 — 4,005 — 4,005 Carrying amount 4,005 — 4,005 — 4,005 __________ (a) Reflects goodwill recorded in 2000 from the PECO/Unicom merger (predecessor parent company of ComEd).	[1],[2]
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, 2018 and 2017 : December 31, 2018 December 31, 2017 Gross Accumulated Amortization Net Gross Accumulated Amortization Net Generation Unamortized Energy Contracts (b) 1,957 (1,588 ) 369 1,938 (1,574 ) 364 Customer Relationships 325 (162 ) 163 305 (133 ) 172 Trade Name 243 (171 ) 72 243 (148 ) 95 ComEd Chicago Settlement Agreements (c) 162 (148 ) 14 162 (141 ) 21 PHI Unamortized Energy Contracts (b) (1,515 ) 954 (561 ) (1,515 ) 766 (749 ) Exelon Corporate Software License (a) 95 (34 ) 61 95 (25 ) 70 Exelon $ 1,267 $ (1,149 ) $ 118 $ 1,228 $ (1,255 ) $ (27 ) __________ (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 in 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.
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, 2018 : For the Years Ending December 31, Exelon Generation ComEd PHI 2019 $ (32 ) $ 70 $ 7 $ (119 ) 2020 (20 ) 78 7 (115 ) 2021 (4 ) 78 — (92 ) 2022 (23 ) 56 — (89 ) 2023 (21 ) 50 — (81 )
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, 2018 , 2017 and 2016 : For the Years Ended December 31, Exelon (a)(b) Generation (a) ComEd PHI (b) 2018 $ (109 ) $ 63 $ 7 $ (188 ) 2017 (237 ) 83 7 (336 ) 2016 (336 ) 79 7 (430 ) __________ (a) At Exelon and Generation, amortization of unamortized energy contracts totaling $14 million , $35 million and $35 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, was recorded in Operating revenues or Purchased power and fuel expense in their Consolidated Statements of Operations and Comprehensive Income
Schedule of Alternative or Renewable Energy Credits [Table Text Block]	The following table summarizes the current and noncurrent Renewable and Alternative Energy Credits as of December 31, 2018 and 2017 : As of December 31, 2018 Exelon Generation PECO PHI DPL ACE Current AEC's $ 2 $ — $ 2 $ — $ — $ — Current REC's 279 270 — 9 8 1 Noncurrent REC's 52 52 — — — — As of December 31, 2017 Exelon Generation PECO PHI DPL ACE Current AEC's $ 1 $ — $ 1 $ — $ — $ — Current REC's 321 312 — 9 8 1 Noncurrent REC's 27 27 — — — —
[1]	(b)Reflects goodwill recorded in 2016 from the PHI merger.
[2]	Reflects goodwill recorded in 2000 from the PECO/Unicom merger (predecessor parent company of ComEd).

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 : Exelon December 31, 2018 Carrying Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 714 $ — $ 714 $ — $ 714 Long-term debt (including amounts due within one year) (a) 35,424 — 33,711 2,158 35,869 Long-term debt to financing trusts (b) 390 — — 400 400 SNF obligation 1,171 — 949 — 949 December 31, 2017 Carrying Amount 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 Generation December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,793 $ — $ 7,467 $ 1,443 $ 8,910 SNF obligation 1,171 — 949 — 949 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 ComEd December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 8,101 $ — $ 8,390 $ — $ 8,390 Long-term debt to financing trusts (b) 205 — — 209 209 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 PECO December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 3,084 $ — $ 3,157 $ 50 $ 3,207 Long-term debt to financing trusts 184 — — 191 191 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 BGE December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 35 $ — $ 35 $ — $ 35 Long-term debt (including amounts due within one year) (a) 2,876 — 2,950 — 2,950 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 PHI December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 179 $ — $ 179 $ — $ 179 Long-term debt (including amounts due within one year) (a) 6,259 — 5,436 665 6,101 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 Pepco December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 40 $ — $ 40 $ — $ 40 Long-term debt (including amounts due within one year) (a) 2,719 — 2,901 196 3,097 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 DPL December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (a) $ 1,494 $ — $ 1,303 $ 193 $ 1,496 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 ACE December 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities $ 139 $ — $ 139 $ — $ 139 Long-term debt (including amounts due within one year) (a) 1,188 — 987 275 1,262 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 __________ (a) Includes unamortized debt issuance costs which are not fair valued of $216 million , $51 million , $63 million , $23 million , $18 million , $14 million , $34 million , $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2018 . 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 . (b) Includes unamortized debt issuance costs which are not fair valued of $0 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018 . 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 .
Assets and liabilities measured and recorded at fair value on recurring basis	The following tables present assets and liabilities measured and recorded at fair value in Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2018 and 2017 : Generation Exelon As of December 31, 2018 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) $ 581 $ — $ — $ — $ 581 $ 1,243 $ — $ — $ — $ 1,243 NDT fund investments Cash equivalents (b) 252 86 — — 338 252 86 — — 338 Equities 2,918 1,591 — 1,381 5,890 2,918 1,591 — 1,381 5,890 Fixed income Corporate debt — 1,593 230 — 1,823 — 1,593 230 — 1,823 U.S. Treasury and agencies 2,081 99 — — 2,180 2,081 99 — — 2,180 Foreign governments — 50 — — 50 — 50 — — 50 State and municipal debt — 149 — — 149 — 149 — — 149 Other (c) — 30 — 846 876 — 30 — 846 876 Fixed income subtotal 2,081 1,921 230 846 5,078 2,081 1,921 230 846 5,078 Middle market lending — — 313 367 680 — — 313 367 680 Private equity — — — 329 329 — — — 329 329 Real estate — — — 510 510 — — — 510 510 NDT fund investments subtotal (d) 5,251 3,598 543 3,433 12,825 5,251 3,598 543 3,433 12,825 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Pledged assets for Zion Station decommissioning Cash equivalents 9 — — — 9 9 — — — 9 Equities — — — — — — — — — — Middle market lending — — — — — — — — — — Pledged assets for Zion Station decommissioning subtotal 9 — — — 9 9 — — — 9 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 24 — — — 24 72 — — — 72 Fixed income — — — — — — 15 — — 15 Life insurance contracts — 22 — — 22 — 70 38 — 108 Rabbi trust investments subtotal (f) 29 22 — — 51 120 85 38 — 243 Commodity derivative assets Economic hedges 541 2,760 1,470 — 4,771 541 2,760 1,470 — 4,771 Proprietary trading — 69 77 — 146 — 69 77 — 146 Effect of netting and allocation of (e) (582 ) (2,357 ) (732 ) — (3,671 ) (582 ) (2,357 ) (732 ) — (3,671 ) Commodity derivative assets subtotal (41 ) 472 815 — 1,246 (41 ) 472 815 — 1,246 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — — — — — Economic hedges — 13 — — 13 — 13 — — 13 Effect of netting and allocation of collateral — (3 ) — — (3 ) — (3 ) — — (3 ) Interest rate and foreign currency derivative assets subtotal — 10 — — 10 — 10 — — 10 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,829 4,102 1,400 3,433 14,764 6,582 4,165 1,438 3,433 15,618 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,027 ) — (4,632 ) (642 ) (2,963 ) (1,276 ) — (4,881 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (240 ) — (698 ) (3 ) (455 ) (489 ) — (947 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Economic hedges — (6 ) — — (6 ) — (6 ) — — (6 ) Effect of netting and allocation of collateral — 3 — — 3 — 3 — — 3 Interest rate and foreign currency derivative liabilities subtotal — (3 ) — — (3 ) — (7 ) — — (7 ) Deferred compensation obligation — (35 ) — — (35 ) — (137 ) — — (137 ) Total liabilities (3 ) (493 ) (240 ) — (736 ) (3 ) (599 ) (489 ) — (1,091 ) Total net assets $ 5,826 $ 3,609 $ 1,160 $ 3,433 $ 14,028 $ 6,579 $ 3,566 $ 949 $ 3,433 $ 14,527 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 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 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 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 (f) 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) (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 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 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 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) 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 __________ (a) Generation excludes cash of $283 million and $259 million at December 31, 2018 and 2017 and restricted cash of $39 million and $127 million at December 31, 2018 and 2017 . Exelon excludes cash of $458 million and $389 million at December 31, 2018 and 2017 and restricted cash of $80 million and $145 million at December 31, 2018 and 2017 and includes long-term restricted cash of $185 million and $85 million at December 31, 2018 and 2017 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) Includes $50 million and $77 million of cash received from outstanding repurchase agreements at December 31, 2018 and 2017 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $44 million and less than $1 million , which have a total notional amount of $1,432 million and $811 million at December 31, 2018 and 2017 , 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 $130 million and $82 million at December 31, 2018 and 2017 , 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) Excludes net assets of less than $1 million at December 31, 2018 and 2017 . These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases. (f) The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the years ended December 31, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the years ended December 31, 2018 and 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $57 million , $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018 . 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 .
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following tables present assets and liabilities measured and recorded at fair value in Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2018 and 2017 : Generation Exelon As of December 31, 2018 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) $ 581 $ — $ — $ — $ 581 $ 1,243 $ — $ — $ — $ 1,243 NDT fund investments Cash equivalents (b) 252 86 — — 338 252 86 — — 338 Equities 2,918 1,591 — 1,381 5,890 2,918 1,591 — 1,381 5,890 Fixed income Corporate debt — 1,593 230 — 1,823 — 1,593 230 — 1,823 U.S. Treasury and agencies 2,081 99 — — 2,180 2,081 99 — — 2,180 Foreign governments — 50 — — 50 — 50 — — 50 State and municipal debt — 149 — — 149 — 149 — — 149 Other (c) — 30 — 846 876 — 30 — 846 876 Fixed income subtotal 2,081 1,921 230 846 5,078 2,081 1,921 230 846 5,078 Middle market lending — — 313 367 680 — — 313 367 680 Private equity — — — 329 329 — — — 329 329 Real estate — — — 510 510 — — — 510 510 NDT fund investments subtotal (d) 5,251 3,598 543 3,433 12,825 5,251 3,598 543 3,433 12,825 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Pledged assets for Zion Station decommissioning Cash equivalents 9 — — — 9 9 — — — 9 Equities — — — — — — — — — — Middle market lending — — — — — — — — — — Pledged assets for Zion Station decommissioning subtotal 9 — — — 9 9 — — — 9 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 24 — — — 24 72 — — — 72 Fixed income — — — — — — 15 — — 15 Life insurance contracts — 22 — — 22 — 70 38 — 108 Rabbi trust investments subtotal (f) 29 22 — — 51 120 85 38 — 243 Commodity derivative assets Economic hedges 541 2,760 1,470 — 4,771 541 2,760 1,470 — 4,771 Proprietary trading — 69 77 — 146 — 69 77 — 146 Effect of netting and allocation of (e) (582 ) (2,357 ) (732 ) — (3,671 ) (582 ) (2,357 ) (732 ) — (3,671 ) Commodity derivative assets subtotal (41 ) 472 815 — 1,246 (41 ) 472 815 — 1,246 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — — — — — Economic hedges — 13 — — 13 — 13 — — 13 Effect of netting and allocation of collateral — (3 ) — — (3 ) — (3 ) — — (3 ) Interest rate and foreign currency derivative assets subtotal — 10 — — 10 — 10 — — 10 Other investments — — 42 — 42 — — 42 — 42 Total assets 5,829 4,102 1,400 3,433 14,764 6,582 4,165 1,438 3,433 15,618 Generation Exelon As of December 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Liabilities Commodity derivative liabilities Economic hedges (642 ) (2,963 ) (1,027 ) — (4,632 ) (642 ) (2,963 ) (1,276 ) — (4,881 ) Proprietary trading — (73 ) (21 ) — (94 ) — (73 ) (21 ) — (94 ) Effect of netting and allocation of (e) 639 2,581 808 — 4,028 639 2,581 808 — 4,028 Commodity derivative liabilities subtotal (3 ) (455 ) (240 ) — (698 ) (3 ) (455 ) (489 ) — (947 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Economic hedges — (6 ) — — (6 ) — (6 ) — — (6 ) Effect of netting and allocation of collateral — 3 — — 3 — 3 — — 3 Interest rate and foreign currency derivative liabilities subtotal — (3 ) — — (3 ) — (7 ) — — (7 ) Deferred compensation obligation — (35 ) — — (35 ) — (137 ) — — (137 ) Total liabilities (3 ) (493 ) (240 ) — (736 ) (3 ) (599 ) (489 ) — (1,091 ) Total net assets $ 5,826 $ 3,609 $ 1,160 $ 3,433 $ 14,028 $ 6,579 $ 3,566 $ 949 $ 3,433 $ 14,527 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 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 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 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 (f) 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) (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 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 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 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) 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 __________ (a) Generation excludes cash of $283 million and $259 million at December 31, 2018 and 2017 and restricted cash of $39 million and $127 million at December 31, 2018 and 2017 . Exelon excludes cash of $458 million and $389 million at December 31, 2018 and 2017 and restricted cash of $80 million and $145 million at December 31, 2018 and 2017 and includes long-term restricted cash of $185 million and $85 million at December 31, 2018 and 2017 , which is reported in Other deferred debits in the Consolidated Balance Sheets. (b) Includes $50 million and $77 million of cash received from outstanding repurchase agreements at December 31, 2018 and 2017 , respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below. (c) Includes derivative instruments of $44 million and less than $1 million , which have a total notional amount of $1,432 million and $811 million at December 31, 2018 and 2017 , 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 $130 million and $82 million at December 31, 2018 and 2017 , 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) Excludes net assets of less than $1 million at December 31, 2018 and 2017 . These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases. (f) The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the years ended December 31, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the years ended December 31, 2018 and 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $57 million , $224 million and $76 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2018 . 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 .
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, 2018 and 2017 : Generation ComEd PHI Exelon For the year ended December 31, 2018 NDT Fund Investments Pledged Assets Mark-to-Market Other Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) Eliminated in Consolidation Total Balance as of January 1, 2018 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 Total realized / unrealized gains (losses) Included in net income — — (105 ) (a) 3 (102 ) — 4 — (98 ) Included in noncurrent payables to affiliates (1 ) — — — (1 ) — — 1 — Included in payable for Zion Station decommissioning — 7 — — 7 — — — 7 Included in regulatory assets/liabilities — — — — — 7 (b) — (1 ) 6 Change in collateral — — (5 ) — (5 ) — — — (5 ) Purchases, sales, issuances and settlements Purchases 36 1 190 (e) 4 231 — — — 231 Sales — (20 ) (4 ) — (24 ) — — — (24 ) Issuances — — — — — — — — — Settlements (140 ) — 5 — (135 ) — 12 — (123 ) Transfers into Level 3 — — (22 ) (d) — (22 ) — — — (22 ) Transfers out of Level 3 — — (36 ) (d) (2 ) (38 ) — — — (38 ) Other miscellaneous — — — — — — — — Balance as of December 31, 2018 $ 543 $ — $ 575 $ 42 $ 1,160 $ (249 ) $ 38 $ — $ 949 The amount of total (losses) gains included in income attributed to the change in unrealized (losses) gains related to assets and liabilities held as of December 31, 2018 $ (5 ) $ — $ 165 $ 3 $ 163 $ — $ — $ — $ 163 Generation ComEd PHI Exelon For the year ended December 31, 2017 NDT Fund Investments Pledged Assets for Zion Station Decommissioning Mark-to-Market Derivatives Other Investments Total Generation Mark-to-Market Derivatives Life Insurance Contracts (c) 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 ) — (110 ) — — — (110 ) Transfers into Level 3 — — (6 ) (d) — (6 ) — — — (6 ) Transfers out of Level 3 — — (50 ) (d) (11 ) (61 ) — — — (61 ) Other miscellaneous $ — $ — $ 31 $ (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 held as of December 31, 2017 $ 1 $ — $ 254 $ 3 $ 258 $ — $ 3 $ — $ 261 __________ (a) Includes a reduction for the reclassification of $265 million and $352 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2018 and 2017 , respectively. (b) Includes $24 million of decreases in fair value and an increase for realized losses due to settlements of $17 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2018 . 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 . (c) The amounts represented are life insurance contracts at Pepco. (d) Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts. (e) Includes $(19) million of fair value from contracts acquired as a result of the Everett Marine Terminal acquisition
Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis	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, 2018 and 2017 : Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Operating and Operating Revenues Purchased Power and Fuel Operating and Other, net Total (losses) gains included in net income for the year ended December 31, 2018 $ (7 ) $ (93 ) $ 3 $ 4 $ (7 ) $ (93 ) $ 4 $ 3 Change in the unrealized gains relating to assets and liabilities held for the year ended December 31, 2018 144 21 (2 ) — 144 21 — (2 ) Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Operating and Operating Revenues Purchased Power and Fuel Operating and Other, net 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 Val

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the derivative fair value	December 31, 2018 : Generation Exelon Corporate Exelon Description Economic Hedges Collateral and Netting (a) Subtotal Economic Total Mark-to-market derivative assets (current assets) $ 5 $ (2 ) $ 3 $ — $ 3 Mark-to-market derivative assets (noncurrent assets) 8 (1 ) 7 — 7 Total mark-to-market derivative assets 13 (3 ) 10 — 10 Mark-to-market derivative liabilities (current liabilities) (4 ) 2 (2 ) — (2 ) Mark-to-market derivative liabilities (noncurrent liabilities) (2 ) 1 (1 ) (4 ) (5 ) Total mark-to-market derivative liabilities (6 ) 3 (3 ) (4 ) (7 ) Total mark-to-market derivative net assets (liabilities) $ 7 $ — $ 7 $ (4 ) $ 3 __________ (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, 2017 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges 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 derivative fair value balances related to commodity contracts recorded by the Registrants as of December 31, 2018 : Generation ComEd Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) Total Derivatives Mark-to-market derivative assets (current assets) $ 3,505 $ 105 $ (2,809 ) $ 801 $ — $ 801 Mark-to-market derivative assets (noncurrent assets) 1,266 41 (862 ) 445 — 445 Total mark-to-market derivative assets 4,771 146 (3,671 ) 1,246 — 1,246 Mark-to-market derivative liabilities (current liabilities) (3,429 ) (74 ) 3,056 (447 ) (26 ) (473 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,203 ) (20 ) 972 (251 ) (223 ) (474 ) Total mark-to-market derivative liabilities (4,632 ) (94 ) 4,028 (698 ) (249 ) (947 ) Total mark-to-market derivative net assets (liabilities) $ 139 $ 52 $ 357 $ 548 $ (249 ) $ 299 __________ (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 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 $121 million and $51 million , respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Of the collateral posted/(received), $(94) 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, 2017 : Generation ComEd Exelon Description Economic Hedges Proprietary Trading Collateral and Netting (a)(d) Subtotal (b) Economic Hedges (c) 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 ) (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 ) (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ 667 __________ (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 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 $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) Of the collateral posted/(received), $(117) million represents variation margin on the exchanges
Derivative Instruments, Gain (Loss)	For the years ended December 31, 2018 , 2017 and 2016 , 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, 2018 2017 2016 Income Statement Location Gain (Loss) Generation Operating Revenues $ 7 $ (6 ) $ (10 ) Generation Purchased Power and Fuel (9 ) — — Generation Interest Expense (7 ) (3 ) — Total Generation $ (9 ) $ (9 ) $ (10 ) For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain (Loss) Exelon Operating Revenues $ 7 $ (6 ) $ (10 ) Exelon Purchased Power and Fuel (9 ) — — Exelon Interest Expense (4 ) (3 ) — Total Exelon $ (6 ) $ (9 ) $ (10 ) 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 2018 2017 2016 2018 2017 2016 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (11 ) $ (13 ) $ (9 ) $ 20 $ 28 $ 23 For the years ended December 31, 2018 , 2017 and 2016 , 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" in the Consolidated Statements of Cash Flows. For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain (Loss) Operating revenues $ (270 ) $ (126 ) $ (490 ) Purchased power and fuel (47 ) (43 ) 459 Total Exelon and Generation $ (317 ) $ (169 ) $ (31 )
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, 2018 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Effective portion of changes in fair value 11 11 Reclassifications from AOCI to net income Interest expense 1 1 AOCI derivative loss at December 31, 2018 $ (4 ) $ (2 ) 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 ) __________ (a) Amount is net of related income tax expense of $1 million for the year ended December 31, 2017 .
Change in fair value of derivative contracts	For the years ended December 31, 2018 , 2017 and 2016 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses). For the Years Ended December 31, 2018 2017 2016 Income Statement Location Loss Operating revenues $ — $ (1 ) $ (1 ) For the years ended December 31, 2018 , 2017 and 2016 , 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" in the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. For the Years Ended December 31, 2018 2017 2016 Income Statement Location Gain Operating revenues $ 17 $ 6 $ 2
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2018 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 268 $ — $ 268 Interest rate swaps 620 800 1,420 Total $ 888 $ 800 $ 1,688 The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 94 $ — $ 94 Interest rate swaps (a) 1 — 1 Total $ 95 $ — $ 95 __________ (a) On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017.
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 $43 million , $30 million , $24 million , $28 million , $7 million and $5 million as of December 31, 2018 , respectively. Rating as of December 31, 2018 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 $ 795 $ — $ 795 1 $ 153 Non-investment grade 133 45 88 — — No external ratings Internally rated — investment grade 181 1 180 — — Internally rated — non-investment grade 92 6 86 — — Total $ 1,201 $ 52 $ 1,149 1 $ 153 Net Credit Exposure by Type of Counterparty December 31, 2018 Financial institutions $ 12 Investor-owned utilities, marketers, power producers 737 Energy cooperatives and municipalities 324 Other 76 Total $ 1,149 __________ (a) As of December 31, 2018 , credit collateral held from counterparties where Generation had credit exposure included $17 million of cash and $35 million of letters of credit. The credit collateral does not include non-liquid collateral.
Fair Value, Concentration of Risk [Table Text Block]	For the Years Ended December 31, Credit-Risk Related Contingent Feature 2018 2017 Gross fair value of derivative contracts containing this feature (a) $ (1,723 ) $ (926 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 1,105 577 Net fair value of derivative contracts containing this feature (c) $ (618 ) $ (349 ) __________ (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, 2018
Debt Disclosure [Abstract]
Schedule of Short-term Debt	The following table reflects the Registrants' commercial paper programs supported by the revolving credit agreements and bilateral credit agreements at December 31, 2018 and 2017 : 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 2018 (a)(b)(c) 2017 (a)(b)(c) 2018 2017 2018 2017 Exelon Corporate $ 600 $ 600 $ — $ — 1.93 % 1.16 % Generation 5,300 5,300 — — 1.96 % 1.23 % ComEd 1,000 1,000 — — 2.14 % 1.24 % PECO 600 600 — — 2.24 % 1.13 % BGE 600 600 35 77 2.18 % 1.28 % Pepco 300 500 40 26 2.24 % 1.06 % DPL 300 500 — 216 2.07 % 1.48 % ACE 300 350 14 108 2.21 % 1.43 % Total $ 9,000 $ 9,450 $ 89 $ 427 __________ (a) Excludes $545 million and $480 million in bilateral credit facilities at December 31, 2018 and 2017 , respectively, and $159 million and $179 million in credit facilities for project finance at December 31, 2018 and 2017 , respectively. These credit facilities do not back Generation's commercial paper program. (b) At December 31, 2018, excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million and $5 million , respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. At December 31, 2017, excludes $128 million of credit facility agreements arranged at minority and community banks at 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. (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. The following tables present the short-term borrowings activity for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE during 2018 , 2017 and 2016 . Exelon 2018 2017 2016 Average borrowings $ 531 $ 823 $ 1,125 Maximum borrowings outstanding 1,237 2,147 3,076 Average interest rates, computed on a daily basis 2.21 % 1.32 % 0.88 % Average interest rates, at December 31 2.15 % 1.24 % 1.12 % Generation 2018 2017 2016 Average borrowings $ 37 $ 405 $ 536 Maximum borrowings outstanding 583 1,455 1,735 Average interest rates, computed on a daily basis 1.96 % 1.23 % 0.94 % Average interest rates, at December 31 1.96 % 1.23 % 1.14 % ComEd 2018 2017 2016 Average borrowings $ 154 $ 200 $ 256 Maximum borrowings outstanding 520 470 755 Average interest rates, computed on a daily basis 2.14 % 1.24 % 0.77 % Average interest rates, at December 31 2.14 % 1.24 % N/A PECO 2018 2017 2016 Average borrowings $ 68 $ 2 $ — Maximum borrowings outstanding 350 60 — Average interest rates, computed on a daily basis 2.24 % 1.13 % N/A Average interest rates, at December 31 2.24 % 1.13 % N/A BGE 2018 2017 2016 Average borrowings $ 65 $ 54 $ 143 Maximum borrowings outstanding 239 165 369 Average interest rates, computed on a daily basis 2.18 % 1.28 % 0.77 % Average interest rates, computed at December 31 2.18 % 1.28 % 0.95 % PHI Corporate 2018 2017 2016 Average borrowings N/A N/A $ 153 Maximum borrowings outstanding N/A N/A 559 Average interest rates, computed on a daily basis N/A N/A 1.03 % Average interest rates, computed at December 31 N/A N/A N/A Pepco 2018 2017 2016 Average borrowings $ 22 $ 51 $ 4 Maximum borrowings outstanding 90 197 73 Average interest rates, computed on a daily basis 2.24 % 1.06 % 0.71 % Average interest rates, computed at December 31 2.24 % 1.06 % 0.90 % DPL 2018 2017 2016 Average borrowings $ 87 $ 40 $ 33 Maximum borrowings outstanding 245 216 116 Average interest rates, computed on a daily basis 2.07 % 1.48 % 0.68 % Average interest rates, computed at December 31 2.07 % 1.48 % N/A ACE 2018 2017 2016 Average borrowings $ 95 $ 30 $ — Maximum borrowings outstanding 210 133 5 Average interest rates, computed on a daily basis 2.21 % 1.43 % 0.65 % Average interest rates, computed at December 31 2.21 % 1.43 % N/A
Schedule of Line of Credit Facilities	At December 31, 2018 , the Registrants had the following aggregate bank commitments, credit facility borrowings and available capacity under their respective credit facilities: Available Capacity at December 31, 2018 Borrower Facility Type Aggregate Bank (a) Facility Draws Outstanding Letters of Credit Actual To Support Additional Commercial (b) Exelon Corporate Syndicated Revolver $ 600 $ — $ 9 $ 591 $ 591 Generation Syndicated Revolver 5,300 — 1,203 4,097 4,097 Generation Bilaterals 545 — 353 192 — Generation Project Finance 159 — 119 40 — ComEd Syndicated Revolver 1,000 — 2 998 998 PECO Syndicated Revolver 600 — — 600 600 BGE Syndicated Revolver 600 — 1 599 564 Pepco Syndicated Revolver 300 — 8 292 252 DPL Syndicated Revolver 300 — 1 299 299 ACE Syndicated Revolver 300 — — 300 286 Total $ 9,704 $ — $ 1,696 $ 8,008 $ 7,687 __________ (a) Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million , $33 million , $34 million , $5 million , $5 million , $5 million and $5 million , respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018 , letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.
Schedule Of Credit Agreement Covenants	The following table summarizes the minimum thresholds reflected in the credit agreements for the year ended December 31, 2018 : 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, 2018 , the interest coverage ratios at the Registrants were as follows: Exelon Generation ComEd PECO BGE Pepco DPL ACE Interest coverage ratio 7.34 10.99 7.34 8.14 9.77 5.98 7.03 5.06
Schedule of Long-term Debt Instruments	Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.70 % - 5.95 % 2021 - 2048 $ 3,075 $ 2,925 Loan Agreement 2.00 % 2023 50 0 Total long-term debt 3,125 2,925 Unamortized debt discount and premium, net (18 ) (5 ) Unamortized debt issuance costs (23 ) (17 ) Long-term debt due within one year — (500 ) Long-term debt $ 3,084 $ 2,403 Long-term debt to financing trusts (b) Subordinated debentures to PECO Trust III 7.38 % - 7.50 % 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 December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 3.38 % - 6.80 % 2021 - 2036 $ 1,137 $ 1,037 Transition bonds (b) 5.55 % 2023 59 90 Total long-term debt 1,196 1,127 Unamortized debt discount and premium, net (1 ) (1 ) Unamortized debt issuance costs (7 ) (5 ) Long-term debt due within one year (18 ) (281 ) Long-term debt $ 1,170 $ 840 __________ (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, 2018 are $18 million in 2019, $20 million in 2020 and $21 million in 2021. Lo Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.81 % - 7.90 % 2021 - 2048 $ 5,242 $ 4,743 Senior unsecured notes 7.45 % 2032 185 185 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Transition bonds (b) 5.55 % 2023 59 90 Notes payable and other (c) 7.28 % - 8.88 % 2019 - 2022 16 33 Total long-term debt 5,636 5,189 Unamortized debt discount and premium, net 4 5 Unamortized debt issuance costs (14 ) (6 ) Fair value adjustment 633 686 Long-term debt due within one year (125 ) (396 ) Long-term debt $ 6,134 $ 5,478 __________ (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 $14 million and $27 million at December 31, 2018 and 2017 , respectively. The following tables present the outstanding long-term debt at the Registrants as of December 31, 2018 and 2017 : Exelon Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.70 % - 7.90 % 2019 - 2048 16,496 15,197 Senior unsecured notes 2.45 % - 7.60 % 2019 - 2046 11,285 11,285 Unsecured notes 2.40 % - 6.35 % 2021 - 2048 2,900 2,600 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % 2020 39 82 Notes payable and other (b)(c) 2.85 % - 8.88 % 2019 - 2053 188 405 Junior subordinated notes 3.50 % 2022 1,150 1,150 Long-term software licensing agreement 3.95 % 2024 73 79 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % — 2024 - 2031 112 112 Medium-Terms Notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Transition bonds 5.55 % 2023 59 90 Loan Agreement 2.00 % 2023 50 — Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,253 1,331 Variable rates (f) 5.81 % 2019 - 2024 849 865 Total long-term debt 34,911 33,657 Unamortized debt discount and premium, net (66 ) (57 ) Unamortized debt issuance costs (216 ) (201 ) Fair value adjustment 795 865 Long-term debt due within one year (e) (1,349 ) (2,088 ) Long-term debt $ 34,075 $ 32,176 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 % - 7.50 % 2028 81 81 Subordinated debentures to PECO Trust IV 5.75 % 2033 103 103 Total long-term debt to financing trusts 390 390 Unamortized debt issuance costs — (1 ) Long-term debt to financing trusts $ 390 $ 389 __________ (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 $36 million and $53 million at December 31, 2018 and 2017 , respectively. Lease payments of $21 million , $5 million , $1 million , $1 million , less than $1 million, and $8 million will be made in 2019 , 2020 , 2021 , 2022 , 2023 , 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. (d) Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets. (e) In January 2019, $300 million of ComEd long-term debt due within one year was paid in full. (f) Excludes interest on CEU Upstream nonrecourse debt, see discussion below. Maturity Date December 31, Rates 2018 2017 Long-term debt Unsecured notes 2.40 % - 6.35 % 2021 - 2048 2,900 2,600 Total long-term debt 2,900 2,600 Unamortized debt discount and premium, net (6 ) (6 ) Unamortized debt issuance costs (18 ) (17 ) Long-term debt $ 2,876 $ 2,577 PHI d Maturity Date December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 2.15 % - 6.45 % 2019 - 2048 $ 8,179 $ 7,529 Notes payable and other (b) 7.49 % 2053 8 147 Total long-term debt 8,187 7,676 Unamortized debt discount and premium, net (23 ) (23 ) Unamortized debt issuance costs (63 ) (52 ) Long-term debt due within one year (d) (300 ) (840 ) Long-term debt $ 7,801 $ 6,761 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, 2018 and 2017 , respectively. Lease payments of less than $1 million annually will be made from 2019 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. (d) ration Maturity Date December 31, Rates 2018 2017 Long-term debt Senior unsecured notes 2.95 % - 7.60 % 2019 - 2042 $ 6,019 $ 6,019 Pollution control notes 2.50 % - 2.70 % 2025 - 2036 435 435 Nuclear fuel procurement contracts 3.15 % 2020 39 82 Notes payable and other (a)(b) 2.85 % - 7.83 % 2019 - 2024 164 223 Nonrecourse debt: Fixed rates 2.29 % - 6.00 % 2031 - 2037 1,253 1,331 Variable rates (c) 5.81 % 2019 - 2024 849 865 Total long-term debt 8,759 8,955 Unamortized debt discount and premium, net (6 ) (8 ) Unamortized debt issuance costs (51 ) (60 ) Fair value adjustment 91 103 Long-term debt due within one year (906 ) (346 ) Long-term debt $ 7,887 $ 8,644 __________ (a) Includes Generation’s capital lease obligations of $14 million and $18 million at December 31, 2018 and 2017 , respectively. Generation will make lease payments of $7 million , $5 million , $1 million , and $1 million in 2019 , 2020 , 2021 , and 2022 , respectively. Lease payments of less than $1 million annually will be made from 2023 through expiration of the final capital lease in 2024. Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 1.81 % - 4.27 % 2023 - 2048 $ 1,370 $ 1,171 Unsecured Tax-Exempt Bonds 1.74 % - 5.40 % 2024 - 2031 112 112 Medium-terms notes (unsecured) 7.61 % - 7.72 % 2019 - 2027 22 26 Total long-term debt 1,504 1,309 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (12 ) (11 ) Long-term debt due within one year (91 ) (83 ) Long-term debt $ 1,403 $ 1,217 ___ o Maturity December 31, Rates 2018 2017 Long-term debt First mortgage bonds (a) 3.05 % - 7.90 % 2022 - 2048 $ 2,735 $ 2,535 Notes payable and other (b) 7.28 % - 8.88 % 2019 - 2022 16 35 Total long-term debt 2,751 2,570 Unamortized debt discount and premium, net 2 2 Unamortized debt issuance costs (34 ) (32 ) Long-term debt due within one year (15 ) (19 ) Long-term debt $ 2,704 $ 2,521 ___
Schedule of Maturities of Long-term Debt	-term debt maturities at Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE in the periods 2019 through 2023 and thereafter are as follows: Year Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 2019 $ 1,349 $ 906 $ 300 $ — $ — $ 125 $ 15 $ 91 $ 18 2020 3,528 2,108 500 — — 20 — — 20 2021 1,511 1 350 300 300 261 1 — 260 2022 3,084 1,024 — 350 250 310 310 — — 2023 850 — — 50 300 500 — 500 — Thereafter 24,979 (a) 4,720 7,243 (b) 2,609 (c) 2,050 4,420 2,425 913 898 Total $ 35,301 $ 8,759 $ 8,393 $ 3,309 $ 2,900 $ 5,636 $ 2,751 $ 1,504 $ 1,196 __________ (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. Jun

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule Of Remeasurements Of Deferred Income Taxes Due To Tax Reform [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 remained in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA.
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 was 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.
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, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Included in operations: Federal Current $ 226 $ 337 $ (63 ) $ 11 $ (5 ) $ (4 ) $ 28 $ (3 ) $ (14 ) Deferred (98 ) (347 ) 145 10 47 24 (21 ) 13 18 Investment tax credit amortization (24 ) (21 ) (2 ) — — (1 ) — — — State Current (1 ) 6 (29 ) 1 — 7 — — — Deferred 17 (83 ) 117 (16 ) 32 9 6 12 8 Total $ 120 $ (108 ) $ 168 $ 6 $ 74 $ 35 $ 13 $ 22 $ 12 For the Year Ended December 31, 2017 (a) 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 (471 ) (2,005 ) 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 162 1 136 (9 ) 49 32 13 13 4 Total $ (126 ) $ (1,376 ) $ 417 $ 104 $ 218 $ 217 $ 105 $ 71 $ 26 Successor Predecessor For the Year Ended December 31, 2016 (a) 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 600 (254 ) 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 78 (2 ) 63 5 31 16 12 — 13 7 Total $ 753 $ 282 $ 301 $ 149 $ 174 $ 41 $ 22 $ (4 ) $ 3 $ 17 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. Net interest receivable (payable) as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ 236 $ (2 ) $ 4 $ — $ — $ 1 $ — $ — $ — December 31, 2017 233 (3 ) 4 — — 2 — — — Net penalties payable as of Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2018 $ (17 ) $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2017 (17 ) — — — — — — — —
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, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE U.S. Federal statutory rate 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % 21.0 % Increase (decrease) due to: State income taxes, net of Federal income tax benefit 0.6 (16.6 ) 8.3 (2.6 ) 6.6 3.0 2.2 6.7 7.4 Qualified NDT fund income (1.9 ) (11.8 ) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.2 ) (6.5 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.3 ) (0.4 ) Plant basis differences (3.5 ) — (0.2 ) (14.1 ) (1.3 ) (1.6 ) (2.7 ) (0.3 ) (0.5 ) Production tax credits and other credits (2.2 ) (13.5 ) — — — — — — — Noncontrolling interests (1.0 ) (6.1 ) — — — — — — — Excess deferred tax amortization (8.3 ) — (9.1 ) (3.2 ) (8.0 ) (14.5 ) (14.8 ) (12.0 ) (14.9 ) Tax Cuts and Jobs Act of 2017 0.9 2.7 (0.1 ) — — 0.1 — — — Other 1.0 1.3 0.5 0.3 0.9 0.3 0.2 0.4 1.2 Effective income tax rate 5.4 % (29.5 )% 20.2 % 1.3 % 19.1 % 8.1 % 5.8 % 15.5 % 13.8 % For the Year Ended December 31, 2017 (a) 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 2.9 5.7 0.6 5.4 4.8 3.2 5.4 5.6 Qualified NDT fund income 3.8 9.9 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9 ) (2.1 ) (0.2 ) (0.1 ) (0.1 ) (0.2 ) (0.1 ) (0.2 ) (0.4 ) Plant basis differences (b) (1.7 ) — 0.3 (13.8 ) 0.1 1.1 (0.4 ) 2.0 3.6 Production tax credits and other credits (1.8 ) (4.7 ) — — — — — — — Like-kind exchange (1.2 ) — 1.3 — — — — — — Merger expenses (3.6 ) (1.2 ) — — — (9.5 ) (6.3 ) (7.8 ) (19.8 ) FitzPatrick bargain purchase gain (2.2 ) (5.6 ) — — — — — — — Tax Cuts and Jobs Act of 2017 (c) (33.1 ) (128.3 ) 0.1 (2.3 ) 0.9 6.4 2.7 2.5 1.6 Other 0.1 (0.5 ) 0.2 (0.1 ) 0.2 (0.1 ) (0.2 ) 0.1 (0.4 ) Effective income tax rate (3.3 )% (94.6 )% 42.4 % 19.3 % 41.5 % 37.5 % 33.9 % 37.0 % 25.2 % Successor Predecessor For the Year Ended December 31, 2016 (a) March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL (d) ACE (d) PHI (d) 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 (e) 3.3 3.2 5.6 1.3 5.0 15.7 52.7 6.2 5.8 11.9 Qualified NDT fund income 3.4 7.9 — — — — — — — — 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 (4.9 ) — (0.6 ) (9.6 ) (2.7 ) (22.8 ) (25.5 ) 10.3 39.0 (13.5 ) Production tax credits and other credits (3.6 ) (8.3 ) — — — — — — — — Noncontrolling interests (0.2 ) (0.6 ) — — — — — — — — Statute of limitations expiration (0.4 ) (1.7 ) — — — — — — — — Penalties 1.9 — 4.5 — — — — — (0.7 ) — Merger Expenses 5.6 1.1 — — — 23.5 112.9 (44.9 ) (89.0 ) 11.1 Other (f) (0.7 ) (1.4 ) 0.1 (1.2 ) — (1.8 ) (2.2 ) 1.3 3.3 3.6 Effective income tax rate 38.2 % 32.9 % 44.3 % 25.4 % 37.2 % 49.4 % 169.2 % 8.7 % (5.2 )% 47.2 % __________ (a) Exelon retrospectively adopted the new standard Revenue from Contracts with Customers. The standard was adopted as of January 1, 2018. The effective income tax rates are recast to reflect the impact of the new standard. (b) 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 Note 4 - Regulatory Matters for additional information. (c) Included are impacts for TCJA 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. (d) 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. (e) Includes a remeasurement of uncertain state income tax positions for Pepco and DPL. (f) 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.
Tax Effects of Temporary Differences	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, 2018 and 2017 are presented below: As of December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,533 ) $ (2,495 ) $ (4,059 ) $ (1,862 ) $ (1,399 ) $ (2,577 ) $ (1,148 ) $ (743 ) $ (645 ) Accrual based contracts 117 (44 ) — — — 161 — — — Derivatives and other financial instruments 89 35 69 — — 3 — — — Deferred pension and postretirement obligation 1,435 (188 ) (255 ) (26 ) (26 ) (102 ) (78 ) (46 ) (14 ) Nuclear decommissioning activities (351 ) (351 ) — — — — — — — Deferred debt refinancing costs 234 23 (7 ) — (3 ) 187 (4 ) (2 ) (1 ) Regulatory assets and liabilities (749 ) — 300 (129 ) 172 (90 ) 58 96 83 Tax loss carryforward 237 78 — 18 25 96 12 52 26 Tax credit carryforward 811 816 — — — — — — — Investment in partnerships (797 ) (775 ) — — — — — — — Other, net 934 239 151 67 12 196 98 17 19 Deferred income tax liabilities (net) $ (10,573 ) $ (2,662 ) $ (3,801 ) $ (1,932 ) $ (1,219 ) $ (2,126 ) $ (1,062 ) $ (626 ) $ (532 ) Unamortized investment tax credits (724 ) (700 ) (12 ) (1 ) (3 ) (8 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,297 ) $ (3,362 ) $ (3,813 ) $ (1,933 ) $ (1,222 ) $ (2,134 ) $ (1,064 ) $ (628 ) $ (535 ) 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 )
Summary of Loss Carryforwards	As of December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Plant basis differences $ (12,533 ) $ (2,495 ) $ (4,059 ) $ (1,862 ) $ (1,399 ) $ (2,577 ) $ (1,148 ) $ (743 ) $ (645 ) Accrual based contracts 117 (44 ) — — — 161 — — — Derivatives and other financial instruments 89 35 69 — — 3 — — — Deferred pension and postretirement obligation 1,435 (188 ) (255 ) (26 ) (26 ) (102 ) (78 ) (46 ) (14 ) Nuclear decommissioning activities (351 ) (351 ) — — — — — — — Deferred debt refinancing costs 234 23 (7 ) — (3 ) 187 (4 ) (2 ) (1 ) Regulatory assets and liabilities (749 ) — 300 (129 ) 172 (90 ) 58 96 83 Tax loss carryforward 237 78 — 18 25 96 12 52 26 Tax credit carryforward 811 816 — — — — — — — Investment in partnerships (797 ) (775 ) — — — — — — — Other, net 934 239 151 67 12 196 98 17 19 Deferred income tax liabilities (net) $ (10,573 ) $ (2,662 ) $ (3,801 ) $ (1,932 ) $ (1,219 ) $ (2,126 ) $ (1,062 ) $ (626 ) $ (532 ) Unamortized investment tax credits (724 ) (700 ) (12 ) (1 ) (3 ) (8 ) (2 ) (2 ) (3 ) Total deferred income tax liabilities (net) and unamortized investment tax credits $ (11,297 ) $ (3,362 ) $ (3,813 ) $ (1,933 ) $ (1,222 ) $ (2,134 ) $ (1,064 ) $ (628 ) $ (535 ) 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. The following table provides the Registrants’ carryforwards and any corresponding valuation allowances as of December 31, 2018 : Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Federal Federal general business credits carryforwards 811 (a) 816 — — — — — — — State State net operating losses 4,103 (b) 1,544 (b) — 224 (c) 395 (d) 1,492 (e) 192 (f) 772 (g) 365 (h) Deferred taxes on state tax attributes (net) 272 104 — 18 26 102 12 52 26 Valuation allowance on state tax attributes 35 26 — — 1 6 — — — __________ (a) Exelon’s federal general business credit carryforwards will begin expiring in 2033. (b) Exelon’s and Generation's state net operating losses and credit carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2019. (c) PECO's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031. (d) BGE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2026. (e) PHI's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2036. (f) Pepco's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2033. (g) DPL's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2030. (h) ACE's state net operating loss carryforwards, which are presented on a post-apportioned basis, will begin expiring in 2031.
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, 2018 , 2017 and 2016 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unrecognized tax benefits at January 1, 2018 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Change to positions that only affect timing 15 15 — — — — — — — Increases based on tax positions prior to 2018 30 21 — — — 8 7 1 — Decreases based on tax positions prior to 2018 (251 ) (36 ) — — (120 ) (88 ) (66 ) (22 ) — Decrease from settlements with taxing authorities (53 ) (53 ) — — — — — — — Decreases from expiration of statute of limitations (7 ) (7 ) — — — — — — — Unrecognized tax benefits at December 31, 2018 $ 477 $ 408 $ 2 $ — $ — $ 45 $ — $ — $ 14 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 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 ) — — — — — — — Unrecognized tax benefits at December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Exelon 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 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 ) — — — — — — — Decreases from settlements with taxing authorities (27 ) (27 ) — — — — — — — Unrecognized tax benefits at December 31, 2016 $ 916 $ 490 $ (12 ) $ — $ 120 $ 172 $ 80 $ 37 $ 22
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, 2018 $ (3 ) $ — $ — $ — $ — $ — $ — $ — December 31, 2017 37 (1 ) 11 — — — — — December 31, 2016 165 (13 ) 117 — — 6 — (1 ) Net penalty expense (income) for the years ended Exelon Generation ComEd PECO BGE Pepco DPL ACE December 31, 2018 $ — $ — $ — $ — $ — $ — $ — $ — December 31, 2017 (2 ) — — — — — — — December 31, 2016 106 — 86 — — — — — Successor Predecessor PHI December 31, 2018 December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Net interest expense $ — $ — $ (2 ) $ —
Summary of Open Tax Years by Jurisdiction	Description of tax years open to assessment by major jurisdiction Taxpayer Open Years Exelon (and predecessors) and subsidiaries consolidated federal income tax returns 1999, 2001-2017 PHI Holdings and subsidiaries consolidated federal income tax returns 2013, 2015-2016 Exelon and subsidiaries Illinois unitary income tax returns 2010-2017 Constellation combined New York corporate income tax returns 2010-March 2012 Exelon combined New York corporate income tax returns 2011-2017 Exelon New Jersey corporate income tax returns 2013-2017 Exelon Pennsylvania corporate net income tax returns 2011-2017 PECO Pennsylvania separate company returns 2015-2017 DPL Delaware separate company returns Same as federal ACE New Jersey separate company returns 2014-2017 Exelon and subsidiaries District of Columbia corporate income tax returns 2015-2017 PHI Holdings and subsidiaries District of Columbia corporate income tax returns 2015-2016 Various separate company Maryland corporate net income tax returns Same as federal

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Nuclear Decommissioning Asset Retirement Obligation Rollforward	The following table provides a rollforward of the non-nuclear AROs reflected in the Registrants’ Consolidated Balance Sheets from January 1, 2017 to December 31, 2018 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Non-nuclear AROs at January 1, 2017 $ 393 $ 199 $ 121 $ 28 $ 24 $ 14 $ 2 $ 9 $ 3 Net (decrease) increase due to changes in, and timing of, estimated future cash flows (11 ) (1 ) (13 ) (1 ) 2 2 1 1 — Development projects 1 1 — — — — — — — Accretion expense (a) 18 10 7 1 — — — — — Deconsolidation of EGTP (7 ) (7 ) — — — — — — — Payments (10 ) (5 ) (2 ) (1 ) (2 ) — — — — Non-nuclear AROs at December 31, 2017 384 197 113 27 24 16 3 10 3 Net increase due to changes in, and timing of, estimated future cash flows (b) 80 35 7 — 2 36 34 1 1 Accretion expense (a) 16 10 4 1 1 — — — — Asset divestitures (3 ) (3 ) — — — — — — — Payments (6 ) (1 ) (3 ) — (2 ) — — — — Non-nuclear AROs at December 31, 2018 $ 471 $ 238 $ 121 $ 28 $ 25 $ 52 $ 37 $ 11 $ 4 __________ (a) For ComEd and PECO, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment. (b) In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981. The following table provides a rollforward of the nuclear decommissioning ARO reflected in Exelon’s and Generation’s Consolidated Balance Sheets, from January 1, 2017 to December 31, 2018 : Nuclear decommissioning ARO at January 1, 2017 $ 8,734 Accretion expense 458 Acquisition of FitzPatrick 444 Net increase due to 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 Accretion expense 478 Net decrease due to changes in, and timing of, estimated future cash flows (77 ) Costs incurred related to decommissioning plants (58 ) Nuclear decommissioning ARO at December 31, 2018 (a) (b) $ 10,005 __________ (a) Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017 , respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.
Unrealized Gains Losses On Nuclear Decommissioning Trust Funds	The following table provides unrealized (losses) gains on NDT funds of Exelon and Generation for the years ended 2018 , 2017 and 2016 : 2018 2017 2016 Net unrealized (losses) gains on NDT funds—Regulatory Agreement Units (a) $ (715 ) $ 455 $ 216 Net unrealized (losses) gains on NDT funds—Non-Regulatory Agreement Units (b) (483 ) 521 194 __________ (a) Net unrealized (losses) gains related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities in Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates in Generation’s Consolidated Balance Sheets. (b) Net unrealized (losses) gains 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 Exelon's and Generation's pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at December 31, 2018 and 2017 : 2018 2017 Carrying value of Zion Station pledged assets $ 9 $ 39 Current payable to ZionSolutions (a) 9 37 Cumulative withdrawals by ZionSolutions to pay decommissioning costs (b) 965 942 _______ (a) Included in Other current liabilities within Exelon's and Generation's Consolidated Balance Sheets. Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized gains and losses associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized. (b) 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, 2018
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, 2018 : 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 X X Exelon Corporation Cash Balance Pension Plan (a) X X X X 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 X X Pension Plan of Constellation Energy Nuclear Group, LLC (c) X 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 X X X X Non-Qualified Pension Plans: Exelon Corporation Supplemental Pension Benefit Plan and 2000 Excess Benefit Plan (a) X X X X X Exelon Corporation Supplemental Management Retirement Plan (a) X 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 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 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 X X X X Exelon Corporation Health Care Program (a) X X X 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 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 2018 2017 2018 2017 Change in benefit obligation: Net benefit obligation at beginning of year $ 22,337 $ 21,060 $ 4,856 $ 4,457 Service cost 405 387 112 106 Interest cost 802 842 175 182 Plan participants’ contributions — — 45 53 Actuarial (gain) loss (a) (1,561 ) 1,182 (540 ) 350 Plan amendments (4 ) 9 — — Acquisitions (b) — 16 — 17 Settlements (48 ) (34 ) (4 ) — Gross benefits paid (1,239 ) (1,125 ) (275 ) (309 ) Net benefit obligation at end of year $ 20,692 $ 22,337 $ 4,369 $ 4,856 Pension Benefits Other Postretirement Benefits Exelon 2018 2017 2018 2017 Change in plan assets: Fair value of net plan assets at beginning of year $ 18,573 $ 16,791 $ 2,732 $ 2,578 Actual return on plan assets (945 ) 2,600 (136 ) 346 Employer contributions 337 341 46 64 Plan participants’ contributions — — 45 53 Gross benefits paid (1,239 ) (1,125 ) (275 ) (309 ) Settlements (48 ) (34 ) (4 ) — Fair value of net plan assets at end of year $ 16,678 $ 18,573 $ 2,408 $ 2,732 __________ (a) The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience. The pension and OPEB actuarial losses in 2017 primarily reflect a decrease in the discount rate. (b) Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017.
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 2018 2017 2018 2017 Other current liabilities $ 26 $ 28 $ 33 $ 31 Pension obligations 3,988 3,736 — — Non-pension postretirement benefit obligations — — 1,928 2,093 Unfunded status (net benefit obligation less plan assets) $ 4,014 $ 3,764 $ 1,961 $ 2,124
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, 2018 , 2017 and 2016 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 2018 2017 (a) 2016 (b) 2018 2017 (a) 2016 (b) Components of net periodic benefit cost: Service cost $ 405 $ 387 $ 354 $ 112 $ 106 $ 107 Interest cost 802 842 830 175 182 185 Expected return on assets (1,252 ) (1,196 ) (1,141 ) (173 ) (162 ) (162 ) Amortization of: Prior service cost (credit) 2 1 14 (186 ) (188 ) (185 ) Actuarial loss 629 607 554 66 61 63 Settlement and other charges (c) 3 3 2 1 — — Net periodic benefit cost $ 589 $ 644 $ 613 $ (5 ) $ (1 ) $ 8 __________ (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 January 1, 2016 to March 23, 2016 Components of net periodic benefit cost: Service cost $ 12 $ 1 Interest cost 26 6 Expected return on assets (30 ) (5 ) Amortization of: Prior service cost (credit) — (3 ) Actuarial loss 14 2 Net periodic benefit cost $ 22 $ 1 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, 2018 and 2017 , respectively, for all plans combined: Exelon Exelon Pension Benefits Other Postretirement Benefits 2018 2017 2018 2017 Prior service (credit) cost $ (29 ) $ (24 ) $ (337 ) $ (522 ) Actuarial loss 7,558 7,556 531 829 Total $ 7,529 $ 7,532 $ 194 $ 307 Total included in AOCI $ 3,899 $ 3,896 $ 70 $ 125 Total included in regulatory assets (liabilities) $ 3,630 $ 3,636 $ 124 $ 182
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, 2018 , 2017 and 2016 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 2018 2017 2016 (a) 2018 2017 2016 (a) Changes in plan assets and benefit obligations recognized in AOCI and regulatory assets (liabilities): Current year actuarial (gain) loss $ 635 $ (222 ) $ 644 $ (232 ) $ 166 $ (101 ) Amortization of actuarial loss (629 ) (607 ) (554 ) (66 ) (61 ) (63 ) Current year prior service cost (credit) (4 ) 9 (60 ) — — — Amortization of prior service (cost) credit (2 ) (1 ) (14 ) 186 188 185 Settlements (3 ) (3 ) — — — — Acquisitions — — 994 — — 94 Total recognized in AOCI and regulatory assets (liabilities) $ (3 ) $ (824 ) $ 1,010 $ (112 ) $ 293 $ 115 Total recognized in AOCI $ 3 $ (401 ) $ 51 $ (55 ) $ 168 $ 20 Total recognized in regulatory assets (liabilities) $ (6 ) $ (423 ) $ 959 $ (57 ) $ 125 $ 95 Predecessor Pension Benefits Other PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Changes in plan assets and benefit Current year actuarial loss (gain) $ — $ — Amortization of actuarial loss (14 ) (2 ) Amortization of prior service (cost) credit — 3 Total recognized in AOCI and regulatory assets (liabilities) $ (14 ) $ 1 Total recognized in AOCI $ (1 ) $ — Total recognized in regulatory assets (liabilities) $ (13 ) $ 1
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]
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, 2018 , 2017 and 2016 . 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 2018 2017 2016 (f) 2018 2017 2016 (f) Discount rate 4.31 % (a) 3.62 % (b) 4.04 % (c) 4.30 % (a) 3.61 % (b) 4.04 % (c) Investment Crediting Rate 4.46 % 4.00 % 4.46 % N/A N/A N/A Rate of compensation increase (d) (d) (e) (d) (d) (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 5.00% __________ (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, 2018 . Certain benefit plans used individual rates ranging from 4.13% - 4.36% and 4.27% - 4.38% 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, 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. (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, 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. (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 for the PHI predecessor for the period from January 1, 2016, to March 23, 2016
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, 2018 , 2017 and 2016 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Pension Benefits Other Postretirement Benefits Exelon 2018 2017 2016 2018 2017 2016 Discount rate 3.62 % (a) 4.04 % (b) 4.29 % (c) 3.61 % (a) 4.04 % (b) 4.29 % (c) Investment Crediting Rate 4.00 % 4.46 % 5.31 % N/A N/A N/A Expected return on plan assets 7.00 % (d) 7.00 % (d) 7.00 % (d) 6.60 % (d) 6.58 % (d) 6.71 % (d) Rate of compensation increase (f) (f) (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% 5.50% Predecessor Pension Benefits Other Postretirement Benefits PHI January 1, 2016 to March 23, 2016 January 1, 2016 to March 23, 2016 Discount rate 4.65%/4.55% (g) 4.55 % Investment crediting rate 2.89 % N/A Expected return on plan assets (h) 6.50 % 6.75 % 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 decreasing to ultimate trend of 5.00% in 2020 __________ (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, 2018 . 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 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. (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, 2016 . Certain benefit plans used the individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively. (d) Not applicable to pension and other postretirement benefit plans that do not have plan assets. (e) 3.25% through 2019 and 3.75% thereafter. (f) 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. (g) The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55% , respectively. (h) Expected return on other postretirement benefit plan assets is pre-tax.
Pension And Other Postretirement Benefit Contributions [Table Text Block]	s The following tables provide contributions to the pension and other postretirement benefit plans: Pension Benefits Other Postretirement Benefits 2018 (a) 2017 (a) 2016 (a) 2018 2017 2016 Exelon $ 337 $ 341 $ 347 $ 46 $ 64 $ 50 Generation 128 137 140 11 11 12 ComEd 38 36 33 4 5 5 PECO 28 24 30 — — — BGE 40 39 31 14 14 18 BSC (b) 41 38 39 5 2 3 Pepco 6 62 24 11 10 8 DPL — — 22 — 2 — ACE 6 — 15 — 20 2 PHISCO (c) 50 5 17 1 — 2 Pension Benefits Other Postretirement Benefits Successor Predecessor Successor Predecessor 2018 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 2018 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 PHI $ 62 $ 67 $ 74 $ 4 $ 12 $ 32 $ 12 $ — __________ (a) Exelon's and Generation's pension contributions include $21 million and $25 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 and 2016 , respectively. There were no pension contributions for the year ended December 31, 2018 . (b) Includes $2 million , $4 million , and $6 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2018 , 2017 , and 2016 , respectively. (c) : Qualified Pension Plans Non-Qualified Pension Plans Other Exelon $ 301 $ 25 $ 44 Generation 135 7 13 ComEd 65 1 2 PECO 25 1 — BGE 34 1 15 BSC 41 7 2 PHI 1 8 12 Pepco — 2 10 DPL — 1 — ACE — — 1 PHISCO 1 5 1
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, 2018 were: Pension Benefits Other Postretirement Benefits 2019 $ 1,196 $ 255 2020 1,221 263 2021 1,258 269 2022 1,284 274 2023 1,302 282 2024 through 2028 6,770 1,483 Total estimated future benefit payments through 2028 $ 13,031 $ 2,826
Schedule Of Pension And Other Postretirement Benefit Costs [Table Text Block]	For the Years Ended December 31, Exelon Generation (a) ComEd PECO BGE BSC (b) Pepco (c) DPL (c) ACE (c) PHISCO (c)(d) 2018 $ 583 $ 204 $ 177 $ 18 $ 60 $ 57 $ 15 $ 6 $ 12 $ 34 2017 643 227 176 29 64 53 25 13 13 43 2016 621 218 166 33 68 48 31 18 15 47 Successor Predecessor PHI For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Pension and Other Postretirement Benefit Costs $ 67 $ 94 $ 88 $ 23 __________ (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]	ively. Exelon’s pension and other postretirement benefit plan target asset allocations at December 31, 2018 and 2017 asset allocations were as follows: Pension Plans Exelon Percentage of Plan Assets at December 31, Asset Category Target Allocation 2018 2017 Equity securities 35 % 32 % 35 % Fixed income securities 37 % 38 39 Alternative investments (a) 28 % 30 26 Total 100 % 100 % Other Postretirement Benefit Plans Exelon Percentage of Plan Assets at December 31, Asset Category Target Allocation 2018 2017 Equity securities 47 % 44 % 47 % Fixed income securities 28 % 28 28 Alternative investments (a) 25 % 28 25 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 in the Registrants' Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy at December 31, 2018 and 2017 : Exelon December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Pension plan assets Cash equivalents $ 350 $ — $ — $ — $ 350 Equities (c) 3,364 — 2 1,980 5,346 Fixed income: U.S. Treasury and agencies 996 173 — — 1,169 State and municipal debt — 59 — — 59 Corporate debt — 3,716 216 — 3,932 Other (c) — 329 — 613 942 Fixed income subtotal 996 4,277 216 613 6,102 Private equity — — — 1,219 1,219 Hedge funds — — — 1,608 1,608 Real estate — — — 1,029 1,029 Private credit — — 268 798 1,066 Pension plan assets subtotal $ 4,710 $ 4,277 $ 486 $ 7,247 $ 16,720 December 31, 2018 (a) Level 1 Level 2 Level 3 Not subject to leveling Total Other postretirement benefit plan assets Cash equivalents $ 22 $ — $ — $ — $ 22 Equities 537 2 — 508 1,047 Fixed income: U.S. Treasury and agencies 11 56 — — 67 State and municipal debt — 126 — — 126 Corporate debt — 48 — — 48 Other 183 72 — 170 425 Fixed income subtotal 194 302 — 170 666 Hedge funds — — — 411 411 Real estate — — — 132 132 Private credit — — — 132 132 Other postretirement benefit plan assets subtotal $ 753 $ 304 $ — $ 1,353 $ 2,410 Total pension and other postretirement benefit plan assets (e) $ 5,463 $ 4,581 $ 486 $ 8,600 $ 19,130 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 (d) — — 224 695 919 Pension plan assets subtotal $ 5,300 $ 4,601 $ 458 $ 8,216 $ 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 (e) $ 6,090 $ 4,913 $ 458 $ 9,842 $ 21,303 __________ (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 less than $1 million and $6 million , which have a total notional amount of $5,991 million and $3,606 million at December 31, 2018 and 2017 , 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) Prior year amounts reflect a reclassification from Not subject to leveling into Level 3. (e) Excludes net liabilities of $44 million and net assets of $2 million at December 31, 2018 and 2017 , respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables or payables related to pending securities sales and purchases, interest and dividends receivable
Schedule of Changes in Fair Value of Plan Assets [Table Text Block]	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, 2018 and 2017 : Exelon Fixed Income Equities Private Credit Total Pension Assets Balance as of January 1, 2018 $ 232 $ 2 $ 224 $ 458 Actual return on plan assets: Relating to assets still held at the (14 ) — 9 (5 ) Relating to assets sold during the period (1 ) — — (1 ) Purchases, sales and settlements: Purchases 19 — 35 54 Sales (8 ) — — (8 ) Settlements (b) (12 ) — — (12 ) Balance as of December 31, 2018 $ 216 $ 2 $ 268 $ 486 Fixed income Equities Private Credit (a) Total Pension Assets Balance as of January 1, 2017 $ 206 $ 2 $ 229 $ 437 Actual return on plan assets: Relating to assets still held at the reporting date 11 — 29 40 Purchases, sales and settlements: Purchases 31 — 5 36 Sales (16 ) — — (16 ) Settlements (b) — — (39 ) (39 ) Balance as of December 31, 2017 $ 232 $ 2 $ 224 $ 458 __________ (a)
Schedule Of Defined Contributions [Table Text Block]	in limits. The following table presents matching contributions to the savings plan for the years ended December 31, 2018 , 2017 and 2016 : For the Year Ended December 31, Exelon (a) Generation (a) ComEd PECO BGE BSC (b) Pepco (c) DPL (c) ACE PHISCO (c)(d) 2018 $ 179 $ 86 $ 37 $ 9 $ 12 $ 22 $ 3 $ 2 $ 2 $ 6 2017 128 55 31 10 10 9 3 2 2 6 2016 164 79 34 10 12 19 3 2 2 6 Successor Predecessor PHI For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Saving Plan Matching Contributions $ 13 $ 13 $ 10 $ 3 __________ (a) Includes $13 million related to CENG for the year ended December 31, 2016. (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, 2018	Dec. 31, 2016
Restructuring and Related Activities [Abstract]
Severance	For the periods ended December 31, 2018 , 2017 and 2016 , the Registrants have recognized costs to achieve the PHI merger as follows: For the Year Ended December 31, Acquisition, Integration and Financing Costs (a) 2018 2017 2016 Exelon $ 7 $ 16 $ 143 Generation 5 22 37 ComEd (b) — 1 (6 ) PECO 1 4 5 BGE (b) 1 4 (1 ) Pepco (b) — (6 ) 28 DPL (b) — (7 ) 20 ACE (b) — (6 ) 19 Successor Predecessor For the Year Ended December 31, March 24, 2016 to December 31, 2016 January 1, 2016 to Acquisition, Integration and Financing Costs (a) 2018 2017 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 as regulatory assets of $24 million , $8 million , $8 million , and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $8 million , $6 million , $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016 , includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.	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: Severance Benefits Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE 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.
Severance Liability	Amounts included in the table below represent the severance liability recorded for employees of each Registrant. Exelon's severance liability includes amounts related to BSC that are billed through intercompany allocations . Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2016 $ 88 $ 36 $ 3 $ — $ — $ 29 $ — $ — $ — Severance costs (a) 35 31 2 — — 3 — — — Payments (29 ) (9 ) (2 ) — — (12 ) — — — Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — Severance costs (a) 35 9 1 — 1 5 1 — — Payments (52 ) (20 ) (2 ) — — (18 ) (1 ) — — Balance at December 31, 2018 $ 77 $ 47 $ 2 $ — $ 1 $ 7 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits.

Shareholders' Equity Sharehold

Shareholders' Equity Shareholder Equity (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 : December 31, 2018 2017 Par Value Shares Authorized Shares Outstanding Common Stock Exelon no par value 2,000,000,000 968,187,955 963,335,888 ComEd $ 12.50 250,000,000 127,021,331 127,021,246 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 Plan_2

Stock-Based Compensation Plans (All Registrants) (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 and 2016 and PHI's predecessor period January 1, 2016 to March 23, 2016 : Exelon Year Ended December 31, Components of Stock-Based Compensation Expense 2018 2017 2016 (a) Performance share awards $ 143 $ 107 $ 93 Restricted stock units 57 77 75 Stock options — — — Other stock-based awards 8 7 7 Total stock-based compensation expense included in operating and maintenance expense 208 191 175 Income tax benefit (54 ) (74 ) (68 ) Total after-tax stock-based compensation expense $ 154 $ 117 $ 107 __________ (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, Components of Stock-Based Compensation Expense 2016 Time-based restricted stock units $ 2 Performance-based restricted stock units 1 Time-based restricted stock awards — Total stock-based compensation expense included in operating and maintenance expense 3 Income tax benefit (1 ) Total after-tax stock-based compensation expense $ 2
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, 2018 , 2017 and 2016 , as well as for the PHI predecessor period January 1, 2016 to March 23, 2016 : Year Ended December 31, Subsidiaries 2018 2017 2016 Exelon $ 208 $ 191 $ 175 Generation 77 88 78 ComEd 8 7 8 PECO 5 3 3 BGE 3 1 1 BSC (a) 111 88 81 PHI Successor (b)(c) 4 4 4 Predecessor January 1 to 2016 PHI $ 3 __________ (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, 2018 and 2017 was not material. (c) These amounts primarily represent amounts billed to PHI’s subsidiaries through PHISCO intercompany allocations.
Stock Based Compensation Tax Benefit	The following tables present information regarding Exelon’s tax benefits for the years ended December 31, 2018 , 2017 and 2016 . Exelon Year Ended December 31, 2018 2017 2016 Realized tax benefit when exercised/distributed: Restricted stock units 28 35 27 Performance share awards 16 29 18
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, 2018 : Shares Weighted Average Exercise Price (per share) Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Balance of shares outstanding at December 31, 2017 6,723,611 $ 47.69 2.65 $ 7 Options exercised (1,522,952 ) 36.54 Options forfeited — — Options expired (1,173,007 ) 74.99 Balance of shares outstanding at December 31, 2018 4,027,652 $ 43.95 2.90 $ 14 Exercisable at December 31, 2018 (a) 4,027,652 $ 43.95 2.90 $ 14 __________ (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, 2018 , 2017 and 2016 : Year Ended 2018 2017 2016 Intrinsic value (a) $ 12 $ 15 $ 11 Cash received for exercise price 56 107 19 __________ (a) The difference between the market value on the date of exercise and the option exercise price.
Schedule of Nonvested Restricted Stock Units Activity	The following table summarizes Exelon’s nonvested restricted stock unit activity for the year ended December 31, 2018 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2017 (a) 3,389,503 $ 32.24 Granted 1,321,988 38.60 Vested (1,845,300 ) 32.03 Forfeited (65,046 ) 32.96 Undistributed vested awards (b) (507,804 ) 36.76 Nonvested at December 31, 2018 (a) 2,293,341 $ 35.06 __________ (a) Excludes 1,131,487 and 1,488,383 of restricted stock units issued to retirement-eligible employees as of December 31, 2018 and 2017 , respectively, as they are fully vested. (b) Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2018 .
Schedule of Nonvested Performance-based Units Activity	The following table summarizes Exelon’s nonvested performance share awards activity for the year ended December 31, 2018 : Exelon Shares Weighted Average Grant Date Fair Value (per share) Nonvested at December 31, 2017 (a) 2,956,966 $ 32.65 Granted 1,637,542 38.15 Change in performance 1,348,029 30.66 Vested (848,574 ) 36.26 Forfeited (50,467 ) 36.24 Undistributed vested awards (b) (1,640,268 ) 33.38 Nonvested at December 31, 2018 (a) 3,403,228 $ 33.13 __________ (a) Excludes 3,586,259 and 2,723,440 of performance share awards issued to retirement-eligible employees as of December 31, 2018 and 2017 , respectively, as they are fully vested. (b) Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2018 . 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, 2018 , 2017 and 2016 : Year Ended 2018 (a) 2017 2016 Weighted average grant date fair value (per share) $ 38.15 $ 35.00 $ 28.85 Fair value of performance shares settled 61 72 45 Fair value of performance shares settled in cash 49 56 28 __________ (a) As of December 31, 2018 , $33 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.7 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, 2018 2017 Current liabilities (a) $ 135 $ 57 Deferred credits and other liabilities (b) 109 100 Common stock 26 26 Total $ 270 $ 183 __________ (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, 2018
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, 2018 2017 2016 Net income attributable to common shareholders $ 2,010 $ 3,786 $ 1,121 Weighted average common shares outstanding — basic 967 947 924 Assumed exercise and/or distributions of stock-based awards 2 2 3 Weighted average common shares outstanding — diluted 969 949 927

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income [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, 2018 and 2017 : For the Year Ended December 31, 2018 Gains and Unrealized Pension and Foreign AOCI of Investments Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 11 — (143 ) (10 ) 1 (141 ) Amounts reclassified from AOCI (b) 1 — 181 — — 182 Net current-period OCI 12 — 38 (10 ) 1 41 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (10 ) — — — (10 ) Ending balance $ (2 ) $ — $ (2,960 ) $ (33 ) $ — $ (2,995 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 11 — — (10 ) — 1 Amounts reclassified from AOCI (b) 1 — — — — 1 Net current-period OCI 12 — — (10 ) — 2 Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (3 ) — — — (3 ) Ending balance $ (4 ) $ — $ — $ (33 ) $ (1 ) $ (38 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Impact of adoption of Recognition and Measurement of Financial Assets and Financial Liabilities standard (c) — (1 ) — — — (1 ) Ending balance $ — $ — $ — $ — $ — $ — For the Year Ended December 31, 2017 Gains and Unrealized Pension and Foreign AOCI of Investments 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 Impact of adoption of Reclassification of Certain Tax Effects from AOCI (d) — — (539 ) — — (539 ) Ending balance $ (14 ) $ 10 $ (2,998 ) $ (23 ) $ (1 ) $ (3,026 ) 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 __________ (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) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Financial Liabilities. The standard was adopted as of January 1, 2018, which resulted in an increase to Retained earnings and Accumulated other comprehensive loss of $10 million , $3 million and $1 million for Exelon, Generation and PECO, respectively. The amounts reclassified related to Rabbi Trusts. See Note 1 — Significant Accounting Policies for additional information. (d) Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million , primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 1 — Significant Accounting Policies for additional information.
Reclassification Out Of Accumulated Other Comprehensive Income	The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the years ended December 31, 2018 and 2017 : For the Year Ended December 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (1 ) $ (1 ) Interest expense (1 ) (1 ) Total before tax — — Tax benefit $ (1 ) $ (1 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 90 $ — Actuarial losses (b) (333 ) — (243 ) — Total before tax 62 — Tax benefit $ (181 ) $ — Net of tax Total Reclassifications $ (182 ) $ (1 ) Net of tax 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 (Losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense (5 ) (5 ) Total before tax 1 1 Tax benefit $ (4 ) $ (4 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 92 $ — Actuarial losses (b) (324 ) — (232 ) — Total before tax 92 — Tax benefit $ (140 ) $ — Net of tax Total Reclassifications $ (144 ) $ (4 ) Net of tax __________ (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 information.
Schedule of Other Comprehensive Income Loss Tax	The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the years ended December 31, 2018 , 2017 and 2016 : For the Year Ended December 31, 2018 2017 2016 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 24 $ 36 $ 30 Actuarial loss reclassified to periodic benefit cost (86 ) (128 ) (118 ) Pension and non-pension postretirement benefit plans valuation adjustment 50 13 115 Change in unrealized gains on cash flow hedges (5 ) (7 ) — Change in unrealized gains (losses) on investments in unconsolidated affiliates — (3 ) 3 Change in unrealized gains on marketable securities — (1 ) — Total $ (17 ) $ (90 ) $ 30 Generation Change in unrealized gains on cash flow hedges $ (4 ) $ (6 ) $ (2 ) Change in unrealized gains (losses) on investments in unconsolidated affiliates (1 ) (3 ) 3 Change in unrealized gains on marketable securities — (1 ) — Total $ (5 ) $ (10 ) $ 1

Commitments and Contingencies_2

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies [Line Items]
Other Commitments	Commercial Commitments (All Registrants). Exelon’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 1,703 $ 1,394 $ 308 $ 1 $ — $ — $ — Surety bonds (a) 1,402 1,331 33 38 — — — Financing trust guarantees 378 — — — — — 378 Guaranteed lease residual values (b) 24 3 3 2 3 3 10 Total commercial commitments $ 3,507 $ 2,728 $ 344 $ 41 $ 3 $ 3 $ 388 __________ (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 $61 million , $19 million of which is a guarantee by Pepco, $26 million by DPL and $16 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, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 1,680 $ 1,380 $ 299 $ 1 $ — $ — $ — Surety bonds (a) 1,220 1,201 19 — — — — Total commercial commitments $ 2,900 $ 2,581 $ 318 $ 1 $ — $ — $ — __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. ComEd’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 2 $ 2 $ — $ — $ — $ — $ — Surety bonds (a) 12 10 — 2 — — — Financing trust guarantees 200 — — — — — 200 Total commercial commitments $ 214 $ 12 $ — $ 2 $ — $ — $ 200 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PECO’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 9 $ 9 $ — $ — $ — $ — $ — Financing trust guarantees 178 — — — — — 178 Total commercial commitments $ 187 $ 9 $ — $ — $ — $ — $ 178 __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. BGE’s commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 3 $ 2 $ 1 $ — $ — $ — $ — Surety bonds (a) 17 3 14 — — — — Total commercial commitments $ 20 $ 5 $ 15 $ — $ — $ — $ — __________ (a) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. PHI commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 8 $ — $ 8 $ — $ — $ — $ — Surety bonds (a) $ 41 $ 41 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 24 3 3 2 3 3 10 Total commercial commitments $ 73 $ 44 $ 11 $ 2 $ 3 $ 3 $ 10 __________ (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 $61 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, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Letters of credit $ 8 $ — $ 8 $ — $ — $ — $ — Surety bonds (a) $ 33 $ 33 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 8 1 1 1 1 1 3 Total commercial commitments $ 49 $ 34 $ 9 $ 1 $ 1 $ 1 $ 3 __________ (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 $19 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 Pepco believes the likelihood of payments being required under the guarantees is remote. DPL commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 5 $ 5 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 10 1 1 1 1 1 5 Total commercial commitments $ 15 $ 6 $ 1 $ 1 $ 1 $ 1 $ 5 __________ (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 $26 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 DPL believes the likelihood of payments being required under the guarantees is remote. ACE commercial commitments as of December 31, 2018 , representing commitments potentially triggered by future events, were as follows: Expiration within Total 2019 2020 2021 2022 2023 2024 and beyond Surety bonds (a) $ 3 $ 3 $ — $ — $ — $ — $ — Guaranteed lease residual values (b) 6 1 1 — 1 1 2 Total commercial commitments $ 9 $ 4 $ 1 $ — $ 1 $ 1 $ 2 __________ (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 ACE believes the likelihood of payments being required under the guarantees is remot
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	mum 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 ACE believes the likelihood of payments being required under the guarantees is remote. Leases (All Registrants) 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, 2018 were: Exelon (a)(b) Generation (a)(b) ComEd (a)(c) PECO (a)(c) BGE (a)(c)(d)(e) PHI (a) Pepco (a) DPL (a)(c) ACE (a) 2019 $ 140 $ 33 $ 7 $ 5 $ 35 $ 48 $ 11 $ 14 $ 7 2020 149 46 5 5 35 46 10 13 6 2021 143 46 4 5 33 43 9 12 5 2022 126 47 4 5 18 42 8 12 5 2023 97 46 3 5 3 39 8 10 4 Remaining years 723 545 — — 19 159 40 35 5 Total minimum future lease payments $ 1,378 $ 763 $ 23 $ 25 $ 143 $ 377 $ 86 $ 96 $ 32 __________ (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 2019 - 2023 , was $3 million , $5 million , $1 million and $1 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 $26 million , $28 million , $28 million and $14 million related to years 2019 - 2022
Accrued environmental liabilities	. As of December 31, 2018 and 2017 , 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, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 496 $ 356 Generation 108 — ComEd 329 327 PECO 27 25 BGE 5 4 PHI 27 — Pepco 25 — DPL 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) $ 1,274 $ 1,100 __________ (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, 2018 and 2017 , 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, 2018 December 31, 2017 DOE receivable - current (a) $ 124 $ 94 DOE receivable - noncurrent (b) 15 15 Amounts owed to co-owners (a)(c) (17 ) (11 ) __________ (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 Inform_2

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Financial Information [Abstract]
Schedule Of Taxes Excluding Income And Excise Taxes [Table Text Block]	The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the years ended December 31, 2018 , 2017 and 2016 . For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Taxes other than income Utility (a) $ 919 $ 114 $ 243 $ 131 $ 94 $ 337 $ 316 $ 21 $ — Property 557 273 30 15 143 94 58 32 3 Payroll 247 130 27 16 17 24 5 3 2 Other 60 39 11 1 — — — — — Total taxes other than income $ 1,783 $ 556 $ 311 $ 163 $ 254 $ 455 $ 379 $ 56 $ 5 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 __________ (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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
Schedule of Other Nonoperating Income, by Component [Table Text Block]	For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on NDT funds (a) Regulatory agreement units $ 506 $ 506 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 302 302 — — — — — — — Net unrealized losses on NDT funds Regulatory agreement units (715 ) (715 ) — — — — — — — Non-regulatory agreement units (483 ) (483 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (8 ) (8 ) — — — — — — — Regulatory offset to NDT fund-related activities (b) 171 171 — — — — — — — Total decommissioning-related activities (227 ) (227 ) — — — — — — — Investment income 43 32 — 1 1 4 2 1 — Interest income related to uncertain income tax positions 5 1 — — — — — — — AFUDC—Equity 69 — 19 7 18 25 22 2 1 Non-service net periodic benefit cost (47 ) — — — — — — — — Other 45 16 14 — — 14 7 7 1 Other, net $ (112 ) $ (178 ) $ 33 $ 8 $ 19 $ 43 $ 31 $ 10 $ 2 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 NDT funds (a) Regulatory agreement units $ 488 $ 488 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 209 209 — — — — — — — Net unrealized gains on NDT 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 NDT 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 ) — — — — — — — Benefit related to uncertain income tax positions (c) 2 — — — — — — — — AFUDC—Equity 73 — 12 9 16 36 23 7 6 Non-service net periodic benefit cost (109 ) — — — — — — — — Other 31 4 10 — — 16 8 7 1 Other, net $ 947 $ 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 NDT funds (a) Regulatory agreement units $ 237 $ 237 $ — $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 126 126 — — — — — — — — Net unrealized gains on NDT 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 NDT 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 Non-service net periodic benefit cost (116 ) — — — — — — — — — Loss on debt extinguishment (3 ) (2 ) — — — — — — — — Other 24 (5 ) 7 1 — 15 8 2 21 (11 ) Other, net $ 297 $ 401 $ (65 ) $ 8 $ 21 $ 36 $ 13 $ 9 $ 44 $ (4 ) __________ (a) Includes investment income and realized gains and losses on sales of investments within the NDT funds. (b) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of net 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. (c) See Note 14 — Income Taxes for additional information on the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position.
Cash Flow Supplemental Disclosures	The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the years ended December 31, 2018 , 2017 and 2016 . For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment $ 3,740 $ 1,748 $ 820 $ 274 $ 335 $ 480 $ 218 $ 131 $ 94 Regulatory assets 555 — 120 27 148 260 167 51 42 Amortization of intangible assets, net 58 49 — — — — — — — Amortization of energy contract assets and liabilities (a) 14 14 — — — — — — — Nuclear fuel (b) 1,115 1,115 — — — — — — — ARO accretion (c) 489 489 — — — — — — — Total depreciation, amortization and accretion $ 5,971 $ 3,415 $ 940 $ 301 $ 483 $ 740 $ 385 $ 182 $ 136 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 __________ (a) Included in Operating revenues or Purchased power and fuel in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (b) Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. For the year ended December 31, 2018 Successor Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash paid (refunded) during the year: Interest (net of amount capitalized) $ 1,421 $ 369 $ 332 $ 125 $ 94 $ 250 $ 123 $ 56 $ 61 Income taxes (net of refunds) 95 746 (153 ) (2 ) 14 (32 ) 41 (6 ) (12 ) Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 583 $ 204 $ 177 $ 18 $ 59 $ 67 $ 15 $ 6 $ 12 Loss (gain) from equity method investments 28 30 — — — (1 ) — — — Provision for uncollectible accounts 159 48 40 33 10 28 11 6 11 Provision for excess and obsolete inventory 24 20 3 — — — — — — Stock-based compensation costs 75 — — — — — — — — Other decommissioning-related activity (a) (2 ) (2 ) — — — — — — — Energy-related options (b) 10 10 — — — — — — — Amortization of regulatory asset related to debt costs 8 — 3 1 — 4 2 1 1 Amortization of rate stabilization deferral 14 — — — — 14 14 — — Amortization of debt fair value adjustment (15 ) (12 ) — — — (3 ) — — — Merger-related commitments (c) — — — — — 5 — 5 — Severance costs 35 9 — — — — — — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Amortization of debt costs 36 14 5 2 1 3 2 — 1 Discrete impacts from EIMA and FEJA (d) 28 — 28 — — — — — — Long-term incentive plan 140 — — — — — — — — Other (19 ) (23 ) (14 ) (3 ) (12 ) 6 (6 ) 7 — Total other non-cash operating activities $ 1,124 $ 298 $ 242 $ 51 $ 58 $ 143 $ 60 $ 24 $ 24 Non-cash investing and financing activities: Change in capital expenditures not paid $ (69 ) $ (199 ) $ 11 $ (12 ) $ 50 $ 93 $ 20 $ 22 $ 46 Change in PPE related to ARO update (107 ) (130 ) 7 — 1 15 12 2 1 Dividends on stock compensation 6 — — — — — — — — Acquisition of land 3 — — — — 3 — — 3 __________ (a) Includes the elimination of decommissioning-related activities 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 5 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 4 — Regulatory Matters for additional information. 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 ) (28 ) (13 ) (7 ) (6 ) Total other non-cash operating activities $ 721 $ 112 $ 164 $ 54 $ 65 $ 58 $ (6 ) $ 9 $ 17 Non-cash investing and financing activities: Change 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 decommissioning-related activities 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 5 - Mergers, Acquisitions and Dispositions for additional information. (d) Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 4 — Regulatory Matters for additional 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 additional information on 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 ) (3 ) (14 ) (6 ) (11 ) (3 ) Total other non-cash operating activities $ 1,333 $ 15 $ 215 $ 65 $ 88 $ 175 $ 114 $ 155 $ 515 $ 46 Non-cash investing and financing activities: Change 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, net of cash (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 5 - Mergers, Acquisitions and Dispositions for additional 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 4 — Regulatory Matters for additional 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 additional information on 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 5 - Mergers, Acquisitions and Dispositions for additional information. The following tables provide a reconciliation of cash, cash equivalents and restricted cash reported within the Registrants' Consolidated Balance Sheets that sum to the total of the same amounts in their Consolidated Statements of Cash Flows. Successor December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,349 $ 750 $ 135 $ 130 $ 7 $ 124 $ 16 $ 23 $ 7 Restricted cash 247 153 29 5 6 43 37 1 4 Restricted cash included in other long-term assets 185 — 166 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 1,781 $ 903 $ 330 $ 135 $ 13 $ 186 $ 53 $ 24 $ 30 Successor December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 898 $ 416 $ 76 $ 271 $ 17 $ 30 $ 5 $ 2 $ 2 Restricted cash 207 138 5 4 1 42 35 — 6 Restricted cash included in other long-term assets 85 — 63 — — 23 — — 23 Total cash, cash equivalents and restricted cash $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 Successor Predecessor December 31, 2016 December 31, 2016 March 23, 2016 Exelon Generation ComEd PECO BGE Pepco DPL ACE PHI PHI Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 9 $ 46 $ 101 $ 170 $ 319 Restricted cash 253 158 2 4 24 33 — 9 43 11 Restricted cash included in other long-term assets 26 — — — 3 — — 23 23 18 Total cash, cash equivalents and restricted cash $ 914 $ 448 $ 58 $ 67 $ 50 $ 42 $ 46 $ 133 $ 236 $ 348 Predecessor December 31, 2015 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 6,502 $ 431 $ 67 $ 295 $ 9 $ 26 $ 5 $ 5 $ 3 Restricted cash 205 123 2 3 24 14 2 — 12 Restricted cash included in other long-term assets 5 2 — — 3 18 — — 18 Total cash, cash equivalents and restricted cash $ 6,712 $ 556 $ 69 $ 298 $ 36 $ 58 $ 7 $ 5 $ 33
Supplemental Balance Sheet Disclosures [Text Block]	The following tables provide additional information about assets and liabilities of the Registrants at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues (a) $ 1,656 $ 965 $ 223 $ 114 $ 168 $ 186 $ 97 $ 59 $ 30 Allowance for uncollectible accounts (b) (319 ) (104 ) (81 ) (61 ) (20 ) (53 ) (21 ) (13 ) (19 ) December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Unbilled customer revenues (a) $ 1,858 $ 1,017 $ 242 $ 162 $ 205 $ 232 $ 133 $ 68 $ 31 Allowance for uncollectible (b) (322 ) (114 ) (73 ) (56 ) (24 ) (55 ) (21 ) (16 ) (18 ) __________ (a) Represents unbilled portion of receivables estimated under Exelon’s unbilled critical accounting policy. (b) Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable. The Utility Registrants are required, under separate legislation and regulations in Illinois, Pennsylvania, Maryland, District of Columbia and New Jersey, to purchase certain receivables from alternative retail electric and, as applicable, natural gas suppliers that participate in the utilities' consolidated billing. ComEd, BGE, Pepco and DPL purchase receivables at a discount to recover primarily uncollectible accounts expense from the suppliers. PECO and ACE purchase receivables at face value and recover uncollectible accounts expense, including those from alternative retail electric and natural gas supplies, through base distribution rates and a rate rider, respectively. Exelon and the Utility Registrants do not record unbilled commodity receivables under their POR programs. Purchased billed receivables are recorded on a net basis in Exelon’s and the Utility Registrant's Consolidated Statements of Operations and Comprehensive Income and are classified in Other accounts receivable, net in their Consolidated Balance Sheets. The following tables provide information about the purchased receivables of those companies as of December 31, 2018 and 2017 . December 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 313 $ 94 $ 74 $ 61 $ 84 $ 57 $ 8 $ 19 Allowance for uncollectible accounts (a) (34 ) (17 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 279 $ 77 $ 69 $ 58 $ 75 $ 52 $ 7 $ 16 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 __________ (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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate. The following tables provide additional information about Registrants' investments at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Investments Equity method investments: Financing trusts (a) $ 14 $ — $ 6 $ 8 $ — $ — $ — $ — $ — Bloom 180 180 — — — — — — — NET Power 70 70 — — — — — — — Other equity method investments 3 1 — — — — — — — Total equity method investments 267 251 6 8 — — — — — Other investments: Employee benefit trusts and investments (b) 244 49 — 17 5 130 105 — — Equity investments without readily determinable fair values 72 72 — — — — — — — Other available for sale debt security investments 40 40 — — — — — — — Other 2 2 — — — — — — — Total investments $ 625 $ 414 $ 6 $ 25 $ 5 $ 130 $ 105 $ — $ — 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 — — Equity investments without readily determinable fair values 62 62 — — — — — — — Other available for sale debt security investments 37 37 — — — — — — — Total investments $ 640 $ 433 $ 6 $ 25 $ 5 $ 132 $ 102 $ — $ — __________ (a) Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments in the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information. (b) The Registrants’ debt and equity security investments are recorded at fair market value. The following tables provide additional information about liabilities of the Registrants at December 31, 2018 and 2017 . December 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Accrued expenses Compensation-related accruals (a) $ 1,191 $ 479 $ 187 $ 49 $ 68 $ 99 $ 29 $ 19 $ 12 Taxes accrued 412 226 71 28 46 74 58 4 5 Interest accrued 334 77 105 33 39 50 25 8 12 Severance accrued 44 26 2 — — 5 — — — Other accrued expenses 131 90 8 3 2 28 14 8 6 Total accrued expenses $ 2,112 $ 898 $ 373 $ 113 $ 155 $ 256 $ 126 $ 39 $ 35 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 100 63 5 2 1 29 17 6 5 Total accrued expenses $ 1,837 $ 1,022 $ 327 $ 114 $ 164 $ 261 $ 137 $ 35 $ 33 __________ (a) Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 , and 2016 is as follows: Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 17,411 $ — $ — $ — $ — $ — $ (1,256 ) $ 16,155 Competitive businesses natural gas revenues 2,718 — — — — — (8 ) 2,710 Competitive businesses other revenues 308 — — — — — (5 ) 303 Rate-regulated electric revenues — 5,882 2,470 2,428 4,609 — (45 ) 15,344 Rate-regulated natural gas revenues — — 568 741 181 — (20 ) 1,470 Shared service and other revenues — — — — 15 1,948 (1,960 ) 3 Total operating revenues $ 20,437 $ 5,882 $ 3,038 $ 3,169 $ 4,805 $ 1,948 $ (3,294 ) $ 35,985 2017 Competitive businesses electric revenues $ 15,332 $ — $ — $ — $ — $ — $ (1,105 ) $ 14,227 Competitive businesses natural gas revenues 2,575 — — — — — — 2,575 Competitive businesses other revenues 593 — — — — — (1 ) 592 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 ) — Total operating revenues $ 18,500 $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 1,831 $ (3,025 ) $ 33,567 Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon 2016 Competitive businesses electric revenues $ 15,400 $ — $ — $ — $ — $ — $ (1,430 ) $ 13,970 Competitive businesses natural gas revenues 2,146 — — — — — — 2,146 Competitive businesses other revenues 211 — — — — — (4 ) 207 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 Total operating revenues $ 17,757 $ 5,254 $ 2,994 $ 3,233 $ 3,643 $ 1,648 $ (3,164 ) $ 31,365 Intersegment revenues (d) : 2018 $ 1,269 $ 27 $ 8 $ 29 $ 15 $ 1,942 $ (3,289 ) $ 1 2017 1,110 15 7 16 50 1,824 (3,020 ) 2 2016 1,428 15 8 21 45 1,647 (3,159 ) 5 Depreciation and amortization: 2018 $ 1,797 $ 940 $ 301 $ 483 $ 740 $ 92 $ — $ 4,353 2017 1,457 850 286 473 675 87 — 3,828 2016 1,879 775 270 423 515 74 — 3,936 Operating expenses (c) : 2018 $ 19,510 $ 4,741 $ 2,452 $ 2,696 $ 4,156 $ 1,929 $ (3,341 ) $ 32,143 2017 18,001 4,214 2,215 2,562 3,911 1,742 (3,026 ) 29,619 2016 16,878 4,056 2,292 2,683 3,549 1,812 (3,164 ) 28,106 Interest expense, net: 2018 $ 432 $ 347 $ 129 $ 106 $ 261 $ 279 $ — $ 1,554 2017 440 361 126 105 245 283 — 1,560 2016 364 461 123 103 195 290 — 1,536 Income (loss) before income taxes: 2018 $ 365 $ 832 $ 466 $ 387 $ 432 $ (249 ) $ (1 ) $ 2,232 2017 1,455 984 538 525 578 (296 ) (2 ) 3,782 2016 857 679 587 468 (58 ) (555 ) (5 ) 1,973 Income taxes: 2018 $ (108 ) $ 168 $ 6 $ 74 $ 35 $ (55 ) $ — $ 120 2017 (1,376 ) 417 104 218 217 294 — (126 ) 2016 282 301 149 174 3 (156 ) — 753 Successor Generation (a) ComEd PECO BGE PHI (e) Other (b) Intersegment Exelon Net income (loss): 2018 $ 443 $ 664 $ 460 $ 313 $ 398 $ (193 ) $ (1 ) $ 2,084 2017 2,798 567 434 307 362 (590 ) (2 ) 3,876 2016 550 378 438 294 (61 ) (398 ) (5 ) 1,196 Capital expenditures: 2018 $ 2,242 $ 2,126 $ 849 $ 959 $ 1,375 $ 43 $ — $ 7,594 2017 $ 2,259 $ 2,250 $ 732 $ 882 $ 1,396 $ 65 $ — $ 7,584 2016 $ 3,078 $ 2,734 $ 686 $ 934 $ 1,008 $ 113 $ — $ 8,553 Total assets: 2018 $ 47,556 $ 31,213 $ 10,642 $ 9,716 $ 21,984 $ 8,355 $ (9,800 ) $ 119,666 2017 48,457 29,726 10,170 9,104 21,247 8,618 (10,552 ) 116,770 __________ (a) See Note 25 — Related Party Transactions for additional information on intersegment revenues. (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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes. (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 authoritative 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, 2018 . Successor and Predecessor PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : December 31, 2018 - Successor Rate-regulated electric revenues $ 2,239 $ 1,151 $ 1,236 $ — $ (17 ) $ 4,609 Rate-regulated natural gas revenues — 181 — — — 181 Shared service and other revenues — — — 435 (420 ) 15 Total operating revenues $ 2,239 $ 1,332 $ 1,236 $ 435 $ (437 ) $ 4,805 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 Total operating revenues $ 2,158 $ 1,300 $ 1,186 $ 52 $ (17 ) $ 4,679 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 Total operating revenues $ 1,675 $ 942 $ 989 $ 50 $ (13 ) $ 3,643 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 — — — — — — Total operating revenues $ 511 $ 335 $ 268 $ 43 $ (4 ) $ 1,153 Intersegment revenues: December 31, 2018 - Successor $ 6 $ 8 $ 3 $ 435 $ (437 ) $ 15 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 ) — Depreciation and amortization: December 31, 2018 - Successor $ 385 $ 182 $ 136 $ 37 $ — $ 740 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 Operating expenses: December 31, 2018 - Successor $ 1,919 $ 1,143 $ 1,087 $ 442 $ (435 ) $ 4,156 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 Pepco DPL ACE Other (b) Intersegment PHI Interest expense, net: December 31, 2018 - Successor $ 128 $ 58 $ 64 $ 11 $ — $ 261 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 Income (loss) before income taxes: December 31, 2018 - Successor $ 223 $ 142 $ 87 $ 388 $ (408 ) $ 432 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 Income taxes: December 31, 2018 - Successor $ 13 $ 22 $ 12 $ (10 ) $ (2 ) $ 35 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 Net income (loss): December 31, 2018 - Successor $ 210 $ 120 $ 75 $ (22 ) $ 15 $ 398 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 Capital expenditures: December 31, 2018 - Successor $ 656 $ 364 $ 335 $ 20 $ — $ 1,375 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 Total assets: December 31, 2018 - Successor $ 8,299 $ 4,588 $ 3,699 $ 10,819 $ (5,421 ) $ 21,984 December 31, 2017 - Successor 7,832 4,357 3,445 10,600 (4,987 ) 21,247 __________ (a) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes. (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	Competitive Business Revenues (Generation): 2018 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,241 $ 233 $ 5,474 $ 13 $ 5,487 Midwest 4,527 190 4,717 (11 ) 4,706 New England 2,660 185 2,845 (4 ) 2,841 New York 1,723 (36 ) 1,687 — 1,687 ERCOT 572 560 1,132 1 1,133 Other Power Regions 870 686 1,556 (62 ) 1,494 Total Competitive Businesses Electric Revenues 15,593 1,818 17,411 (63 ) 17,348 Competitive Businesses Natural Gas Revenues 1,524 1,194 2,718 62 2,780 Competitive Businesses Other Revenues (c) 510 (202 ) 308 1 309 Total Generation Consolidated Operating Revenues 17,627 2,810 $ 20,437 $ — $ 20,437 2017 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 5,523 $ (8 ) $ 5,515 $ 25 $ 5,540 Midwest 3,923 283 4,206 (25 ) 4,181 New England 2,064 (54 ) 2,010 (8 ) 2,002 New York 1,605 (38 ) 1,567 (17 ) 1,550 ERCOT 641 317 958 4 962 Other Power Regions 594 482 1,076 (27 ) 1,049 Total Competitive Businesses Electric Revenues 14,350 982 15,332 (48 ) 15,284 Competitive Businesses Natural Gas Revenues 1,658 917 2,575 53 2,628 Competitive Businesses Other Revenues (c) 744 (151 ) 593 (5 ) 588 Total Generation Consolidated Operating Revenues $ 16,752 $ 1,748 $ 18,500 $ — $ 18,500 2016 Revenues from external customers (a) Contracts with customers Other (b) Total Intersegment Revenues Total Revenues Mid-Atlantic $ 6,182 $ 30 $ 6,212 $ (33 ) $ 6,179 Midwest 4,007 395 4,402 10 4,412 New England 1,953 (175 ) 1,778 (9 ) 1,769 New York 1,198 10 1,208 (42 ) 1,166 ERCOT 810 21 831 6 837 Other Power Regions 670 299 969 (62 ) 907 Total Competitive Businesses Electric Revenues 14,820 580 15,400 (130 ) 15,270 Competitive Businesses Natural Gas Revenues 1,953 193 2,146 135 2,281 Competitive Businesses Other Revenues (c) 756 (545 ) 211 (5 ) 206 Total Generation Consolidated Operating Revenues $ 17,529 $ 228 $ 17,757 $ — $ 17,757 __________ (a) Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants. (b) Includes revenues from derivatives and leases. (c) Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $38 million and $52 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 and 2016 , respectively, unrealized mark-to-market losses of $262 million , $131 million , and $500 million in 2018 , 2017 , and 2016 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): 2018 2017 2016 RNF from external (a) Intersegment Total RNF RNF from external (a) Intersegment RNF Total RNF RNF from external (a) Intersegment Total RNF Mid-Atlantic $ 3,022 $ 51 $ 3,073 $ 3,105 $ 109 $ 3,214 $ 3,282 $ 35 $ 3,317 Midwest 3,112 23 3,135 2,810 10 2,820 2,969 2 2,971 New England 368 (14 ) 354 538 (24 ) 514 467 (29 ) 438 New York 1,112 10 1,122 1,007 1 1,008 771 (19 ) 752 ERCOT 501 (243 ) 258 575 (243 ) 332 412 (131 ) 281 Other Power Regions 515 (140 ) 375 476 (171 ) 305 483 (147 ) 336 Total Revenues net of purchased power and fuel for Reportable Segments $ 8,630 $ (313 ) $ 8,317 $ 8,511 $ (318 ) $ 8,193 $ 8,384 $ (289 ) $ 8,095 Other (b) 114 313 427 299 318 617 543 289 832 Total Generation Revenues net of purchased power and fuel expense $ 8,744 $ — $ 8,744 $ 8,810 $ — $ 8,810 $ 8,927 $ — $ 8,927 __________ (a) Includes purchases and sales from/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. Includes a $54 million and $57 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 and 2016 , respectively, unrealized mark-to-market losses of $319 million , $175 million , and $41 million in 2018 , 2017 , and 2016 , respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $57 million , $12 million and $60 million for the year ended December 31, 2018 , 2017 , and 2016 and the elimination of intersegment RNF.
Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]	Electric and Gas Revenue by Customer Class (Utility Registrants): 2018 Successor Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,942 $ 1,566 $ 1,382 $ 2,351 $ 1,021 $ 669 $ 661 Small commercial & industrial 1,487 404 257 488 140 186 162 Large commercial & industrial 538 223 429 1,124 846 100 178 Public authorities & electric railroads 47 28 28 58 32 14 12 Other (a) 867 243 327 593 193 175 227 Total rate-regulated electric revenues (b) 5,881 2,464 2,423 4,614 2,232 1,144 1,240 Rate-regulated natural gas revenues Residential — 395 491 99 — 99 — Small commercial & industrial — 143 77 44 — 44 — Large commercial & industrial — 1 124 8 — 8 — Transportation — 23 — 16 — 16 — Other (c) — 6 63 13 — 13 — Total rate-regulated natural gas revenues (d) — 568 755 180 — 180 — Total rate-regulated revenues from contracts with customers 5,881 3,032 3,178 4,794 2,232 1,324 1,240 Other revenues Revenues from alternative revenue programs (29 ) (7 ) (26 ) — — 4 (4 ) Other rate-regulated electric revenues (e) 30 12 13 10 7 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Total other revenues 1 6 (9 ) 11 7 8 (4 ) Total rate-regulated revenues for reportable segments $ 5,882 $ 3,038 $ 3,169 $ 4,805 $ 2,239 $ 1,332 $ 1,236 2017 Successor Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,715 $ 1,505 $ 1,365 $ 2,246 $ 964 $ 663 $ 619 Small commercial & industrial 1,363 401 254 490 137 187 166 Large commercial & industrial 455 223 427 1,086 794 103 189 Public authorities & electric railroads 44 30 31 60 33 14 13 Other (a) 886 204 299 541 199 163 191 Total rate-regulated electric revenues (b) 5,463 2,363 2,376 4,423 2,127 1,130 1,178 Rate-regulated natural gas revenues Residential — 331 437 90 — 90 — Small commercial & industrial — 131 75 38 — 38 — Large commercial & industrial — 1 119 8 — 8 — Transportation — 23 — 15 — 15 — Other (c) — 8 28 9 — 9 — Total rate-regulated natural gas revenues (d) — 494 659 160 — 160 — Total rate-regulated revenues from contracts with customers 5,463 2,857 3,035 4,583 2,127 1,290 1,178 Other revenues Revenues from alternative revenue programs 43 — 124 40 26 6 8 Other rate-regulated electric revenues (e) 30 12 13 8 5 3 — Other rate-regulated natural gas revenues (e) — 1 4 1 — 1 — Other revenues (f) — — — 47 — — — Total other revenues 73 13 141 96 31 10 8 Total rate-regulated revenues for reportable segments $ 5,536 $ 2,870 $ 3,176 $ 4,679 $ 2,158 $ 1,300 $ 1,186 Successor Predecessor 2016 March 24, 2016 to December 31, 2016 January 1, 2016 to March 23, 2016 Revenues from contracts with customers ComEd PECO BGE Pepco DPL ACE PHI PHI Rate-regulated electric revenues Residential $ 2,603 $ 1,631 $ 1,504 $ 1,004 $ 672 $ 664 $ 1,779 $ 561 Small commercial & industrial 1,318 430 276 150 188 183 400 121 Large commercial & industrial 462 234 434 790 99 201 835 255 Public authorities & electric railroads 45 32 35 32 13 13 45 13 Other (a) 820 192 276 190 160 187 400 169 Total rate-regulated electric revenues (b) 5,248 2,519 2,525 2,166 1,132 1,248 3,459 1,119 Rate-regulated natural gas revenues Residential — 309 432 — 86 — 50 36 Small commercial & industrial — 121 66 — 35 — 21 14 Large commercial & industrial — — 114 — 6 — 4 2 Transportation — 24 — — 13 — 10 3 Other (c) — 9 28 — 8 — 7 2 Total rate-regulated natural gas revenues (d) — 463 640 — 148 — 92 57 Total rate-regulated revenues from contracts with customers 5,248 2,982 3,165 2,166 1,280 1,248 3,551 1,176 Other revenues Revenues from alternative revenue programs (24 ) — 53 14 (6 ) 9 43 (26 ) Other rate-regulated electric revenues (e) 30 12 13 6 3 — 6 3 Other rate-regulated natural gas revenues (e) — — 2 — — — — — Other revenues (f) — — — — — — 43 — Total other revenues 6 12 68 20 (3 ) 9 92 (23 ) Total rate-regulated revenues for reportable segments $ 5,254 $ 2,994 $ 3,233 $ 2,186 $ 1,277 $ 1,257 $ 3,643 $ 1,153 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $ 27 million , $7 million , $8 million , $15 million , $6 million , $8 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018 , $15 million , $6 million , $5 million , $3 million , $6 million , $8 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, in 2017 , and $15 million , $7 million , $7 million , $2 million , $5 million , $7 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2016 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of $1 million and $21 million at PECO and BGE, respectively, in 2018 , $1 million and $11 million at PECO and BGE, respectively, in 2017 , and $1 million and $14 million at PECO and BGE, respectively, in 2016 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $47 million and $43 million at PHI in 2017 and 2016 , respectively.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Schedule of Related Party Transactions [Table Text Block]	The financial statements of PECO include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 2 $ 1 $ 3 BSC 3 5 3 ComEd 1 — 1 BGE 1 1 1 ACE 1 — — Total operating revenues from affiliates $ 8 $ 7 $ 8 Purchased power from affiliates Generation (b) $ 126 $ 135 $ 287 Operating and maintenance from affiliates: BSC (c) $ 146 $ 146 $ 142 Generation 2 2 2 ComEd 7 — 1 BGE 1 1 1 Total operating and maintenance from affiliates $ 156 $ 149 $ 146 Interest expense to affiliates, net: PECO Trust III $ 6 $ 6 $ 6 PECO Trust IV 6 6 6 Exelon Corporate 2 — — Generation — (1 ) — Total interest expense to affiliates, net: $ 14 $ 11 $ 12 Capitalized costs BSC (c) $ 64 $ 59 $ 57 Cash dividends paid to parent $ 306 $ 288 $ 277 Contributions from parent $ 89 $ 16 $ 18 PHI The financial statements of PHI include related party transactions as presented in the tables below: Successor For the Year Ended December 31, For the Year Ended December 31, March 24, 2016 to December 31, 2018 2017 2016 Operating revenues from affiliates: BSC $ 12 $ 48 $ 44 PHISCO 1 2 — Generation 2 — 1 Total operating revenues from affiliates $ 15 $ 50 $ 45 Purchased power from affiliates Generation $ 355 $ 463 $ 486 Operating and maintenance from affiliates: BSC (a) $ 147 $ 145 $ 86 Other 5 5 3 Total operating and maintenance from affiliates $ 152 $ 150 $ 89 Earnings (losses) in equity method investments: Other $ 1 $ — $ — Capitalized costs: BSC (a) $ 102 $ — $ — PHISCO (a) 79 — — Total capitalized costs $ 181 $ — $ — Cash dividends paid to parent $ 326 $ 311 $ 273 Contributions from parent $ 385 $ 758 $ 1,251 December 31, 2018 2017 Receivables from affiliates (current): ComEd (a) $ 69 $ 28 PECO (b) 30 26 BGE (c) 24 24 Pepco (d) 28 36 DPL (e) 7 12 ACE (f) 5 6 PHISCO (h) — 1 Other 10 7 Total receivables from affiliates (current) $ 173 $ 140 Intercompany money pool (current): Exelon Corporate $ 100 $ — PCI — 54 Total intercompany money pool (current) $ 100 $ 54 Payables to affiliates (current): Exelon Corporate (i) $ 17 $ 21 BSC (h) 95 74 ComEd 19 12 PECO (b) — 4 Other 8 12 Total payables to affiliates (current) $ 139 $ 123 Other liabilities to affiliates (current): ComEd (a) $ 14 $ — Long-term debt to affiliates (noncurrent): Exelon Corporate (k) $ 898 $ 910 Payables to affiliates (noncurrent): ComEd (j) $ 2,217 $ 2,528 PECO (j) 389 537 Total payables to affiliates (noncurrent) $ 2,606 $ 3,065 __________ (a) Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs and ZECs to ComEd. (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. (c) Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. (d) Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC. (e) Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs. (f) Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process. (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 for additional information. (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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in Exelon’s Consolidated Balance Sheets. December 31, 2018 2017 Prepaid voluntary employee beneficiary association trust (c) $ 5 $ 2 Receivables from affiliates (current): Voluntary employee beneficiary association trust $ 1 $ 1 Generation 19 12 Total receivables from affiliates (current) $ 20 $ 13 Receivables from affiliates (noncurrent): Generation (d) $ 2,217 $ 2,528 Payables to affiliates (current): Generation (a) $ 55 $ 28 BSC (b) 56 39 ComEd Financing III 4 4 Exelon Corporate 4 3 Total payables to affiliates (current) $ 119 $ 74 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 and ZECs from Generation. (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) 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, 2018 2017 Receivables from affiliates (current): DPL $ 1 $ — Payables to affiliates (current): Exelon Corporation $ 1 $ — Generation (b) 28 36 BSC (c) 19 11 PHISCO (c) 14 27 Total payables to affiliates (current) $ 62 $ 74 __________ (a) Pepco provides energy to Generation for Generation’s own use. (b) Pepco procures a portion of its electricity supply requirements from Generation under its MDPSC and DCPSC approved market based SOS commodity programs. (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 performed underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco. The financial statements of DPL include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: BSC $ 1 $ — $ — PHISCO 4 6 5 ComEd 1 — — ACE 1 — — Other 1 2 2 Total operating revenues from affiliates $ 8 $ 8 $ 7 Purchased power from affiliates Generation (a) $ 120 $ 179 $ 154 Operating and maintenance: PHISCO (b), (d) $ — $ 165 $ 194 PES (c) — 9 8 Total operating and maintenance $ — $ 174 $ 202 Operating and maintenance from affiliates: BSC (b) $ 51 $ 31 $ 18 PHISCO (b), (d) 111 — — Other — 1 1 Total operating and maintenance from affiliates $ 162 $ 32 $ 19 Capitalized costs: BSC (b) $ 28 $ — $ — PHISCO (b) 25 — — Total capitalized costs $ 53 $ — $ — Cash dividends paid to parent $ 96 $ 112 $ 54 Contributions from parent $ 150 $ — $ 152 December 31, 2018 2017 Payables to affiliates (current): Generation $ 40 $ 54 BGE — 1 BSC (a) 41 24 Exelon Corporate 6 6 Other 7 5 Total payables to affiliates (current) $ 94 $ 90 __________ (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. December 31, 2018 2017 Payables to affiliates (current): Exelon Corporate $ 1 $ — Generation (a) 7 12 BSC (b) 11 7 PHISCO (b) 12 27 Pepco 1 — ACE 1 — Total payables to affiliates (current) $ 33 $ 46 The financial statements of ComEd include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates Generation $ 9 $ 9 $ 7 BSC 7 6 6 PECO 10 — 1 BGE 1 — 1 Total operating revenues from affiliates $ 27 $ 15 $ 15 Purchased power from affiliates Generation (a) $ 529 $ 108 $ 47 Operating and maintenance from affiliates BSC (b) $ 265 $ 270 $ 225 PECO 1 — 1 BGE 1 — 1 Total operating and maintenance from affiliates $ 267 $ 270 $ 227 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 13 $ 13 Capitalized costs BSC (b) $ 135 $ 118 $ 112 Cash dividends paid to parent $ 459 $ 422 $ 369 Contributions from parent $ 500 $ 651 $ 315 December 31, 2018 2017 Prepaid voluntary employee beneficiary association trust (d) $ 1 $ — Receivables from affiliates (noncurrent): Generation (e) $ 389 $ 537 Payables to affiliates (current): Generation (b) $ 30 $ 22 BSC (c) 26 29 Exelon Corporate 2 1 PECO Trust III 1 1 Total payables to affiliates (current) $ 59 $ 53 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. (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, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 22 $ 10 $ 13 BSC 5 5 6 ComEd 1 — 1 PECO 1 1 1 Total operating revenues from affiliates $ 29 $ 16 $ 21 Purchased power from affiliates Generation (b) $ 257 $ 384 $ 604 Operating and maintenance from affiliates: BSC (c) $ 157 $ 152 $ 130 Generation 3 — — ComEd 1 — 1 PECO 1 1 1 Total operating and maintenance from affiliates $ 162 $ 153 $ 132 Interest expense to affiliates, net: BGE Capital Trust II $ — $ 10 $ 16 Capitalized costs BSC (c) $ 79 $ 54 $ 36 Cash dividends paid to parent $ 209 $ 198 $ 179 Contributions from parent $ 109 $ 184 $ 61 December 31, 2018 2017 Receivables from affiliates (current): Other $ 1 $ 1 Payables to affiliates (current): Generation (b) $ 24 $ 24 BSC (c) 38 25 Exelon Corporate 2 1 Other 1 2 Total payables to affiliates (current) $ 65 $ 52 __________ (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. (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. The financial statements of Generation include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: ComEd (a) $ 523 $ 121 $ 47 PECO (b) 128 138 290 BGE (c) 260 388 608 Pepco (d) 206 255 295 DPL (e) 120 179 154 ACE (f) 29 29 37 BSC 2 1 2 Other — 4 6 Total operating revenues from affiliates $ 1,268 $ 1,115 $ 1,439 Purchased power and fuel from affiliates: ComEd $ (6 ) $ 13 $ — BGE 20 9 12 Other — (3 ) — Total purchased power and fuel from affiliates $ 14 $ 19 $ 12 Operating and maintenance from affiliates: ComEd (g) $ 7 $ 7 $ 7 PECO (g) 2 1 3 BGE (g) 2 1 1 Pepco 1 — 1 PHISCO 1 1 1 BSC (h) 652 689 650 Other (4 ) (2 ) — Total operating and maintenance from affiliates $ 661 $ 697 $ 663 Interest expense to affiliates, net: Exelon Corporate (i) $ 36 $ 37 $ 39 PCI — 1 — PECO — 1 — Total interest expense to affiliates, net: $ 36 $ 39 $ 39 Earnings (losses) in equity method investments Qualifying facilities and domestic power projects $ (30 ) $ (33 ) $ (25 ) Capitalized costs BSC (h) $ 67 $ 98 $ 98 Cash distributions paid to member $ 1,001 $ 659 $ 922 Contributions from member $ 155 $ 102 $ 142 December 31, 2018 2017 Payables to affiliates (current): ComEd Financing III $ 4 $ 4 PECO Trust III 1 1 Total payables to affiliates (current) $ 5 $ 5 Long-term debt to financing trusts: ComEd Financing III $ 206 $ 205 PECO Trust III 81 81 PECO Trust IV 103 103 Total long-term debt to financing trusts $ 390 $ 389 __________ (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 authoritative guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 4 — Regulatory Matters for additional information. The financial statements of Pepco include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: Generation (a) $ 1 $ — $ 1 BSC 1 — — PHISCO 4 6 4 Total operating revenues from affiliates $ 6 $ 6 $ 5 Purchased power from affiliates Generation (b) $ 206 $ 255 $ 295 Operating and maintenance: PHISCO (c), (e) $ — $ 219 $ 263 PES (d) — 29 39 Total operating and maintenance $ — $ 248 $ 302 Operating and maintenance from affiliates: BSC (c) $ 89 $ 53 $ 31 PHISCO (c), (e) 137 5 4 Total operating and maintenance from affiliates $ 226 $ 58 $ 35 Capitalized costs: BSC (c) $ 40 $ — $ — PHISCO (c) 32 — — Total capitalized costs $ 72 $ — $ — Cash dividends paid to parent $ 169 $ 133 $ 136 Contributions from parent $ 166 $ 161 $ 187 The financial statements of Exelon include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: Generation (a) (2 ) — PECO (a) — 1 1 BGE (a) — 4 4 ACE (a) — — — Other 1 2 5 Total operating revenues from affiliates $ (1 ) $ 7 $ 10 Interest expense to affiliates, net: ComEd Financing III $ 13 $ 14 $ 13 PECO Trust III 6 6 6 PECO Trust IV 6 6 6 BGE Capital Trust II — 10 16 Total interest expense to affiliates, net $ 25 $ 36 $ 41 Earnings (losses) in equity method investments: Qualifying facilities and domestic power projects $ (29 ) $ (33 ) $ (25 ) Other 1 1 1 Total losses in equity method investments $ (28 ) $ (32 ) $ (24 ) ACE The financial statements of ACE include related party transactions as presented in the tables below: For the Years Ended December 31, 2018 2017 2016 Operating revenues from affiliates: PHISCO $ 2 $ 1 $ 2 Other 1 1 1 Total operating revenues from affiliates $ 3 $ 2 $ 3 Purchased power from affiliates Generation (a) $ 29 $ 29 $ 37 Operating and maintenance: PHISCO (b), (c) $ — $ 135 $ 155 Operating and maintenance from affiliates: BSC (b) $ 42 $ 25 $ 15 PHISCO (b), (c) 98 — — Other 2 3 3 Total operating and maintenance from affiliates $ 142 $ 28 $ 18 Capitalized costs: BSC (b) $ 20 $ — $ — PHISCO (b) 21 — — Total capitalized costs $ 41 $ — $ — Cash dividends paid to parent $ 59 $ 68 $ 63 Contributions from parent $ 67 $ — $ 139 December 31, 2018 2017 Receivable from affiliate (current): DPL $ 1 $ — Payables to affiliates (current): Generation (a) $ 5 $ 6 BSC (b) 8 5 PHISCO (b) 13 18 Other 2 — Total payables to affiliates (current) $ 28 $ 29 __________ (a) ACE purchases electric supply from Generation under contracts executed through its competitive procurement process. (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. (c) Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Quarterly Financial Information	The data shown below includes all adjustments that BGE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 977 $ 951 $ 177 $ 228 $ 128 $ 125 June 30 662 674 85 98 51 45 September 30 731 738 103 124 63 62 December 31 799 813 109 163 71 76 The data shown below includes all adjustments that ACE considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income (Loss) 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 310 $ 275 $ 23 $ 25 $ 7 $ 28 June 30 265 270 25 25 8 8 September 30 406 370 84 79 61 41 December 31 254 271 14 28 (1 ) — The data shown below includes all adjustments that PHI considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income Attributable to Membership Interest 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 1,251 $ 1,175 $ 126 $ 180 $ 65 $ 140 June 30 1,076 1,074 153 148 84 66 September 30 1,361 1,310 245 285 187 153 December 31 1,117 1,121 126 159 62 4 The data shown below includes all adjustments that DPL considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 384 $ 362 $ 49 $ 78 $ 31 $ 57 June 30 289 282 42 41 26 19 September 30 328 327 51 59 33 31 December 31 331 330 48 52 30 14 The data shown below includes all adjustments that ComEd considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 1,512 $ 1,298 $ 292 $ 314 $ 165 $ 141 June 30 1,398 1,357 288 319 164 118 September 30 1,598 1,571 323 404 193 189 December 31 1,373 1,309 242 286 141 120 The data shown below includes all adjustments that Pepco considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 557 $ 530 $ 56 $ 79 $ 31 $ 58 June 30 523 514 85 84 54 43 September 30 628 604 112 149 89 87 December 31 531 510 65 87 36 17 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 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 9,693 $ 8,747 $ 1,101 $ 1,308 $ 585 $ 990 June 30 8,076 7,665 942 300 539 95 September 30 9,403 8,768 1,146 1,499 733 823 December 31 8,814 8,384 708 1,288 152 1,880 Net Income Net Income 2018 2017 2018 2017 Quarter ended: March 31 $ 0.61 $ 1.07 $ 0.60 $ 1.06 June 30 0.56 0.10 0.56 0.10 September 30 0.76 0.86 0.76 0.85 December 31 0.16 1.95 0.16 1.94 The data shown below includes all adjustments that PECO considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income Net Income 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 866 $ 796 $ 142 $ 192 $ 113 $ 127 June 30 653 630 127 137 96 88 September 30 757 715 154 169 126 112 December 31 765 729 165 157 124 107 The data shown below includes all adjustments that Generation considers necessary for a fair presentation of such amounts: Operating Revenues Operating Income (Loss) Net Income (Loss) 2018 2017 2018 2017 2018 2017 Quarter ended: March 31 $ 5,512 $ 4,878 $ 347 $ 373 $ 136 $ 418 June 30 4,579 4,216 282 (427 ) 178 (235 ) September 30 5,278 4,750 311 497 234 304 December 31 5,069 4,657 35 504 (178 ) 2,224

Significant Accounting Polici_4

Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Significant Accounting Policies Additional Narrative Information [Line Items]
Stockholders' Equity Attributable to Noncontrolling Interest	$ 2,306	$ 2,291
Percentage ownership of consolidated subsidiaries	100.00%
Minimum expectation of tax position to be realized	50.00%
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Stockholders' Equity Attributable to Noncontrolling Interest		$ 1
Percentage ownership of consolidated subsidiaries	99.00%
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	50.01%
ExGen Renewables [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Ownership interest	51.00%
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 Polici_5

Significant Accounting Policies Balance Sheet Classification of Deferred Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other noncurrent assets	$ 1,575	$ 1,330
Other noncurrent liabilities	2,130	2,097
Commonwealth Edison Co [Member]
Other noncurrent assets	395	238
Other noncurrent liabilities	630	562
Exelon Generation Co L L C [Member]
Other noncurrent assets	755	670
Other noncurrent liabilities	610	658
PECO Energy Co [Member]
Other noncurrent assets	27	12
Other noncurrent liabilities	76	86
Baltimore Gas and Electric Company [Member]
Other noncurrent assets	5	4
Other noncurrent liabilities	$ 73	$ 56

Significant Accounting Polici_6

Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended									9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue											$ 19,168	$ 17,394	$ 16,330
Regulated Operating Revenue											(16,879)	(15,964)	(14,988)
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues	$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747			35,985	33,565	31,366
Revenue from Contract with Customer, Including Assessed Tax											(62)	207	48
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												17,360	16,324
Regulated Operating Revenue												(16,171)	(15,036)
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												33,531	31,360
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												34	6
Regulated Operating Revenue												207	48
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												34	6
Revenue from Contract with Customer, Including Assessed Tax												207	48
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue											19,169	17,385	16,318
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											1,268	1,115	1,439
Revenues	5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878			20,437	18,500	17,757
Revenue from Contract with Customer, Including Assessed Tax												0	0
Exelon Generation Co L L C [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												17,351	16,312
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												1,115	1,439
Revenues												18,466	17,751
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												34	6
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												34	6
Revenue from Contract with Customer, Including Assessed Tax												0	0
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											5,884	5,478	5,263
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											27	15	15
Revenues	1,373	1,598	1,398	1,512	1,309	1,571	1,357	1,298			5,882	5,536	5,254
Revenue from Contract with Customer, Including Assessed Tax											(29)	43	(24)
Commonwealth Edison Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												5,521	5,239
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												15	15
Revenues												5,536	5,254
Commonwealth Edison Co [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(43)	24
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												43	(24)
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,469	2,369	2,524
Gas Domestic Regulated Revenue											568	494	462
Operating revenues from affiliates											8	7	8
Revenues	765	757	653	866	729	715	630	796			3,038	2,870	2,994
Revenue from Contract with Customer, Including Assessed Tax											(7)	0	0
PECO Energy Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,369	2,524
Gas Domestic Regulated Revenue												494	462
Operating revenues from affiliates												7	8
Revenues												2,870	2,994
PECO Energy Co [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												0	0
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												0	0
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,428	2,384	2,531
Gas Domestic Regulated Revenue											738	652	628
Operating revenues from affiliates											29	16	21
Revenues	799	731	662	977	813	738	674	951			3,169	3,176	3,233
Revenue from Contract with Customer, Including Assessed Tax											(26)	124	53
Baltimore Gas and Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,484	2,603
Gas Domestic Regulated Revenue												676	609
Operating revenues from affiliates												16	21
Revenues												3,176	3,233
Baltimore Gas and Electric Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(100)	(72)
Gas Domestic Regulated Revenue												(24)	19
Operating revenues from affiliates													0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												124	53
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electric Revenue											4,609	4,428
Gas Domestic Regulated Revenue											181	161
Operating revenues from affiliates											15	50
Revenues	1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175			4,805	4,679
Revenue from Contract with Customer, Including Assessed Tax											0	40
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											2,233	2,126	2,167
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											6	6	5
Revenues	531	628	523	557	510	604	514	530			2,239	2,158	2,186
Revenue from Contract with Customer, Including Assessed Tax											0	26	14
Potomac Electric Power Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												2,152	2,181
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												6	5
Revenues												2,158	2,186
Potomac Electric Power Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(26)	(14)
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												26	14
Delmarva Power & Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											1,139	1,125	1,128
Gas Domestic Regulated Revenue											181	161	148
Operating revenues from affiliates											8	8	7
Revenues	331	328	289	384	330	327	282	362			1,332	1,300	1,277
Revenue from Contract with Customer, Including Assessed Tax											4	6	(6)
Delmarva Power & Light Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												1,131	1,122
Gas Domestic Regulated Revenue												161	148
Operating revenues from affiliates												8	7
Revenues												1,300	1,277
Delmarva Power & Light Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(6)	6
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												6	(6)
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue											1,237	1,176	1,245
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates											3	2	3
Revenues	$ 254	$ 406	$ 265	$ 310	$ 271	$ 370	$ 270	$ 275			1,236	1,186	1,257
Revenue from Contract with Customer, Including Assessed Tax											(4)	8	9
Atlantic City Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												1,184	1,254
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												2	3
Revenues												1,186	1,257
Atlantic City Electric Company [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue												0	0
Regulated Operating Revenue												0	0
Electric Revenue												(8)	(9)
Gas Domestic Regulated Revenue												0	0
Operating revenues from affiliates												0	0
Revenues												0	0
Revenue from Contract with Customer, Including Assessed Tax												8	$ 9
Successor [Member] | Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										$ 0		0
Regulated Operating Revenue										0		0
Electric Revenue										3,463		4,428
Gas Domestic Regulated Revenue										92		161
Operating revenues from affiliates										45	$ 15	50
Revenues										3,643		4,679
Revenue from Contract with Customer, Including Assessed Tax										43		40
Successor [Member] | Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										0		0
Regulated Operating Revenue										0		0
Electric Revenue										3,506		4,468
Gas Domestic Regulated Revenue										92		161
Operating revenues from affiliates										45		50
Revenues										3,643		4,679
Successor [Member] | Pepco Holdings LLC [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue										0		0
Regulated Operating Revenue										0		0
Electric Revenue										(43)		(40)
Gas Domestic Regulated Revenue										0		0
Operating revenues from affiliates										0		0
Revenues										0		0
Revenue from Contract with Customer, Including Assessed Tax										$ 43		$ 40
Predecessor [Member] | Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									$ 0
Regulated Operating Revenue									0
Electric Revenue									1,122
Gas Domestic Regulated Revenue									57
Operating revenues from affiliates									0
Revenues									1,153
Revenue from Contract with Customer, Including Assessed Tax									(26)
Predecessor [Member] | Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									0
Regulated Operating Revenue									0
Electric Revenue									1,096
Gas Domestic Regulated Revenue									57
Operating revenues from affiliates									0
Revenues									1,153
Predecessor [Member] | Pepco Holdings LLC [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue									0
Regulated Operating Revenue									0
Electric Revenue									26
Gas Domestic Regulated Revenue									0
Operating revenues from affiliates									0
Revenues									0
Revenue from Contract with Customer, Including Assessed Tax									$ (26)

Significant Accounting Polici_7

Significant Accounting Policies Expected Right of Use Assets and Lease Obligations (Details)	12 Months Ended
	Dec. 31, 2018
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1,400-$1,500
Estimated Operating Lease, Lease Liability	$1,600-$1,700
Exelon Generation Co L L C [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1,000-$1,100
Estimated Operating Lease, Lease Liability	$1,200-$1,300
Commonwealth Edison Co [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$5-$10
Estimated Operating Lease, Lease Liability	$5-$10
PECO Energy Co [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1-$5
Estimated Operating Lease, Lease Liability	$1-$5
Baltimore Gas and Electric Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$100-$120
Estimated Operating Lease, Lease Liability	$100-$120
Pepco Holdings LLC [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$250-$270
Estimated Operating Lease, Lease Liability	$300-$320
Potomac Electric Power Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$60-$65
Estimated Operating Lease, Lease Liability	$60-$65
Delmarva Power & Light Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$70-$75
Estimated Operating Lease, Lease Liability	$75-$80
Atlantic City Electric Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$20-$25
Estimated Operating Lease, Lease Liability	$20-$25

Variable Interest Entities Vari

Variable Interest Entities Variable Interest Entities - Narrative (Details) $ in Millions	1 Months Ended				12 Months Ended
	Jul. 31, 2017USD ($)	Nov. 30, 2015	Jun. 30, 2015	Jul. 30, 2014	Dec. 31, 2018USD ($)VIEproject	Dec. 31, 2017USD ($)VIE	Dec. 31, 2016USD ($)	Jul. 18, 2014USD ($)	Apr. 01, 2014USD ($)
Variable Interest Entity [Line Items]
Number of variable interest entities consolidated | VIE					5	5
Number of variable interest entities not consolidated by equity holders | VIE					7	7
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net					$ 15
Guarantee obligations maximum exposure					61
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount					15
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]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net					13
Parental guarantee provided					$ 34
Ownership Percentage Of Consolidated Variable Interest Entities					62.00%
Wind project entities with noncontrolling equity interests | project					4
Noncontrolling equity interest ownership percentage held by third parties					1.00%
Number of projects with significant economic power | project					3
Ownership interests in project entities					99.00%
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount					$ 13
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] | CENG [Member]
Variable Interest Entity [Line Items]
Parental guarantee provided					$ 688
Ownership interest					50.01%
Due from Affiliates					$ 196				$ 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%
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantee obligations maximum exposure					16
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Cash Remitted To VIE					$ 30	$ 48	$ 60

Variable Interest Entities Va_2

Variable Interest Entities Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 938	$ 662
Noncurrent assets	[1]	9,071	9,317
Total assets	[1]	10,009	9,979
Current liabilities	[1]	274	308
Noncurrent liabilities	[1]	3,280	3,316
Total liabilities	[1]	3,554	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		931	652
Noncurrent assets		9,045	9,286
Total assets		9,976	9,938
Current liabilities		252	272
Noncurrent liabilities		3,233	3,250
Total liabilities		3,485	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	7	10
Noncurrent assets	[1]	26	31
Total assets	[1]	33	41
Current liabilities	[1]	22	36
Noncurrent liabilities	[1]	47	66
Total liabilities	[1]	69	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		4	6
Noncurrent assets		19	23
Total assets		23	29
Current liabilities		19	32
Noncurrent liabilities		40	58
Total liabilities		$ 59	$ 90
[1]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

Variable Interest Entities Va_3

Variable Interest Entities Variable Interest Entities - Assets and Liabilities of VIEs which Creditors or Beneficiaries have No Recourse (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,349	$ 898	$ 635	$ 6,502
Restricted cash		247	207	253	205
Customer		4,607	4,445
Other		1,256	1,132
Mark-to-market derivative assets, current		804	976
Other current assets		1,238	1,260
Total current assets		13,360	11,896
Property, plant and equipment, net		76,707	74,202
Nuclear decommissioning trust funds		11,661	13,272
Goodwill		6,677	6,677	6,677
Mark-to-market derivative assets, noncurrent		452	337
Other noncurrent assets		1,575	1,330
Total assets	[1]	119,666	116,770
Long-term debt due within one year		1,349	2,088
Accounts payable		3,800	3,532
Accrued expenses		2,112	1,837
Mark-to-market derivative liabilities, current		475	232
Unamortized energy contract liabilities		149	231
Other current liabilities		1,035	1,069
Total current liabilities		11,404	10,798
Long-term debt		34,075	32,176
Asset retirement obligations		9,679	10,029
Pension obligations		3,988	3,736
Unamortized energy contract liabilities		463	609
Other noncurrent liabilities		2,130	2,097
Total liabilities	[1]	86,596	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	414	126
Restricted cash	[2]	66	64
Customer	[2]	146	170
Other	[2]	23	25
Materials and supplies	[2]	212	205
Other current assets	[2]	52	45
Total current assets	[2]	913	635
Property, plant and equipment, net	[2]	6,145	6,186
Nuclear decommissioning trust funds	[2]	2,351	2,502
Other noncurrent assets	[2]	258	274
Total noncurrent assets	[2]	8,754	8,962
Total assets	[2]	9,667	9,597
Long-term debt due within one year	[2]	87	102
Accounts payable	[2]	96	114
Accrued expenses	[2]	72	67
Unamortized energy contract liabilities	[2]	15	18
Other current liabilities	[2]	3	7
Total current liabilities	[2]	273	308
Long-term debt	[2]	1,072	1,154
Asset retirement obligations	[2]	2,160	2,035
Unamortized energy contract liabilities		1
Other noncurrent liabilities	[2]	42	121
Total noncurrent liabilities	[2]	3,275	3,310
Total liabilities	[2]	3,548	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		750	416	290	431
Restricted cash		153	138	158	123
Customer		2,941	2,697
Other		562	321
Mark-to-market derivative assets, current		804	976
Other current assets		883	933
Total current assets		8,433	6,882
Property, plant and equipment, net		23,981	24,906
Nuclear decommissioning trust funds		11,661	13,272
Goodwill		47	47
Mark-to-market derivative assets, noncurrent		452	334
Other noncurrent assets		755	670
Total assets	[3]	47,556	48,457
Long-term debt due within one year		906	346
Accounts payable		1,847	1,773
Accrued expenses		898	1,022
Mark-to-market derivative liabilities, current		449	211
Unamortized energy contract liabilities		31	43
Other current liabilities		279	265
Total current liabilities		5,769	4,191
Long-term debt		6,989	7,734
Asset retirement obligations		9,450	9,844
Unamortized energy contract liabilities		20	48
Other noncurrent liabilities		610	658
Total liabilities	[3]	32,048	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		414	126
Restricted cash		62	58
Customer		146	170
Other		23	25
Materials and supplies		212	205
Other current assets		49	41
Total current assets		906	625
Property, plant and equipment, net		6,145	6,186
Nuclear decommissioning trust funds		2,351	2,502
Other noncurrent assets		232	243
Total noncurrent assets		8,728	8,931
Total assets		9,634	9,556
Long-term debt due within one year		66	67
Accounts payable		96	114
Accrued expenses		72	66
Unamortized energy contract liabilities		15	18
Other current liabilities		3	7
Total current liabilities		252	272
Long-term debt		1,025	1,088
Asset retirement obligations		2,160	2,035
Unamortized energy contract liabilities		1
Other noncurrent liabilities		42	121
Total noncurrent liabilities		3,228	3,244
Total liabilities		3,480	3,516
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		124	30
Restricted cash		43	42
Customer		453	486
Other		177	206
Other current assets		75	75
Total current assets		1,533	1,551
Property, plant and equipment, net		13,446	12,498
Goodwill		4,005	4,005	4,005
Other noncurrent assets		60	70
Total assets	[4]	21,984	21,247
Long-term debt due within one year		125	396
Accounts payable		496	348
Accrued expenses		256	261
Unamortized energy contract liabilities		119	188
Other current liabilities		123	123
Total current liabilities		1,592	1,931
Long-term debt		6,134	5,478
Asset retirement obligations		52	16
Unamortized energy contract liabilities		442	561
Other noncurrent liabilities		369	389
Total liabilities	[4]	12,702	12,422
Pepco Holdings LLC [Member] | Successor [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents				170
Restricted cash				43
Pepco Holdings LLC [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	0	0
Restricted cash	[2]	4	6
Customer	[2]	0	0
Other	[2]	0	0
Materials and supplies	[2]	0	0
Other current assets	[2]	3	4
Total current assets	[2]	7	10
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Other noncurrent assets	[2]	26	31
Total noncurrent assets	[2]	26	31
Total assets	[2]	33	41
Long-term debt due within one year	[2]	21	35
Accounts payable	[2]	0	0
Accrued expenses	[2]	1	1
Unamortized energy contract liabilities	[2]	0	0
Other current liabilities	[2]	0	0
Total current liabilities	[2]	22	36
Long-term debt	[2]	47	66
Asset retirement obligations	[2]	0	0
Unamortized energy contract liabilities		0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	47	66
Total liabilities	[2]	69	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		7	2	101	3
Restricted cash		4	6	$ 9	$ 12
Customer		95	92
Other		55	56
Other current assets		5	2
Total current assets		240	258
Property, plant and equipment, net		2,966	2,706
Other noncurrent assets		40	45
Total assets	[5]	3,699	3,445
Long-term debt due within one year		18	281
Accounts payable		154	118
Accrued expenses		35	33
Other current liabilities		4	8
Total current liabilities		422	619
Long-term debt		1,170	840
Other noncurrent liabilities		27	25
Total liabilities	[5]	2,573	2,402
Atlantic City Electric Company [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		0	0
Restricted cash		4	6
Customer		0	0
Other		0	0
Materials and supplies		0	0
Other current assets		0	0
Total current assets		4	6
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Other noncurrent assets		19	23
Total noncurrent assets		19	23
Total assets		23	29
Long-term debt due within one year		18	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other current liabilities		0	0
Total current liabilities		19	32
Long-term debt		40	58
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		40	58
Total liabilities		$ 59	$ 90
[1]	Exelon’s consolidated assets include $9,667 million and $9,597 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,548 million and $3,618 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities for additional information.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[3]	Generation’s consolidated assets include $9,634 million and $9,556 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,480 million and $3,516 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities for additional information.
[4]	PHI’s consolidated total assets include $33 million and $41 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $69 million and $102 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities for additional information.
[5]	ACE’s consolidated assets include $23 million and $29 million at December 31, 2018 and 2017, respectively, of ACE’s consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated liabilities include $59 million and $90 million at December 31, 2018 and 2017, respectively, of ACE’s consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 2 - Variable Interest Entities for additional information.

Variable Interest Entities Va_4

Variable Interest Entities Variable Intereste Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,069	$ 1,134
Total liabilities	[1]	259	265
Exelon's ownership interest in VIE	[1]	223	251
Other ownership interests in VIE	[1]	587	618
Registrants maximum exposure to loss		15
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		223	251
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		7	8
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss	[2]	0	2
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets		597	625
Total liabilities		37	37
Exelon's ownership interest in VIE		0	0
Other ownership interests in VIE		560	588
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		7	8
Commercial Agreement Variable Interest Entities [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	2
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets		472	509
Total liabilities		222	228
Exelon's ownership interest in VIE		223	251
Other ownership interests in VIE		27	30
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		223	251
Equity Investment VIE [Member] | Contract intangible asset
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Equity Investment VIE [Member] | Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Registrants maximum exposure to loss		13
Nuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Held-to-maturity Securities Pledged as Collateral	[3]	9	39
Accounts Payable, Interest-bearing, Noncurrent		$ 9	$ 37
[1]	These items represent amounts on the unconsolidated VIE balance sheets, not in 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 in 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 $9 million and $39 million as of December 31, 2018 and December 31, 2017, respectively; offset by payables to ZionSolutions LLC of $9 million and $37 million as of December 31, 2018 and December 31, 2017, respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE.
[3]	(a)Included in Other current liabilities within Exelon's and Generation's Consolidated Balance Sheets. Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized gains and losses associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.

Revenue Recognition Revenue R_3

Revenue Recognition Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Gross	$ 32	$ 26
Capitalized Contract Cost, Amortization	22	30
Exelon Generation Co L L C [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Gross	32	26
Capitalized Contract Cost, Amortization	$ 22	$ 30

Revenue Recognition Contract As

Revenue Recognition Contract Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	$ 50
Contract with Customer, Asset, Reclassified to Receivable	(146)
Contract with Customer, Asset, Net, Current	187	$ 283
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	179
Contract with Customer, Liability, Current	27	35
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	(187)
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	50
Contract with Customer, Asset, Reclassified to Receivable	(146)
Contract with Customer, Asset, Net, Current	187	283
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	465
Contract with Customer, Liability, Current	42	$ 35
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	$ (458)

Revenue Recognition Performance

Revenue Recognition Performance Obligations (Details) $ in Millions	Dec. 31, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 631
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	329
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	119
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	47
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	138
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	1,264
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	631
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	329
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	119
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	47
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	138
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 1,264

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters- Narrative (Details)		Jan. 15, 2019USD ($)	Jan. 04, 2019USD ($)	Dec. 20, 2018USD ($)	Dec. 04, 2018USD ($)	Nov. 19, 2018USD ($)	Sep. 07, 2018USD ($)	Aug. 21, 2018USD ($)	Jul. 01, 2018USD ($)	Jun. 27, 2018USD ($)	Jun. 08, 2018USD ($)	Apr. 20, 2018USD ($)	[7]	Apr. 17, 2018USD ($)	[7]	Apr. 16, 2018USD ($)	Mar. 29, 2018USD ($)	Mar. 08, 2018USD ($)	[7]	Mar. 02, 2018USD ($)	Feb. 09, 2018USD ($)		Feb. 06, 2018USD ($)	Jan. 31, 2018USD ($)	Jan. 18, 2018USD ($)	Dec. 19, 2017USD ($)	Dec. 18, 2017USD ($)	Nov. 16, 2017USD ($)	Apr. 30, 2016USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)	Dec. 31, 2022USD ($)	Dec. 31, 2023USD ($)	Dec. 31, 2023USD ($)	Jul. 21, 2017USD ($)	Aug. 31, 2010USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																														$ 127,000,000											$ 127,000,000
Regulatory Assets																														9,459,000,000				$ 9,288,000,000				$ 9,288,000,000			9,459,000,000		$ 9,288,000,000
Amortization Rate Stabilization Deferral																																									14,000,000		(10,000,000)		$ 76,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																		35,000,000				35,000,000					35,000,000
Regulatory Liability, Current																														644,000,000				523,000,000				523,000,000			644,000,000		523,000,000
Regulatory liabilities, noncurrent																														9,559,000,000				9,865,000,000				9,865,000,000			9,559,000,000		9,865,000,000
Revenues																														8,814,000,000	$ 9,403,000,000	$ 8,076,000,000	$ 9,693,000,000	8,384,000,000	$ 8,768,000,000	$ 7,665,000,000	$ 8,747,000,000				35,985,000,000		33,565,000,000		31,366,000,000
Business Combination, Integration Related Costs																																									7,000,000	[1]	16,000,000	[1]	143,000,000
Regulatory Liabilities																														10,203,000,000				10,388,000,000				10,388,000,000			10,203,000,000		10,388,000,000
Accounts Payable, Current																														3,800,000,000				3,532,000,000				3,532,000,000			3,800,000,000		3,532,000,000
Payments to Acquire Property, Plant, and Equipment																																									7,594,000,000		7,584,000,000		8,553,000,000
PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																176,000,000
DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														159,000,000				190,000,000				190,000,000			159,000,000		190,000,000
Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		758,000,000				758,000,000					758,000,000
Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														328,000,000				223,000,000				223,000,000			328,000,000		223,000,000
Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														193,000,000				47,000,000				47,000,000			193,000,000		47,000,000
Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														42,000,000				45,000,000				45,000,000			42,000,000		45,000,000
Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														545,000,000				596,000,000				596,000,000			545,000,000		596,000,000
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																																									4,670,000,000		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																														5,069,000,000	5,278,000,000	4,579,000,000	5,512,000,000	4,657,000,000	4,750,000,000	4,216,000,000	4,878,000,000				20,437,000,000		18,500,000,000		17,757,000,000
Purchase Obligation																																																	$ 235,000,000
Business Combination, Integration Related Costs																																									5,000,000	[1]	22,000,000	[1]	37,000,000
Accounts Payable, Current																														1,847,000,000				1,773,000,000				1,773,000,000			1,847,000,000		1,773,000,000
Payments to Acquire Property, Plant, and Equipment																																									2,242,000,000		2,259,000,000		3,078,000,000
Exelon Generation Co L L C [Member] | Conowingo [Member]
Regulatory Matters Additional Narrative Information [Line Items]
License Costs																																									37,000,000
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] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current	[2]																															41,000,000
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																																									438,000,000		$ 311,000,000
Other Revenue, Net																																						150,000,000			373,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
SocialCarbonCost																																											16.50
Public Utilities, Requested Rate Increase (Decrease), Amount	[3]																																								$ (44,000,000)
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint																																									55.00%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[3],[4]																																								$ (26,000,000)
Public Utilities, Approved Return on Equity, Percentage	[3],[5]																																								11.50%
Regulatory Assets																																		1,279,000,000				1,279,000,000					$ 1,279,000,000
Amortization Rate Stabilization Deferral																																									$ 0		0		0
Amount of Impairment to Carrying Amount of Regulatory Assets																																		3,000,000				3,000,000					3,000,000
Regulatory Liability, Current																														293,000,000				249,000,000				249,000,000			293,000,000		249,000,000
Regulatory liabilities, noncurrent																														6,050,000,000				6,328,000,000				6,328,000,000			6,050,000,000		6,328,000,000
Revenues																														1,373,000,000	1,598,000,000	1,398,000,000	1,512,000,000	1,309,000,000	1,571,000,000	1,357,000,000	1,298,000,000				5,882,000,000		5,536,000,000		5,254,000,000
Purchase Obligation																																																	$ 170,000,000
Business Combination, Integration Related Costs																																									0	[1],[6]	1,000,000	[1],[6]	(6,000,000)
Regulatory Liabilities																														6,343,000,000				6,577,000,000				6,577,000,000			6,343,000,000		6,577,000,000
Prior Year Revenue Adjustment	[3]																																								18,000,000
Tax Savings From Tax Cuts and Jobs Act																									$ 201,000,000
Accounts Payable, Current																														607,000,000				568,000,000				568,000,000			607,000,000		568,000,000
Payments to Acquire Property, Plant, and Equipment																																									2,126,000,000		2,250,000,000		2,734,000,000
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																									(58,000,000)
Public Utilities, Approved Rate Increase (Decrease), Amount																																											34,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[7]				$ (24,000,000)											$ (23,000,000)
Public Utilities, Requested Equity Capital Structure, Percentage					8.69%
Commonwealth Edison Co [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																									69,000,000
Commonwealth Edison Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																0
Commonwealth Edison Co [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		0				0					0
Commonwealth Edison Co [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		0				0					0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														136,000,000				155,000,000				155,000,000			136,000,000		155,000,000
Commonwealth Edison Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		0				0					0
Commonwealth Edison Co [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		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
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																																									22,000,000
Regulatory Assets																																		410,000,000				410,000,000					410,000,000
Amortization Rate Stabilization Deferral																																									0		0		0
Regulatory Liability, Current																														175,000,000				141,000,000				141,000,000			175,000,000		141,000,000
Regulatory liabilities, noncurrent																														421,000,000				549,000,000				549,000,000			421,000,000		549,000,000
Revenues																														765,000,000	757,000,000	653,000,000	866,000,000	729,000,000	715,000,000	630,000,000	796,000,000				3,038,000,000		2,870,000,000		2,994,000,000
Business Combination, Integration Related Costs																																									1,000,000	[1]	4,000,000	[1]	5,000,000
Regulatory Liabilities																														596,000,000				690,000,000				690,000,000			$ 596,000,000		690,000,000
Public Utilities, Requested Equity Capital Structure, Percentage																																									11.00%
Prior Year Revenue Adjustment																																							$ 6,000,000
Tax Savings From Tax Cuts and Jobs Act																	$ 71,000,000
Accounts Payable, Current																														370,000,000				370,000,000				370,000,000			$ 370,000,000		370,000,000
Payments to Acquire Property, Plant, and Equipment																																									849,000,000		732,000,000		686,000,000
PECO Energy Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[7]																$ 82,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[7]			$ 25,000,000
PECO Energy Co [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 4,000,000
PECO Energy Co [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																							0
PECO Energy Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																0
PECO Energy Co [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		0				0					0
PECO Energy Co [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		0				0					0
PECO Energy Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		36,000,000				36,000,000					36,000,000
PECO Energy Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		1,000,000				1,000,000					1,000,000
PECO Energy Co [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		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
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[3]																																								10,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[3],[4],[8]																																								$ 26,000,000
Public Utilities, Approved Return on Equity, Percentage																																									10.50%
Proposed Capital Expenditure																																									$ 12,000,000
Regulatory Assets																																		571,000,000				571,000,000					571,000,000
Amortization Rate Stabilization Deferral																																									0		7,000,000		81,000,000
Estimated number of smart meters to be installed																																																		0
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					5,000,000
Regulatory Liability, Current																														77,000,000				62,000,000				62,000,000			77,000,000		62,000,000
Regulatory liabilities, noncurrent																														1,192,000,000				1,101,000,000				1,101,000,000			1,192,000,000		1,101,000,000
Revenues																														799,000,000	731,000,000	662,000,000	977,000,000	813,000,000	738,000,000	674,000,000	951,000,000				3,169,000,000		3,176,000,000		3,233,000,000
Business Combination, Integration Related Costs																																									1,000,000	[1],[6]	4,000,000	[1],[6]	(1,000,000)
Regulatory Liabilities																														1,269,000,000				1,163,000,000				1,163,000,000			1,269,000,000		1,163,000,000
Prior Year Revenue Adjustment	[3]																																								4,000,000
Accounts Payable, Current																														295,000,000				265,000,000				265,000,000			295,000,000		265,000,000
Payments to Acquire Property, Plant, and Equipment																																									959,000,000		882,000,000		934,000,000
Baltimore Gas and Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																															$ 200,000,000
Proposed Capital Expenditure																																															$ 732,000,000
Baltimore Gas and Electric Company [Member] | Electric Distribution [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											$ 61,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 43,000,000
Tax Savings From Tax Cuts and Jobs Act																								$ 31,000,000
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																									18,000,000
Baltimore Gas and Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																51,000,000
Baltimore Gas and Electric Company [Member] | Difference between Carrying Value and Fair Value [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														133,000,000				139,000,000				139,000,000			133,000,000		139,000,000
Baltimore Gas and Electric Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Baltimore Gas and Electric Company [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Baltimore Gas and Electric Company [Member] | AMI programs - Deployment Costs
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																				52,000,000
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														48,000,000				53,000,000		56,000,000		53,000,000			48,000,000		53,000,000
Baltimore Gas and Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		16,000,000				16,000,000					16,000,000
Baltimore Gas and Electric Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																		6,000,000				6,000,000					6,000,000
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
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																																					444,000,000
Regulatory Assets																																		3,047,000,000				3,047,000,000					3,047,000,000
Amortization Rate Stabilization Deferral																																									14,000,000		(17,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets																																		27,000,000				27,000,000					27,000,000
Regulatory Liability, Current																														84,000,000				56,000,000				56,000,000			84,000,000		56,000,000
Regulatory liabilities, noncurrent																														1,864,000,000				1,872,000,000				1,872,000,000			1,864,000,000		1,872,000,000
Revenues																														1,117,000,000	1,361,000,000	1,076,000,000	1,251,000,000	1,121,000,000	1,310,000,000	1,074,000,000	1,175,000,000				4,805,000,000		4,679,000,000
Business Combination, Integration Related Costs																																									0	[1],[6]	(6,000,000)	[1],[6]	28,000,000
Regulatory Liabilities																														1,948,000,000				1,928,000,000				1,928,000,000			1,948,000,000		1,928,000,000
Impairment of Long-Lived Assets to be Disposed of																																				25,000,000
Accounts Payable, Current																														496,000,000				348,000,000				348,000,000			496,000,000		348,000,000
Payments to Acquire Property, Plant, and Equipment																																									1,375,000,000		1,396,000,000
Pepco Holdings LLC [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																84,000,000
Pepco Holdings LLC [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amortization Rate Stabilization Deferral																																								$ (5,000,000)
Revenues																																								3,643,000,000			4,679,000,000
Business Combination, Integration Related Costs	[6]																																							69,000,000	0		(18,000,000)	[1]
Payments to Acquire Property, Plant, and Equipment																																								$ 1,008,000,000
Pepco Holdings LLC [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														159,000,000				190,000,000				190,000,000			159,000,000		190,000,000
Pepco Holdings LLC [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														569,000,000				619,000,000				619,000,000			569,000,000		619,000,000
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														120,000,000				134,000,000				134,000,000			120,000,000		134,000,000
Pepco Holdings LLC [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														93,000,000				30,000,000				30,000,000			93,000,000		30,000,000
Pepco Holdings LLC [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														39,000,000				39,000,000				39,000,000			39,000,000		39,000,000
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														255,000,000				310,000,000				310,000,000			255,000,000		310,000,000
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																														320,000,000											320,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																									6,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[4]																																								$ 8,000,000
Public Utilities, Approved Return on Equity, Percentage	[5]																																								10.50%
Projected Capital Expenditures																																			500,000,000
Regulatory Assets																																		891,000,000				891,000,000					891,000,000
Amortization Rate Stabilization Deferral																																									$ 14,000,000		(17,000,000)		(12,000,000)
Amount of Impairment to Carrying Amount of Regulatory Assets																																		14,000,000				14,000,000					14,000,000
Regulatory Liability, Current																														7,000,000				3,000,000				3,000,000			7,000,000		3,000,000
Regulatory liabilities, noncurrent																														822,000,000				829,000,000				829,000,000			822,000,000		829,000,000
Revenues																														531,000,000	628,000,000	523,000,000	557,000,000	510,000,000	604,000,000	514,000,000	530,000,000				2,239,000,000		2,158,000,000		2,186,000,000
Regulatory Liabilities																														829,000,000				832,000,000				832,000,000			829,000,000		832,000,000
Alternative Net Capital Requirement																																			250,000,000
Capital ProjectFundedByBonds																																			187,500,000						30,000,000							$ 127,000,000
CapitalProjectFundedByAgency																																			62,500,000
Prior Year Revenue Adjustment																																									2,000,000
Accounts Payable, Current																														214,000,000				139,000,000				139,000,000			214,000,000		139,000,000
Payments to Acquire Property, Plant, and Equipment																																									656,000,000		628,000,000		586,000,000
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 30,000,000																								$ 66,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							$ 4,000,000					$ (15,000,000)		$ (24,000,000)				$ 3,000,000
Tax Savings From Tax Cuts and Jobs Act																							$ 39,000,000
Potomac Electric Power Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																									13,000,000
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																84,000,000
Potomac Electric Power Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														159,000,000				190,000,000				190,000,000			159,000,000		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				9,000,000			9,000,000		9,000,000
Potomac Electric Power Company [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														9,000,000				11,000,000				11,000,000			9,000,000		11,000,000
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														90,000,000				100,000,000				100,000,000			90,000,000		100,000,000
Potomac Electric Power Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														84,000,000				8,000,000				8,000,000			84,000,000		8,000,000
Potomac Electric Power Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														18,000,000				20,000,000				20,000,000			18,000,000		20,000,000
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														188,000,000				229,000,000				229,000,000			188,000,000		229,000,000
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 & Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																																									14,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[4]																																								$ 27,000,000
Public Utilities, Approved Return on Equity, Percentage	[5]																																								10.50%
Regulatory Assets																																		314,000,000				314,000,000					314,000,000
Amortization Rate Stabilization Deferral																																									$ 0		0		2,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets																																		6,000,000				6,000,000					6,000,000
Regulatory Liability, Current																														59,000,000				42,000,000				42,000,000			59,000,000		42,000,000
Regulatory liabilities, noncurrent																														606,000,000				593,000,000				593,000,000			606,000,000		593,000,000
Revenues																														331,000,000	328,000,000	289,000,000	384,000,000	330,000,000	327,000,000	282,000,000	362,000,000				1,332,000,000		1,300,000,000		1,277,000,000
Business Combination, Integration Related Costs																																									0	[1],[6]	(7,000,000)	[1],[6]	20,000,000
Regulatory Liabilities																														665,000,000				635,000,000				635,000,000			665,000,000		635,000,000
Prior Year Revenue Adjustment																																									13,000,000
Accounts Payable, Current																														111,000,000				82,000,000				82,000,000			111,000,000		82,000,000
Payments to Acquire Property, Plant, and Equipment																																									364,000,000		428,000,000		349,000,000
Delmarva Power & Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[7]									$ (7,000,000)
Public Utilities, Approved Rate Increase (Decrease), Amount																											$ 13,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																					$ 12,000,000	[7]						$ 19,000,000
Public Utilities, Approved Return on Equity, Percentage																											9.50%
Tax Savings From Tax Cuts and Jobs Act																					19,000,000
Delmarva Power & Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[7]						$ (4,000,000)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[7]																				4,000,000
Tax Savings From Tax Cuts and Jobs Act																					$ 7,000,000
Delmarva Power & Light Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																									12,000,000
Delmarva Power & Light Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																0
Delmarva Power & Light Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Delmarva Power & Light Company [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														30,000,000				34,000,000				34,000,000			30,000,000		34,000,000
Delmarva Power & Light Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				7,000,000				7,000,000			0		7,000,000
Delmarva Power & Light Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														11,000,000				10,000,000				10,000,000			11,000,000		10,000,000
Delmarva Power & Light Company [Member] | Energy efficiency and demand response programs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														67,000,000				81,000,000				81,000,000			67,000,000		81,000,000
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment																														89,000,000											89,000,000
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount								$ 40,000,000																																	4,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[4]																																								$ 0
Public Utilities, Approved Return on Equity, Percentage	[5]																																								10.50%
Regulatory Assets																																		430,000,000				430,000,000					430,000,000
Amortization Rate Stabilization Deferral																																									$ 0		0		0
Amount of Impairment to Carrying Amount of Regulatory Assets																																		7,000,000				7,000,000					7,000,000
Regulatory Liability, Current																														18,000,000				11,000,000				11,000,000			18,000,000		11,000,000
Regulatory liabilities, noncurrent																														402,000,000				411,000,000				411,000,000			402,000,000		411,000,000
Revenues																														254,000,000	406,000,000	265,000,000	$ 310,000,000	271,000,000	$ 370,000,000	$ 270,000,000	$ 275,000,000				1,236,000,000		1,186,000,000		1,257,000,000
Business Combination, Integration Related Costs																																									0	[1],[6]	(6,000,000)	[1],[6]	19,000,000
Regulatory Liabilities																														420,000,000				422,000,000				422,000,000			420,000,000		422,000,000
Prior Year Revenue Adjustment																																									(4,000,000)
Tax Savings From Tax Cuts and Jobs Act																				$ 23,000,000
Accounts Payable, Current																														154,000,000				118,000,000				118,000,000			154,000,000		118,000,000
Payments to Acquire Property, Plant, and Equipment																																									335,000,000		312,000,000		$ 311,000,000
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment																																														$ 338,000,000
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[9]					$ 122,000,000
Atlantic City Electric Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																									11,000,000
Atlantic City Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Accounts Payable, Current																																$ 0
Atlantic City Electric Company [Member] | DC PLUG charge
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Atlantic City Electric Company [Member] | Fair value of long-term debt
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														0				0				0			0		0
Atlantic City Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														9,000,000				15,000,000				15,000,000			9,000,000		15,000,000
Atlantic City Electric Company [Member] | Merger integration costs
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																														10,000,000				9,000,000				9,000,000			10,000,000		9,000,000
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
One-Time Revenue Adjustment [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															76,000,000								76,000,000
One-Time Revenue Adjustment [Member] | Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															51,000,000								51,000,000
One-Time Revenue Adjustment [Member] | Baltimore Gas and Electric Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															15,000,000								15,000,000
One-Time Revenue Adjustment [Member] | Pepco Holdings LLC [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															10,000,000								10,000,000
One-Time Revenue Adjustment [Member] | Potomac Electric Power 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
One-Time Revenue Adjustment [Member] | Delmarva Power & Light Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															5,000,000								5,000,000
One-Time Revenue Adjustment [Member] | Atlantic City Electric Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																															$ 2,000,000								$ 2,000,000
[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]	Does not include an offsetting receivable from New Jersey Utilities of $16 million as of December 31, 2018.
[3]	The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted.
[4]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MzY0MUFFQzNGNTE3Mzk3OTI2RjIxNTRFRUQyNkYyMzMM}
[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]	(b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs as regulatory assets of $24 million, $8 million, $8 million, and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $8 million, $6 million, $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.
[7]	Includes the annual ongoing TCJA tax savings further discussed below.
[8]	BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $12 million to recover the costs of providing transmission service to specifically designated load by BGE.
[9]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NUYyM0EwMDI1MDhGQUUyMUZEMzExNTNGOUY0NjExNDUM}

Regulatory Matters Regulatory_2

Regulatory Matters Regulatory Matters - Annual Electric Distribution/Transmission Filings (Details) - USD ($) $ in Millions

Jan. 15, 2019

Dec. 04, 2018

Nov. 19, 2018

Sep. 07, 2018

Aug. 21, 2018

Jun. 27, 2018

May 31, 2018

Apr. 20, 2018

[4]

Apr. 17, 2018

Apr. 16, 2018

Mar. 08, 2018

[4]

Mar. 02, 2018

Feb. 09, 2018

Feb. 06, 2018

Jan. 31, 2018

Jan. 18, 2018

Dec. 19, 2017

Dec. 18, 2017

Nov. 16, 2017

Dec. 31, 2018

Dec. 31, 2017

Commonwealth Edison Co [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

[1]

$ (44)

Tax Savings From Tax Cuts and Jobs Act

$ 201

Prior Year Revenue Adjustment

[1]

$ 18

Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint

55.00%

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[1],[2]

$ (26)

Public Utilities, Approved Equity Capital Structure, Percentage

[1]

8.32%

Public Utilities, Approved Return on Equity, Percentage

[1],[3]

11.50%

Commonwealth Edison Co [Member] | Electric Distribution [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ (58)

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 34

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[4]

$ (24)

$ (23)

Public Utilities, Approved Equity Capital Structure, Percentage

6.52%

Public Utilities, Requested Equity Capital Structure, Percentage

8.69%

Commonwealth Edison Co [Member] | Electric Transmission [Member]

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 69

Baltimore Gas and Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

[1]

10

Prior Year Revenue Adjustment

[1]

4

Proposed Capital Expenditure

12

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[1],[2],[5]

$ 26

Public Utilities, Approved Equity Capital Structure, Percentage

[1]

7.61%

Public Utilities, Approved Return on Equity, Percentage

10.50%

Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 72

Baltimore Gas and Electric Company [Member] | Electric Transmission [Member]

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 18

Potomac Electric Power Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

6

Prior Year Revenue Adjustment

2

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[2]

$ 8

Public Utilities, Approved Equity Capital Structure, Percentage

7.82%

Public Utilities, Approved Return on Equity, Percentage

[3]

10.50%

Potomac Electric Power Company [Member] | Electric Distribution [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 30

$ 66

Tax Savings From Tax Cuts and Jobs Act

$ 39

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 4

$ (15)

$ (24)

[4]

$ 3

Public Utilities, Requested Return on Equity, Percentage

10.30%

9.50%

9.525%

Potomac Electric Power Company [Member] | Electric Transmission [Member]

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 13

Delmarva Power & Light Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

14

Prior Year Revenue Adjustment

13

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[2]

$ 27

Public Utilities, Approved Equity Capital Structure, Percentage

7.29%

Public Utilities, Approved Return on Equity, Percentage

[3]

10.50%

Delmarva Power & Light Company [Member] | Electric Distribution [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

[4]

$ (7)

Tax Savings From Tax Cuts and Jobs Act

$ 19

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 13

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 12

[4]

$ 19

Public Utilities, Approved Return on Equity, Percentage

9.50%

Public Utilities, Requested Return on Equity, Percentage

9.70%

Delmarva Power & Light Company [Member] | Electric Transmission [Member]

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 12

Atlantic City Electric Company [Member]

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 40

4

Tax Savings From Tax Cuts and Jobs Act

$ 23

Prior Year Revenue Adjustment

(4)

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[2]

$ 0

Public Utilities, Approved Equity Capital Structure, Percentage

8.02%

Public Utilities, Approved Return on Equity, Percentage

[3]

10.50%

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

Public Utilities, General Disclosures [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

[6]

$ 122

Public Utilities, Requested Return on Equity, Percentage

10.10%

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

Public Utilities, General Disclosures [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 11

[1]

The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted.

[2]

{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MzY0MUFFQzNGNTE3Mzk3OTI2RjIxNTRFRUQyNkYyMzMM}

[3]

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.

[4]

Includes the annual ongoing TCJA tax savings further discussed below.

[5]

BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $12 million to recover the costs of providing transmission service to specifically designated load by BGE.

[6]

{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NUYyM0EwMDI1MDhGQUUyMUZEMzExNTNGOUY0NjExNDUM}

Regulatory Matters Regulatory_3

Regulatory Matters Regulatory Matters - Schedule of Regulatory Asset Impairment (Details) $ in Millions	Dec. 31, 2017USD ($)
Amount of Impairment to Carrying Amount of Regulatory Assets	$ 35
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
Potomac Electric Power Company [Member]
Amount of Impairment to Carrying Amount of Regulatory Assets	14
Delmarva Power & 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

Regulatory Matters Regulatory_4

Regulatory Matters Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) - USD ($) $ in Millions		Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2017
Other Commitments [Line Items]
Other Receivables		$ 1,256		$ 1,132
Total		127
Accounts Payable, Current		3,800		3,532
Regulatory Assets		9,459		9,288
Regulatory Liabilities		10,203		10,388
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables		562		321
Accounts Payable, Current		1,847		1,773
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables		320		266
Accounts Payable, Current		607		568
Regulatory Assets				1,279
Regulatory Liabilities		6,343		6,577
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables		151		105
Accounts Payable, Current		370		370
Regulatory Assets				410
Regulatory Liabilities		596		690
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		90		94
Accounts Payable, Current		295		265
Regulatory Assets				571
Regulatory Liabilities		1,269		1,163
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables		81		87
Accounts Payable, Current		214		139
Regulatory Assets				891
Regulatory Liabilities		829		832
Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables		46		38
Accounts Payable, Current		111		82
Regulatory Assets				314
Regulatory Liabilities		665		635
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables		55		56
Accounts Payable, Current		154		118
Regulatory Assets				430
Regulatory Liabilities		420		422
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables		177		206
Total					$ 444
Accounts Payable, Current		496		348
Regulatory Assets				3,047
Regulatory Liabilities		1,948		$ 1,928
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Other Receivables			$ 220
Accounts Payable, Current			176
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Receivables	[1]		0
Accounts Payable, Current	[1]		41
Accounts Receivable, Gross, Current		$ 16
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Receivables			122
Accounts Payable, Current			0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Other Receivables			85
Accounts Payable, Current			0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Receivables			0
Accounts Payable, Current			51
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Receivables			0
Accounts Payable, Current			84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Receivables			10
Accounts Payable, Current			0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Receivables			3
Accounts Payable, Current			0
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Receivables			13
Accounts Payable, Current			84
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Assets			136
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Assets	[1]		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Assets			0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Assets			0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets			51
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Assets			84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Assets			0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Assets			1
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Assets			85
PJM Transmission Rate Design Settlement [Member]
Other Commitments [Line Items]
Regulatory Liabilities			221
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Regulatory Liabilities	[1]		0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities			122
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Other Commitments [Line Items]
Regulatory Liabilities			85
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities			0
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities			0
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities			10
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Regulatory Liabilities			4
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Regulatory Liabilities			$ 14
[1]	Does not include an offsetting receivable from New Jersey Utilities of $16 million as of December 31, 2018.

Regulatory Matters Regulatory_5

Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Regulatory Assets [Line Items]
Regulatory Assets	$ 9,459	$ 9,288
Current regulatory assets	1,222	1,267
Noncurrent regulatory assets	8,237	8,021
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,455
Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	1,266	1,393
Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	414	306
Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	202	385
Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	328	223
Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	32	32
Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	158	186
Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	81	58
Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	472	166
Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets		758
Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	561	750
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	118	109
MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	326	295
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	249	258
Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	193	47
Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	41	35
Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	545	596
Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	42	45
Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	59	55
Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	50	79
Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	564	529
DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	159	190
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	41	27
Other
Regulatory Assets [Line Items]
Regulatory Assets	303	311
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,279
Current regulatory assets	293	225
Noncurrent regulatory assets	1,307	1,054
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	136	155
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	158	186
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	81	58
Commonwealth Edison Co [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets		166
Commonwealth Edison Co [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	79	73
Commonwealth Edison Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	309	273
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		256
Commonwealth Edison Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	6	6
Commonwealth Edison Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets		0
Commonwealth Edison Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Commonwealth Edison Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets		106
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		410
Current regulatory assets	81	29
Noncurrent regulatory assets	460	381
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets		297
PECO Energy Co [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36
PECO Energy Co [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Electric Distribution Formula Rate One-time Events [Member]
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] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets		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
PECO Energy Co [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets		22
PECO Energy Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets		1
PECO Energy Co [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets		1
PECO Energy Co [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets		0
PECO Energy Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
PECO Energy Co [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets		31
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		571
Current regulatory assets	177	174
Noncurrent regulatory assets	398	397
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets		0
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		129
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	48	53	$ 56
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	32	32
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
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
Baltimore Gas and Electric Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets		0
Baltimore Gas and Electric Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0
Baltimore Gas and Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets		16
Baltimore Gas and Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	4	7
Baltimore Gas and Electric Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets		285
Baltimore Gas and Electric Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets		6
Baltimore Gas and Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets		14
Baltimore Gas and Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets		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	0
Baltimore Gas and Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets		15
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3,047
Current regulatory assets	489	554
Noncurrent regulatory assets	2,312	2,493
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	9
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	89	101
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	120	134
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	569	619
Pepco Holdings LLC [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	561	750
Pepco Holdings LLC [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	1	0
Pepco Holdings LLC [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Pepco Holdings LLC [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	2
Pepco Holdings LLC [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	93	30
Pepco Holdings LLC [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	31	22
Pepco Holdings LLC [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	255	310
Pepco Holdings LLC [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	39	39
Pepco Holdings LLC [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	57	41
Pepco Holdings LLC [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	50	79
Pepco Holdings LLC [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	564	529
Pepco Holdings LLC [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	159	190
Pepco Holdings LLC [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	41	27
Pepco Holdings LLC [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	162	165
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		891
Current regulatory assets	270	213
Noncurrent regulatory assets	643	678
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	10	9
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	50	58
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	90	100
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
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	1	0
Potomac Electric Power Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	84	8
Potomac Electric Power Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	10	3
Potomac Electric Power Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	188	229
Potomac Electric Power Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	18	20
Potomac Electric Power Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	57	38
Potomac Electric Power Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Potomac Electric Power Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	158	150
Potomac Electric Power Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	159	190
Potomac Electric Power Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	9	7
Potomac Electric Power Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	79	79
Delmarva Power & Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		314
Current regulatory assets	59	69
Noncurrent regulatory assets	231	245
Delmarva Power & Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	39	43
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	30	34
Delmarva Power & Light Company [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Fair value of long-term debt
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Fair value of PHI's unamortized energy contracts
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | MGP remediation costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	1
Delmarva Power & Light Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	0	7
Delmarva Power & Light Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	14	8
Delmarva Power & Light Company [Member] | Energy efficiency and demand response programs
Regulatory Assets [Line Items]
Regulatory Assets	67	81
Delmarva Power & Light Company [Member] | Merger integration costs
Regulatory Assets [Line Items]
Regulatory Assets	11	10
Delmarva Power & Light Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	3
Delmarva Power & Light Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	97	93
Delmarva Power & Light Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Delmarva Power & Light Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	4	5
Delmarva Power & Light Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	28	29
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		430
Current regulatory assets	40	71
Noncurrent regulatory assets	386	359
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Pension and Post Retirement Plan Merger Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Legacy Meter Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Incremental Deployment Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate One-time Events [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Energy efficiency costs
Regulatory Assets [Line Items]
Regulatory Assets	0	0
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] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets	0	1
Atlantic City Electric Company [Member] | Electric Energy and Natural Gas Costs
Regulatory Assets [Line Items]
Regulatory Assets	9	15
Atlantic City Electric Company [Member] | Under Recovered Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	7	11
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	10	9
Atlantic City Electric Company [Member] | Under-recovered revenue decoupling
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Securitized stranded costs
Regulatory Assets [Line Items]
Regulatory Assets	50	79
Atlantic City Electric Company [Member] | Removal costs
Regulatory Assets [Line Items]
Regulatory Assets	309	286
Atlantic City Electric Company [Member] | DC PLUG charge
Regulatory Assets [Line Items]
Regulatory Assets	0	0
Atlantic City Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	28	15
Atlantic City Electric Company [Member] | Other
Regulatory Assets [Line Items]
Regulatory Assets	$ 13	$ 14

Regulatory Matters Regulatory_6

Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 10,203	$ 10,388
Regulatory Liability, Current	644	523
Noncurrent regulatory liabilities	9,559	9,865
Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	5,228	5,241
Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,606	3,064
Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,547	1,573
Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	294	111
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	528	399
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6,343	6,577
Regulatory Liability, Current	293	249
Noncurrent regulatory liabilities	6,050	6,328
Commonwealth Edison Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,394	2,479
Commonwealth Edison Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	2,217	2,528
Commonwealth Edison Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,368	1,338
Commonwealth Edison Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	137	47
Commonwealth Edison Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	227	185
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	596	690
Regulatory Liability, Current	175	141
Noncurrent regulatory liabilities	421	549
PECO Energy Co [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	389	536
PECO Energy Co [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
PECO Energy Co [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	132	60
PECO Energy Co [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	75	94
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,269	1,163
Regulatory Liability, Current	77	62
Noncurrent regulatory liabilities	1,192	1,101
Baltimore Gas and Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,132	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	52	105
Baltimore Gas and Electric Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	6	0
Baltimore Gas and Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	79	26
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,948	1,928
Regulatory Liability, Current	84	56
Noncurrent regulatory liabilities	1,864	1,872
Pepco Holdings LLC [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1,702	1,730
Pepco Holdings LLC [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Pepco Holdings LLC [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	127	130
Pepco Holdings LLC [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	19	4
Pepco Holdings LLC [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	100	64
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	829	832
Regulatory Liability, Current	7	3
Noncurrent regulatory liabilities	822	829
Potomac Electric Power Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	798	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	20
Potomac Electric Power Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Potomac Electric Power Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	11	3
Delmarva Power & Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	665	635
Regulatory Liability, Current	59	42
Noncurrent regulatory liabilities	606	593
Delmarva Power & Light Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	510	510
Delmarva Power & Light Company [Member] | Nuclear decommissioning
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0	0
Delmarva Power & Light Company [Member] | Removal costs
Regulatory Liabilities [Line Items]
Regulatory Liabilities	107	110
Delmarva Power & Light Company [Member] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	18	1
Delmarva Power & Light Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	30	14
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	420	422
Regulatory Liability, Current	18	11
Noncurrent regulatory liabilities	402	411
Atlantic City Electric Company [Member] | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	394	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] | Over Recovered Energy and Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	1	3
Atlantic City Electric Company [Member] | Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 25	$ 8

Regulatory Matters Regulatory_7

Regulatory Matters Regulatory Matters - Capitalized Ratemaking Amounts Not Recognized (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 65	$ 69
Commonwealth Edison Co [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[1]	8	6
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]	49	53
Pepco Holdings LLC [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		8	10
Potomac Electric Power Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	5	6
Delmarva Power & Light Company [Member]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	3	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 electric distribution formula rate 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 Regulatory_8

Regulatory Matters Regulatory Matters - Schedule of Completed Rate Cases (Details) - USD ($) $ in Millions

Jan. 15, 2019

Jan. 04, 2019

Dec. 20, 2018

Dec. 04, 2018

Sep. 07, 2018

Jun. 27, 2018

Jun. 08, 2018

May 31, 2018

Apr. 20, 2018

[4]

Apr. 17, 2018

Apr. 16, 2018

Mar. 29, 2018

Mar. 08, 2018

[4]

Feb. 09, 2018

Dec. 19, 2017

Dec. 18, 2017

Nov. 16, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2023

Commonwealth Edison Co [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[1],[2]

$ (26)

Public Utilities, Approved Equity Capital Structure, Percentage

[1]

8.32%

Public Utilities, Requested Rate Increase (Decrease), Amount

[1]

$ (44)

Public Utilities, Approved Return on Equity, Percentage

[1],[3]

11.50%

Commonwealth Edison Co [Member] | Electric Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[4]

$ (24)

$ (23)

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 34

Public Utilities, Approved Equity Capital Structure, Percentage

6.52%

Public Utilities, Requested Equity Capital Structure, Percentage

8.69%

Public Utilities, Requested Rate Increase (Decrease), Amount

$ (58)

PECO Energy Co [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 22

Public Utilities, Requested Equity Capital Structure, Percentage

11.00%

PECO Energy Co [Member] | Electric Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[4]

$ 25

Public Utilities, Requested Rate Increase (Decrease), Amount

[4]

$ 82

Baltimore Gas and Electric Company [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[1],[2],[5]

$ 26

Public Utilities, Approved Equity Capital Structure, Percentage

[1]

7.61%

Public Utilities, Requested Rate Increase (Decrease), Amount

[1]

$ 10

Public Utilities, Approved Return on Equity, Percentage

10.50%

Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 43

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 61

Public Utilities, Requested Return on Equity, Percentage

9.80%

Potomac Electric Power Company [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[2]

$ 8

Public Utilities, Approved Equity Capital Structure, Percentage

7.82%

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 6

Public Utilities, Approved Return on Equity, Percentage

[3]

10.50%

Potomac Electric Power Company [Member] | Electric Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 4

$ (15)

$ (24)

[4]

$ 3

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 30

$ 66

Public Utilities, Requested Return on Equity, Percentage

10.30%

9.50%

9.525%

Delmarva Power & Light Company [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[2]

$ 27

Public Utilities, Approved Equity Capital Structure, Percentage

7.29%

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 14

Public Utilities, Approved Return on Equity, Percentage

[3]

10.50%

Delmarva Power & Light Company [Member] | Electric Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 12

[4]

$ 19

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 13

Public Utilities, Requested Rate Increase (Decrease), Amount

[4]

$ (7)

Public Utilities, Requested Return on Equity, Percentage

9.70%

Public Utilities, Approved Return on Equity, Percentage

9.50%

Delmarva Power & Light Company [Member] | Gas Distribution [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

[4]

$ 4

Public Utilities, Requested Rate Increase (Decrease), Amount

[4]

$ (4)

Public Utilities, Requested Return on Equity, Percentage

9.70%

Subsequent Event [Member] | Baltimore Gas and Electric Company [Member]

Regulatory Matters Completed Rate Cases [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 200

[1]

The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted.

[2]

{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MzY0MUFFQzNGNTE3Mzk3OTI2RjIxNTRFRUQyNkYyMzMM}

[3]

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.

[4]

Includes the annual ongoing TCJA tax savings further discussed below.

[5]

BGE's transmission revenue requirement includes a FERC approved dedicated facilities charge of $12 million to recover the costs of providing transmission service to specifically designated load by BGE.

Regulatory Matters Regulatory_9

Regulatory Matters Regulatory Matters - Schedule of Pending Rate Cases (Details) - USD ($) $ in Millions		Jan. 15, 2019	Nov. 19, 2018	Aug. 21, 2018	May 31, 2018	Apr. 17, 2018	Dec. 19, 2017	Dec. 31, 2018
Atlantic City Electric Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 40				$ 4
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[1]		$ 122
Public Utilities, Requested Return on Equity, Percentage				10.10%
Potomac Electric Power Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount								$ 6
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 30					$ 66
Public Utilities, Requested Return on Equity, Percentage		10.30%			9.50%	9.525%
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NUYyM0EwMDI1MDhGQUUyMUZEMzExNTNGOUY0NjExNDUM}

Regulatory Matters Regulator_10

Regulatory Matters Regulatory Matters - Schedule of TCJA Savings (Details) - USD ($) $ in Millions

Sep. 07, 2018

Aug. 29, 2018

Jul. 01, 2018

Jun. 27, 2018

Apr. 20, 2018

Mar. 29, 2018

Mar. 02, 2018

Feb. 09, 2018

Feb. 06, 2018

Feb. 05, 2018

Jan. 31, 2018

Jan. 18, 2018

Sep. 30, 2018

Commonwealth Edison Co [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 201

PECO Energy Co [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 71

Atlantic City Electric Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 23

Gas Distribution [Member] | PECO Energy Co [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 4

Gas Distribution [Member] | Baltimore Gas and Electric Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 31

Public Utilities, Rate Credit

2

Gas Distribution [Member] | Delmarva Power & Light Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 7

Public Utilities, Rate Credit

$ 1

Electric Distribution [Member] | PECO Energy Co [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Public Utilities, Rate Credit

67

Electric Distribution [Member] | Baltimore Gas and Electric Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 72

Electric Distribution [Member] | Delmarva Power & Light Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 19

Public Utilities, Rate Credit

$ 3

Electric Distribution [Member] | Potomac Electric Power Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 39

Public Utilities, Rate Credit

$ 20

$ 10

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

Regulatory Matters Schedule of TCJA Savings [Line Items]

Public Utilities, Rate Credit

$ 6

Maryland Service Territory [Member] | Electric Distribution [Member] | Delmarva Power & Light Company [Member]

Regulatory Matters Schedule of TCJA Savings [Line Items]

Tax Savings From Tax Cuts and Jobs Act

$ 31

$ 14

Public Utilities, Rate Credit

$ 2

Regulatory Matters Regulator_11

Regulatory Matters Regulatory Matters - Schedule of Revenue Increases (Decreases) (Details) - Commonwealth Edison Co [Member] - USD ($) $ in Millions		Dec. 04, 2018	Apr. 16, 2018	Dec. 31, 2018	Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	[1]			$ (44)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]			(26)
Electric Distribution [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ (58)
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 34
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[3]	$ (24)	$ (23)
Public Utilities, Requested Equity Capital Structure, Percentage		8.69%
[1]	The time period for any formal challenges to the annual transmission formula rate update filings expired with no formal challenges submitted.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MzY0MUFFQzNGNTE3Mzk3OTI2RjIxNTRFRUQyNkYyMzMM}
[3]	Includes the annual ongoing TCJA tax savings further discussed below.

Mergers, Acquisitions and Dis_3

Mergers, Acquisitions and Dispositions Mergers, Acquisitions and Dispositions - Narrative (Details) $ in Millions		Jul. 09, 2018USD ($)	Apr. 04, 2018USD ($)	Feb. 28, 2018USD ($)	Nov. 07, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 01, 2016USD ($)	Jun. 16, 2016USD ($)	Mar. 23, 2016USD ($)	Dec. 31, 2018USD ($)MW	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Mar. 23, 2016USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018USD ($)MW		Dec. 31, 2017USD ($)MW		Dec. 31, 2016USD ($)		Jun. 30, 2016USD ($)	Mar. 24, 2016USD ($)
Business Acquisition [Line Items]
Assets held for sale										$ 904				$ 0									$ 904		$ 0
Liabilities held for sale										777				0									777		0
Asset Retirement Obligation, Revision of Estimate																							20				$ 2
Deconsolidation, Gain (Loss), Amount					$ 213																		0		213		0
Business Combination, Contingent Consideration, Asset																														$ 235
Payments to Acquire Businesses, Gross																							154		208		6,923
Business Combination, Integration Related Costs																							7	[1]	16	[1]	143
Line of credit facility, maximum borrowing capacity	[2]									9,704													9,704
Other Commitment										127													127
Revenues										8,814	$ 9,403	$ 8,076	$ 9,693	8,384	$ 8,768	$ 7,665	$ 8,747						35,985		33,565		31,366
Business Combination, Bargain Purchase, Gain Recognized, Amount																							0		233		0
Net income (Loss)																							2,084		3,876		1,196
Noncash Merger Related Costs																							$ 0	[3]	$ 0	[4]	558	[5],[6]
Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							40
Exelon Corporation Affiliate [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment										$ 5													$ 5
Delmarva Power & Light Company [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW										40													120		40
Delmarva Power & Light Company [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										$ 12													$ 12
Exelon Consolidations [Member]
Business Acquisition [Line Items]
Other Commitment										508													508
Exelon Consolidations [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										259													259
Exelon Consolidations [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										29													29
Exelon Consolidations [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										117													117
Exelon Consolidations [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										50													50
Exelon Consolidations [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										22													22
Exelon Consolidations [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										14													14
Exelon Consolidations [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										17													17
Exelon Consolidations [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										128													128
Pepco Holdings [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross									$ 7,142
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Revenues																							4,670		$ 4,829		3,785
Net income (Loss)																							$ 453		$ 364		(66)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets									$ 4,005										$ 4,005
Pepco Holdings LLC [Member] | Other Solar Projects [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							27		37
Pepco Holdings LLC [Member] | Wind Assets [Member]
Business Acquisition [Line Items]
Other Non-Financial Commitment1 | MW																							100
Pepco Holdings LLC [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Commitment																		$ 513			$ 513	$ 513					513
Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Business Acquisition [Line Items]
Other Commitment										92													$ 92
ConEdison Solutions [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross							$ 257
Net Working Capital							$ 204
Oyster Creek [Member]
Business Acquisition [Line Items]
Assets held for sale										897													897
Baltimore Gas and Electric Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							0				0
Business Combination, Integration Related Costs																							1	[1],[7]	$ 4	[1],[7]	(1)
Revenues										799	731	662	977	813	738	674	951						3,169		3,176		3,233
Net income (Loss)										71	63	51	128	76	62	45	125						313		307		294
Noncash Merger Related Costs																							0	[3]	0	[4]	0	[5],[6]
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Assets held for sale										904				0									904		0
Liabilities held for sale										777				0									777		0
Asset Retirement Obligation, Revision of Estimate										203	84									$ 138			0				0
Deconsolidation, Gain (Loss), Amount																							0		213		0
Proceeds from Divestiture of Businesses				$ 87
Membership interest										9,518				9,357									9,518		9,357
Business Combination, Contingent Consideration, Asset																														163
Payments to Acquire Businesses, Gross																							154		208		293
Business Combination, Integration Related Costs																							5	[1]	22	[1]	37
Line of credit facility, maximum borrowing capacity										200		45											200
Gain (Loss) on Disposition of Property Plant Equipment																10											69
Proceeds from Sale of Productive Assets								$ 37
Revenues										5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878						20,437		18,500		17,757
Business Combination, Bargain Purchase, Gain Recognized, Amount																							0		233		0
Net income (Loss)																							443		2,798		550
Noncash Merger Related Costs																							0	[3]	0	[4]	53	[5],[6]
Asset Impairment Charges																		$ 23
Exelon Generation Co L L C [Member] | FirstEnergy [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 140
Exelon Generation Co L L C [Member] | Handley [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 62
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						$ 289																			289
Payments to Acquire Businesses, Gross																									110
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets														60											60
Business Combination, Integration Related Costs																									57
Business Combination, Consideration Transferred, Other						179																			54
Business Combination, Bargain Purchase, Gain Recognized, Amount																									233
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent														149											149
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets														114											114
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities														444											444
Total net assets														522											522
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred						110
Payments to Acquire Businesses, Gross																									125
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Membership interest										9,220				8,835									9,220		8,835
Business Combination, Integration Related Costs																							0	[1],[7]	(6)	[1],[7]	28
Other Commitment						$ 444											444
Revenues										1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175						4,805		4,679
Net income (Loss)																							398		362
Noncash Merger Related Costs																							5	[3]	(8)	[4]
Impairment of Long-Lived Assets to be Disposed of																25
Pepco Holdings LLC [Member] | Predecessor [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																			0
Business Combination, Integration Related Costs	[7]																		29
Revenues																			1,153
Net income (Loss)																			19
Noncash Merger Related Costs	[5],[6]																		$ 0
Pepco Holdings LLC [Member] | Successor [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																						2	20
Business Combination, Contingent Consideration, Asset																														235
Business Combination, Integration Related Costs	[7]																					69	0		(18)	[1]
Business Combination, Consideration Transferred, Other																	59
Revenues																						3,643			4,679
Net income (Loss)																					$ (61)	(61)
Noncash Merger Related Costs	[5],[6]																					$ 317
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										320													320
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										264													264
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										6													6
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										50													50
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							22				0
Revenues										531	628	523	557	510	604	514	530						2,239		2,158		2,186
Net income (Loss)										36	89	54	31	17	87	43	58						210		205		42
Noncash Merger Related Costs																							0	[3]	(6)	[4]	125	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														2,100
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														400
Potomac Electric Power Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													$ 73
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										120													120
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										91													91
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										1													1
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										28													28
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Potomac Electric Power Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							(1)				1
Business Combination, Integration Related Costs																							0	[1],[7]	(7)	[1],[7]	20
Revenues										331	328	289	384	330	327	282	362						1,332		1,300		1,277
Net income (Loss)										30	33	26	31	14	31	19	57						120		121		(9)
Noncash Merger Related Costs																							5	[3]	(2)	[4]	82	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														1,400
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														300
Delmarva Power & Light Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													46
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										89													89
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										72													72
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Commitment Adjustment [Member]
Business Acquisition [Line Items]
Other Commitment										5													5
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										5													5
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										12													12
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Delmarva Power & Light Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation, Revision of Estimate																							(1)				2
Business Combination, Integration Related Costs																							0	[1],[7]	(6)	[1],[7]	19
Revenues										254	406	265	310	271	370	270	275						1,236		1,186		1,257
Net income (Loss)										(1)	$ 61	8	$ 7	$ 0	$ 41	8	$ 28						75		77		(42)
Noncash Merger Related Costs																							0	[3]	$ 0	[4]	$ 110	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets																														500
Fresh-Start Adjustment, Increase (Decrease), Goodwill																														$ (700)
Atlantic City Electric Company [Member] | Commitments [Member]
Business Acquisition [Line Items]
Other Additional Capital																													$ 49
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Other Commitment										111													111
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Business Acquisition [Line Items]
Other Commitment										101													101
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Business Acquisition [Line Items]
Other Commitment										10													10
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Atlantic City Electric Company [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Business Acquisition [Line Items]
Other Commitment										0													0
Exelon Corporation Affiliate [Member] | Other commitments [Member]
Business Acquisition [Line Items]
Other Commitment										$ 83													$ 83
Electricity Generation Plant, Non-Nuclear [Member]
Business Acquisition [Line Items]
Impairment of Long-Lived Assets to be Disposed of												$ 41				$ 460				$ 460
[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]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.
[3]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[4]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[5]	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.
[6]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[7]	(b)For the year ended December 31, 2017, includes deferrals of previously incurred integration costs as regulatory assets of $24 million, $8 million, $8 million, and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $8 million, $6 million, $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.

Mergers, Acquisitions and Dis_4

Mergers, Acquisitions and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 154	$ 208	$ 6,923
Business Combination, Bargain Purchase, Gain Recognized, Amount		0	233	0
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		154	208	293
Business Combination, Bargain Purchase, Gain Recognized, Amount		$ 0	233	$ 0
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			110
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets			110
Business Combination, Consideration Transferred, Other	$ 179		54
Business Combination, Consideration Transferred	289		289
Current assets			60
Property, plant and equipment			298
Unamortized energy contracts			807
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets			114
Total assets			1,279
Current liabilities			6
Unamortized energy contract liabilities			(444)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent			149
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRegulatedLiabilities			110
Other liabilities			(15)
Total liabilities			757
Total net assets			522
_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedRetirmentObligations			33
Business Combination, Bargain Purchase, Gain Recognized, Amount			233
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross			$ 125
Business Combination, Consideration Transferred	$ 110

Mergers, Acquisitions and Dis_5

Mergers, Acquisitions and Dispositions Purchase Price allocation Table - Con Edison (Details) - USD ($) $ in Millions	Sep. 01, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Combination Segment Allocation [Line Items]
Payments to Acquire Businesses, Gross		$ 154	$ 208	$ 6,923
Energy Marketing Contracts Assets, Noncurrent		$ 372	$ 395
ConEdison Solutions [Member]
Business Combination Segment Allocation [Line Items]
Payments to Acquire Businesses, Gross	$ 257

Mergers, Acquisitions and Dis_6

Mergers, Acquisitions and Dispositions Merger Commitments Table (Details) - USD ($) $ in Millions	Dec. 31, 2018	Mar. 31, 2017
Other Commitments [Line Items]
Other Commitment	$ 127
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment		$ 444
Exelon Consolidations [Member]
Other Commitments [Line Items]
Other Commitment	508
Exelon Consolidations [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Exelon Consolidations [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	117
Exelon Consolidations [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Exelon Consolidations [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Exelon Consolidations [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Exelon Consolidations [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Exelon Consolidations [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Exelon Consolidations [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	128
Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	7
Delmarva Power & Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	73
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	320
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings LLC [Member] | Delmarva Power & Light Company [Member]
Other Commitments [Line Items]
Other Commitment	89
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings LLC [Member] | Rate Bill Credits [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	264
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 & Light Company [Member]
Other Commitments [Line Items]
Other Commitment	72
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] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
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 & 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] | Pepco Holdings LLC [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 & 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] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
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 & 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] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
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 & 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] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	0
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 & 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] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	6
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 & 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
Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 92

Mergers, Acquisitions and Dis_7

Mergers, Acquisitions and Dispositions Merger Transaction Table (Details) - USD ($) $ in Millions	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Payments to Acquire Businesses, Gross			$ 154	$ 208	$ 6,923
Pepco Holdings [Member]
Payments to Acquire Businesses, Gross	$ 7,142
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Deferred Compensation, Share-based Payments [Member]
Stockholders' Equity, Other		$ 29

Mergers, Acquisitions and Dis_8

Mergers, Acquisitions and Dispositions Purchase Price Allocation Table - (PHI) (Details) $ in Millions	Mar. 23, 2016USD ($)
Pepco Holdings LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 4,005

Mergers, Acquisitions and Dis_9

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, 2018		Dec. 31, 2017		Dec. 31, 2016	Mar. 31, 2017
Other Commitment				$ 127
Business Combination, Integration Related Costs				7	[1]	$ 16	[1]	$ 143
Exelon Generation Co L L C [Member]
Business Combination, Integration Related Costs				5	[1]	22	[1]	37
PECO Energy Co [Member]
Business Combination, Integration Related Costs				1	[1]	4	[1]	5
Baltimore Gas and Electric Company [Member]
Business Combination, Integration Related Costs				1	[1],[2]	4	[1],[2]	(1)
Pepco Holdings LLC [Member]
Other Commitment									$ 444
Business Combination, Integration Related Costs				0	[1],[2]	(6)	[1],[2]	28
Delmarva Power & Light Company [Member]
Business Combination, Integration Related Costs				0	[1],[2]	(7)	[1],[2]	20
Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs				0	[1],[2]	(6)	[1],[2]	19
Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs				0	[1],[2]	1	[1],[2]	$ (6)
Predecessor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[2]	$ 29
Successor [Member] | Pepco Holdings LLC [Member]
Business Combination, Integration Related Costs	[2]		$ 69	0		(18)	[1]
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			11			8
Regulatory Assets [Member] | Delmarva Power & Light Company [Member]
Business Combination, Integration Related Costs			4			8
Regulatory Assets [Member] | Atlantic City Electric Company [Member]
Business Combination, Integration Related Costs						$ 8
Regulatory Assets [Member] | Commonwealth Edison Co [Member]
Business Combination, Integration Related Costs			$ 8
Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitment				$ 73
[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 as regulatory assets of $24 million, $8 million, $8 million, and $8 million at PHI, Pepco, DPL and ACE, respectively. For the year ended December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $8 million, $6 million, $11 million and $4 million at ComEd, BGE, Pepco and DPL, respectively. For the Successor period March 24, 2016 to December 31, 2016, includes deferrals of previously incurred integration costs as regulatory assets of $16 million at PHI. See Note 4 - Regulatory Matters for additional information.

Mergers, Acquisitions and Di_10

Mergers, Acquisitions and Dispositions Proforma Impact of Merger (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	[3]	Dec. 31, 2017		Dec. 31, 2016
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		$ 0	[4]	$ 558	[5],[6]
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
[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
[3]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[4]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[5]	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.
[6]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 99,609	$ 95,266
Less: accumulated depreciation	[1]		22,902	21,064
Property, plant and equipment, net			76,707	74,202
Impairment of Long-Lived Assets Held-for-use			50	573	$ 306
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 53,090	49,506
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			$ 29,170	29,019
Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
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			$ 5,530	5,050
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			$ 1,627	1,447
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]		$ 5,957	6,420
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			$ 3,377	2,825
Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[3]		$ 858	999
Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
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			$ 36,187	36,334
Less: accumulated depreciation	[4]		12,206	11,428
Property, plant and equipment, net			23,981	24,906
Nuclear fuel - work in progress			1,004	1,196
Capital Leases, Balance Sheet, Assets by Major Class, Net			5	7
Capital Leased Assets, Gross			47	47
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation			42	40
Impairment of Long-Lived Assets Held-for-use			50	510	243
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 29,170	29,019
Exelon Generation Co L L C [Member] | Electric—generation | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
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]		$ 5,957	6,420
Less: accumulated depreciation			$ 2,969	3,159
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			$ 997	838
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[6]		$ 63	57
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			1 year
Exelon Generation Co L L C [Member] | Other Property Plant and Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			8 years
Commonwealth Edison Co [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 26,742	24,992
Less: accumulated depreciation			4,684	4,269
Property, plant and equipment, net			22,058	20,723
Capital Leases, Balance Sheet, Assets by Major Class, Net			7	7
Capital Leased Assets, Gross			8	8
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation			1	1
Plant Held for Future Use Amount			39
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 25,991	24,423
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			$ 705	517
Commonwealth Edison Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[7],[8]		$ 46	52
Commonwealth Edison Co [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			35 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			$ 12,171	11,464
Less: accumulated depreciation			3,561	3,411
Property, plant and equipment, net			8,610	8,053
Plant Held for Future Use Amount			19
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 8,359	7,975
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			$ 2,694	2,504
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			$ 756	710
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			$ 343	254
PECO Energy Co [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[9]		$ 19	21
Average Service Life (years)			50 years
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 11,876	11,007
Less: accumulated depreciation			3,633	3,405
Property, plant and equipment, net			8,243	7,602
Plant Held for Future Use Amount			25
Impairment of Long-Lived Assets Held-for-use			0	7	52
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 7,951	7,464
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			$ 2,630	2,379
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			$ 860	771
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			$ 410	367
Baltimore Gas and Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[10]		$ 25	26
Average Service Life (years)			20 years
Pepco Holdings LLC [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 14,287	12,985
Less: accumulated depreciation			841	487
Property, plant and equipment, net			13,446	12,498
Impairment of Long-Lived Assets Held-for-use			0	52
Pepco Holdings LLC [Member] | Successor [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use		$ 0
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 12,664	11,517
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
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 486	449
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
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 126	82
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
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 912	835
Pepco Holdings LLC [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[11]		$ 99	102
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			$ 9,814	9,178
Less: accumulated depreciation			3,354	3,177
Property, plant and equipment, net			6,460	6,001
Plant Held for Future Use Amount			61
Impairment of Long-Lived Assets Held-for-use			0	14	0
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 9,217	8,646
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			$ 536	473
Potomac Electric Power Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[12]		$ 61	59
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 & Light Company [Member]
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 5,150	4,826
Less: accumulated depreciation			1,329	1,247
Property, plant and equipment, net			3,821	3,579
Plant Held for Future Use Amount			17
Impairment of Long-Lived Assets Held-for-use			0	6	0
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 4,195	3,875
Delmarva Power & Light Company [Member] | Electric—transmission and distribution | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power & Light Company [Member] | Electric—transmission and distribution | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			70 years
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 651	614
Delmarva Power & Light Company [Member] | Gas Distribution Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power & Light Company [Member] | Gas Distribution Equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 136	117
Delmarva Power & Light Company [Member] | Common—electric and gas | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			5 years
Delmarva Power & Light Company [Member] | Common—electric and gas | Maximum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			75 years
Delmarva Power & Light Company [Member] | Construction work in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 151	205
Delmarva Power & Light Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[13]		$ 17	15
Delmarva Power & Light Company [Member] | Other Property Plant and Equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Average Service Life (years)			10 years
Delmarva Power & 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			$ 4,103	3,772
Less: accumulated depreciation			1,137	1,066
Property, plant and equipment, net			2,966	2,706
Plant Held for Future Use Amount			28
Impairment of Long-Lived Assets Held-for-use			0	7	$ 0
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 3,866	3,607
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			$ 209	138
Atlantic City Electric Company [Member] | Other Property Plant and Equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	[14]		$ 28	$ 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 $2,969 million and $3,159 million as of December 31, 2018 and 2017, respectively.
[2]	Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017, respectively.
[3]	Includes Generation’s buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017, respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017, and total accumulated amortization was $42 million and $40 million, as of December 31, 2018 and 2017, respectively. Also includes ComEd’s buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 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, 2018 and 2017. Includes land held for future use and non-utility property at ComEd, PECO, BGE, Pepco, DPL and ACE of $39 million, $19 million, $25 million, $61 million, $17 million and $28 million, respectively, at December 31, 2018.
[4]	Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million and $3,159 million as of December 31, 2018 and 2017, respectively
[5]	Includes nuclear fuel that is in the fabrication and installation phase of $1,004 million and $1,196 million at December 31, 2018 and 2017, respectively
[6]	Includes buildings under capital lease with a net carrying value of $5 million and $7 million at December 31, 2018 and 2017, respectively. The original cost basis of the buildings was $47 million as of both December 31, 2018 and 2017, and total accumulated amortization was $42 million and $40 million, as of December 31, 2018 and 2017, respectively.
[7]	Includes buildings under capital lease with a net carrying value at both December 31, 2018 and 2017 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, 2018 and 2017
[8]	Represents land held for future use and non-utility property.
[9]	Represents land held for future use and non-utility property.
[10]	Represents plant held for future use and non-utility property
[11]	Represents plant held for future use and non-utility property.
[12]	Represents plant held for future use and non-utility property.
[13]	Represents plant held for future use and non-utility property.
[14]	Represents plant held for future use and non-utility property.

Property, Plant and Equipment_2

Property, Plant and Equipment Property, Plant and Equipment- Annual Depreciation Provisions as Percentage of Average Service Life (Details)	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.73%		2.75%		2.73%
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.37%	[1]	4.36%	[1]	5.94%
Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.07%		2.10%		2.17%
Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.98%		7.05%		7.41%
PECO Energy Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.35%		2.37%		2.32%
PECO Energy Co [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.90%		1.89%		1.82%
PECO Energy Co [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.44%		5.47%		5.11%
Baltimore Gas and Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.61%		2.58%		2.56%
Baltimore Gas and Electric Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.36%		2.33%		2.45%
Baltimore Gas and Electric Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	8.50%		8.64%		9.45%
Pepco Holdings LLC [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.61%		2.63%		2.52%
Pepco Holdings LLC [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.59%		2.07%		2.57%
Pepco Holdings LLC [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	6.30%		6.50%		8.12%
Delmarva Power & Light Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.77%		2.75%		2.49%
Delmarva Power & Light Company [Member] | Gas Distribution Equipment
Property, Plant and Equipment [Line Items]
Annual depreciation rate	1.59%		2.07%		2.57%
Delmarva Power & Light Company [Member] | Common—electric and gas
Property, Plant and Equipment [Line Items]
Annual depreciation rate	3.70%		4.14%		4.99%
[1]	See Note 8 — Early Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI.

Property, Plant and Equipment_3

Property, Plant and Equipment Property, Plant and Equipment- Narrative (Details)	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.37%	[1]	4.36%	[1]	5.94%
Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.73%		2.75%		2.73%
Exelon Generation Co L L C [Member] | Electric—generation
Property, Plant and Equipment [Line Items]
Annual depreciation rate	5.37%		4.36%		5.94%
Commonwealth Edison Co [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.95%		2.99%		3.03%
Potomac Electric Power Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.40%		2.35%		2.17%
Atlantic City Electric Company [Member] | Electric—transmission and distribution
Property, Plant and Equipment [Line Items]
Annual depreciation rate	2.45%		2.46%		2.45%
[1]	See Note 8 — Early Plant Retirements for additional information on the accelerated net depreciation and amortization of Clinton, Quad Cities, Oyster Creek and TMI.

Property, Plant and Equipment_4

Property, Plant and Equipment Property, Plant and Equipment - 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Software [Line Items]
Capitalized Computer Software, Net			$ 810	$ 834
Capitalized Computer Software, Amortization			282	270	$ 255
Exelon Generation Co L L C [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			164	173
Capitalized Computer Software, Amortization			78	73	72
Commonwealth Edison Co [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			206	227
Capitalized Computer Software, Amortization			79	73	62
PECO Energy Co [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			98	111
Capitalized Computer Software, Amortization			37	39	33
Baltimore Gas and Electric Company [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			166	179
Capitalized Computer Software, Amortization			48	46	44
Potomac Electric Power Company [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			26	2
Capitalized Computer Software, Amortization			2	0	0
Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			165	133
Capitalized Computer Software, Amortization			33	34
Delmarva Power & Light Company [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			21	1
Capitalized Computer Software, Amortization			2	0	0
Atlantic City Electric Company [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Net			14	1
Capitalized Computer Software, Amortization			$ 1	$ 0	$ 0
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Amortization		$ 29
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Software [Line Items]
Capitalized Computer Software, Amortization	$ 8

Property, Plant and Equipment_5

Property, Plant and Equipment Property, Plant and Equipment - Summary of Capitalized Interest and AFUDC (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			$ 1,695	$ 1,658	$ 1,678
Interest Costs Capitalized				31	63	108
Allowance for Funds Used During Construction, Capitalized Interest				109	108	98
Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			305	263
Allowance for Funds Used During Construction, Capitalized Interest				44	54
Exelon Generation Co L L C [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			464	502	472
Interest Costs Capitalized				31	63	107
Allowance for Funds Used During Construction, Capitalized Interest				0	0	0
Commonwealth Edison Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			377	369	469
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				30	20	22
PECO Energy Co [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			141	130	127
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				12	12	11
Baltimore Gas and Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			130	111	114
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				24	22	30
Potomac Electric Power Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			162	133	137
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				34	34	29
Delmarva Power & Light Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			62	54	52
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				4	10	7
Atlantic City Electric Company [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]			68	64	65
Interest Costs Capitalized				0	0	0
Allowance for Funds Used During Construction, Capitalized Interest				$ 4	$ 9	$ 9
Successor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]		$ 207
Allowance for Funds Used During Construction, Capitalized Interest			$ 35
Predecessor [Member] | Pepco Holdings LLC [Member]
Capitalized Interest And AFUDC [Line Items]
Interest Costs Incurred	[1]	$ 68
Allowance for Funds Used During Construction, Capitalized Interest		$ 10
[1]	Includes interest expense to affiliates.

Impairment of Long-lived Asse_2

Impairment of Long-lived Assets Impairment of Long-Lived Assets - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended					9 Months Ended
	Mar. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2015
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Tangible Asset Impairment Charges					$ 36
Property, plant and equipment, net								$ 76,707		$ 74,202
Gain (Loss) on Contract Termination						$ 4
Finite-Lived Intangible Assets, Gross								1,267		1,228
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
Property, Plant, and Equipment, Fair Value Disclosure					$ 24
Pepco Holdings LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impairment of Long-Lived Assets to be Disposed of			$ 25
Property, plant and equipment, net								13,446		12,498
Finite-Lived Intangible Assets, Gross											$ 25
Exelon Generation Co L L C [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Property, plant and equipment, net								$ 23,981		$ 24,906
Constellation Energy Group LLC [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Tangible Asset Impairment Charges	$ 119			$ 15
Electricity Generation Plant, Non-Nuclear [Member]
Capital Leases Net Investment In Direct Financing Leases [Line Items]
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset									$ 41
Impairment of Long-Lived Assets to be Disposed of		$ 41	$ 460				$ 460

Early Plant Retirements Early_3

Early Plant Retirements Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions	Oct. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross		$ 154	$ 208	$ 6,923
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross		$ 154	$ 208	$ 293
Exelon Generation Co L L C [Member] | Nuclear Plant [Member]
Property, Plant and Equipment [Line Items]
Ownership interest		42.59%
Everett Marine Terminal [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Businesses, Gross	$ 81
Business Combination, Separately Recognized Transactions, Net Gains and Losses	$ 75

Early Plant Retirements Early_4

Early Plant Retirements Early Plant Retirements - Pretax Expense (Details) - USD ($) $ in Millions		Dec. 17, 2016	Jun. 16, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Other, net				$ (112)	$ 947	$ 297
Facility Closing [Member] | TMOysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[1],[2]			539
Nuclear Fuel Amortization	[1]			57
Other Cost and Expense, Operating	[1],[3]			32
Accretion Expense, Including Asset Retirement Obligations	[1]			0
Other, net	[1]			0
Other Expenses	[1]			628
Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[4]				250
Nuclear Fuel Amortization	[4]				12
Other Cost and Expense, Operating	[3],[4]				77
Accretion Expense, Including Asset Retirement Obligations	[4]				0
Other, net	[4]				0
Other Expenses	[4]				339
Facility Closing [Member] | Clinton and Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[5]					712
Nuclear Fuel Amortization	[5]					60
Other Cost and Expense, Operating		$ (120)	$ 146			26	[3],[5],[6]
Accretion Expense, Including Asset Retirement Obligations	[5],[7]					2
Other, net	[5],[7]					(86)
Other Expenses	[5]					714
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Other, net				(178)	948	401
Exelon Generation Co L L C [Member] | Facility Closing [Member] | TMOysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[1],[2]			539
Nuclear Fuel Amortization	[1]			57
Other Cost and Expense, Operating	[1],[3]			32
Accretion Expense, Including Asset Retirement Obligations	[1]			0
Other, net	[1]			0
Other Expenses	[1]			$ 628
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[4]				250
Nuclear Fuel Amortization	[4]				12
Other Cost and Expense, Operating	[3],[4]				77
Accretion Expense, Including Asset Retirement Obligations	[4]				0
Other, net	[4]				0
Other Expenses	[4]				$ 339
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Clinton and Quad Cities [Member]
Property, Plant and Equipment [Line Items]
Restructuring Reserve, Accelerated Depreciation	[2],[5]					712
Nuclear Fuel Amortization	[5]					60
Other Cost and Expense, Operating		$ (120)	$ 146			26	[3],[5],[6]
Accretion Expense, Including Asset Retirement Obligations	[5],[7]					2
Other, net	[5],[7]					(86)
Other Expenses	[5]					$ 714
[1]	Reflects incremental accelerated depreciation for TMI and Oyster Creek. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 2018.
[2]	Reflects incremental accelerated depreciation of plant assets, including any ARC.
[3]	Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Excludes the charge to Operating and maintenance expense from the ARO remeasurement due to the announced sale of Oyster Creek. See Note 5 — Mergers, Acquisitions and Dispositions for additional information.
[4]	Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017.
[5]	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.
[6]	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.
[7]	For Quad Cities based on the regulatory agreement with the ICC, 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.

Early Plant Retirements Early_5

Early Plant Retirements Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Implications of Potential Early Plant Retirement [Line Items]
Property, plant and equipment, net	$ 76,707	$ 74,202
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Property, plant and equipment, net	23,981	$ 24,906
Exelon Generation Co L L C [Member] | Salem [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials and Supplies, Gross	45
Nuclear Fuel, Net of Amortization	118
Property, plant and equipment, net	538
Construction in Progress, Gross	44
Asset Retirement Obligation	(395)
Exelon Generation Co L L C [Member] | Mystic Generating Station [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Inventory, Raw Materials and Supplies, Gross	30
Nuclear Fuel, Net of Amortization	20
Property, plant and equipment, net	901
Construction in Progress, Gross	9
Asset Retirement Obligation	$ (1)

Jointly Owned Electric Utilit_3

Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions		12 Months Ended
		Dec. 31, 2018USD ($)Vmi	Dec. 31, 2017USD ($)
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]	$ 28	$ 27
Accumulated depreciation	[1],[2]	16	15
Construction work in progress	[2]	1	0
Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	[1],[3]	103	102
Accumulated depreciation	[1],[3]	53	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]	$ 1,131	1,074
Accumulated depreciation	[1]	587	550
Construction work in progress		$ 13	35
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]	$ 1,451	1,417
Accumulated depreciation	[1]	523	461
Construction work in progress		$ 15	18
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]	$ 648	631
Accumulated depreciation	[1],[5]	227	205
Construction work in progress	[5]	$ 44	33
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]	$ 910	839
Accumulated depreciation	[1]	126	97
Construction work in progress		56	55
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]	$ 4	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 & Light Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		9.00%
Delmarva Power & Light Company [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		1.00%
Delmarva Power & Light Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		3.72%
Delmarva Power & Light Company [Member] | Delaware River Crossing [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.45%
Delmarva Power & Light Company [Member] | Merrill Creek [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		11.91%
Delmarva Power & 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		4.83%
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 and general plant.
[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 of the Salem generating plant substation. 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%, 11.91% and 4.83% 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, 2018 and 2017.

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, Gross	$ 8,660	$ 8,660	$ 8,660
Goodwill, beginning balance	6,677	6,677
Impairment losses	0	0
Goodwill, ending balance	6,677	6,677
Goodwill, Impaired, Accumulated Impairment Loss	1,983	1,983	1,983
Exelon Generation Co L L C [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	47
Goodwill, ending balance	47	47
Commonwealth Edison Co [Member]
Goodwill [Roll Forward]
Goodwill, Gross	4,608	4,608	4,608
Goodwill, beginning balance	2,625	2,625
Impairment losses	0	0
Goodwill, ending balance	2,625	2,625
Goodwill, Impaired, Accumulated Impairment Loss	1,983	1,983	1,983
Delmarva Power & Light Company [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	8
Goodwill, ending balance	8	8
Pepco Holdings LLC [Member]
Goodwill [Roll Forward]
Goodwill, Gross	4,005	4,005	$ 4,005
Goodwill, beginning balance	4,005	4,005
Impairment losses	0
Goodwill, ending balance	$ 4,005	$ 4,005

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 01, 2016	Mar. 24, 2016
Goodwill [Line Items]
Goodwill	$ 6,677	$ 6,677	$ 6,677
Amortization of Intangible Assets	(109)	(237)	(336)
Exelon Generation Co L L C [Member]
Goodwill [Line Items]
Goodwill	47	47
Amortization of Intangible Assets	63	83	79
Commonwealth Edison Co [Member]
Goodwill [Line Items]
Goodwill	2,625	2,625	2,625
Amortization of Intangible Assets	7	7	7
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				30.00%
Pepco Holdings LLC [Member]
Goodwill [Line Items]
Goodwill	4,005	4,005	$ 4,005
Potomac Electric Power Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets					$ 2,100
Fresh-Start Adjustment, Increase (Decrease), Goodwill					400
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				30.00%
Delmarva Power & Light Company [Member]
Goodwill [Line Items]
Goodwill	$ 8	$ 8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets					1,400
Fresh-Start Adjustment, Increase (Decrease), Goodwill					300
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				20.00%
Atlantic City Electric Company [Member]
Goodwill [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets					500
Fresh-Start Adjustment, Increase (Decrease), Goodwill					$ (700)
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				30.00%
Constellation Energy Group LLC [Member] | Trade Names [Member]
Goodwill [Line Items]
Useful life	10 years

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Gross		$ 1,267	$ 1,228
Accumulated Amortization		(1,149)	(1,255)
Net		118	(27)
Finite-Lived Intangible Assets, Gross		1,267	1,228
Exelon Enterprise [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	(32)
2,019	[1]	(20)
2,020	[1]	(4)
2,021	[1]	(23)
2,022	[1]	(21)
Exelon Enterprise [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[1]	95	95
Accumulated Amortization	[1]	(34)	(25)
Net	[1]	61	70
Finite-Lived Intangible Assets, Gross	[1]	95	95
Exelon Generation Consolidated [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	70
2,019	[1]	78
2,020	[1]	78
2,021	[1]	56
2,022	[1]	50
Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[2],[3]	1,957	1,938
Accumulated Amortization	[2],[3]	(1,588)	(1,574)
Net	[2],[3]	369	364
Finite-Lived Intangible Assets, Gross	[2],[3]	1,957	1,938
Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		325	305
Accumulated Amortization		(162)	(133)
Net		163	172
Finite-Lived Intangible Assets, Gross		325	305
Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		243	243
Accumulated Amortization		(171)	(148)
Net		72	95
Finite-Lived Intangible Assets, Gross		243	243
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	7
2,019	[1]	7
2,020	[1]	0
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		(148)	(141)
Net		14	21
Finite-Lived Intangible Assets, Gross		162	162
PHI Service Co Affiliate [Member]
Finite-Lived Intangible Assets [Line Items]
2,018	[1]	(119)
2,019	[1]	(115)
2,020	[1]	(92)
2,021	[1]	(89)
2,022	[1]	(81)
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		954	766
Net		(561)	(749)
Finite-Lived Intangible Assets, Gross		$ (1,515)	$ (1,515)
[1]	(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.
[2]	(b)Includes unamortized energy contract assets and liabilities in Exelon's, Generations and PHI's Consolidated Balance Sheets.
[3]	(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.

Intangible Assets - Summary of

Intangible Assets - Summary of Amortization Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		$ (109)	$ (237)	$ (336)
Potomac Electric Power Company [Member]
Finite-Lived Intangible Assets [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Goodwill					$ 400
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		63	83	79
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		7	7	7
PHI Service Co Affiliate [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset amortization expense		(188)	(336)	(430)
Delmarva Power & Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Fresh-Start Adjustment, Increase (Decrease), Goodwill					$ 300
Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	[1]	14	35	35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Power Contracts Emission Credits	[1]	$ 14	$ 35	$ 35
[1]	Included in Operating revenues or Purchased power and fuel in 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, 2018	Dec. 31, 2017	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		$ 1,267	$ 1,228
Finite-Lived Intangible Assets, Accumulated Amortization		1,149	1,255
Finite-Lived Intangible Assets, Net		118	(27)
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] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		270	312
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		52	27
Exelon Consolidations [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		2	1
Exelon Consolidations [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		279	321
Exelon Consolidations [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		52	27
PECO Energy Co [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		2	1
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
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross				$ 25
Pepco Holdings LLC [Member] | Alternative energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Pepco Holdings LLC [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		9	9
Pepco Holdings LLC [Member] | Renewable energy credit noncurrent [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		0	0
Exelon Enterprise [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	95	95
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	34	25
Finite-Lived Intangible Assets, Net	[1]	61	70
Delmarva Power & 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 & Light Company [Member] | Renewable energy credit current [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value		8	8
Delmarva Power & 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] | 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
[1]	(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.

Fair Value of Financial Asset_3

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, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		$ 795	$ 865
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Debt Issuance Costs, Net		216	201
Financing Trust Member [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		0	(1)
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		714	929
Long-term debt (including amounts due within one year)(a)	[1]	35,869	36,705
Due to Related Parties, Noncurrent	[2]	400	431
Spent Nuclear Fuel Obligation, Noncurrent		949	936
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	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		714	929
Long-term debt (including amounts due within one year)(a)	[1]	33,711	34,735
Due to Related Parties, Noncurrent	[2]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		949	936
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]	2,158	1,970
Due to Related Parties, Noncurrent	[2]	400	431
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		714	929
Long-term debt (including amounts due within one year)(a)	[1]	35,424	34,264
Due to Related Parties, Noncurrent	[2]	390	389
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)(a)		91	103
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Debt Issuance Costs, Net		51	60
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
Long-term debt (including amounts due within one year)(a)	[1]	8,910	9,512
Spent Nuclear Fuel Obligation, Noncurrent		949	936
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
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
Long-term debt (including amounts due within one year)(a)	[1]	7,467	7,839
Spent Nuclear Fuel Obligation, Noncurrent		949	936
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
Long-term debt (including amounts due within one year)(a)	[1]	1,443	1,673
Spent Nuclear Fuel Obligation, Noncurrent		0	0
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
Long-term debt (including amounts due within one year)(a)	[1]	8,793	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,171	1,147
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		63	52
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] | 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]	8,390	8,418
Due to Related Parties, Noncurrent	[2]	209	227
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]	8,390	8,418
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]	209	227
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]	8,101	7,601
Due to Related Parties, Noncurrent	[2]	205	205
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		23	17
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]	3,207	3,194
Due to Related Parties, Noncurrent		191	204
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]	3,157	3,194
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]	50	0
Due to Related Parties, Noncurrent		191	204
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]	3,084	2,903
Due to Related Parties, Noncurrent		184	184
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		18	17
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		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,950	2,825
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
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		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,950	2,825
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
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		35	77
Long-term debt (including amounts due within one year)(a)	[1]	2,876	2,577
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)		633	686
Pepco Holdings LLC [Member] | Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		14	6
Pepco Holdings LLC [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		179	350
Long-term debt (including amounts due within one year)(a)	[1]	6,101	6,019
Pepco Holdings LLC [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
Pepco Holdings LLC [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		179	350
Long-term debt (including amounts due within one year)(a)	[1]	5,436	5,722
Pepco Holdings LLC [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]	665	297
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt, Fair Value		179	350
Long-term debt (including amounts due within one year)(a)	[1]	6,259	5,874
Potomac Electric Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		34	32
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		40	26
Long-term debt (including amounts due within one year)(a)	[1]	3,097	3,123
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		40	26
Long-term debt (including amounts due within one year)(a)	[1]	2,901	3,114
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]	196	9
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		40	26
Long-term debt (including amounts due within one year)(a)	[1]	2,719	2,540
Delmarva Power & Light Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		12	11
Delmarva Power & 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]	1,496	1,393
Delmarva Power & 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 & 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]	1,303	1,393
Delmarva Power & 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]	193	0
Delmarva Power & 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]	1,494	1,300
Atlantic City Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Issuance Costs, Net		7	5
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		139	108
Long-term debt (including amounts due within one year)(a)	[1]	1,262	1,237
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	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		139	108
Long-term debt (including amounts due within one year)(a)	[1]	987	949
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	0
Long-term debt (including amounts due within one year)(a)	[1]	275	288
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		139	108
Long-term debt (including amounts due within one year)(a)	[1]	$ 1,188	$ 1,121
[1]	Includes unamortized debt issuance costs which are not fair valued of $216 million, $51 million, $63 million, $23 million, $18 million, $14 million, $34 million, $12 million and $7 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE respectively, as of December 31, 2018. 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.
[2]	Includes unamortized debt issuance costs which are not fair valued of $0 million and $1 million for Exelon and ComEd, respectively, as of December 31, 2018. 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.

Fair Value of Financial Asset_4

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, 2018	Dec. 31, 2017
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		$ (475)	$ (232)
Derivative Liability, Noncurrent		(479)	(409)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, collateral, right to reclaim cash		50	77
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		44	1
Derivative Asset, Notional Amount		1,432	811
Margin Deposit Assets		(94)	(117)
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		458	389
Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		80	145
Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		185	85
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		(130)	(82)
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]	1,243	656
FinancialAssetsFairValueDisclosure1		15,618	15,716
Deferred Compensation Liability, Current and Noncurrent		(137)	(145)
Financial Liabilities Fair Value Disclosure		(1,091)	(786)
Financial Asset Liabilities Net Fair Value Disclosure1		14,527	14,930
Alternative Investment, Fair Value Disclosure		3,433	3,534
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(947)	(637)
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(4,881)	(4,040)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(94)	(53)
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]	4,028	3,456
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		(7)	(4)
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		(4)	(2)
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability		(6)	(9)
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		3	7
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]	12,825	13,431
Alternative Investment, Fair Value Disclosure	[4]	3,433	3,510
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]	338	220
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5,890	7,254
Alternative Investment, Fair Value Disclosure		1,381	2,176
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		5,078	4,736
Alternative Investment, Fair Value Disclosure		846	510
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		1,823	1,865
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		2,180	1,969
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		50	82
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		149	263
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]	876	557
Alternative Investment, Fair Value Disclosure	[6]	846	510
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		680	528
Alternative Investment, Fair Value Disclosure		367	131
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		329	222
Alternative Investment, Fair Value Disclosure		329	222
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		510	471
Alternative Investment, Fair Value Disclosure		510	471
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		9	39
Alternative Investment, Fair Value Disclosure		0	24
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		9	2
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	1
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	36
Alternative Investment, Fair Value Disclosure		0	24
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		243	240
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48	77
Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		72	58
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		15	12
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		108	93
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,246	1,304
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4,771	4,225
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		146	68
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]	(3,671)	(2,989)
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		10	9
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	6
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		13	10
Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(3)	(7)
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42	37
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		57	65
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]	1,243	656
FinancialAssetsFairValueDisclosure1		6,582	6,980
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(3)	(63)
Financial Asset Liabilities Net Fair Value Disclosure1		6,579	6,917
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		(3)	(64)
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		(642)	(713)
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		0	(2)
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]	639	651
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		0	1
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		0	(1)
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		0	2
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]	5,251	6,215
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]	252	135
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		2,918	4,163
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		2,081	1,917
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		2,081	1,917
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		9	2
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		9	2
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] | 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		120	135
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		48	77
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		72	58
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		(41)	(26)
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		541	557
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		0	2
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]	(582)	(585)
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		0	(2)
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] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	(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		224	320
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		4,165	3,793
Deferred Compensation Liability, Current and Noncurrent		(137)	(145)
Financial Liabilities Fair Value Disclosure		(599)	(329)
Financial Asset Liabilities Net Fair Value Disclosure1		3,566	3,464
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		(455)	(179)
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		(2,963)	(2,226)
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		(73)	(42)
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]	2,581	2,089
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		(7)	(5)
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		(4)	(2)
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		(6)	(8)
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		3	5
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]	3,598	3,058
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]	86	85
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		1,591	915
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		1,921	2,058
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		1,593	1,614
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		99	52
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		50	82
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		149	263
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]	30	47
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		0	1
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		0	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		85	83
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		15	12
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		70	71
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		472	640
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		2,760	2,378
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		69	31
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]	(2,357)	(1,769)
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		10	11
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		0	6
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		13	10
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		(3)	(5)
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		76	81
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		1,438	1,409
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(489)	(394)
Financial Asset Liabilities Net Fair Value Disclosure1		949	1,015
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		(489)	(394)
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		(1,276)	(1,101)
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		(21)	(9)
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]	808	716
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] | 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]	543	648
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		230	251
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		230	251
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		313	397
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		0	12
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] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	12
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		38	22
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		38	22
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		815	690
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		1,470	1,290
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		77	35
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]	(732)	(635)
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] | 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		42	37
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		(449)	(211)
Derivative Liability, Noncurrent		(252)	(174)
Derivative liabilities, fair value	[7]	618	349
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		283	259
Exelon Generation Co L L C [Member] | Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		39	127
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]	581	168
FinancialAssetsFairValueDisclosure1		14,764	15,035
Deferred Compensation Liability, Current and Noncurrent		(35)	(38)
Financial Liabilities Fair Value Disclosure		(736)	(423)
Financial Asset Liabilities Net Fair Value Disclosure1		14,028	14,612
Alternative Investment, Fair Value Disclosure		3,433	3,534
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		(698)	(381)
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		(4,632)	(3,783)
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		(94)	(53)
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]	4,028	3,455
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		(3)	(4)
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		0	(2)
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		(6)	(9)
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		3	7
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]	12,825	13,431
Alternative Investment, Fair Value Disclosure	[4]	3,433	3,510
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]	338	220
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		5,890	7,254
Alternative Investment, Fair Value Disclosure		1,381	2,176
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		5,078	4,736
Alternative Investment, Fair Value Disclosure		846	510
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		1,823	1,865
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		2,180	1,969
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		50	82
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		149	263
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]	876	557
Alternative Investment, Fair Value Disclosure	[6]	846	510
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		680	528
Alternative Investment, Fair Value Disclosure		367	131
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		329	222
Alternative Investment, Fair Value Disclosure		329	222
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		510	471
Alternative Investment, Fair Value Disclosure		510	471
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		9	39
Alternative Investment, Fair Value Disclosure		0	24
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		9	2
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		0	1
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		0	36
Alternative Investment, Fair Value Disclosure		0	24
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		51	50
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	5
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		24	23
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	22
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		1,246	1,304
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		4,771	4,225
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		146	68
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]	(3,671)	(2,989)
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		10	6
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		0	3
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		13	10
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		(3)	(7)
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		42	37
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]	581	168
FinancialAssetsFairValueDisclosure1		5,829	6,385
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(3)	(63)
Financial Asset Liabilities Net Fair Value Disclosure1		5,826	6,322
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		(3)	(64)
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		(642)	(712)
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		0	(2)
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]	639	650
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		0	1
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		0	(1)
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		0	2
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]	5,251	6,215
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]	252	135
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		2,918	4,163
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		2,081	1,917
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		2,081	1,917
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		9	2
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		9	2
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] | 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		29	28
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	5
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		24	23
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		(41)	(26)
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		541	557
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		0	2
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]	(582)	(585)
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		0	(2)
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] | EffectsofNettingandAllocationofCollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0	(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		4,102	3,729
Deferred Compensation Liability, Current and Noncurrent		(35)	(38)
Financial Liabilities Fair Value Disclosure		(493)	(222)
Financial Asset Liabilities Net Fair Value Disclosure1		3,609	3,507
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		(455)	(179)
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		(2,963)	(2,226)
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		(73)	(42)
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]	2,581	2,089
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		(3)	(5)
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		0	(2)
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		(6)	(8)
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		3	5
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]	3,598	3,058
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]	86	85
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		1,591	915
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		1,921	2,058
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		1,593	1,614
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		99	52
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		50	82
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		149	263
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]	30	47
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		0	1
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		0	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	22
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	22
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		472	640
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		2,760	2,378
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		69	31
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]	(2,357)	(1,769)
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		10	8
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		0	3
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		13	10
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		(3)	(5)
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		1,400	1,387
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(240)	(138)
Financial Asset Liabilities Net Fair Value Disclosure1		1,160	1,249
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		(240)	(138)
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		(1,027)	(845)
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		(21)	(9)
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]	808	716
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] | 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]	543	648
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		230	251
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		230	251
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		313	397
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		0	12
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] | MiddleMarketLending Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0	12
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		815	690
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		1,470	1,290
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		77	35
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]	(732)	(635)
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] | 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		42	37
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Current		(26)	(21)
Derivative Liability, Noncurrent		(223)	(235)
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		93	45
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		166
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]	209	98
FinancialAssetsFairValueDisclosure1		209	98
Derivative Liability	[9]	(249)	(256)
Deferred Compensation Liability, Current and Noncurrent		(6)	(8)
Financial Liabilities Fair Value Disclosure		(255)	(264)
Financial Asset Liabilities Net Fair Value Disclosure1		(46)	(166)
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]	209	98
FinancialAssetsFairValueDisclosure1		209	98
Derivative Liability	[9]	0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		209	98
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		(6)	(8)
Financial Liabilities Fair Value Disclosure		(6)	(8)
Financial Asset Liabilities Net Fair Value Disclosure1		(6)	(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		(26)	(21)
Derivative Liability, Noncurrent		(223)	(235)
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]	(249)	(256)
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		(249)	(256)
Financial Asset Liabilities Net Fair Value Disclosure1		(249)	(256)
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		24	47
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]	111	228
FinancialAssetsFairValueDisclosure1		128	245
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(10)	(11)
Financial Liabilities Fair Value Disclosure		(10)	(11)
Financial Asset Liabilities Net Fair Value Disclosure1		118	234
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]	111	228
FinancialAssetsFairValueDisclosure1		118	235
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		118	235
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		(10)	(11)
Financial Liabilities Fair Value Disclosure		(10)	(11)
Financial Asset Liabilities Net Fair Value Disclosure1		0	(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
Financial Asset Liabilities Net Fair Value Disclosure1		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		7	17
Baltimore Gas and Electric Company [Member] | Restricted cash [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		2	1
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]	4	0
FinancialAssetsFairValueDisclosure1		10	6
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(5)	(5)
Financial Liabilities Fair Value Disclosure		(5)	(5)
Financial Asset Liabilities Net Fair Value Disclosure1		5	1
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	6
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	6
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]	4	0
FinancialAssetsFairValueDisclosure1		10	6
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		10	6
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	6
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	6
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)	(5)
Financial Liabilities Fair Value Disclosure		(5)	(5)
Financial Asset Liabilities Net Fair Value Disclosure1		(5)	(5)
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
Financial Asset Liabilities Net Fair Value Disclosure1		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] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		39	12
Pepco Holdings LLC [Member] | Other assets
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure		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
Pepco Holdings LLC [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]	147	83
FinancialAssetsFairValueDisclosure1		277	212
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(21)	(25)
Financial Liabilities Fair Value Disclosure		(21)	(25)
Financial Asset Liabilities Net Fair Value Disclosure1		256	187
Pepco Holdings LLC [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	[11]	0	(1)
Pepco Holdings LLC [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	1
Pepco Holdings LLC [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		130	129
Pepco Holdings LLC [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		42	72
Pepco Holdings LLC [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		15	12
Pepco Holdings LLC [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		60	45
Pepco Holdings LLC [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]	147	83
FinancialAssetsFairValueDisclosure1		202	155
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		202	155
Pepco Holdings LLC [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	[11]	0	(1)
Pepco Holdings LLC [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	1
Pepco Holdings LLC [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		55	72
Pepco Holdings LLC [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		42	72
Pepco Holdings LLC [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
Pepco Holdings LLC [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
Pepco Holdings LLC [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
FinancialAssetsFairValueDisclosure1		37	35
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		(21)	(25)
Financial Liabilities Fair Value Disclosure		(21)	(25)
Financial Asset Liabilities Net Fair Value Disclosure1		16	10
Pepco Holdings LLC [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	[11]	0	0
Pepco Holdings LLC [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	0
Pepco Holdings LLC [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		37	35
Pepco Holdings LLC [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
Pepco Holdings LLC [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		15	12
Pepco Holdings LLC [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	23
Pepco Holdings LLC [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
FinancialAssetsFairValueDisclosure1		38	22
Derivative Liability		0	0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		38	22
Pepco Holdings LLC [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	[11]	0	0
Pepco Holdings LLC [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	0
Pepco Holdings LLC [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		38	22
Pepco Holdings LLC [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
Pepco Holdings LLC [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
Pepco Holdings LLC [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		38	22
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		15	4
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]	38	36
FinancialAssetsFairValueDisclosure1		143	137
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		(3)	(4)
Financial Liabilities Fair Value Disclosure		(3)	(4)
Financial Asset Liabilities Net Fair Value Disclosure1		140	133
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, Noncurrent			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, Noncurrent			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		105	101
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		41	44
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		5	12
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		59	45
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]	38	36
FinancialAssetsFairValueDisclosure1		79	80
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		79	80
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, Noncurrent			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, Noncurrent			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		41	44
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		41	44
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
FinancialAssetsFairValueDisclosure1		27	35
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		(3)	(4)
Financial Liabilities Fair Value Disclosure		(3)	(4)
Financial Asset Liabilities Net Fair Value Disclosure1		24	31
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, Noncurrent			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, Noncurrent			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		27	35
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		5	12
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		22	23
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
FinancialAssetsFairValueDisclosure1		37	22
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		37	22
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, Noncurrent			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, Noncurrent			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		37	22
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		37	22
Delmarva Power & 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		8	2
Delmarva Power & 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]	16	0
FinancialAssetsFairValueDisclosure1		16	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		(1)	(1)
Financial Liabilities Fair Value Disclosure		(1)	(1)
Financial Asset Liabilities Net Fair Value Disclosure1		15	(1)
Delmarva Power & 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, Noncurrent	[11]		(1)
Delmarva Power & 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, Noncurrent			1
Delmarva Power & 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 & 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 & 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 & 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 & 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]	16	0
FinancialAssetsFairValueDisclosure1		16	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		16	0
Delmarva Power & 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, Noncurrent	[11]		(1)
Delmarva Power & 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, Noncurrent			1
Delmarva Power & 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 & 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 & 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 & 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 & 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
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		(1)	(1)
Financial Liabilities Fair Value Disclosure		(1)	(1)
Financial Asset Liabilities Net Fair Value Disclosure1		(1)	(1)
Delmarva Power & 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, Noncurrent	[11]		0
Delmarva Power & 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, Noncurrent			0
Delmarva Power & 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 & 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 & 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 & 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 & 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
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		0	0
Delmarva Power & 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, Noncurrent	[11]		0
Delmarva Power & 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, Noncurrent			0
Delmarva Power & 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 & 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 & 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 & 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		7	2
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		19	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]	23	29
FinancialAssetsFairValueDisclosure1		23	29
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		23	29
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, Noncurrent			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, Noncurrent			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]	23	29
FinancialAssetsFairValueDisclosure1		23	29
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		23	29
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, Noncurrent			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, Noncurrent			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
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		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, Noncurrent			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, Noncurrent			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
FinancialAssetsFairValueDisclosure1		0	0
Derivative Liability			0
Deferred Compensation Liability, Current and Noncurrent		0	0
Financial Liabilities Fair Value Disclosure		0	0
Financial Asset Liabilities Net Fair Value Disclosure1		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, Noncurrent			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, Noncurrent			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 $283 million and $259 million at December 31, 2018 and 2017 and restricted cash of $39 million and $127 million at December 31, 2018 and 2017. Exelon excludes cash of $458 million and $389 million at December 31, 2018 and 2017 and restricted cash of $80 million and $145 million at December 31, 2018 and 2017 and includes long-term restricted cash of $185 million and $85 million at December 31, 2018 and 2017, which is reported in Other deferred debits in the Consolidated Balance Sheets.
[2]	Excludes net assets of less than $1 million at December 31, 2018 and 2017. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.
[3]	The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the years ended December 31, 2018 and 2017, respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the years ended December 31, 2018 and 2017, respectively.
[4]	Excludes net liabilities of $130 million and $82 million at December 31, 2018 and 2017, 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 $50 million and $77 million of cash received from outstanding repurchase agreements at December 31, 2018 and 2017, respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below.
[6]	Includes derivative instruments of $44 million and less than $1 million, which have a total notional amount of $1,432 million and $811 million at December 31, 2018 and 2017, 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 $93 million and $45 million at December 31, 2018 and 2017 and restricted cash of $28 million at December 31, 2018 and includes long-term restricted cash of $166 million and $62 million at December 31, 2018 and December 31, 2017, which is reported in Other deferred debits in the Consolidated Balance Sheets. PECO excludes cash of $24 million and $47 million at December 31, 2018 and 2017. BGE excludes cash of $7 million and $17 million at December 31, 2018 and 2017 and restricted cash of $2 million and $1 million at December 31, 2018 and December 31, 2017.
[9]	The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the years ended December 31, 2018 and December 31, 2017.
[10]	PHI excludes cash of $39 million and $12 million at December 31, 2018 and 2017 and includes long term restricted cash of $19 million and $23 million at December 31, 2018 and 2017 which is reported in Other deferred debits in the Consolidated Balance Sheets. Pepco excludes cash of $15 million and $4 million at December 31, 2018 and 2017. DPL excludes cash of $8 million and $2 million at December 31, 2018 and 2017. ACE excludes cash of $7 million and $2 million at December 31, 2018 and 2017 and includes long-term restricted cash of $19 million and $23 million at December 31, 2018 and 2017 at December 31, 2018 and 2017 which is reported in Other deferred debits in the Consolidated Balance Sheets.
[11]	The amount of unrealized gains/(losses) at PHI totaled $1 million for the years ended December 31, 2018 and 2017, respectively. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for the years ended December 31, 2018 and 2017, respectively.

Fair Value of Financial Asset_5

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		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
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		$ 949		$ 1,015		$ 993
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		(98)		(81)
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		7		(8)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets		6		8
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral		(5)		20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		231		248
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(24)		(16)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances		0		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(123)		(110)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		(22)		(6)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(38)		(61)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		163		261
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		1		(6)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets		(1)		6
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		1,160		1,249		1,231
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		(102)		(84)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		(1)		6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		7		(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		(5)		20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		231		248
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(24)		(16)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(135)		(110)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		(22)		(6)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(38)		(61)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		163		258
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		543		648		677
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		3
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		(1)		6
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0		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		36		64
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		(140)		(102)
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)		(5)		1
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		0		12		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		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		7		(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		1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(20)		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] | 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		575		552		493
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]	(105)		(90)
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		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		(5)		20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		190		178	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		(4)		(16)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		5	[3]	(8)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		(22)		(6)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(36)		(50)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous	[4]	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		165		254
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		(265)		352
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		42		37		42
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 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		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		4		5
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		(2)		(11)
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		3		3
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)		17		20
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)		(24)		(18)
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		(249)		(256)		$ (258)
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		0	[1]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets	[5]	7		2
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] | 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		38		22
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
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
FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisOtherMiscellaneous		$ 0
[1]	Includes a reduction for the reclassification of $265 million and $352 million of realized gains due to the settlement of derivative contracts for the years ended December 31, 2018 and 2017, respectively.
[2]	Includes $(19) million of fair value from contracts acquired as a result of the Everett Marine Terminal acquisition
[3]	The amounts represented are life insurance contracts at Pepco
[4]	Transfers into and out of Level 3 generally occur when the contract tenor becomes less and more observable respectively, primarily due to changes in market liquidity or assumptions for certain commodity contracts.
[5]	Includes $24 million of decreases in fair value and an increase for realized losses due to settlements of $17 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the year ended December 31, 2018. 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.

Fair Value of Financial Asset_6

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	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
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		$ (7)	$ 28
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		144	290
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		(93)	(126)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		21	(36)
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		3	6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(2)	4
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		4
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0
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		(7)	28
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		144	290
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		(93)	(126)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		21	(36)
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		3	6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(2)	4
Pepco Holdings LLC [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	$ 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		98	81
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		163	261
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		102	84
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 163	$ 258

Fair Value of Financial Asset_7

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, 2018		Dec. 31, 2017
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted		$ 76,000,000		$ 81,000,000
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	[1],[2]	443,000,000		445,000,000
Derivative liabilities, fair value		$ (249,000,000)		$ (256,000,000)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		12		3
Forward gas price assets		0.78		1.27
Marketability Reserve		4.00%		4.00%
Renewable factor		86.00%		88.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		174		124
Forward gas price assets		12.38		12.8
Marketability Reserve		8.00%		8.00%
Renewable factor		120.00%		120.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage		10.00%		11.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage		277.00%		139.00%
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	[1],[2]	$ 56,000,000		$ 26,000,000
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		14		14
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Collateral Posted		$ 418,000,000		$ 497,000,000
Derivative liabilities, fair value	[3]	618,000,000		349,000,000
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		$ 443,000,000	[1],[2]	$ 445,000,000	[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		12		3
Forward gas price assets		0.78		1.27
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		174		124
Forward gas price assets		12.38		12.8
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		10.00%		11.00%
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		277.00%		139.00%
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		$ 56,000,000	[1],[2]	$ 26,000,000	[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		14
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		174		94
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		$ (249,000,000)		$ (256,000,000)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve		4.00%		4.00%
Renewable factor		86.00%		88.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve		8.00%		8.00%
Renewable factor		120.00%		120.00%
[1]	The fair values do not include cash collateral posted on level three positions of $76 million as of December 31, 2018.
[2]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[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.
[4]	The fair values do not include cash collateral posted on level three positions $81 million as of December 31, 2017.
[5]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions

Fair Value of Financial Asset_8

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,171,000,000	$ 1,147,000,000
Forward Power Basis	3.18
Forward Gas Basis	0.64
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	1,171,000,000	1,147,000,000
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	$ 119,000,000	$ 114,000,000

Derivative Financial Instrume_3

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Derivative [Line Items]
Ineffective portion recognized in income	$ 9,000		$ 15,000		$ 14,000
Cash collateral held	(17,000)
Letters of credit held	35,000
Derivative, Fair Value, Net	1,000		6,000
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	3,000		5,000
Commodity Contract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	299,000		667,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Credit exposure under off system sales	3,000
Incremental collateral for loss of investment grade credit rating	69,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Letters of credit posted	367,000		293,000
Cash collateral held	(47,000)		(35,000)
Letters of credit held	44,000		33,000
Cash collateral posted	418,000		497,000
Incremental collateral for loss of investment grade credit rating	2,100,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	7,000
Derivative, Collateral, Obligation to Return Cash	2,000		4,000
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	7,000		2,000
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Fair Value, Net			1,000
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	$ 548,000	[1]	$ 923,000	[2]
Commonwealth Edison Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	38,000,000
Commonwealth Edison Company [Member] | Other Contract [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19,000,000
Commonwealth Edison Company [Member] | Renewable Energy Program [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	31,000,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Incremental collateral for loss of investment grade credit rating	$ 7,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated Percent Of Gas Purchases Being Hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 39,000
Delmarva Power & Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	11,000
Delmarva Power & 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 Percent Of Gas Purchases Being Hedged	10.00%
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	89.00%
Expected generation hedged in year two	56.00%
Expected generation hedged in year three	32.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated Percent Of Gas Purchases Being Hedged	20.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	92.00%
Expected generation hedged in year two	59.00%
Expected generation hedged in year three	35.00%
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	$ 5,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	30,000
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]
Due From Affiliate Current Electric Utility	28,000
Delmarva Power & Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	7,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	43,000
Derivative, Collateral, Obligation to Return Cash	$ 12,000
[1]	Current and noncurrent assets are shown net of collateral of $121 million and $51 million, respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018.
[2]	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.

Derivative Financial Instrume_4

Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		$ 804	$ 976
Mark-to-market derivative assets (noncurrent assets)		452	337
Derivative Liability, Current		(475)	(232)
Derivative Liability, Noncurrent		(479)	(409)
Total mark-to-market derivative net assets (liabilities)		1	6
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		804	976
Mark-to-market derivative assets (noncurrent assets)		452	334
Derivative Liability, Current		(449)	(211)
Derivative Liability, Noncurrent		(252)	(174)
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	3
Mark-to-market derivative assets (noncurrent assets)		7	6
Total mark-to-market derivative assets		10	9
Derivative Liability, Current		(2)	(2)
Derivative Liability, Noncurrent		(5)	(2)
Total mark-to-market derivative liabilities		7	4
Total mark-to-market derivative net assets (liabilities)		3	5
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		3	3
Mark-to-market derivative assets (noncurrent assets)		7	3
Total mark-to-market derivative assets		10	6
Derivative Liability, Current		(2)	(2)
Derivative Liability, Noncurrent		(1)	(2)
Total mark-to-market derivative liabilities		3	4
Total mark-to-market derivative net assets (liabilities)		7	2
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
Mark-to-market derivative assets (noncurrent assets)			3
Total mark-to-market derivative assets			3
Derivative Liability, Current			(2)
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			2
Total mark-to-market derivative net assets (liabilities)			1
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)		5	10
Mark-to-market derivative assets (noncurrent assets)		8	0
Total mark-to-market derivative assets		13	10
Derivative Liability, Current		(4)	(7)
Derivative Liability, Noncurrent		(2)	(2)
Total mark-to-market derivative liabilities		6	9
Total mark-to-market derivative net assets (liabilities)		7	1
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)			0
Mark-to-market derivative assets (noncurrent assets)			3
Total mark-to-market derivative assets			3
Derivative Liability, Current			0
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			0
Total mark-to-market derivative net assets (liabilities)			3
Corporate, Non-Segment [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		0
Mark-to-market derivative assets (noncurrent assets)		0
Total mark-to-market derivative assets		0
Derivative Liability, Current		0
Derivative Liability, Noncurrent		(4)
Total mark-to-market derivative liabilities		4
Total mark-to-market derivative net assets (liabilities)		(4)
Collateral and Netting | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[1]	(2)	(7)
Mark-to-market derivative assets (noncurrent assets)	[1]	(1)	0
Total mark-to-market derivative assets	[1]	(3)	(7)
Derivative Liability, Current	[1]	2	7
Derivative Liability, Noncurrent	[1]	1	0
Total mark-to-market derivative liabilities	[1]	(3)	(7)
Total mark-to-market derivative net assets (liabilities)	[1]	$ 0	$ 0
[1]	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 Instrume_5

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ (11)	$ (13)	$ (9)
Price Risk Derivative [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge	$ 20	$ 28	$ 23

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions		Dec. 31, 2018		Dec. 31, 2017
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		$ 50		$ 77
Mark-to-market derivative assets (current assets)		804		976
Mark-to-market derivative assets (noncurrent assets)		452		337
Derivative Liability, Current		(475)		(232)
Derivative Liability, Noncurrent		(479)		(409)
Total mark-to-market derivative net assets (liabilities)		1		6
Margin Deposit Assets		(94)		(117)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		804		976
Mark-to-market derivative assets (noncurrent assets)		452		334
Derivative Liability, Current		(449)		(211)
Derivative Liability, Noncurrent		(252)		(174)
Derivative, Collateral, Obligation to Return Cash		2		4
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current		(26)		(21)
Derivative Liability, Noncurrent		(223)		(235)
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		801		973
Mark-to-market derivative assets (noncurrent assets)		445		331
Total mark-to-market derivative assets		1,246		1,304
Derivative Liability, Current		(473)		(230)
Derivative Liability, Noncurrent		(474)		(407)
Total mark-to-market derivative liabilities		(947)		(637)
Total mark-to-market derivative net assets (liabilities)		299		667
Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)		801	[1]	973	[2]
Mark-to-market derivative assets (noncurrent assets)		445	[1]	331	[2]
Total mark-to-market derivative assets		1,246	[1]	1,304	[2]
Derivative Liability, Current		(447)	[1]	(209)	[2]
Derivative Liability, Noncurrent		(251)	[1]	(172)	[2]
Total mark-to-market derivative liabilities		(698)	[1]	(381)	[2]
Total mark-to-market derivative net assets (liabilities)		548	[1]	923	[2]
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(357)		(466)
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)		3,505		3,061
Mark-to-market derivative assets (noncurrent assets)		1,266		1,164
Total mark-to-market derivative assets		4,771		4,225
Derivative Liability, Current		(3,429)		(2,646)
Derivative Liability, Noncurrent		(1,203)		(1,137)
Total mark-to-market derivative liabilities		(4,632)		(3,783)
Total mark-to-market derivative net assets (liabilities)		139		442
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]	(26)		(21)
Derivative Liability, Noncurrent	[3]	(223)		(235)
Total mark-to-market derivative liabilities	[3]	(249)		(256)
Total mark-to-market derivative net assets (liabilities)	[3]	(249)		(256)
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)		105		56
Mark-to-market derivative assets (noncurrent assets)		41		12
Total mark-to-market derivative assets		146		68
Derivative Liability, Current		(74)		(43)
Derivative Liability, Noncurrent		(20)		(10)
Total mark-to-market derivative liabilities		(94)		(53)
Total mark-to-market derivative net assets (liabilities)		52		15
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		121		169
Margin Deposit Assets		(94)		(117)
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		51		53
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		125		167
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		60		77
Collateral and Netting | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative assets (current assets)	[4]	(2,809)	[5]	(2,144)	[6]
Mark-to-market derivative assets (noncurrent assets)	[4]	(862)	[5]	(845)	[6]
Total mark-to-market derivative assets	[4]	(3,671)	[5]	(2,989)	[6]
Derivative Liability, Current	[4]	3,056	[5]	2,480	[6]
Derivative Liability, Noncurrent	[4]	972	[5]	975	[6]
Total mark-to-market derivative liabilities	[4]	4,028	[5]	3,455	[6]
Total mark-to-market derivative net assets (liabilities)	[4]	$ 357	[5]	$ 466	[6]
[1]	Current and noncurrent assets are shown net of collateral of $121 million and $51 million, respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018.
[2]	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.
[3]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[4]	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 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.
[5]	Of the collateral posted/(received), $(94) million represents variation margin on the exchanges.
[6]	Of the collateral posted/(received), $(117) million represents variation margin on the exchanges

Derivative Financial Instrume_7

Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Derivative [Line Items]
Beginning Balance			$ (3,026)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]		(182)	$ (144)
Ending Balance		$ (2,995)	(2,995)	(3,026)
Income Tax Expense (Benefit)		(26)	(120)	126		$ (753)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance			(37)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]		(1)	(4)
Ending Balance		(38)	(38)	(37)
Income Tax Expense (Benefit)			108	1,376		(282)
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance			(14)	(17)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			11	(1)
Ending Balance		(2)	(2)	(14)		(17)
Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			1	4	[2]
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance			(16)	(19)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			11	(1)
Ending Balance		$ (4)	(4)	(16)		$ (19)
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			$ 1	4	[2]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income Tax Expense (Benefit)				$ 1
[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.

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (294)	$ (151)	$ (24)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(307)	(167)	(40)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(6)	(9)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	7	(6)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(4)	(3)	0
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	(317)	(169)	(31)
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	(270)	(126)	(490)
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	(47)	(43)	459
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)	(9)	(10)
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	7	(6)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	0	0
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	$ (7)	$ (3)	$ 0

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (294)	$ (151)	$ (24)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(307)	(167)	(40)
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	17	6	2
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	$ 0	$ (1)	$ (1)

Derivative Financial Instrum_10

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Cash collateral held		$ 17
Letters of credit held		35
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral held		47	$ 35
Letters of credit held		44	$ 33
Total Exposure Before Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		795
Non-investment grade		133
Internally rated — investment grade		181
Internally rated — non-investment grade		92
Total		1,201
Credit Collateral [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		0
Non-investment grade		45
Internally rated — investment grade		1
Internally rated — non-investment grade		6
Total	[1]	52
Net Exposure [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Investment grade		795
Non-investment grade		88
Internally rated — investment grade		180
Internally rated — non-investment grade		86
Total		1,149
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		153
Non-investment grade		0
Internally rated — investment grade		0
Internally rated — non-investment grade		0
Total		$ 153
[1]	As of December 31, 2018, credit collateral held from counterparties where Generation had credit exposure included $17 million of cash and $35 million of letters of credit. The credit collateral does not include non-liquid collateral.

Derivative Financial Instrum_11

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, 2018USD ($)
Derivative [Line Items]
Financial institutions	$ 12
Investor-owned utilities, marketers, power producers	737
Energy cooperatives and municipalities	324
Other	76
Total	$ 1,149

Derivative Financial Instrum_12

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Liability	[1]	$ (1,723)	$ (926)
Offsetting Fair Value of In-the-Money Contracts Under Master Netting Arrangements	[2]	1,105	577
Derivative liabilities, fair value	[3]	$ (618)	$ (349)
[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 Instrum_13

Derivative Financial Instruments - Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative, Notional Amount	$ 5,991	$ 3,606
Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,688	95
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	268	94
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,420	1	[1]
Exelon Generation Co L L C [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount	888	95
Exelon Generation Co L L C [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	268	94
Exelon Generation Co L L C [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	620	1
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	0	636
Corporate, Non-Segment [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount	800	0
Corporate, Non-Segment [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	0	0
Corporate, Non-Segment [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800	0
Corporate, Non-Segment [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 0	$ 800
[1]	On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017.

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings Outstanding (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 30, 2018	Jun. 30, 2018	Dec. 31, 2017		Dec. 31, 2016	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704
Average Interest Rate on Commercial Paper Borrowings		2.15%			1.24%		1.12%
Letters of Credit Outstanding, Amount		$ 1,696
Credit facility agreements with minority and community banks		135			$ 128
Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3],[4]	9,000			9,450
Outstanding commercial paper		89			427
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity								$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		9
Exelon Corporate [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		1.93%			1.16%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200		$ 45
Average Interest Rate on Commercial Paper Borrowings		1.96%			1.23%		1.14%
Credit facility agreements with minority and community banks		$ 49	$ 75		$ 49
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			5,300	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		1.96%			1.23%
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 545			$ 480
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		159			$ 179
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 5
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.14%			1.24%
Letters of Credit Outstanding, Amount		$ 2
Credit facility agreements with minority and community banks		33			$ 34
Commonwealth Edison Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	1,000			1,000	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		2.14%			1.24%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.13%
Letters of Credit Outstanding, Amount		$ 0
Credit facility agreements with minority and community banks		34			$ 34
PECO Energy Co [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 0			$ 0
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.13%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.18%			1.28%		0.95%
Letters of Credit Outstanding, Amount		$ 1
Credit facility agreements with minority and community banks		5			$ 5
Baltimore Gas and Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	600			600	[4]
Outstanding commercial paper		$ 35			$ 77
Average Interest Rate on Commercial Paper Borrowings		2.18%			1.28%
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount		$ 2
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,500
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.06%		0.90%
Letters of Credit Outstanding, Amount		$ 8
Credit facility agreements with minority and community banks		5			$ 2
Potomac Electric Power Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			500	[4]
Outstanding commercial paper		$ 40			$ 26
Average Interest Rate on Commercial Paper Borrowings		2.24%			1.06%
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.07%			1.48%
Letters of Credit Outstanding, Amount		$ 1
Credit facility agreements with minority and community banks		5			$ 2
Delmarva Power & Light Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			500	[4]
Outstanding commercial paper		$ 0			$ 216
Average Interest Rate on Commercial Paper Borrowings		2.07%			1.48%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Average Interest Rate on Commercial Paper Borrowings		2.21%			1.43%
Letters of Credit Outstanding, Amount		$ 0
Credit facility agreements with minority and community banks		5			$ 2
Atlantic City Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[2],[3]	300			350	[4]
Outstanding commercial paper		$ 14			$ 108
Average Interest Rate on Commercial Paper Borrowings		2.21%			1.43%
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 900
Maximum [Member] | Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		0
Maximum [Member] | Atlantic City Electric Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 0
[1]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.
[2]	At December 31, 2018, excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. At December 31, 2017, excludes $128 million of credit facility agreements arranged at minority and community banks at 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.
[3]	Excludes $545 million and $480 million in bilateral credit facilities at December 31, 2018 and 2017, respectively, and $159 million and $179 million in credit facilities for project finance at December 31, 2018 and 2017, respectively. These credit facilities do not back Generation's commercial paper program.
[4]	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.

Debt and Credit Agreements - Su

Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2016
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704
Facility draws		0
Outstanding letters of credit		1,696
Actual available capacity		8,008
To Support Additional Commercial Paper		7,687
Credit facility agreements with minority and community banks		135			$ 128
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity						$ 500
Exelon Corporate [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		9
Actual available capacity		591
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		200		$ 45
To Support Additional Commercial Paper		4,097
Credit facility agreements with minority and community banks		49	$ 75		49
Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		159			179
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		545			480
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		5
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		150
Actual available capacity		192
To Support Additional Commercial Paper		0
Credit facility agreements with minority and community banks		30
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		2
Actual available capacity		998
To Support Additional Commercial Paper		998
Credit facility agreements with minority and community banks		33			34
PECO Energy Co [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		0
Actual available capacity		600
To Support Additional Commercial Paper		600
Credit facility agreements with minority and community banks		34			34
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		1
Actual available capacity		599
To Support Additional Commercial Paper		564
Credit facility agreements with minority and community banks		5			5
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member]
Short-term Debt [Line Items]
Outstanding letters of credit		2
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		8
Actual available capacity		292
To Support Additional Commercial Paper		252
Credit facility agreements with minority and community banks		5			2
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		1,500
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		1
Actual available capacity		299
To Support Additional Commercial Paper		299
Credit facility agreements with minority and community banks		5			2
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Facility draws		0
Outstanding letters of credit		0
Actual available capacity		300
To Support Additional Commercial Paper		286
Credit facility agreements with minority and community banks		5			$ 2
Line of Credit [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	545
Facility draws		0
Outstanding letters of credit		353
Line of Credit [Member] | Exelon Generation Co L L C [Member] | Secured Debt [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	159
Facility draws		0
Outstanding letters of credit		119
Actual available capacity		40
To Support Additional Commercial Paper		0
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
To Support Additional Commercial Paper		591
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	5,300
Facility draws		0
Outstanding letters of credit		1,203
Actual available capacity		4,097
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	1,000
Revolving Credit Facility [Member] | PECO Energy Co [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	600
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	300
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		900
Maximum [Member] | Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		0
Maximum [Member] | Atlantic City Electric Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity		$ 0
[1]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Debt and Credit Agreements - _2

Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Average borrowings	$ 531	$ 823	$ 1,125
Maximum borrowings outstanding	$ 1,237	$ 2,147	$ 3,076
Short-term Debt, Weighted Average Interest Rate, over Time	2.21%	1.32%	0.88%
Average interest rates at year end	2.15%	1.24%	1.12%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 37	$ 405	$ 536
Maximum borrowings outstanding	$ 583	$ 1,455	$ 1,735
Short-term Debt, Weighted Average Interest Rate, over Time	1.96%	1.23%	0.94%
Average interest rates at year end	1.96%	1.23%	1.14%
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 154	$ 200	$ 256
Maximum borrowings outstanding	$ 520	$ 470	$ 755
Short-term Debt, Weighted Average Interest Rate, over Time	2.14%	1.24%	0.77%
Average interest rates at year end	2.14%	1.24%
PECO Energy Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 68	$ 2	$ 0
Maximum borrowings outstanding	$ 350	$ 60	0
Short-term Debt, Weighted Average Interest Rate, over Time	2.24%	1.13%
Average interest rates at year end	2.24%	1.13%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 65	$ 54	143
Maximum borrowings outstanding	$ 239	$ 165	$ 369
Short-term Debt, Weighted Average Interest Rate, over Time	2.18%	1.28%	0.77%
Average interest rates at year end	2.18%	1.28%	0.95%
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
Average borrowings			$ 153
Maximum borrowings outstanding			$ 559
Short-term Debt, Weighted Average Interest Rate, over Time			1.03%
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Average borrowings	22	$ 51	$ 4
Maximum borrowings outstanding	$ 90	$ 197	$ 73
Short-term Debt, Weighted Average Interest Rate, over Time	2.24%	1.06%	0.71%
Average interest rates at year end	2.24%	1.06%	0.90%
Delmarva Power & Light Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 87	$ 40	$ 33
Maximum borrowings outstanding	$ 245	$ 216	$ 116
Short-term Debt, Weighted Average Interest Rate, over Time	2.07%	1.48%	0.68%
Average interest rates at year end	2.07%	1.48%
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Short-term Bank Loans and Notes Payable	$ 125
Average borrowings	95	$ 30	$ 0
Maximum borrowings outstanding	$ 210	$ 133	$ 5
Short-term Debt, Weighted Average Interest Rate, over Time	2.21%	1.43%	0.65%
Average interest rates at year end	2.21%	1.43%

Debt and Credit Agreements - _3

Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details)	12 Months Ended
	Dec. 31, 2018
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	127.50%
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	127.50%
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	107.50%
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	90.00%
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	100.00%
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	107.50%
Delmarva Power & Light Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2
Delmarva Power & 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 & Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	107.50%
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	107.50%

Debt and Credit Agreements - _4

Debt and Credit Agreements - Summary of Interest Coverage Ratios (Details)	12 Months Ended
	Dec. 31, 2018
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	7.34
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	10.99
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	7.34
PECO Energy Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	8.14
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	9.77
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	5.98
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	7.03
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Compliance	5.06

Debt and Credit Agreements - _5

Debt and Credit Agreements - Summary of Outstanding Long-term Debt (Details) - USD ($) $ in Millions		1 Months Ended	9 Months Ended	12 Months Ended
		Feb. 08, 2019	Sep. 30, 2018	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2014
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 1,349
Long-term Debt, Gross				34,911		$ 33,657
Unamortized debt discount and premium, net				(66)		(57)
Unamortized Debt Issuance Expense				(216)		(201)
Fair value adjustment				795		865
Long-term debt due within one year				(1,349)	[1]	(2,088)
Long-term debt				34,075		32,176
Long-term debt to financing trusts				390		389
2,020				3,528
2,021				1,511
Repayments of Long-term Debt				1,786		2,490	$ 1,936
ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				206		205
PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				81		81
PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				103		103
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[2]			$ 16,496		15,197
Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]			1.70%
Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[2]			7.90%
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 11,285		11,285
Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.45%
Senior Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.60%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 2,900		2,600
Unsecured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.40%
Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.35%
Pollution Control Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 435		435
Pollution Control Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.50%
Pollution Control Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.70%
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 39		82
Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				3.15%
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[3],[4]			$ 188		405
Unamortized Debt Issuance Expense				$ 0		$ (1)
Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3],[4]			2.85%
Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[3],[4]			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
Junior Subordinated Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				3.50%
Software License Arrangement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 73		79
Software License Arrangement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				3.95%
Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 112		112
Tax-exempt Money Market Funds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				1.74%
Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.40%
Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 22		26
Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.61%
Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.72%
Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 59		90
Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.55%
Loans Payable [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 50		0
Loans Payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.00%
Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 1,253		1,331
Non Recourse Fixed Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.29%
Non Recourse Fixed Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				6.00%
Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[5]			$ 849		865
Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[5]			5.81%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent				$ 36		53
Due in 2019				21
Due in 2020				5
Due in 2021				1
Due in 2022				1
Due in 2023				0
Thereafter				8
Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				390		390
Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[6]			$ 206		206
Long-term Debt [Member] | ComEd Financing III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[6]			6.35%
Long-term Debt [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[6]			$ 81		81
Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[6]			7.38%
Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[6]			7.50%
Long-term Debt [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[6]			$ 103		103
Long-term Debt [Member] | PECO Trust IV Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[6]			5.75%
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 906
Long-term Debt, Gross				8,759		8,955
Unamortized debt discount and premium, net				(6)		(8)
Unamortized Debt Issuance Expense				(51)		(60)
Fair value adjustment				91		103
Long-term debt due within one year				(906)		(346)
Long-term debt				6,989		7,734
Debt and Capital Lease Obligations				7,887		8,644
2,020				2,108
2,021				1
Repayments of Long-term Debt				141		1,261	202
Exelon Generation Co L L C [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 6,019		6,019
Exelon Generation Co L L C [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				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%
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%
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%
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 39		82
Exelon Generation Co L L C [Member] | Notes Payable to Banks [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				3.15%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[7],[8]			$ 164		223
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[7],[8]			2.85%
Exelon Generation Co L L C [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[7],[8]			7.83%
Exelon Generation Co L L C [Member] | Non Recourse Fixed Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 1,253		1,331
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%
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%
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[9]			$ 849		865
Exelon Generation Co L L C [Member] | Non Recourse Variable Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[9]			5.81%
Exelon Generation Co L L C [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent				$ 14		18
Due in 2019				7
Due in 2020				5
Due in 2021				1
Due in 2022				1
Due in 2023				0
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				300
Long-term Debt, Gross				8,187		7,676
Unamortized debt discount and premium, net				(23)		(23)
Unamortized Debt Issuance Expense				(63)		(52)
Long-term debt due within one year				(300)	[10]	(840)
Long-term debt				7,801		6,761
Long-term debt to financing trusts				205		205
Debt and Capital Lease Obligations				7,801		6,761
2,020				500
2,021				350
Repayments of Long-term Debt				840		425	665
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense				(1)		(1)
Long-term debt to financing trusts				205		205
Commonwealth Edison Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[11]			$ 8,179		7,529
Commonwealth Edison Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[11]			2.15%
Commonwealth Edison Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[11]			6.45%
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[12]			$ 8		147
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[12]
Commonwealth Edison Co [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[12]			7.49%
Commonwealth Edison Co [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, noncurrent				$ 8
Thereafter				1
Commonwealth Edison Co [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				206		206
Commonwealth Edison Co [Member] | Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[13]			$ 206		206
Commonwealth Edison Co [Member] | Long-term Debt [Member] | ComEd Financing III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[13]			6.35%
PECO Energy Co [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 0
Long-term Debt, Gross				3,125		2,925
Unamortized debt discount and premium, net				(18)		(5)
Unamortized Debt Issuance Expense				(23)		(17)
Long-term debt				3,084		2,403
Long-term debt to financing trusts	[14]			184		184
Long-term debt due within one year				0		(500)
Debt and Capital Lease Obligations				3,084		2,403
2,020				0
2,021				300
Repayments of Long-term Debt				500		0	300
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				81		81
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts				103		103
PECO Energy Co [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[15]			$ 3,075		2,925
PECO Energy Co [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[15]			1.70%
PECO Energy Co [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[15]			5.95%
PECO Energy Co [Member] | Loans Payable [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 50		0
PECO Energy Co [Member] | Loans Payable [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				2.00%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[14]			$ 81		81
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[14]			7.38%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust III Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[14]			7.50%
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust IV Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[14]			$ 103		103
PECO Energy Co [Member] | Long-term Debt [Member] | PECO Trust IV Affiliate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[14]			5.75%
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 0
Long-term Debt, Gross				2,900		2,600
Unamortized debt discount and premium, net				(6)		(6)
Unamortized Debt Issuance Expense				(18)		(17)
Long-term debt				2,876		2,577
Long-term debt				2,876		2,577
2,020				0
2,021				300
Repayments of Long-term Debt				0		41	379
Baltimore Gas and Electric Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 2,900		2,600
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				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%
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 125
Long-term Debt, Gross				5,636		5,189
Unamortized debt discount and premium, net				4		5
Unamortized Debt Issuance Expense				(14)		(6)
Fair value adjustment				633		686
Long-term debt				6,134		5,478
Long-term debt due within one year				(125)		(396)
Long-term debt				6,134		5,478
2,020				20
2,021				261
Repayments of Long-term Debt				299		169
Pepco Holdings LLC [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[16]			$ 5,242		4,743
Pepco Holdings LLC [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[16]			1.81%
Pepco Holdings LLC [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[16]			7.90%
Pepco Holdings LLC [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 185		185
Pepco Holdings LLC [Member] | Unsecured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.45%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[17]			$ 16		33
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[17]			7.28%
Pepco Holdings LLC [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[17]			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] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				1.74%
Pepco Holdings LLC [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.40%
Pepco Holdings LLC [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 22		26
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.61%
Pepco Holdings LLC [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.72%
Pepco Holdings LLC [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[18]			$ 59		90
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[18]
Pepco Holdings LLC [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[18]			5.55%
Pepco Holdings LLC [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital lease obligations, current				$ 14
Capital lease obligations, noncurrent						27
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				15
Long-term Debt, Gross				2,751		2,570
Unamortized debt discount and premium, net				2		2
Unamortized Debt Issuance Expense				(34)		(32)
Long-term debt				2,704		2,521
Long-term debt due within one year				(15)		(19)
Long-term debt				2,704		2,521
Due in 2019				14
2,020				0
2,021				1
Repayments of Long-term Debt				14		13	11
Potomac Electric Power Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[19]			$ 2,735		2,535
Potomac Electric Power Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[19]			3.05%
Potomac Electric Power Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[19]			7.90%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[20]			$ 16		35
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[20]			7.28%
Potomac Electric Power Company [Member] | Notes Payable, Other Payables [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[20]			8.88%
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 91
Long-term Debt, Gross				1,504		1,309
Unamortized debt discount and premium, net				2		2
Unamortized Debt Issuance Expense				(12)		(11)
Long-term debt due within one year				(79)		(79)
Long-term debt				1,403		1,217
Long-term debt due within one year				(91)		(83)
Long-term debt				1,403		1,217
2,020				0
2,021				0
Repayments of Long-term Debt				4		40	100
Delmarva Power & Light Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[21]			$ 1,370		1,171
Delmarva Power & Light Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[21]			1.81%
Delmarva Power & Light Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[21]			4.27%
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 112		112
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				1.74%
Delmarva Power & Light Company [Member] | Tax-exempt Money Market Funds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				5.40%
Delmarva Power & Light Company [Member] | Medium-term Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 22		26
Delmarva Power & Light Company [Member] | Medium-term Notes [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.61%
Delmarva Power & Light Company [Member] | Medium-term Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage				7.72%
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 18
Long-term Debt, Gross				1,196		1,127
Unamortized debt discount and premium, net				(1)		(1)
Unamortized Debt Issuance Expense				(7)		(5)
Long-term debt				1,170		840
Long-term debt due within one year				(18)		(281)
Long-term debt				1,170		840
2,020				20
2,021				260
Repayments of Long-term Debt				281		35	$ 48
Atlantic City Electric Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[22]			$ 1,137		1,037
Atlantic City Electric Company [Member] | Secured Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[22]			3.38%
Atlantic City Electric Company [Member] | Secured Debt [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[22]			6.80%
Atlantic City Electric Company [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months				$ 18
Long-term Debt, Gross	[23]			59		$ 90
2,020				20
2,021				$ 21
Atlantic City Electric Company [Member] | Transition Bonds [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[23]			5.55%
AGEPFNotesNov2017 [Member] | AGE Biomass project [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt			$ 228
Subsequent Event [Member]
Debt Instrument [Line Items]
Repayments of Debt		$ 300
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Repayments of Debt		$ 300
[1]	In January 2019, $300 million of ComEd long-term debt due within one year was paid in full.
[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 $36 million and $53 million at December 31, 2018 and 2017, respectively. Lease payments of $21 million, $5 million, $1 million, $1 million, less than $1 million, and $8 million will be made in 2019, 2020, 2021, 2022, 2023, 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.
[5]	Excludes interest on CEU Upstream nonrecourse debt, see discussion below.
[6]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[7]	Includes Generation’s capital lease obligations of $14 million and $18 million at December 31, 2018 and 2017, respectively. Generation will make lease payments of $7 million, $5 million, $1 million, and $1 million in 2019, 2020, 2021, and 2022, respectively. Lease payments of less than $1 million annually will be made from 2023 through expiration of the final capital lease in 2024.
[8]	Includes financing related to Albany Green Energy, LLC (AGE). During the third quarter of 2017, Generation retired $228 million of its outstanding debt balance.
[9]	Excludes interest on CEU Upstream nonrecourse debt, see discussion below.
[10]	In January 2019, the $300 million balance was paid in full.
[11]	Substantially all of ComEd’s assets, other than expressly excepted property, are subject to the lien of its mortgage indenture.
[12]	Includes ComEd’s capital lease obligations of $8 million at both December 31, 2018 and 2017, respectively. Lease payments of less than $1 million annually will be made from 2019 through expiration at 2053.
[13]	Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets.
[14]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[15]	Substantially all of PECO’s assets are subject to the lien of its mortgage indenture.
[16]	Substantially all of Pepco's, DPL's, and ACE's assets are subject to the lien of its respective mortgage indenture.
[17]	Includes Pepco's capital lease obligations of $14 million and $27 million at December 31, 2018 and 2017, respectively.
[18]	Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets.
[19]	Substantially all of Pepco's assets are subject to the lien of its respective mortgage indenture.
[20]	Includes capital lease obligations of $14 million and $27 million at December 31, 2018 and 2017, respectively. Lease payments of $14 million will be made in 2019.
[21]	Substantially all of DPL's assets are subject to the lien of its respective mortgage indenture.
[22]	Substantially all of ACE's assets are subject to the lien of its respective mortgage indenture.
[23]	Maturities of ACE's Transition Bonds outstanding at December 31, 2018 are $18 million in 2019, $20 million in 2020 and $21 million in 2021.

Debt and Credit Agreements - Sc

Debt and Credit Agreements - Schedule of Long-term Debt Maturities (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
2,019		$ 1,349
2,020		3,528
2,021		1,511
2,022		3,084
2,023		850
Thereafter	[1]	24,979
Total		35,301
Long-term debt to financing trusts		390	$ 389
ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		206	205
Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
2,019		906
2,020		2,108
2,021		1
2,022		1,024
2,023		0
Thereafter		4,720
Total		8,759
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2,019		300
2,020		500
2,021		350
2,022		0
2,023		0
Thereafter	[2]	7,243
Total		8,393
Long-term debt to financing trusts		205	205
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		205	205
PECO Energy Co [Member]
Debt Instrument [Line Items]
2,019		0
2,020		0
2,021		300
2,022		350
2,023		50
Thereafter	[3]	2,609
Total		3,309
Long-term debt to financing trusts	[4]	184	184
Baltimore Gas and Electric Company [Member]
Debt Instrument [Line Items]
2,019		0
2,020		0
2,021		300
2,022		250
2,023		300
Thereafter		2,050
Total		2,900
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
2,019		125
2,020		20
2,021		261
2,022		310
2,023		500
Thereafter		4,420
Total		5,636
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2,019		15
2,020		0
2,021		1
2,022		310
2,023		0
Thereafter		2,425
Total		2,751
Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
2,019		91
2,020		0
2,021		0
2,022		0
2,023		500
Thereafter		913
Total		1,504
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2,019		18
2,020		20
2,021		260
2,022		0
2,023		0
Thereafter		898
Total		1,196
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Leases, Future Minimum Payments Due Thereafter		0
Capital Lease Obligations [Member] | Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Capital Leases, Future Minimum Payments Due Thereafter		0
Long-term Debt [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		390	390
Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[5]	206	206
Long-term Debt [Member] | Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		206	206
Long-term Debt [Member] | Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts	[6]	206	$ 206
Long-term Debt [Member] | PECO Energy Co [Member] | PECO Financing Trusts [Member]
Debt Instrument [Line Items]
Long-term debt to financing trusts		$ 184
Minimum [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.74%
Minimum [Member] | Tax-exempt Money Market Funds [Member] | Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.74%
Minimum [Member] | Tax-exempt Money Market Funds [Member] | Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.74%
Maximum [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.40%
Maximum [Member] | Tax-exempt Money Market Funds [Member] | Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.40%
Maximum [Member] | Tax-exempt Money Market Funds [Member] | Delmarva Power & Light Company [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.40%
Maximum [Member] | Long-term Debt [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[5]	6.35%
Maximum [Member] | Long-term Debt [Member] | Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[6]	6.35%
[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.
[4]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[5]	Amounts owed to these financing trusts are recorded as Long-term debt to financing trusts within Exelon’s Consolidated Balance Sheets.
[6]	Amount owed to this financing trust is recorded as Long-term debt to financing trust within ComEd’s Consolidated Balance Sheets.

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions		12 Months Ended
		Dec. 31, 2018USD ($)MW		Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)$ / shares	Dec. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2016USD ($)	Oct. 23, 2015USD ($)	Jun. 30, 2014USD ($)$ / sharesshares
Debt Instrument [Line Items]
2,019		$ 1,349,000,000
Long-term Debt, Current Maturities		1,349,000,000	[1]	$ 2,088,000,000
Repayments of Long-term Debt		1,786,000,000		2,490,000,000	$ 1,936,000,000
Line of credit facility, maximum borrowing capacity	[2]	9,704,000,000
Outstanding letters of credit		1,696,000,000
Long-term debt, gross		34,911,000,000		33,657,000,000
Long-term debt		35,301,000,000
Collateral amount of debt		3,000,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 135,000,000		128,000,000
Credit agreement threshold		2.50
Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 59,000,000		90,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross		11,285,000,000		11,285,000,000
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						$ 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		90.00%
Basis points adders for LIBOR-based borrowings		1.7
Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		5.55%
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								$ 500,000,000
Exelon Corporate [Member]
Debt Instrument [Line Items]
2,019		$ 0
Repayments of Long-term Debt		0		569,000,000	46,000,000
Outstanding letters of credit		9,000,000
Long-term debt, gross		7,039,000,000		7,039,000,000
Long-term debt		7,039,000,000
Outstanding borrowings/facility draws		0
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[3]	5,889,000,000		5,889,000,000
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,150,000,000		1,150,000,000
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[3]	7.60%
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt		3.50%
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]
2,019		906,000,000
Long-term Debt, Current Maturities		906,000,000		346,000,000
Repayments of Long-term Debt		141,000,000		1,261,000,000	202,000,000
Line of credit facility, maximum borrowing capacity		200,000,000					$ 45,000,000
Long-term debt, gross		8,759,000,000		8,955,000,000
Long-term debt		8,759,000,000
Line of Credit Facility, Current Borrowing Capacity		$ 49,000,000		49,000,000		$ 75,000,000
Credit agreement threshold		3
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		6,019,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					31,000,000
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		38,000,000
Non-recourse debt, commitment		$ 646,000,000
Debt, Weighted Average Interest Rate		2.82%
Non-recourse debt		$ 508,000,000
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		8,000,000
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member]
Debt Instrument [Line Items]
Repayments of Long-term Debt					15,000,000
Escrow Deposit					6,000,000
Gain (Loss) on Sale of Debt Investments					37,000,000
Long-term debt		$ 15,000,000		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		$ 137,000,000
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		115,000,000
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
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities		10,000,000
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
Non-recourse debt		$ 479,000,000
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		$ 834,000,000
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	[2]	$ 5,300,000,000
Outstanding letters of credit		1,203,000,000
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]	545,000,000
Outstanding letters of credit		353,000,000
Outstanding borrowings/facility draws		0
Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		95,000,000				$ 100,000,000
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		150,000,000
Line of Credit Facility, Current Borrowing Capacity		30,000,000
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Outstanding letters of credit		545,000,000		480,000,000
Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
2,019		300,000,000
Long-term Debt, Current Maturities		300,000,000	[4]	840,000,000
Repayments of Long-term Debt		840,000,000		425,000,000	665,000,000
Outstanding letters of credit		2,000,000
Long-term debt, gross		8,187,000,000		7,676,000,000
Long-term debt		8,393,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 33,000,000		34,000,000
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]
2,019		0
Repayments of Long-term Debt		500,000,000		0	300,000,000
Outstanding letters of credit		0
Long-term debt, gross		3,125,000,000		2,925,000,000
Long-term debt		3,309,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 34,000,000		34,000,000
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]
2,019		0
Repayments of Long-term Debt		0		41,000,000	$ 379,000,000
Outstanding letters of credit		1,000,000
Long-term debt, gross		2,900,000,000		2,600,000,000
Long-term debt		2,900,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		5,000,000
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		$ 2,900,000,000		2,600,000,000
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]
2,019		125,000,000
Repayments of Long-term Debt		299,000,000		169,000,000
Long-term debt, gross		5,636,000,000		5,189,000,000
Long-term debt		5,636,000,000
Short-term Bank Loans and Notes Payable		$ 500,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 1%
Pepco Holdings LLC [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, gross	[5]	$ 59,000,000		90,000,000
Pepco Holdings LLC [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[5]	5.55%
Pepco Holdings LLC [Member] | Minimum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[5]
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 1,500,000,000
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		900,000,000
Potomac Electric Power Company [Member]
Debt Instrument [Line Items]
2,019		15,000,000
Repayments of Long-term Debt		14,000,000		13,000,000	$ 11,000,000
Outstanding letters of credit		8,000,000
Long-term debt, gross		2,751,000,000		2,570,000,000
Long-term debt		2,751,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
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 & Light Company [Member]
Debt Instrument [Line Items]
2,019		91,000,000
Long-term Debt, Current Maturities		79,000,000		79,000,000
Repayments of Long-term Debt		4,000,000		40,000,000	100,000,000
Outstanding letters of credit		1,000,000
Long-term debt, gross		1,504,000,000		1,309,000,000
Long-term debt		1,504,000,000
Outstanding borrowings/facility draws		0
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
Credit agreement threshold		2
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	[2]	$ 300,000,000
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		0
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
2,019		18,000,000
Repayments of Long-term Debt		281,000,000		35,000,000	$ 48,000,000
Outstanding letters of credit		0
Long-term debt, gross		1,196,000,000		1,127,000,000
Long-term debt		1,196,000,000
Outstanding borrowings/facility draws		0
Short-term Bank Loans and Notes Payable		$ 125,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 0.55%
Line of Credit Facility, Current Borrowing Capacity		$ 5,000,000		2,000,000
Credit agreement threshold		2
Atlantic City Electric Company [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
2,019		$ 18,000,000
Long-term debt, gross	[6]	$ 59,000,000		$ 90,000,000
Atlantic City Electric Company [Member] | Maximum [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Interest rate on long-term debt	[6]	5.55%
Atlantic City Electric 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] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		0
Corporate, Non-Segment [Member] | Exelon Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable		$ 500,000,000
Debt Instrument, Interest Rate Terms		LIBOR plus 1%
CENG [Member] | Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 200,000,000
CENG [Member] | Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity									$ 100,000,000
[1]	In January 2019, $300 million of ComEd long-term debt due within one year was paid in full.
[2]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, 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.
[4]	In January 2019, the $300 million balance was paid in full.
[5]	Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets.
[6]	Maturities of ACE's Transition Bonds outstanding at December 31, 2018 are $18 million in 2019, $20 million in 2020 and $21 million in 2021.

Income Taxes Deferred Tax Revis

Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2018
Regulatory Liabilities		$ 10,388	$ 10,203
Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability	[1]	8,624
Regulatory Liabilities	[2]	7,315
Deferred Income Tax Expense (Benefit)	[1]	1,309
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		3,040
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		1,694
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		4,734
Exelon Generation Co L L C [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,895
Deferred Income Tax Expense (Benefit)		1,895
Commonwealth Edison Co [Member]
Regulatory Liabilities		6,577	6,343
Commonwealth Edison Co [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		2,819
Regulatory Liabilities	[2]	2,818
Deferred Income Tax Expense (Benefit)		1
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		1,400
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		573
Commonwealth Edison Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		1,973
PECO Energy Co [Member]
Regulatory Liabilities		690	596
PECO Energy Co [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,407
Regulatory Liabilities	[2]	1,394
Deferred Income Tax Expense (Benefit)		13
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities	[3]	533
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities	[3]	43
PECO Energy Co [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities	[3]	576
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities		1,163	1,269
Baltimore Gas and Electric Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [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] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		459
Baltimore Gas and Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		324
Baltimore Gas and Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		783
Pepco Holdings LLC [Member]
Regulatory Liabilities		1,928	1,948
Pepco Holdings LLC [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		1,944
Regulatory Liabilities	[2]	1,979
Deferred Income Tax Expense (Benefit)		(35)
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		648
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		754
Pepco Holdings LLC [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		1,402
Potomac Electric Power Company [Member]
Regulatory Liabilities		832	829
Potomac Electric Power Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		968
Regulatory Liabilities	[2]	976
Deferred Income Tax Expense (Benefit)		(8)
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		299
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		391
Potomac Electric Power Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		690
Delmarva Power & Light Company [Member]
Regulatory Liabilities		635	665
Delmarva Power & Light Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		540
Regulatory Liabilities	[2]	545
Deferred Income Tax Expense (Benefit)		(5)
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		195
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		194
Delmarva Power & Light Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [Member]
Regulatory Liabilities		389
Atlantic City Electric Company [Member]
Regulatory Liabilities		422	$ 420
Atlantic City Electric Company [Member] | Remeasurement Of Deferred Income Taxes DueTo Tax Reform [Member]
Increase (Decrease) in Other Deferred Liability		456
Regulatory Liabilities	[2]	458
Deferred Income Tax Expense (Benefit)		(2)
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules [Member]
Regulatory Liabilities		153
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations [Member]
Regulatory Liabilities		170
Atlantic City Electric Company [Member] | Net Regulatory Liabilities Associated With Ultimate Settlement To Customers [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 was 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.

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
	Dec. 31, 2018	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Income taxes	$ 26			$ 120	$ (126)	$ 753
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income taxes				(108)	(1,376)	282
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income taxes				168	417	301
PECO Energy Co [Member]
Income Taxes [Line Items]
Income taxes				6	104	149
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income taxes				74	218	174
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income taxes				13	105	41
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Income taxes				22	71	22
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income taxes				12	26	(4)
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income taxes				35	217
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Income taxes			$ 3
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Income taxes		$ 17
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Current				226	194	60
Deferred				(98)	(471)	600
Investment Tax Credit				(24)	(25)	(24)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current				337	584	513
Deferred				(347)	(2,005)	(254)
Investment Tax Credit				(21)	(21)	(20)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current				(63)	(191)	(135)
Deferred				145	523	379
Investment Tax Credit				(2)	(2)	(2)
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current				11	71	63
Deferred				10	28	72
Investment Tax Credit				0	0	0
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current				(5)	74	51
Deferred				47	101	88
Investment Tax Credit				0	(1)	(1)
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current				28	(20)	(118)
Deferred				(21)	114	136
Investment Tax Credit				0	0	0
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current				(3)	(24)	(88)
Deferred				13	82	97
Investment Tax Credit				0	0	0
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current				(14)	(12)	(26)
Deferred				18	34	22
Investment Tax Credit				0	0	0
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current				(4)	(60)
Deferred				24	250
Investment Tax Credit				(1)	(1)
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Current			(281)
Deferred			283
Investment Tax Credit			(1)
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Current		0
Deferred		10
Investment Tax Credit		0
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Current				(1)	14	39
Deferred				17	162	78
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Current				6	65	45
Deferred				(83)	1	(2)
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Current				(29)	(49)	(4)
Deferred				117	136	63
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Current				1	14	9
Deferred				(16)	(9)	5
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Current				0	(5)	5
Deferred				32	49	31
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Current				0	(2)	7
Deferred				6	13	16
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Current				0	0	1
Deferred				12	13	12
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Current				0	0	0
Deferred				8	4	$ 0
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Current				7	(4)
Deferred				$ 9	$ 32
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Current			(11)
Deferred			$ 13
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Current		0
Deferred		$ 7

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	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				0.60%		2.30%		3.30%	[1]
Qualified nuclear decommissioning trust fund income				(1.90%)		3.80%		3.40%
Amortization of investment tax credit, including deferred taxes on basis difference				(1.20%)		(0.90%)		(1.20%)
Plant basis differences				(3.50%)	[2]	(1.70%)		(4.90%)
Production tax credits and other credits				(2.20%)		(1.80%)		(3.60%)
Noncontrolling interests				(1.00%)				(0.20%)
Like-Kind Exchange				(8.30%)		(1.20%)
Statute of limitations expiration								(0.40%)
Penalties								1.90%
Merger expenses						(3.60%)		5.60%
FitzPatrick bargain purchase gain						(2.20%)
Tax Cuts and Jobs Act of 2017	[3]			0.90%		(33.10%)
Other				1.00%		0.10%		(0.70%)	[4]
Effective income tax rate				5.40%		(3.30%)		38.20%
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 35
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				(16.60%)		2.90%		3.20%	[1]
Qualified nuclear decommissioning trust fund income				(11.80%)		9.90%		7.90%
Amortization of investment tax credit, including deferred taxes on basis difference				(6.50%)		(2.10%)		(2.30%)
Plant basis differences				(0.00%)	[2]	(0.00%)	[2]	(0.00%)
Production tax credits and other credits				(13.50%)		(4.70%)		(8.30%)
Noncontrolling interests				(6.10%)				(0.60%)
Like-Kind Exchange				0.00%		0.00%
Statute of limitations expiration								(1.70%)
Penalties								0.00%
Merger expenses						(1.20%)		1.10%
FitzPatrick bargain purchase gain						(5.60%)
Tax Cuts and Jobs Act of 2017	[3]			2.70%		(128.30%)
Other				1.30%		(0.50%)		(1.40%)	[4]
Effective income tax rate				(29.50%)		(94.60%)		32.90%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				8.30%		5.70%		5.60%	[1]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference				(0.20%)		(0.20%)		(0.30%)
Plant basis differences				(0.20%)	[2]	0.30%	[2]	(0.60%)
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)
Noncontrolling interests				(0.00%)				(0.00%)
Like-Kind Exchange				(9.10%)		1.30%
Statute of limitations expiration								0.00%
Penalties								4.50%
Merger expenses						0.00%		0.00%
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			(0.10%)		0.10%
Other				0.50%		0.20%		0.10%	[4]
Effective income tax rate				20.20%		42.40%		44.30%
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 3
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				(2.60%)		0.60%		1.30%	[1]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference				(0.10%)		(0.10%)		(0.10%)
Plant basis differences				(14.10%)	[2]	(13.80%)	[2]	(9.60%)
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)
Noncontrolling interests				(0.00%)				(0.00%)
Like-Kind Exchange				(3.20%)		0.00%
Statute of limitations expiration								0.00%
Penalties								0.00%
Merger expenses						0.00%		0.00%
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.00%		(2.30%)
Other				0.30%		(0.10%)		(1.20%)	[4]
Effective income tax rate				1.30%		19.30%		25.40%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				6.60%		5.40%		5.00%	[1]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference				(0.10%)		(0.10%)		(0.10%)
Plant basis differences				(1.30%)	[2]	0.10%	[2]	(2.70%)
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)
Noncontrolling interests				(0.00%)				(0.00%)
Like-Kind Exchange				(8.00%)		0.00%
Statute of limitations expiration								0.00%
Penalties								0.00%
Merger expenses						0.00%		0.00%
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.00%		0.90%
Other				0.90%		0.20%		0.00%	[4]
Effective income tax rate				19.10%		41.50%		37.20%
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 5
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit				2.20%		3.20%		15.70%	[1]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference				(0.10%)		(0.10%)		(0.20%)
Plant basis differences				(2.70%)	[2]	(0.40%)	[2]	(22.80%)
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)
Noncontrolling interests				(0.00%)				(0.00%)
Like-Kind Exchange				(14.80%)		0.00%
Statute of limitations expiration								0.00%
Penalties								0.00%
Merger expenses						(6.30%)		23.50%
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.00%		2.70%
Other				0.20%		(0.20%)		(1.80%)	[4]
Effective income tax rate				5.80%		33.90%		49.40%
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 14
Delmarva Power & Light Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%	[5]
State income taxes, net of Federal income tax benefit				6.70%		5.40%		52.70%	[1],[5]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%	[5]
Amortization of investment tax credit, including deferred taxes on basis difference				(0.30%)		(0.20%)		(3.70%)	[5]
Plant basis differences				(0.30%)	[2]	2.00%	[2]	(25.50%)	[5]
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)	[5]
Noncontrolling interests				(0.00%)				(0.00%)	[5]
Like-Kind Exchange				(12.00%)		0.00%
Statute of limitations expiration	[5]							0.00%
Penalties	[5]							0.00%
Merger expenses						(7.80%)		112.90%	[5]
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.00%		2.50%
Other				0.40%		0.10%		(2.20%)	[4],[5]
Effective income tax rate				15.50%		37.00%		169.20%	[5]
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 6
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%		35.00%	[5]
State income taxes, net of Federal income tax benefit				7.40%		5.60%		6.20%	[1],[5]
Qualified nuclear decommissioning trust fund income				0.00%		0.00%		0.00%	[5]
Amortization of investment tax credit, including deferred taxes on basis difference				(0.40%)		(0.40%)		0.80%	[5]
Plant basis differences				(0.50%)	[2]	3.60%	[2]	10.30%	[5]
Production tax credits and other credits				(0.00%)		(0.00%)		(0.00%)	[5]
Noncontrolling interests				(0.00%)				(0.00%)	[5]
Like-Kind Exchange				(14.90%)		0.00%
Statute of limitations expiration	[5]							0.00%
Penalties	[5]							0.00%
Merger expenses						(19.80%)		(44.90%)	[5]
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.00%		1.60%
Other				1.20%		(0.40%)		1.30%	[4],[5]
Effective income tax rate				13.80%		25.20%		8.70%	[5]
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 7
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate				21.00%		35.00%
State income taxes, net of Federal income tax benefit				3.00%		4.80%
Qualified nuclear decommissioning trust fund income				0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference				(0.20%)		(0.20%)
Plant basis differences	[2]			(1.60%)		1.10%
Production tax credits and other credits				(0.00%)		(0.00%)
Noncontrolling interests				(0.00%)
Like-Kind Exchange				(14.50%)		0.00%
Merger expenses						(9.50%)
FitzPatrick bargain purchase gain						0.00%
Tax Cuts and Jobs Act of 2017	[3]			0.10%		6.40%
Other				0.30%		(0.10%)
Effective income tax rate				8.10%		37.50%
Amount of Impairment to Carrying Amount of Regulatory Assets						$ 27
Pepco Holdings LLC [Member] | Successor [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	[5]		35.00%
State income taxes, net of Federal income tax benefit	[1],[5]		5.80%
Qualified nuclear decommissioning trust fund income	[5]		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	[5]		1.40%
Plant basis differences	[5]		39.00%
Production tax credits and other credits	[5]		(0.00%)
Noncontrolling interests	[5]		(0.00%)
Statute of limitations expiration	[5]		0.00%
Penalties	[5]		(0.70%)
Merger expenses	[5]		(89.00%)
Other	[4],[5]		3.30%
Effective income tax rate	[5]		(5.20%)
Pepco Holdings LLC [Member] | Predecessor [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate		35.00%
State income taxes, net of Federal income tax benefit	[1]	11.90%
Qualified nuclear decommissioning trust fund income		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference		(0.90%)
Plant basis differences		(13.50%)
Production tax credits and other credits		(0.00%)
Noncontrolling interests		(0.00%)
Statute of limitations expiration		0.00%
Penalties		0.00%
Merger expenses		11.10%
Other	[4]	3.60%
Effective income tax rate		47.20%
[1]	Includes a remeasurement of uncertain state income tax positions for Pepco and DPL.
[2]	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 Note 4 - Regulatory Matters for additional information.
[3]	Included are impacts for TCJA 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.
[4]	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
[5]	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, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (12,533)	$ (12,490)
Deferred Tax Liabilities, Other Finite-Lived Assets	117	150
Derivatives and other financial instruments	89	(85)
Deferred pension and postretirement obligation	1,435	1,463
Deferred Tax Liabilities, Investments	(351)	(553)
Deferred debt refinancing costs	234	217
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(749)	(688)
Tax loss carryforward	237	344
Tax credit carryforward	811	861
Investment in partnerships	(797)	(434)
Other, net	934	746
Deferred income tax liabilities (net)	(10,573)	(10,469)
Unamortized investment tax credits	(724)	(732)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(11,297)	(11,201)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,495)	(2,819)
Deferred Tax Liabilities, Other Finite-Lived Assets	(44)	(66)
Derivatives and other financial instruments	35	(66)
Deferred pension and postretirement obligation	(188)	(205)
Deferred Tax Liabilities, Investments	(351)	(553)
Deferred debt refinancing costs	23	26
Deferred Tax Liabilities, Regulatory Assets and Liabilities	0	0
Tax loss carryforward	78	76
Tax credit carryforward	816	868
Investment in partnerships	(775)	(416)
Other, net	239	78
Deferred income tax liabilities (net)	(2,662)	(3,077)
Unamortized investment tax credits	(700)	(705)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,362)	(3,782)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,059)	(3,825)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	69	(2)
Deferred pension and postretirement obligation	(255)	(285)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(7)	(8)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	300	489
Tax loss carryforward	0	33
Tax credit carryforward	0	1
Investment in partnerships	0	0
Other, net	151	141
Deferred income tax liabilities (net)	(3,801)	(3,456)
Unamortized investment tax credits	(12)	(13)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,813)	(3,469)
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,862)	(1,762)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(26)	(15)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	0	(1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(129)	(90)
Tax loss carryforward	18	9
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	67	71
Deferred income tax liabilities (net)	(1,932)	(1,788)
Unamortized investment tax credits	(1)	(1)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,933)	(1,789)
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,399)	(1,368)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(26)	(29)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(3)	(3)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	172	136
Tax loss carryforward	25	11
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	12	13
Deferred income tax liabilities (net)	(1,219)	(1,240)
Unamortized investment tax credits	(3)	(4)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,222)	(1,244)
Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,577)	(2,521)
Deferred Tax Liabilities, Other Finite-Lived Assets	161	216
Derivatives and other financial instruments	3	3
Deferred pension and postretirement obligation	(102)	(130)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	187	203
Deferred Tax Liabilities, Regulatory Assets and Liabilities	(90)	(184)
Tax loss carryforward	96	156
Tax credit carryforward	0	6
Investment in partnerships	0	0
Other, net	196	193
Deferred income tax liabilities (net)	(2,126)	(2,058)
Unamortized investment tax credits	(8)	(8)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,134)	(2,066)
Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(645)	(607)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(14)	(18)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(1)	(1)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	83	86
Tax loss carryforward	26	35
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	19	16
Deferred income tax liabilities (net)	(532)	(489)
Unamortized investment tax credits	(3)	(4)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(535)	(493)
Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(743)	(717)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(46)	(51)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(2)	(2)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	96	88
Tax loss carryforward	52	68
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	17	14
Deferred income tax liabilities (net)	(626)	(600)
Unamortized investment tax credits	(2)	(3)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(628)	(603)
Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,148)	(1,152)
Deferred Tax Liabilities, Other Finite-Lived Assets	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(78)	(78)
Deferred Tax Liabilities, Investments	0	0
Deferred debt refinancing costs	(4)	(4)
Deferred Tax Liabilities, Regulatory Assets and Liabilities	58	39
Tax loss carryforward	12	40
Tax credit carryforward	0	0
Investment in partnerships	0	0
Other, net	98	94
Deferred income tax liabilities (net)	(1,062)	(1,061)
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	$ (1,064)	$ (1,063)

Income Taxes - Schedule of Carr

Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	Dec. 31, 2018USD ($)
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	$ 811	[1]
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	816
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	0
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	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
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 & 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	4,103	[2]
Deferred taxes on state tax attributes (net)	272
Valuation allowance on state tax attributes	35
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,544	[2]
Deferred taxes on state tax attributes (net)	104
Valuation allowance on state tax attributes	26
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	224	[3]
Deferred taxes on state tax attributes (net)	18
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	395	[4]
Deferred taxes on state tax attributes (net)	26
Valuation allowance on state tax attributes	1
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,492	[5]
Deferred taxes on state tax attributes (net)	102
Valuation allowance on state tax attributes	6
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	192	[6]
Deferred taxes on state tax attributes (net)	12
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	772	[7]
Deferred taxes on state tax attributes (net)	52
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	365	[8]
Deferred taxes on state tax attributes (net)	26
Valuation allowance on state tax attributes	$ 0
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NUYzQjUwOTBEOUJENTE4OUJFODU2NDRDNjVGNkZEQzYM}
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MDkyRDA3MDExQ0UwNUM3Q0JGMTJENTVGQjRDRkUxMEUM}
[3]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NTg5NzdDOUEwOTQ4NTk2NzlDM0NDM0NCREMxNDZGNEMM}
[4]	.
[5]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246RjE3NUQ0OEVCOEU4NTZBNjhDMkY3MzUwQUY0NTc3MDAM}
[6]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246NzBCNTFENTBCREJGNTIxMzhFRURCRkZFQzYxRDA1MDMM}
[7]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246OEMzNEQ1NEJCRDI5NTIxNUJCNTY4MkZEOEE3MEExOTcM}
[8]	.

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			$ 22
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	$ 743	$ 916	1,078
Increases based on tax positions related to current year			108
Increases based on tax positions prior to current year	15		(332)
Decreases based on tax positions prior to current year	30	28	88
Unrecognized Tax Benefits, Period Increase (Decrease)	(251)	(196)	(21)
Decrease from settlements with taxing authorities	(53)	(5)	(27)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(7)
Unrecognized tax benefits - ending balance	477	743	916
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			5
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	468	490	534
Increases based on tax positions related to current year			10
Increases based on tax positions prior to current year	15		(12)
Decreases based on tax positions prior to current year	21	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	(36)	(17)	(20)
Decrease from settlements with taxing authorities	(53)	(5)	(27)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	(7)
Unrecognized tax benefits - ending balance	408	468	490
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	2	(12)	142
Increases based on tax positions related to current year			0
Increases based on tax positions prior to current year	0		(154)
Decreases based on tax positions prior to current year	0	14	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	2	2	(12)
PECO Energy Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	0	0	0
Increases based on tax positions related to current year			0
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	0	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	0	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	120	120	120
Increases based on tax positions related to current year			0
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	0	0	0
Unrecognized Tax Benefits, Period Increase (Decrease)	(120)	0	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	0	120	120
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	59	80	8
Increases based on tax positions related to current year			21
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	7	0	51
Unrecognized Tax Benefits, Period Increase (Decrease)	(66)	(21)	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	0	59	80
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	21	37	3
Increases based on tax positions related to current year			16
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	1	0	18
Unrecognized Tax Benefits, Period Increase (Decrease)	(22)	(16)	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	0	21	37
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	14	22	0
Increases based on tax positions related to current year			22
Increases based on tax positions prior to current year	0		0
Decreases based on tax positions prior to current year	0	14	0
Unrecognized Tax Benefits, Period Increase (Decrease)	0	(22)	0
Decrease from settlements with taxing authorities	0	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	14	14	22
Pepco Holdings LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance	125	172
Increases based on tax positions prior to current year	0
Decreases based on tax positions prior to current year	8	14
Unrecognized Tax Benefits, Period Increase (Decrease)	(88)	(61)
Decrease from settlements with taxing authorities	0	0
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0
Unrecognized tax benefits - ending balance	$ 45	125	172
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Acquisition			(5)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits - beginning balance		$ 172	22
Increases based on tax positions related to current year			59
Increases based on tax positions prior to current year			0
Decreases based on tax positions prior to current year			96
Unrecognized Tax Benefits, Period Increase (Decrease)			0
Decrease from settlements with taxing authorities			0
Unrecognized tax benefits - ending balance			$ 172

Income Taxes - Summary of Inter

Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 236	$ 233
Unrecognized Tax Benefits, Income Tax Penalties Accrued	(17)	(17)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	(2)	(3)
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	4	4
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
PECO Energy Co [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
Baltimore Gas and Electric 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
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	1	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	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Delmarva Power & 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	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	$ 0	$ 0

Income Taxes - Summary of Int_2

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			$ 0	$ (2)	$ 106
Net interest (income) expense recognized related to uncertain tax positions			(3)	37	165
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			0	(1)	(13)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			0	0	86
Net interest (income) expense recognized related to uncertain tax positions			0	11	117
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]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions		$ (2)
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 0
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	0	6
Delmarva Power & 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	$ 0	$ (1)

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions		Jul. 27, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 1999
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible		$ 71
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Limitation on Deductible Interest Expense									100.00%
Allowable Expensing For Cost Of Qualified Property									30.00%
Unrecognized Tax Benefits			$ 477				$ 916	$ 477	$ 743	$ 916		$ 1,078
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	(2)	106
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		9
Decrease in Unrecognized Tax Benefits is Reasonably Possible		90	241					241
Income taxes			26					120	(126)	753
Unrecognized Tax Benefits, Period Increase (Decrease)								(251)	(196)	(21)
Taxes accrued			412					412	373
Unrecognized Tax Benefits, Income Tax Penalties Accrued			(17)					(17)	(17)
Tax positions for which there is uncertainty about the timing of tax benefits							83		7	83
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 20	463				633	463	523	$ 633
Regulatory Liabilities			10,203					10,203	10,388
Regulatory Assets			9,459					9,459	$ 9,288
Like kind exchange [Member]
Income Taxes [Line Items]
Deferred gain on sale of property													$ 1,200
Unrecognized Tax Benefits, Income Tax Penalties Expense								$ 90
Decrease in Unrecognized Tax Benefits is Reasonably Possible				$ 33
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			408				490	$ 408	$ 468	$ 490		534
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			33					33
Income taxes								(108)	(1,376)	282
Unrecognized Tax Benefits, Period Increase (Decrease)								(36)	(17)	(20)
Taxes accrued			226					226	444
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Tax positions for which there is uncertainty about the timing of tax benefits							7			7
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			408				483	408	461	483
Allocation of federal tax benefit under tax sharing agreement			155				94	$ 155	$ 102	$ 94
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			2				(12)	$ 2	$ 2	$ (12)		142
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	86
Income taxes								168	417	301
Unrecognized Tax Benefits, Period Increase (Decrease)								0	0	0
Taxes accrued			71					71	60
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Tax positions for which there is uncertainty about the timing of tax benefits							(12)			$ (12)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			2					2	2
Allocation of federal tax benefit under tax sharing agreement			1					1
Regulatory Liabilities			6,343					$ 6,343	6,577
Regulatory Assets									$ 1,279
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible				2
PECO Energy Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				0	$ 0	$ 0	$ 0		0
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Income taxes								6	104	149
Unrecognized Tax Benefits, Period Increase (Decrease)								0	0	0
Taxes accrued			28					28	15
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Allocation of federal tax benefit under tax sharing agreement			48				18	48	16	18
Regulatory Liabilities			596					$ 596	690
Regulatory Assets									410
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							120		$ 120	$ 120
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				120	$ 0	$ 120	$ 120		120
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			120					120
Income taxes								74	218	174
Unrecognized Tax Benefits, Period Increase (Decrease)								(120)	0	0
Taxes accrued			46					46	71
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Allocation of federal tax benefit under tax sharing agreement			26				8	26	10	8
Regulatory Liabilities			1,269					$ 1,269	1,163
Regulatory Assets									571
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							59		$ 59	$ 59
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				80	$ 0	$ 59	$ 80		8
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			66					66
Income taxes								13	105	41
Unrecognized Tax Benefits, Period Increase (Decrease)								(66)	(21)	0
Taxes accrued			58					58	68
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							21			21
Regulatory Liabilities			829					$ 829	832
Regulatory Assets									891
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							21		$ 21	$ 21
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%	[1]
Unrecognized Tax Benefits			0				37	$ 0	$ 21	$ 37		3
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			22					22
Income taxes								22	71	22
Unrecognized Tax Benefits, Period Increase (Decrease)								(22)	(16)	0
Taxes accrued			4					4	4
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							16			$ 16
Regulatory Liabilities			665					$ 665	635
Regulatory Assets									314
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible									$ 14
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%	[1]
Unrecognized Tax Benefits			14				22	$ 14	$ 14	$ 22		0
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Income taxes								12	26	(4)
Unrecognized Tax Benefits, Period Increase (Decrease)								0	(22)	0
Taxes accrued			5					5	5
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							22			22
Regulatory Liabilities			420					$ 420	422
Regulatory Assets									430
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							80		$ 94	80
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%
Unrecognized Tax Benefits			45				$ 172	$ 45	$ 125	172
Income taxes								35	217
Unrecognized Tax Benefits, Period Increase (Decrease)								(88)	(61)
Taxes accrued			74					74	61
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate									32
Allocation of federal tax benefit under tax sharing agreement			2					2	7
Regulatory Liabilities			1,948					1,948	1,928
Regulatory Assets									3,047
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	[1]						35.00%
Income taxes							$ 3
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			31				93	31		93
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent						35.00%
Unrecognized Tax Benefits							172			172		$ 22
Decrease in Unrecognized Tax Benefits is Reasonably Possible			88					88
Income taxes						$ 17
Unrecognized Tax Benefits, Period Increase (Decrease)										0
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Deferred								(98)	(471)	600
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									146
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred								(347)	(2,005)	(254)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									19
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred								145	523	379
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred								10	28	72
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred								47	101	88
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred								(21)	114	136
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									21
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Deferred								13	82	97
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									16
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred								18	34	22
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									22
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Deferred								24	250
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Deferred							283
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									59
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						10
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Deferred								17	162	78
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			425					425
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			411					411
Increase (Decrease) in Deferred Income Taxes				50	$ 16
Increase (Decrease) in Income Taxes				50
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred								(83)	1	(2)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			411					411
Increase (Decrease) in Deferred Income Taxes				53	5
Increase (Decrease) in Income Taxes				53
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred								117	136	63
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred								(16)	(9)	5
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred								32	49	31
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred								6	13	16
Increase (Decrease) in Deferred Income Taxes				1	16
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Deferred								12	13	12
Increase (Decrease) in Deferred Income Taxes				2	1
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred								8	4	$ 0
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			14					14
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			14					14
Deferred								9	$ 32
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			14					14
Increase (Decrease) in Deferred Income Taxes				4	$ 17
Increase (Decrease) in Income Taxes				3
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			$ 21					$ 21
Deferred							$ 13
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						$ 7
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Regulatory Liabilities				1
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Regulatory Liabilities				2
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Regulatory Liabilities				1
Net Regulatory Assets Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Regulatory Assets				$ 1
[1]	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 ($)		3 Months Ended		9 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]				$ 489,000,000		$ 468,000,000		$ 446,000,000
Asset Retirement Obligation, Revision of Estimate					20,000,000				2,000,000
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]				0		0		0
Asset Retirement Obligation, Revision of Estimate					(1,000,000)				2,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]				489,000,000		468,000,000		446,000,000
Asset Retirement Obligation, Revision of Estimate		$ 203,000,000	$ 84,000,000	$ 138,000,000	0				0
Asset Retirement Obligation, Period Increase (Decrease)				180,000,000					34,000,000
Nuclear decommissioning
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Proceeds from Customers					144,000,000		77,000,000
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				8,734,000,000	9,662,000,000	[2]	8,734,000,000
Asset Retirement Obligation, Accretion Expense					478,000,000		458,000,000
Asset Retirement Obligation, Revision of Estimate			$ 772,000,000				444,000,000
Asset Retirement Obligation, Period Increase (Decrease)					(77,000,000)		34,000,000
ARO ending balance		10,005,000,000			10,005,000,000		9,662,000,000	[2]	8,734,000,000
Asset Retirement Obligation, Current		22,000,000			22,000,000		13,000,000
Asset Retirement Obligation, Liabilities Incurred					(58,000,000)		8,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)					(3,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				3,000,000	3,000,000		3,000,000
Asset Retirement Obligation, Accretion Expense					0		0
Asset Retirement Obligation, Revision of Estimate					1,000,000		0
Asset Retirement Obligation, Period Increase (Decrease)					0		0
ARO ending balance		4,000,000			4,000,000		3,000,000		3,000,000
Asset Retirement Obligation, Liabilities Incurred	[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				$ 199,000,000	197,000,000		199,000,000
Asset Retirement Obligation, Accretion Expense					10,000,000		10,000,000
Asset Retirement Obligation, Revision of Estimate					35,000,000		(1,000,000)
Asset Retirement Obligation, Period Increase (Decrease)					(3,000,000)		(7,000,000)
ARO ending balance		$ 238,000,000			$ 238,000,000		197,000,000		$ 199,000,000
Asset Retirement Obligation, Liabilities Incurred	[3]						$ 1,000,000
[1]	Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.
[3]	.

Asset Retirement Obligations _2

Asset Retirement Obligations - Narrative (Details) - USD ($)		3 Months Ended			9 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2018
Asset Retirement Obligations [Line Items]
Asset retirement obligations, noncurrent		$ 9,679,000,000				$ 9,679,000,000	$ 10,029,000,000
Asset Retirement Obligation, Revision of Estimate						$ 20,000,000		$ 2,000,000
Percent of additional decommissioning shortfall with recourse		50.00%				50.00%
Nuclear decommissioning trust funds		$ 11,661,000,000				$ 11,661,000,000	13,272,000,000
Spent Nuclear Fuel Obligation, Noncurrent		1,171,000,000				1,171,000,000	1,147,000,000
Line of credit facility, maximum borrowing capacity	[1]	9,704,000,000				9,704,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)					$ 180,000,000			34,000,000
Recovery Stranded Costs				$ 4,000,000			24,000,000
Asset retirement obligations, noncurrent		9,450,000,000				9,450,000,000	9,844,000,000
Asset Retirement Obligation, Revision of Estimate		203,000,000	$ 84,000,000		$ 138,000,000	0		0
Shortfall of decommissioning funds with recourse		0				0	50,000,000
Nuclear decommissioning trust funds		11,661,000,000				11,661,000,000	13,272,000,000
Spent Nuclear Fuel Obligation, Noncurrent		1,171,000,000				1,171,000,000	1,147,000,000
ZionSolutions rent payable						1
Line of credit facility, maximum borrowing capacity		$ 200,000,000				$ 200,000,000			$ 45,000,000
Annual average accretion of the ARO						4.863%
Number of years used in present value measurement						30 years
Historical five-year annual average after-tax return on NDT funds						5.00%
Exelon Generation Co L L C [Member] | Minimum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						1000.00%
Estimated annual after tax return on nuclear decommissioning funds		5.00%				5.00%
Exelon Generation Co L L C [Member] | Maximum [Member]
Asset Retirement Obligations [Line Items]
Investment Interest Rate						7000.00%
Estimated annual after tax return on nuclear decommissioning funds		6.20%				6.20%
Nuclear Plant [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Revision of Estimate						$ 890,000,000
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)		$ 116,000,000						$ 178,000,000
Asset Retirement Obligation, Revision of Estimate						122,000,000
Decommissioning Liability, Noncurrent		120,000,000				120,000,000
Nuclear decommissioning
Asset Retirement Obligations [Line Items]
Proceeds from Customers						144,000,000	77,000,000
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)						(77,000,000)	34,000,000
Asset Retirement Obligation, Revision of Estimate			$ 772,000,000				444,000,000
Zion Station [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent		0				0
Zion Station [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent		0				0
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning trust funds		$ 12,695,000,000				$ 12,695,000,000	$ 13,349,000,000
[1]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Asset Retirement Obligations _3

Asset Retirement Obligations - Unrealized Gain on NDT Funds (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments	$ 11,661	$ 13,272
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments	11,661	13,272
Collateral Pledged [Member] | Unregulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	(483)	521	$ 194
Collateral Pledged [Member] | Regulated Operation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Unrealized Gain (Loss) on Investments	(715)	455	$ 216
Assets, Total [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments	$ 12,695	$ 13,349

Asset Retirement Obligations _4

Asset Retirement Obligations - Pledged Assets and Payables to ZionSolutions (Details) - USD ($)		Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity	[1]	$ 9,704,000,000
Asset retirement obligations, noncurrent		9,679,000,000		$ 10,029,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligations [Line Items]
Line of credit facility, maximum borrowing capacity		200,000,000	$ 45,000,000
Asset retirement obligations, noncurrent		9,450,000,000		9,844,000,000
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligations [Line Items]
Held-to-maturity Securities Pledged as Collateral	[2]	9,000,000		39,000,000
Accounts Payable, Interest-bearing, Noncurrent		9,000,000		37,000,000
Accounts Payable, Interest-bearing, Current		$ 965		$ 942,000,000
[1]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.
[2]	(a)Included in Other current liabilities within Exelon's and Generation's Consolidated Balance Sheets. Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized gains and losses 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 Obligations _5

Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($)		3 Months Ended			9 Months Ended		12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 23, 2016	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							$ 20,000,000				$ 2,000,000
Asset Retirement Obligation, Accretion Expense	[1]						489,000,000		$ 468,000,000		446,000,000
Asset Retirement Obligation, Revision of Estimate							20,000,000				2,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		$ 203,000,000	$ 84,000,000		$ 138,000,000		0				0
Asset Retirement Obligation, Accretion Expense	[1]						489,000,000		468,000,000		446,000,000
Asset Retirement Obligation, Period Increase (Decrease)					180,000,000						34,000,000
Asset Retirement Obligation, Revision of Estimate		203,000,000	84,000,000		138,000,000		0				0
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]						0		0
Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate						$ 2,000,000	20,000,000
Asset Retirement Obligation, Accretion Expense	[1]					0
Asset Retirement Obligation, Revision of Estimate						2,000,000	20,000,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate				$ 0
Asset Retirement Obligation, Accretion Expense	[1]			0
Asset Retirement Obligation, Revision of Estimate				0
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							22,000,000				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							22,000,000				0
Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				1,000,000
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				1,000,000
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				2,000,000
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				2,000,000
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)							(3,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					199,000,000		197,000,000		199,000,000
Asset Retirement Obligation, Revision of Estimate							35,000,000		(1,000,000)
Development projects	[2]								1,000,000
Asset Retirement Obligation, Accretion Expense							10,000,000		10,000,000
Asset Retirement Obligation, Period Increase (Decrease)							(3,000,000)		(7,000,000)
Payments							(1,000,000)		(5,000,000)
ARO ending balance		238,000,000				199,000,000	238,000,000		197,000,000		199,000,000
Asset Retirement Obligation, Revision of Estimate							35,000,000		(1,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					28,000,000		27,000,000		28,000,000
Asset Retirement Obligation, Revision of Estimate							0		(1,000,000)
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						1,000,000		1,000,000
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		(1,000,000)
ARO ending balance		28,000,000				28,000,000	28,000,000		27,000,000		28,000,000
Asset Retirement Obligation, Revision of Estimate							0		(1,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					24,000,000		24,000,000		24,000,000
Asset Retirement Obligation, Revision of Estimate							2,000,000		2,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						1,000,000		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							(2,000,000)		(2,000,000)
ARO ending balance		25,000,000				24,000,000	25,000,000		24,000,000		24,000,000
Asset Retirement Obligation, Revision of Estimate							2,000,000		2,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					14,000,000		16,000,000		14,000,000
Asset Retirement Obligation, Revision of Estimate							36,000,000		2,000,000
Development projects	[2]			$ 0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)									0
Payments							0		0
ARO ending balance		52,000,000				14,000,000	52,000,000		16,000,000		14,000,000
Asset Retirement Obligation, Revision of Estimate							36,000,000		2,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)							0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					2,000,000		3,000,000		2,000,000
Asset Retirement Obligation, Revision of Estimate			22,000,000				34,000,000		1,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		37,000,000				2,000,000	37,000,000		3,000,000		2,000,000
Asset Retirement Obligation, Revision of Estimate			22,000,000				34,000,000		1,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					9,000,000		10,000,000		9,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		1,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		11,000,000				9,000,000	11,000,000		10,000,000		9,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		1,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					3,000,000		3,000,000		3,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		0
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		4,000,000				3,000,000	4,000,000		3,000,000		3,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)									(7,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					121,000,000		113,000,000		121,000,000
Asset Retirement Obligation, Revision of Estimate							7,000,000		(13,000,000)
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						4,000,000		7,000,000
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							(3,000,000)		(2,000,000)
ARO ending balance		121,000,000				121,000,000	121,000,000		113,000,000		121,000,000
Asset Retirement Obligation, Revision of Estimate							7,000,000		(13,000,000)
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					8,734,000,000		9,662,000,000	[4]	8,734,000,000
Asset Retirement Obligation, Revision of Estimate			772,000,000						444,000,000
Development projects							(58,000,000)		8,000,000
Asset Retirement Obligation, Accretion Expense							478,000,000		458,000,000
Asset Retirement Obligation, Period Increase (Decrease)							(77,000,000)		34,000,000
ARO ending balance		10,005,000,000				8,734,000,000	10,005,000,000		9,662,000,000	[4]	8,734,000,000
Asset Retirement Obligation, Revision of Estimate			$ 772,000,000						444,000,000
Asset Retirement Obligation, Current		22,000,000					22,000,000		13,000,000
Nuclear decommissioning | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					$ 393,000,000		384,000,000		393,000,000
Asset Retirement Obligation, Revision of Estimate							80,000,000		(11,000,000)
Development projects	[2]								1,000,000
Asset Retirement Obligation, Accretion Expense							16,000,000		18,000,000
Payments							(6,000,000)		(10,000,000)
ARO ending balance		$ 471,000,000				$ 393,000,000	471,000,000		384,000,000		$ 393,000,000
Asset Retirement Obligation, Revision of Estimate							$ 80,000,000		$ (11,000,000)
[1]	Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	.
[3]	(b)In 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981.
[4]	Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.

Retirement Benefits Retirement

Retirement Benefits Retirement Benefits- Narrative (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase (Decrease) in Obligation, Pension Benefits		$ 23
Benefit obligation increase (decrease) reflecting actual census data		(14)
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		18
Regulatory asset increase (decrease) due to updated valuation adjustment		61
Defined benefit plan, amounts recognized In regulatory liabilities, before tax		$ 1
Defined Contribution Plan, Employer Discretionary Contribution Amount	[1]			$ 179		$ 128		$ 164
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				81.00%		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				85.00%		88.00%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset increase (decrease) due to updated valuation adjustment				$ (6)		$ (423)	[2]	$ 959
Expected return on plan assets				7.00%		7.00%		7.00%
Discount rate	[4]			3.62%	[3],[5]	4.04%	[6],[7]	4.29%	[8]
Defined Contribution Plan, Employer Discretionary Contribution Amount				$ 300
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset increase (decrease) due to updated valuation adjustment				$ (57)		$ 125	[2]	$ 95
Expected return on plan assets				6.60%		6.58%		6.71%
Discount rate	[4]			3.61%	[3],[5]	4.04%	[6],[7]	4.29%	[7],[8]
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				3.62%
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				6.60%
Discount rate				3.61%
Assets [Member] | Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate				(4.86%)
Assets [Member] | Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate				(4.66%)
Subsequent Event [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%
Subsequent Event [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			6.67%
[1]	Includes $13 million related to CENG for the year ended December 31, 2016
[2]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.
[3]	(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, 2018. Certain benefit plans used individual rates ranging from 3.49%-3.65% and 3.57%-3.68% for pension and other postretirement plans, respectively.
[4]	(d)Not applicable to pension and other postretirement benefit plans that do not have plan assets.
[5]	(e)3.25% through 2019 and 3.75% thereafter.
[6]	(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, 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.
[7]	(f)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.
[8]	(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, 2016. Certain benefit plans used the individual rates ranging from 3.68%-4.14% and 4.32%-4.43% for pension and other postretirement plans, respectively.

Retirement Benefits Retiremen_2

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, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Employer contributions					$ 13
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			$ 48		(34)
Net benefit obligation at beginning of year			22,337		21,060
Service cost			405	[1]	387	[2]	$ 354
Interest cost			802	[1]	842	[2]	830
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant			0		0
Actuarial (gain) loss(a)	[3]		(1,561)		1,182
Plan amendments			(4)		9
Acquisitions(b)	[4]		0		16
Defined Benefit Plan, Benefit Obligation, Benefits Paid			(1,239)		(1,125)
Net benefit obligation at end of year			20,692		22,337		21,060
Fair value of net plan assets at beginning of year			18,573		16,791
Actual return on plan assets			(945)		2,600
Employer contributions			337		341
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant			0		0
Defined Benefit Plan, Plan Assets, Benefits Paid			(1,239)		(1,125)
Defined Benefit Plan, Fair Value of Plan Assets			16,678		18,573		16,791
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost		$ 12
Interest cost		26
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			4		0
Net benefit obligation at beginning of year			4,856		4,457
Service cost			112	[1]	106	[2]	107
Interest cost			175	[1]	182	[2]	185
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant			45		53
Actuarial (gain) loss(a)	[3]		(540)		350
Plan amendments			0		0
Acquisitions(b)	[4]		0		17
Defined Benefit Plan, Benefit Obligation, Benefits Paid			(275)		(309)
Net benefit obligation at end of year			4,369		4,856		4,457
Fair value of net plan assets at beginning of year			2,732		2,578
Actual return on plan assets			(136)		346
Employer contributions			46		64
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant			45		53
Defined Benefit Plan, Plan Assets, Benefits Paid			(275)		(309)
Defined Benefit Plan, Fair Value of Plan Assets			$ 2,408		$ 2,732		$ 2,578
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost		1
Interest cost		$ 6
[1]	FitzPatrick net benefit costs are included for the period after acquisition.
[2]	PHI net periodic benefit costs for the period prior to the merger are not included in the table above.
[3]	(a)The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience. The pension and OPEB actuarial losses in 2017 primarily reflect a decrease in the discount rate.
[4]	(b)Exelon recorded pension and OPEB obligations associated with its acquisition of Fitzpatrick on March 31, 2017.

Retirement Benefits Retiremen_3

Retirement Benefits Retirement Benefits - Balance Sheet locations of Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	$ 26	$ 28
Pension obligations	3,988	3,736
Non-pension postretirement benefit obligations	0	0
Unfunded status (net benefit obligation less plan assets)	4,014	3,764
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Other current liabilities	33	31
Pension obligations	0	0
Non-pension postretirement benefit obligations	1,928	2,093
Unfunded status (net benefit obligation less plan assets)	$ 1,961	$ 2,124

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, 2018	Dec. 31, 2017
Projected Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 20,692	$ 22,337
Fair value of net plan assets	16,678	18,573
Accumulated Benefit Obligation In Excess Of Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 19,656	$ 21,153

Retirement Benefits Retiremen_4

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, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost			$ 47		$ 109		$ 116
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	[1]		(1,561)		1,182
Service cost			405	[2]	387	[3]	354
Interest cost			802	[2]	842	[3]	830
Expected return on assets			(1,252)	[2]	(1,196)	[3]	(1,141)
Prior service cost (credit)			2	[2]	1	[3]	14
Actuarial loss			629	[2]	607	[3]	554
Settlement and other charges(c)			3	[2],[4]	3	[3],[4]	2
Net periodic benefit cost			589	[2]	644	[3]	613
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 12
Interest cost		26
Expected return on assets		30
Prior service cost (credit)		0
Actuarial loss		(14)
Net periodic benefit cost		22
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	[1]		(540)		350
Service cost			112	[2]	106	[3]	107
Interest cost			175	[2]	182	[3]	185
Expected return on assets			(173)	[2]	(162)	[3]	(162)
Prior service cost (credit)			(186)	[2]	(188)	[3]	(185)
Actuarial loss			66	[2]	61	[3]	63
Settlement and other charges(c)			1	[2],[4]	0	[3],[4]	0
Net periodic benefit cost			$ (5)	[2]	$ (1)	[3]	$ 8
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		1
Interest cost		6
Expected return on assets		5
Prior service cost (credit)		(3)
Actuarial loss		(2)
Net periodic benefit cost		$ 1
[1]	(a)The pension actuarial gain in 2018 primarily reflects an increase in the discount rate. The OPEB actuarial gain in 2018 primarily reflects an increase in the discount rate and favorable health care claims experience. The pension and OPEB actuarial losses in 2017 primarily reflect a decrease in the discount rate.
[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 Retiremen_5

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, 2018	Mar. 23, 2016	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, amounts recognized in regulatory assets, before tax		$ 61
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss				$ 635	$ (222)	[1]	$ 644
Amortization of actuarial loss				(629)	(607)	[1]	(554)
Current year prior service cost (credit)				(4)	9	[1]	(60)
Amortization of prior service (cost) credit				(2)	(1)	[1]	(14)
Settlements				3	(3)	[1]	0
DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeAndRegulatoryAssetsAcqusition				0	0	[1]	994
Total recognized in AOCI and regulatory assets (liabilities)	[1]			(3)	(824)		1,010
Defined benefit plan, amounts recognized in OCI, before tax				3	(401)	[1]	51
Defined benefit plan, amounts recognized in regulatory assets, before tax				(6)	(423)	[1]	959
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss			$ 0
Amortization of actuarial loss			(14)
Amortization of prior service (cost) credit			0
Total recognized in AOCI and regulatory assets (liabilities)	[1]		(14)
Defined benefit plan, amounts recognized in OCI, before tax			(1)
Defined benefit plan, amounts recognized in regulatory assets, before tax			(13)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial (gain) loss				(232)	166	[1]	(101)
Amortization of actuarial loss				(66)	(61)	[1]	(63)
Current year prior service cost (credit)				0	0	[1]	0
Amortization of prior service (cost) credit				186	188	[1]	185
Settlements				0	0	[1]	0
DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeAndRegulatoryAssetsAcqusition				0	0	[1]	94
Total recognized in AOCI and regulatory assets (liabilities)	[1]			(112)	293		115
Defined benefit plan, amounts recognized in OCI, before tax				(55)	168	[1]	20
Defined benefit plan, amounts recognized in regulatory assets, before tax				$ (57)	$ 125	[1]	$ 95
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
Amortization of actuarial loss			(2)
Amortization of prior service (cost) credit			3
Total recognized in AOCI and regulatory assets (liabilities)	[1]		1
Defined benefit plan, amounts recognized in OCI, before tax			0
Defined benefit plan, amounts recognized in regulatory assets, before tax			$ 1
[1]	2016 amounts include PHI for the period of March 24, 2016 through December 31, 2016.

Retirement Benefits Retiremen_6

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, 2018	Dec. 31, 2017
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	$ (29)	$ (24)
Actuarial loss	7,558	7,556
Total	7,529	7,532
Benefits included in accumulated other comprehensive income	3,899	3,896
Benefits included in regulatory assets	3,630	3,636
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	(337)	(522)
Actuarial loss	531	829
Total	194	307
Benefits included in accumulated other comprehensive income	70	125
Benefits included in regulatory assets	$ 124	$ 182

Retirement Benefits Retiremen_7

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		Mar. 24, 2016	[8]
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%
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]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Net Periodic Benefit Cost Investment Crediting Rate			4.00%		4.46%		5.31%
Benefit Obligation Investment Crediting Rate			4.46%		4.00%		4.46%
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%
Discount rate			4.31%	[1],[2]	3.62%	[2],[3]	4.04%	[4],[5],[6]
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			4.13%		3.49%		3.66%
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			4.36%		3.65%		4.11%
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%
Net Periodic Benefit Cost Investment Crediting Rate		2.89%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[7]	6.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%
Qualified Plan [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate	[8]	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%							4.55%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Health care cost trend rate			5.00%		5.00%		5.50%
Ultimate health care cost trend rate			5.00%		5.00%		5.00%
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%
Discount rate			4.30%	[1],[2]	3.61%	[2],[3]	4.04%	[4],[5],[6]
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			3.57%		4.00%		4.32%
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			3.68%		4.17%		4.43%
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			4.27%		3.57%		4.00%
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			4.38%		3.68%		4.17%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[7]	6.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%
Discount rate		4.55%
[1]	(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, 2018. Certain benefit plans used individual rates ranging from 4.13% - 4.36% and 4.27% - 4.38% for pension and other postretirement plans, respectively.
[2]	(d)3.25% through 2019 and 3.75% thereafter.
[3]	(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, 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.
[4]	(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, 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.
[5]	(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.
[6]	(f)Obligation was not remeasured for the PHI predecessor for the period from January 1, 2016, to March 23, 2016.
[7]	(h)Expected return on other postretirement benefit plan assets is pre-tax.
[8]	(g)The discount rate for the qualified and non-qualified pension plans was 4.65% and 4.55%, respectively.

Retirement Benefits Retiremen_8

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, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					$ 383		$ 405		$ 397
Expected qualified pension plan contributions					301
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					25
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					44
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions					41
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					7
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					2
Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[1]				0		21		25
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					139		148		152
Expected qualified pension plan contributions					135
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					7
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					13
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					42		41		38
Expected qualified pension plan contributions					65
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					2
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					28		24		30
Expected qualified pension plan contributions					25
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					0
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					54		53		49
Expected qualified pension plan contributions					34
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					15
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					(74)		(99)
Expected qualified pension plan contributions					1
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					8
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					12
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected qualified pension plan contributions					1
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					5
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					1
Pepco Holdings LLC [Member] | Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				$ (86)
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions		$ (4)
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					17		72		32
Expected qualified pension plan contributions					0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					2
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					10
Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					0		2		22
Expected qualified pension plan contributions					0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					0
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					6		20		17
Expected qualified pension plan contributions					0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					0
Defined Other Postretirement Benefit Plan Estimated Future Employer Contributions In Next Fiscal Year					1
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					337	[2]	341	[2]	347
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					1,196
Pension Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[1],[2]				41		38		39
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	[2]				128		137		140
Pension Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				38		36		33
Pension Plan, Defined Benefit [Member] | PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				28		24		30
Pension Plan, Defined Benefit [Member] | Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				40		39		31
Pension Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				67	62
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	[1]		50	[2],[3]	5	[2],[3]	17	[2],[3]
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
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
Pension Plan, Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					2	[1]	4		6
Pension Plan, Defined Benefit [Member] | Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				6		62		24
Pension Plan, Defined Benefit [Member] | Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				0		0		22
Pension Plan, Defined Benefit [Member] | Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[2]				6		0		15
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					46		64		50
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months					255
Other Postretirement Benefit Plan, Defined Benefit [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions	[1]				5		2		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		11		12
Other Postretirement Benefit Plan, Defined Benefit [Member] | Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					4		5		5
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		14		18
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions				$ 32	12
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	[3]				1		0		2
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
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
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					11		10		8
Other Postretirement Benefit Plan, Defined Benefit [Member] | Delmarva Power & Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and non-pension postretirement benefit contributions					0		2		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					$ 0		$ 20		$ 2
[1]	)Includes $2 million, $4 million, and $6 million of pension contributions funded by Exelon Corporate, for the years ended December 31, 2018, 2017, and 2016, respectively.
[2]	Exelon's and Generation's pension contributions include $21 million and $25 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 and 2016, respectively
[3]	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 Retiremen_9

Retirement Benefits Retirement Benefits - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2018USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	$ 25
Pension Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	1,196
2,019	1,221
2,020	1,258
2,021	1,284
2,022	1,302
2022 through 2026	6,770
Total estimated future benefit payments through 2028	13,031
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2,018	255
2,019	263
2,020	269
2,021	274
2,022	282
2022 through 2026	1,483
Total estimated future benefit payments through 2028	$ 2,826

Retirement Benefits Retireme_10

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, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount included in capital and operating & maintenance expense				$ 583		$ 643		$ 621
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]			57		53		48
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]			204		227		218
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				177		176		166
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				18		29		33
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				60		64		68
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			$ 67
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		$ 94				88		23
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		34	[3],[4]	43	[3],[4]	47	[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		15	[3]	25	[3]	31	[3]
Delmarva Power & 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		6	[3]	13	[3]	18	[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		$ 12	[3]	$ 13	[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 Retireme_11

Retirement Benefits Retirement Benefits - Pension and Other Postretirement Benefit Plan Target Asset Allocations (Details)		Dec. 31, 2018	Dec. 31, 2017
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		32.00%	35.00%
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		37.00%
Percentage of Plan Assets		38.00%	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]	28.00%
Percentage of Plan Assets	[1]	30.00%	26.00%
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		47.00%
Percentage of Plan Assets		44.00%	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%	28.00%
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]	25.00%
Percentage of Plan Assets	[1]	28.00%	25.00%
[1]	Alternative investments include private equity, hedge funds, real estate, and private credit

Retirement Benefits Retireme_12

Retirement Benefits Retirement Benefits - Fair Value Measurements of Pension and Postretirement Benefit Plan Assets (Details) - USD ($) $ in Millions		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Derivative, Fair Value, Net		$ 1		$ 6
Derivative, Notional Amount		5,991		3,606
Net assets pending transactions excluded		44		(2)
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]	19,130	[1]	21,303
Alternative Investment, Fair Value Disclosure		3,433		3,534
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]	5,463	[1]	6,090
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]	4,581	[1]	4,913
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]	486	[1]	458
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		16,678		18,573	$ 16,791
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		486		458	437
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		216		232	206
Pension Plan, Defined Benefit [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		268		224	229	[4]
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]	16,720	[1]	18,575
Alternative Investment, Fair Value Disclosure	[3]	7,247	[1]	8,216
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]	350	[1]	585
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
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],[5]	5,346	[1]	6,644
Alternative Investment, Fair Value Disclosure		1,980	[1],[3],[5]	3,077
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]	1,169	[1]	1,309
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
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]	59	[1]	64
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
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]	3,932	[1]	4,163
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
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],[5]	942	[1]	1,203
Alternative Investment, Fair Value Disclosure	[3],[5]	613	[1]	756
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]	6,102	[1]	6,739
Alternative Investment, Fair Value Disclosure	[3]	613	[1]	756
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]	1,219	[1]	1,034
Alternative Investment, Fair Value Disclosure	[3]	1,219	[1]	1,034
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]	1,608	[1]	1,770
Alternative Investment, Fair Value Disclosure	[3]	1,608	[1]	1,770
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]	1,029	[1]	884
Alternative Investment, Fair Value Disclosure	[3]	1,029	[1]	884
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]	1,066	[1]	919
Alternative Investment, Fair Value Disclosure	[3]	798	[1]	695
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]	4,710	[1]	5,300
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]	350	[1]	585
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],[5]	3,364	[1]	3,565
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]	996	[1]	1,150
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
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
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],[5]	0	[1]	0
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]	996	[1]	1,150
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
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
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
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
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]	4,277	[1]	4,601
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
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],[5]	0	[1]	0
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]	173	[1]	159
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]	59	[1]	64
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]	3,716	[1]	3,931
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],[5]	329	[1]	447
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]	4,277	[1]	4,601
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
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
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
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
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]	486	[1]	458
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
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],[5]	2	[1]	2
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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]	0	[1]	0
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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]	216	[1]	232
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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],[5]	0	[1]	0
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [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	[3]	216	[1]	232
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
Pension Plan, Defined Benefit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
Pension Plan, Defined Benefit [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]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0
Pension Plan, Defined Benefit [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]	268	[1]	224
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2,408		2,732	$ 2,578
Other Postretirement Benefits Plan [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]	2,410	[1]	2,728
Alternative Investment, Fair Value Disclosure	[2],[3]	8,600	[1]	9,842
Other Postretirement Benefits Plan [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]	22	[1]	29
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
Other Postretirement Benefits Plan [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]	1,047	[1]	1,289
Alternative Investment, Fair Value Disclosure	[3]	508	[1]	764
Other Postretirement Benefits Plan [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]	67	[1]	69
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
Other Postretirement Benefits Plan [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]	126	[1]	136
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
Other Postretirement Benefits Plan [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]	48	[1]	47
Alternative Investment, Fair Value Disclosure	[3]	0	[1]	0
Other Postretirement Benefits Plan [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]	425	[1]	481
Alternative Investment, Fair Value Disclosure	[3]	170	[1]	185
Other Postretirement Benefits Plan [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]	666	[1]	733
Alternative Investment, Fair Value Disclosure	[3]	170	[1]	185
Other Postretirement Benefits Plan [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]	411	[1]	430
Alternative Investment, Fair Value Disclosure	[3]	411	[1]	430
Other Postretirement Benefits Plan [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]	132	[1]	124
Alternative Investment, Fair Value Disclosure	[3]	132	[1]	124
Other Postretirement Benefits Plan [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]	132	[1]	123
Alternative Investment, Fair Value Disclosure	[3]	132	[1]	123
Other Postretirement Benefits Plan [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]	753	[1]	790
Other Postretirement Benefits Plan [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]	22	[1]	29
Other Postretirement Benefits Plan [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]	537	[1]	523
Other Postretirement Benefits Plan [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]	11	[1]	13
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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]	183	[1]	225
Other Postretirement Benefits Plan [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]	194	[1]	238
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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]	304	[1]	312
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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]	2	[1]	2
Other Postretirement Benefits Plan [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]	56	[1]	56
Other Postretirement Benefits Plan [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]	126	[1]	136
Other Postretirement Benefits Plan [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]	48	[1]	47
Other Postretirement Benefits Plan [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]	72	[1]	71
Other Postretirement Benefits Plan [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]	302	[1]	310
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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]	0	[1]	0
Alternative Investment, Fair Value Disclosure		1,353		1,626
Other Postretirement Benefits Plan [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
Other Postretirement Benefits Plan [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]	0	[1]	0
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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]	0	[1]	0
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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]	0	[1]	0
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [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	[3]	0	[1]	0
Other Postretirement Benefits Plan [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [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
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]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	0	[1]	0
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
[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 liabilities of $44 million and net assets of $2 million at December 31, 2018 and 2017, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables or payables related to pending securities sales and purchases, interest and dividends receivable
[3]	See Note 11—Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy
[4]	(a)Prior year amounts reflect a reclassification from Not subject to leveling into Level 3.
[5]	Includes derivative instruments of less than $1 million and $6 million, which have a total notional amount of $5,991 million and $3,606 million at December 31, 2018 and 2017, 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 Retireme_13

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, 2018		Dec. 31, 2017
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		$ 18,573		$ 16,791
Defined Benefit Plan, Fair Value of Plan Assets		16,678		18,573
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		458		437
Relating to assets still held at the reporting date		(5)		40
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold		(1)
Defined Benefit Plan Purchases		54		36
Defined Benefit Plan Sales		8		16
Settlements		(12)	[1]	(39)
Defined Benefit Plan, Fair Value of Plan Assets		486		458
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		232		206
Relating to assets still held at the reporting date		(14)		11
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold		(1)
Defined Benefit Plan Purchases		19		31
Defined Benefit Plan Sales		8		16
Settlements		(12)	[1]	0
Defined Benefit Plan, Fair Value of Plan Assets		216		232
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, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold		0
Defined Benefit Plan Purchases		0		0
Defined Benefit Plan Sales		0		0
Settlements		0	[1]	0
Defined Benefit Plan, Fair Value of Plan Assets		2		2
Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year		224		229	[2]
Relating to assets still held at the reporting date		9		29
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold		0
Defined Benefit Plan Purchases		35		5
Defined Benefit Plan Sales		0		0
Settlements		0	[1]	(39)
Defined Benefit Plan, Fair Value of Plan Assets		268		224
Fair Value, Measurements, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment, Fair Value Disclosure		3,433		3,534
Fair value of net plan assets at beginning of year	[3],[4]	21,303
Defined Benefit Plan, Fair Value of Plan Assets	[3],[4]	19,130	[5]	21,303
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]	458
Defined Benefit Plan, Fair Value of Plan Assets	[3],[4]	486	[5]	458
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	[4]	7,247	[5]	8,216
Fair value of net plan assets at beginning of year	[4]	18,575
Defined Benefit Plan, Fair Value of Plan Assets	[4]	16,720	[5]	18,575
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	[4]	613	[5]	756
Fair value of net plan assets at beginning of year	[4]	6,739
Defined Benefit Plan, Fair Value of Plan Assets	[4]	6,102	[5]	6,739
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Alternative Investment, Fair Value Disclosure	[4]	798	[5]	695
Fair value of net plan assets at beginning of year	[4]	919
Defined Benefit Plan, Fair Value of Plan Assets	[4]	1,066	[5]	919
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	[4]	458
Defined Benefit Plan, Fair Value of Plan Assets	[4]	486	[5]	458
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	[4]	232
Defined Benefit Plan, Fair Value of Plan Assets	[4]	216	[5]	232
Fair Value, Measurements, Recurring [Member] | Pension Plan, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of net plan assets at beginning of year	[4]	224
Defined Benefit Plan, Fair Value of Plan Assets	[4]	$ 268	[5]	$ 224
[1]	(b)Represents cash settlements only.
[2]	(a)Prior year amounts reflect a reclassification from Not subject to leveling into Level 3.
[3]	Excludes net liabilities of $44 million and net assets of $2 million at December 31, 2018 and 2017, respectively, which are required to reconcile to the fair value of net plan assets. These items consist primarily of receivables or payables related to pending securities sales and purchases, interest and dividends receivable
[4]	See Note 11—Fair Value of Financial Assets and Liabilities for a description of levels within the fair value hierarchy
[5]	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 Retireme_14

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, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[1]			$ 179		$ 128		$ 164
Employer contributions						13
Corporate, Non-Segment [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions	[2]			22		9		19
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]			86		55		79
Commonwealth Edison Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				37		31		34
PECO Energy Co [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				9		10		10
Baltimore Gas and Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions				12		10		12
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			$ 13	13
Pepco Holdings LLC [Member] | Predecessor [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Savings plan matching contributions		10				3
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 & 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 related to CENG for the year ended December 31, 2016
[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 - PHI Merge

Severance Severance - PHI Merger (Details) - PHI Merger [Member] $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Restructuring Cost and Reserve [Line Items]
Severance Costs	$ 57
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	9
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	2
PECO Energy Co [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
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	44
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	21
Delmarva Power & Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	13
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	$ 10

Severance Severance - Liabiliti

Severance Severance - Liabilities Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 77	$ 94	$ 88
Payments for Restructuring		(29)
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	35	35
Payments for Restructuring	(52)
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	47	58	36
Payments for Restructuring		(9)
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	9	31
Payments for Restructuring	(20)
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2	3	3
Payments for Restructuring		(2)
Commonwealth Edison Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	2
Payments for Restructuring	(2)
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
PECO Energy Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	0
Payments for Restructuring	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1	0	0
Payments for Restructuring		0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	0
Payments for Restructuring	0
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	7	20	29
Payments for Restructuring		(12)
Pepco Holdings LLC [Member] | Successor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	5	3
Payments for Restructuring	(18)
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
Potomac Electric Power Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	0
Payments for Restructuring	(1)
Delmarva Power & Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
Delmarva Power & Light Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	0
Payments for Restructuring	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	$ 0
Payments for Restructuring		0
Atlantic City Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	$ 0
Payments for Restructuring	$ 0

Shareholders' Equity Schedule

Shareholders' Equity Schedule of Common Stock Authorized and Outstanding (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares outstanding	968,187,955	963,335,888
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized	2,000,000,000	2,000,000,000
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	127,021,331	127,021,246
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 & 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, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017	Jul. 30, 2015	Jun. 30, 2014
Schedule of Capitalization, Equity [Line Items]
Stock Repurchased During Period, Shares							33,000,000	0
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	2,000,000
Treasury stock, at cost						$ 123	$ 123
Stock Repurchased During Period, Value						$ 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						60,285	60,584
Commonwealth Edison Co [Member] | Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Common Stock Shares Reserved For Warrant Conversion						20,095	20,195
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	400,000	600,000
Preferred Stock, Dividend Rate, Percentage		6.70%	6.97%	7.125%	6.99%
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				$ 1,150
Equity units issued											23,000,000
Stock Issued During Period, Shares, Treasury Stock Reissued							33,000,000

Stock-Based Compensation Plan_3

Stock-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Common Stock Narrative Information [Line Items]
Obligations of outstanding restricted stock not settled	$ 83		$ 108
Settlement of restricted stock	106		$ 88	$ 68
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 33
Weighted Average Period Non Vested Performance Share Awards Are Expected To Be Recognized Over	1 year 8 months
Performance Shares [Member]
Common Stock Narrative Information [Line Items]
Granted, Weighted Average Grant Date Fair Value (in usd per share)	$ 38.15	[1]	$ 35	$ 28.85
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)	$ 38.60		$ 34.98	$ 28.14
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 38
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	11
[1]	(a)As of December 31, 2018, $33 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.7 years.

Stock-Based Compensation Plan_4

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 208	$ 191	$ 175	[1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense				(18)
Allocated Share-based Compensation Expense, Net of Tax		154	117	107	[1]
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		143	107	93	[1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		(16)	(29)	(18)
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		57	77	75	[1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		(28)	(35)	(27)
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		0	0	0	[1]
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		8	7	7	[1]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		$ (54)	$ (74)	$ (68)	[1]
Predecessor [Member] | Pepco Holdings LLC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 3
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	(1)
Allocated Share-based Compensation Expense, Net of Tax	2
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
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
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]	(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 Plan_5

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			$ 208	$ 191	$ 175	[1]
Exelon Generation Co L L C [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			77	88	78
Commonwealth Edison Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			8	7	8
PECO Energy Co [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			5	3	3
Baltimore Gas and Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense			3	1	1
Pepco Holdings LLC [Member] | Predecessor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 3
Corporate, Non-Segment [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	[2]		111	88	81
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	[3],[4]		$ 4	$ 4	$ 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]	Pepco's, DPL's and ACE's stock-based compensation expense for the years ended December 31, 2018 and 2017 was not material.
[4]	These amounts primarily represent amounts billed to PHI’s subsidiaries through PHISCO intercompany allocations.

Stock-Based Compensation Plan_6

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation				$ (18)
Restricted Stock Units (RSUs) [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation		$ (28)	$ (35)	(27)
Performance Shares [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation		$ (16)	$ (29)	$ (18)
Pepco Holdings LLC [Member] | Predecessor [Member]
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Tax benefit on stock compensation	$ (1)

Stock-Based Compensation Plan_7

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, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance		6,723,611
Options exercised		(1,522,952)
Options forfeited		0
Options expired		(1,173,007)
Ending Balance		4,027,652	6,723,611
Weighted Average Exercise Price (in usd per share)		$ 43.95	$ 47.69
Options Exercised, Weighted Average Exercise Price (in usd per share)		36.54
Options Forfeited, Weighted Average Exercise Price (in usd per share)		0
Options Expired, Weighted Average Exercise Price (in usd per share)		$ 74.99
Shares Outstanding, Weighted Average Remaining Contractual Life		2 years 10 months 24 days	2 years 7 months 24 days
Exercisable at December 31, 2017	[1]	4,027,652
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	[1]	$ 43.95
Shares Exercisable, Weighted Average Remaining Contractual Life	[1]	2 years 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value		$ 14	$ 7
Shares Exercisable, Aggregate Intrinsic Value	[1]	$ 14
[1]	Includes stock options issued to retirement eligible employees.

Stock-Based Compensation Plan_8

Stock-Based Compensation Plans - Summary of Information of Stock Options Exercised (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock [Abstract]
Aggregate value	[1]	$ 12	$ 15	$ 11
Cash received for exercise price		$ 56	$ 107	$ 19
[1]	The difference between the market value on the date of exercise and the option exercise price.

Stock-Based Compensation Plan_9

Stock-Based Compensation Plans - Summary of Nonvested Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance	[1]	3,389,503
Granted		1,321,988
Vested		(1,845,300)
Forfeited		(65,046)
Undistributed vested awards	[2]	(507,804)
Ending Balance	[1]	2,293,341	3,389,503
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 32.24
Granted, Weighted Average Grant Date Fair Value (in usd per share)		38.60	$ 34.98	$ 28.14
Vested, Weighted Average Exercise Price (in usd per share)		32.03
Forfeited, Weighted Average Exercise Price (in usd per share)		32.96
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[2]	36.76
Nonvested, Weighted Average Exercise Price (in usd per share)	[1]	$ 35.06	$ 32.24
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		1,131,487	1,488,383
[1]	Excludes 1,131,487 and 1,488,383 of restricted stock units issued to retirement-eligible employees as of December 31, 2018 and 2017, respectively, as they are fully vested.
[2]	Represents restricted stock units that vested but were not distributed to retirement-eligible employees during 2018.

Stock-Based Compensation Pla_10

Stock-Based Compensation Plans - Summary of Nonvested Performance Share Awards Activity (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
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		$ 33
Weighted Average Period Non Vested Performance Share Awards Are Expected To Be Recognized Over		1 year 8 months
Fair Value Of Settled Performance Share Awards		$ 61	[1]	$ 72	$ 45
Performance Share Awards Obligations Settled In Cash		$ 49	[1]	$ 56	$ 28
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]	2,956,966
Granted		1,637,542
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)		1,348,029
Vested		(848,574)
Forfeited		(50,467)
Undistributed vested awards	[3]	(1,640,268)
Ending Balance	[2]	3,403,228		2,956,966
Nonvested, Weighted Average Exercise Price (in usd per share)	[2]	$ 33.13		$ 32.65
Granted, Weighted Average Grant Date Fair Value (in usd per share)		38.15	[1]	$ 35	$ 28.85
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Change in Performance, Weighted Average Grant Date Fair Value		30.66
Vested, Weighted Average Exercise Price (in usd per share)		36.26
Forfeited, Weighted Average Exercise Price (in usd per share)		36.24
Undistributed Vested Awards, Weighted Average Grant Date Fair Value (in usd per share)	[3]	$ 33.38
Fully Vested Stock Based Compensation Issued To Retirement Eligible Employees		3,586,259		2,723,440
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, 2018, $33 million of total unrecognized compensation costs related to nonvested performance shares are expected to be recognized over the remaining weighted-average period of 1.7 years.
[2]	Excludes 3,586,259 and 2,723,440 of performance share awards issued to retirement-eligible employees as of December 31, 2018 and 2017, respectively, as they are fully vested.
[3]	Represents performance share awards that vested but were not distributed to retirement-eligible employees during 2018.

Stock-Based Compensation Pla_11

Stock-Based Compensation Plans - Balance Sheet Classification of Obligations related to Outstanding Performance Share Awards Not Yet Settled (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
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]	$ 135	$ 57
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Deferred Credits And Other Liabilities	[2]	109	100
Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled Common Stock		26	26
Total Balance Sheet Classification Of Obligations Related To Outstanding Performance Share Awards Not Yet Settled		$ 270	$ 183
[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 P_2

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income (loss) attributable to common shareholders	$ 152	$ 733	$ 539	$ 585	$ 1,880	$ 823	$ 95	$ 990	$ 2,010	$ 3,786	$ 1,121
Weighted average common shares outstanding — basic									967	947	924
Assumed exercise and/or distributions of stock-based awards									2	2	3
Weighted average common shares outstanding — diluted									969	949	927

Earnings Per Share Earnings P_3

Earnings Per Share Earnings Per Share - Narrative (Details) - shares shares in Millions	Jun. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	0
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)		3	8	12

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Income Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		$ 32,187		$ 27,640		$ 27,330
Amounts reclassified from AOCI	[1]	182		144
Other comprehensive income (loss)		42		171		(36)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings				539
Ending Balance		33,070		32,187		27,640
Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(14)		(17)
OCI before reclassifications	[2]	11		(1)
Amounts reclassified from AOCI	[2],[3]	1		4
Other comprehensive income (loss)	[2]	12		3
Ending Balance	[2]	(2)		(14)		(17)
Gains and (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	10		4
OCI before reclassifications	[2]	0		6
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	0		6
Ending Balance	[2]	0		10		4
Unrealized Gains and (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	(10)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(2,998)		(2,610)
OCI before reclassifications	[2]	(143)		11
Amounts reclassified from AOCI	[1],[2],[3]	181		140
Other comprehensive income (loss)	[2]	38		151
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings	[2],[5]			(539)
Ending Balance	[2]	(2,960)		(2,998)		(2,610)
Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(23)		(30)
OCI before reclassifications	[2]	(10)		7
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	(10)		7
Ending Balance	[2]	(33)		(23)		(30)
Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
AOCI of Investments Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(1)		(7)
OCI before reclassifications	[2]	1		6
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	1		6
Ending Balance	[2]	0		(1)		(7)
AOCI of Investments Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		(3,026)	[2]	(2,660)	[2]	(2,624)
OCI before reclassifications	[2]	(141)		29
Amounts reclassified from AOCI	[2],[3]	182		144
Other comprehensive income (loss)		41	[2]	173	[2]	(36)
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings	[2],[5]			(539)
Ending Balance	[2]	(2,995)		(3,026)		(2,660)
Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	(10)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	[1]	1		4
Other comprehensive income (loss)		3		15		9
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(16)		(19)
OCI before reclassifications	[2]	11		(1)
Amounts reclassified from AOCI	[2],[3]	1		4
Other comprehensive income (loss)	[2]	12		3
Ending Balance	[2]	(4)		(16)		(19)
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Exelon Generation Co L L C [Member] | Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	3		2
OCI before reclassifications	[2]	0		1
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	0		1
Ending Balance	[2]	0		3		2
Exelon Generation Co L L C [Member] | Unrealized Gains and (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	(3)
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Exelon Generation Co L L C [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(23)		(30)
OCI before reclassifications	[2]	(10)		7
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	(10)		7
Ending Balance	[2]	(33)		(23)		(30)
Exelon Generation Co L L C [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Exelon Generation Co L L C [Member] | AOCI of Investments Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(1)		(7)
OCI before reclassifications	[2]	0		6
Amounts reclassified from AOCI	[2],[3]	0		0
Other comprehensive income (loss)	[2]	0		6
Ending Balance	[2]	(1)		(1)		(7)
Exelon Generation Co L L C [Member] | AOCI of Investments Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
Exelon Generation Co L L C [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	(37)		(54)
OCI before reclassifications	[2]	1		13
Amounts reclassified from AOCI	[2],[3]	1		4
Other comprehensive income (loss)		2	[2]	17	[2]	9
Ending Balance	[2]	(38)		(37)		(54)
Exelon Generation Co L L C [Member] | Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	(3)
PECO Energy Co [Member] | Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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
PECO Energy Co [Member] | Gains and (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
PECO Energy Co [Member] | Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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]	0		1		1
PECO Energy Co [Member] | Unrealized Gains and (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	(1)
PECO Energy Co [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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
PECO Energy Co [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
PECO Energy Co [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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
PECO Energy Co [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
PECO Energy Co [Member] | AOCI of Investments Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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
PECO Energy Co [Member] | AOCI of Investments Unconsolidated Affiliates | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	0
PECO Energy Co [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]	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]	0		$ 1		$ 1
PECO Energy Co [Member] | Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]	$ (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]	Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and Financial Liabilities. The standard was adopted as of January 1, 2018, which resulted in an increase to Retained earnings and Accumulated other comprehensive loss of $10 million, $3 million and $1 million for Exelon, Generation and PECO, respectively. The amounts reclassified related to Rabbi Trusts. See Note 1 — Significant Accounting Policies for additional information.
[5]	Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million, primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 1 — Significant Accounting Policies for additional information.

Changes in Accumulated Other _4

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
		Dec. 31, 2018	Mar. 23, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss				$ (112)	$ 947	$ 297
Income Tax Expense (Benefit)		$ 26		120	(126)	753
Net income (loss)				2,084	3,876	1,196
Amortization of pension and other postretirement benefit plan items				4
Amounts reclassified from AOCI	[1]			(182)	(144)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)					(1)
Gains and (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]			(1)	(4)
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 [Line Items]
Other cash flow hedges	[1]			(1)	(5)
Total before tax	[1]			(1)	(5)
Income Tax Expense (Benefit)	[1]			0	1
Net of tax	[1]			(1)	(4)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]			90	92
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]			(333)	(324)
Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]			(243)	(232)
Tax benefit	[1]			62	92
Amounts reclassified from AOCI	[1],[2],[3]			(181)	(140)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss				(178)	948	401
Income Tax Expense (Benefit)				(108)	(1,376)	282
Net income (loss)				443	2,798	$ 550
Amortization of pension and other postretirement benefit plan items				3
Amounts reclassified from AOCI	[1]			(1)	(4)
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]			(1)	(4)
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 [Line Items]
Other cash flow hedges	[1]			(1)	(5)
Total before tax	[1]			(1)	(5)
Income Tax Expense (Benefit)	[1]			0	1
Net of tax	[1]			(1)	(4)
Exelon Generation Co L L C [Member] | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [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 [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 [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]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss				43	54
Income Tax Expense (Benefit)				35	217
Net income (loss)				$ 398	$ 362
Pepco Holdings LLC [Member] | Predecessor [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss			$ (4)
Income Tax Expense (Benefit)			17
Net income (loss)			$ 19
[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 information.

Changes in Accumulated Other _5

Changes in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ (17)	$ (90)	$ 30
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	24	36	30
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(86)	(128)	(118)
Pension and Non-Pension Postretirement Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	50	13	115
Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(5)	(7)	0
Unrealized Gains and (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gains (losses) on investments in unconsolidated affiliates	0	(3)	3
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0	(1)	0
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(5)	(10)	1
Exelon Generation Co L L C [Member] | Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(4)	(6)	(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 gains (losses) on investments in unconsolidated affiliates	(1)	(3)	3
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 0	$ (1)	$ 0

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies - Narrative (Details)		Nov. 04, 2016	Nov. 01, 2015USD ($)	Sep. 23, 2015USD ($)	Dec. 31, 2018USD ($)employeeOpen_claimMGPSite	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)MW	Dec. 31, 2018USD ($)employeeOpen_claimMGPSiteMW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Feb. 17, 2012USD ($)
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[1],[2]				$ 1,378,000,000			$ 1,378,000,000
Direct Investment Commitment											$ 1,000,000,000
Power Volume | MW							10	220
Business Acquisition Residual Commitment | MW							55
Loss Contingency, Loss in Period										$ 50,000,000
Nontrade Receivables, Current	[3]				124,000,000		$ 94,000,000	$ 124,000,000	94,000,000
Nontrade Receivables, Noncurrent	[4]				15,000,000		15,000,000	15,000,000	15,000,000
Accounts Payable, Other, Current	[3],[5]				(17,000,000)		(11,000,000)	(17,000,000)	(11,000,000)
DOE Spent Nuclear Fuel One Time Fee					34,000,000			34,000,000
Operating Expenses	[6]							32,143,000,000	29,619,000,000	28,106,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[1],[2]				763,000,000			763,000,000
Direct Investment Commitment
Entity Number of Employees | employee					1,500			1,500
Leasehold Improvements, Gross					$ 90,000,000			$ 90,000,000
Lessee, Operating Lease, Term of Contract		20 years
Costs Incurred, Development Costs								458,000,000
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					13,600,000,000			13,600,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident					3,100,000,000			3,100,000,000
Mutual Insurance Total Retrospective Premium Obligation					345,000,000			345,000,000
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	[7]							1,274,000,000
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[7],[8]							1,100,000,000
DOE Spent Nuclear Fuel One Time Fee					277,000,000			277,000,000
DOE Spent Nuclear Fuel One Time Fee With Interest					1,171,000,000		1,147,000,000	$ 1,171,000,000	1,147,000,000
Spent Nuclear Fuel Treasury Interest Rate								2.351%
Loss Contingency Accrual, Provision					20,000,000
Environmental loss contingencies							90,000,000		90,000,000
Asbestos Liability Reserve					$ 79,000,000		78,000,000	$ 79,000,000	78,000,000
Open Asbestos Liability Claims | Open_claim					238			238
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					280,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident					14,100,000,000			$ 14,100,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 454,000,000
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					58,000,000		60,000,000	58,000,000	60,000,000	$ 21,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				23,000,000			23,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					42			42
Sites approved for clean-up | MGPSite					21			21
Sites under study/remediation | MGPSite					21			21
Other Increase (Decrease) in Environmental Liabilities						$ 48,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				$ 25,000,000			$ 25,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					26			26
Sites approved for clean-up | MGPSite					17			17
Sites under study/remediation | MGPSite					9			9
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9],[10],[11]				$ 143,000,000			$ 143,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					13			13
Sites approved for clean-up | MGPSite					9			9
Sites under study/remediation | MGPSite					4			4
Common Equity Tier One Capital Ratio					48.00%			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]
Operating Leases, Future Minimum Payments Due	[2]				$ 377,000,000			$ 377,000,000
Direct Investment Commitment
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2]				86,000,000			86,000,000
Direct Investment Commitment
Accrued Liabilities and Other Liabilities					30,000,000		28,000,000	30,000,000	28,000,000
Delmarva Power & Light Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2],[9]				96,000,000			96,000,000
Direct Investment Commitment
Total number of MGP sites | MGPSite					3			3
Sites approved for clean-up | MGPSite					2			2
Common Equity Tier One Capital Ratio					48.00%			48.00%
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Operating Leases, Future Minimum Payments Due	[2]				$ 32,000,000			$ 32,000,000
Direct Investment Commitment
Common Equity Tier One Capital Ratio					30.00%			30.00%
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve					$ 24,000,000			$ 24,000,000
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Asbestos Liability Reserve					$ 55,000,000			$ 55,000,000
[1]	)Excludes Generation’s contingent operating lease payments associated with contracted generation agreement
[2]	)Includes amounts related to shared use land arrangement
[3]	)Recorded in Accounts receivable, other.
[4]	)Recorded in Deferred debits and other assets, oth
[5]	)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
[6]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[7]	)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 CEN
[8]	)Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Cree
[9]	)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 2019 - 2023, was $3 million, $5 million, $1 million and $1 million respectivel
[10]	)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 $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel
[11]	)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 $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel

Commitments and Contingencies_3

Commitments and Contingencies Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Dec. 31, 2018USD ($)
Guarantor Obligations [Line Items]
Contractual Obligation	$ 3,507
Contractual Obligation, Due in Next Fiscal Year	2,728
Contractual Obligation, Due in Second Year	344
Contractual Obligation, Due in Third Year	41
Contractual Obligation, Due in Fourth Year	3
Contractual Obligation, Due in Fifth Year	3
Contractual Obligation, Due after Fifth Year	388
Guarantee obligations maximum exposure	61
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	2,900
Contractual Obligation, Due in Next Fiscal Year	2,581
Contractual Obligation, Due in Second Year	318
Contractual Obligation, Due in Third Year	1
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	214
Contractual Obligation, Due in Next Fiscal Year	12
Contractual Obligation, Due in Second Year	0
Contractual Obligation, Due in Third Year	2
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	9
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
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	20
Contractual Obligation, Due in Next Fiscal Year	5
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
Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	73
Contractual Obligation, Due in Next Fiscal Year	44
Contractual Obligation, Due in Second Year	11
Contractual Obligation, Due in Third Year	2
Contractual Obligation, Due in Fourth Year	3
Contractual Obligation, Due in Fifth Year	3
Contractual Obligation, Due after Fifth Year	10
Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	49
Contractual Obligation, Due in Next Fiscal Year	34
Contractual Obligation, Due in Second Year	9
Contractual Obligation, Due in Third Year	1
Contractual Obligation, Due in Fourth Year	1
Contractual Obligation, Due in Fifth Year	1
Contractual Obligation, Due after Fifth Year	3
Guarantee obligations maximum exposure	19
Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	15
Contractual Obligation, Due in Next Fiscal Year	6
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	1
Contractual Obligation, Due in Fourth Year	1
Contractual Obligation, Due in Fifth Year	1
Contractual Obligation, Due after Fifth Year	5
Guarantee obligations maximum exposure	26
Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	9
Contractual Obligation, Due in Next Fiscal Year	4
Contractual Obligation, Due in Second Year	1
Contractual Obligation, Due in Third Year	0
Contractual Obligation, Due in Fourth Year	1
Contractual Obligation, Due in Fifth Year	1
Contractual Obligation, Due after Fifth Year	2
Guarantee obligations maximum exposure	16
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	1,703	[1]
Contractual Obligation, Due in Next Fiscal Year	1,394	[1]
Contractual Obligation, Due in Second Year	308	[1]
Contractual Obligation, Due in Third Year	1	[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	1,680	[2]
Contractual Obligation, Due in Next Fiscal Year	1,380	[2]
Contractual Obligation, Due in Second Year	299	[2]
Contractual Obligation, Due in Third Year	1	[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	3	[4]
Contractual Obligation, Due in Next Fiscal Year	2	[4]
Contractual Obligation, Due in Second Year	1	[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]
Financial Standby Letter of Credit [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	8
Contractual Obligation, Due in Next Fiscal Year	0
Contractual Obligation, Due in Second Year	8
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
Financial Standby Letter of Credit [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	8
Contractual Obligation, Due in Next Fiscal Year	0
Contractual Obligation, Due in Second Year	8
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]
Guarantor Obligations [Line Items]
Contractual Obligation	1,402	[5]
Contractual Obligation, Due in Next Fiscal Year	1,331	[5]
Contractual Obligation, Due in Second Year	33	[5]
Contractual Obligation, Due in Third Year	38	[5]
Contractual Obligation, Due in Fourth Year	0	[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	1,220
Contractual Obligation, Due in Next Fiscal Year	1,201
Contractual Obligation, Due in Second Year	19
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	12	[6]
Contractual Obligation, Due in Next Fiscal Year	10	[6]
Contractual Obligation, Due in Second Year	0	[6]
Contractual Obligation, Due in Third Year	2	[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	9	[7]
Contractual Obligation, Due in Second Year	0	[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	17	[8]
Contractual Obligation, Due in Next Fiscal Year	3	[8]
Contractual Obligation, Due in Second Year	14	[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] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	41
Contractual Obligation, Due in Next Fiscal Year	41
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	0
Surety Bond [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	33	[9]
Contractual Obligation, Due in Next Fiscal Year	33	[9]
Contractual Obligation, Due in Second Year	0	[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 & Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	5	[10]
Contractual Obligation, Due in Next Fiscal Year	5	[10]
Contractual Obligation, Due in Second Year	0	[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	3
Contractual Obligation, Due in Next Fiscal Year	3
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	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	24	[11]
Contractual Obligation, Due in Next Fiscal Year	3	[11]
Contractual Obligation, Due in Second Year	3	[11]
Contractual Obligation, Due in Third Year	2	[11]
Contractual Obligation, Due in Fourth Year	3	[11]
Contractual Obligation, Due in Fifth Year	3	[11]
Contractual Obligation, Due after Fifth Year	10	[11]
GuaranteedLeaseResidualValues [Member] | Pepco Holdings LLC [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	24	[12]
Contractual Obligation, Due in Next Fiscal Year	3	[12]
Contractual Obligation, Due in Second Year	3	[12]
Contractual Obligation, Due in Third Year	2	[12]
Contractual Obligation, Due in Fourth Year	3	[12]
Contractual Obligation, Due in Fifth Year	3	[12]
Contractual Obligation, Due after Fifth Year	10	[12]
GuaranteedLeaseResidualValues [Member] | Potomac Electric Power Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	8	[13]
Contractual Obligation, Due in Next Fiscal Year	1	[13]
Contractual Obligation, Due in Second Year	1	[13]
Contractual Obligation, Due in Third Year	1	[13]
Contractual Obligation, Due in Fourth Year	1	[13]
Contractual Obligation, Due in Fifth Year	1	[13]
Contractual Obligation, Due after Fifth Year	3	[13]
GuaranteedLeaseResidualValues [Member] | Delmarva Power & Light Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	10	[14]
Contractual Obligation, Due in Next Fiscal Year	1	[14]
Contractual Obligation, Due in Second Year	1	[14]
Contractual Obligation, Due in Third Year	1	[14]
Contractual Obligation, Due in Fourth Year	1	[14]
Contractual Obligation, Due in Fifth Year	1	[14]
Contractual Obligation, Due after Fifth Year	5	[14]
GuaranteedLeaseResidualValues [Member] | Atlantic City Electric Company [Member]
Guarantor Obligations [Line Items]
Contractual Obligation	6	[15]
Contractual Obligation, Due in Next Fiscal Year	1	[15]
Contractual Obligation, Due in Second Year	1	[15]
Contractual Obligation, Due in Third Year	0	[15]
Contractual Obligation, Due in Fourth Year	1	[15]
Contractual Obligation, Due in Fifth Year	1	[15]
Contractual Obligation, Due after Fifth Year	$ 2	[15]
[1]	_
[2]	_
[3]	_
[4]	_
[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 bond
[7]	)Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bond
[8]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bond
[9]	(a)Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bond
[10]	)Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bond
[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 $61 million, $19 million of which is a guarantee by Pepco, $26 million by DPL and $16 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]	(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 $61 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 remot
[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 $19 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 Pepco believes the likelihood of payments being required under the guarantees is remot
[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 $26 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 DPL believes the likelihood of payments being required under the guarantees is remot
[15]	)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 ACE believes the likelihood of payments being required under the guarantees is remot

Commitments and Contingencies_4

Commitments and Contingencies Commitments and Contingencies - Schedule of Minimum Future Operating Lease Payments (Details) - USD ($) $ in Millions		Dec. 31, 2018		Nov. 30, 2016
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[1],[2]	$ 140
2,019	[1],[2]	149
2,020	[1],[2]	143
2,021	[1],[2]	126
2,022	[1],[2]	97
Remaining Years	[1],[2]	723
Total minimum future lease payments	[1],[2]	1,378
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[1],[2]	33
2,019	[1],[2]	46
2,020	[1],[2]	46
2,021	[1],[2]	47
2,022	[1],[2]	46
Remaining Years	[1],[2]	545
Total minimum future lease payments	[1],[2]	763
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2],[3]	7
2,019	[2],[3]	5
2,020	[2],[3]	4
2,021	[2],[3]	4
2,022	[2],[3]	3
Remaining Years	[2],[3]	0
Total minimum future lease payments	[2],[3]	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		3
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2],[3]	5
2,019	[2],[3]	5
2,020	[2],[3]	5
2,021	[2],[3]	5
2,022	[2],[3]	5
Remaining Years	[2],[3]	0
Total minimum future lease payments	[2],[3]	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		35	[2],[3],[4],[5]	$ 26
2,019		35	[2],[3],[4],[5]	28
2,020		33	[2],[3],[4],[5]	28
2,021		18	[2],[3],[4],[5]	$ 14
2,022	[2],[3],[4],[5]	3
Remaining Years	[2],[3],[4],[5]	19
Total minimum future lease payments	[2],[3],[4],[5]	143
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]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	48
2,019	[2]	46
2,020	[2]	43
2,021	[2]	42
2,022	[2]	39
Remaining Years	[2]	159
Total minimum future lease payments	[2]	377
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	11
2,019	[2]	10
2,020	[2]	9
2,021	[2]	8
2,022	[2]	8
Remaining Years	[2]	40
Total minimum future lease payments	[2]	86
Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2],[3]	14
2,019	[2],[3]	13
2,020	[2],[3]	12
2,021	[2],[3]	12
2,022	[2],[3]	10
Remaining Years	[2],[3]	35
Total minimum future lease payments	[2],[3]	96
Delmarva Power & Light Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		1
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2,018	[2]	7
2,019	[2]	6
2,020	[2]	5
2,021	[2]	5
2,022	[2]	4
Remaining Years	[2]	5
Total minimum future lease payments	[2]	$ 32
[1]	)Excludes Generation’s contingent operating lease payments associated with contracted generation agreement
[2]	)Includes amounts related to shared use land arrangement
[3]	)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 2019 - 2023, was $3 million, $5 million, $1 million and $1 million respectivel
[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 $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel
[5]	)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 $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel

Commitments and Contingencies_5

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				$ 670	$ 709	$ 777
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense	[1]			558	578	667
Long Term Contract For Purchase Of Electric Power Capacity			$ 604	493	508	604
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				7	9	15
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				10	9	7
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				35	32	22
Pepco Holdings LLC [Member] | Successor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense			$ 49	48	63
Pepco Holdings LLC [Member] | Predecessor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense		$ 12
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				10	11	8
Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				13	16	15
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Lease and rental expense				$ 8	$ 14	$ 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 $493 million, $508 million and $604 million during 2018, 2017 and 2016, respectively. Excludes contract amortization associated with purchase accounting and contract acquisition

Commitments and Contingencies_6

Commitments and Contingencies Commitments and Contingencies - Settlement Agreements (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2014	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Nontrade Receivables, Current	[1]		$ 124	$ 94
Nontrade Receivables, Noncurrent	[2]		15	15
Accounts Payable, Other, Current	[1],[3]		(17)	$ (11)
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Spent Nuclear Fuel Storage Reimbursement	[4]		1,274
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[4],[5]		$ 1,100
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, oth
[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 CEN
[5]	)Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Cree

Commitments and Contingencies_7

Commitments and Contingencies Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 496	$ 466
Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	356	315
Exelon Generation Co L L C [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	108	117
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	329	285
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	327	283
PECO Energy Co [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	30
PECO Energy Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	25	28
Baltimore Gas and Electric Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	5	5
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	4	4
Pepco Holdings LLC [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	29
Pepco Holdings LLC [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Potomac Electric Power Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	25	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 & Light Company [Member] | Total Accrual For Environmental Loss Contingencies [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Delmarva Power & Light Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
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

Supplemental Financial Inform_3

Supplemental Financial Information 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			$ 919	$ 898	$ 753
Property				557	545	483
Payroll				247	230	226
Other				60	58	114
Total taxes other than income				1,783	1,731	1,576
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			114	126	122
Property				273	269	246
Payroll				130	121	117
Other				39	39	21
Total taxes other than income				556	555	506
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			243	240	242
Property				30	28	27
Payroll				27	26	28
Other				11	2	(4)
Total taxes other than income				311	296	293
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			131	125	136
Property				15	14	13
Payroll				16	15	15
Other				1	0	0
Total taxes other than income				163	154	164
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			94	89	85
Property				143	132	123
Payroll				17	15	17
Other				0	4	4
Total taxes other than income				254	240	229
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			337	318
Property				94	101
Payroll				24	26
Other				0	7
Total taxes other than income				455	452
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]		$ 253
Property			73
Payroll			23
Other			5
Total taxes other than income			$ 354
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]	$ 78
Property		18
Payroll		8
Other		1
Total taxes other than income		$ 105
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			316	300	312
Property				58	62	53
Payroll				5	6	8
Other				0	3	4
Total taxes other than income				379	371	377
Delmarva Power & Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			21	18	18
Property				32	32	31
Payroll				3	4	5
Other				0	3	1
Total taxes other than income				56	57	55
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			0	0	0
Property				3	3	3
Payroll				2	2	3
Other				0	1	1
Total taxes other than income				$ 5	$ 6	$ 7
[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 in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Supplemental Financial Inform_4

Supplemental Financial Information 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1]			$ 506	$ 488	$ 237
Net realized income on NDT funds - Non-regulatory agreement units	[1]			302	209	126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units				(715)	455	216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement				(483)	521	194
Net unrealized income (losses) on pledged assets				(8)	(10)	(1)
Regulatory offset to NDT fund-related activities	[2]			171	(724)	(372)
Total decommissioning-related activities				(227)	939	400
Investment income (loss)				43	8	17
Long-term lease income						4
Interest income (expense) related to uncertain income tax positions				5	3	13
Benefit (penalty) related to uncertain income tax positions	[3]				2	(106)
AFUDC—Equity				69	73	64
Non-service net periodic benefit cost				(47)	(109)	(116)
Loss on debt extinguishment						(3)
Other				45	31	24
Other, net				(112)	947	297
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	[1]			506	488	237
Net realized income on NDT funds - Non-regulatory agreement units	[1]			302	209	126
Net unrealized gains (losses) on NDT funds - Regulatory agreement units				(715)	455	216
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement				(483)	521	194
Net unrealized income (losses) on pledged assets				(8)	(10)	(1)
Regulatory offset to NDT fund-related activities	[2]			171	(724)	(372)
Total decommissioning-related activities				(227)	939	400
Investment income (loss)				32	6	8
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				1	(1)	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				0	0	0
Loss on debt extinguishment						(2)
Other				16	4	(5)
Other, net				(178)	948	401
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				0	0	0
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	(86)
AFUDC—Equity				19	12	14
Loss on debt extinguishment						0
Other				14	10	7
Other, net				33	22	(65)
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	(1)
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				7	9	8
Loss on debt extinguishment						0
Other				0	0	1
Other, net				8	9	8
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	2
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				18	16	19
Loss on debt extinguishment						0
Other				0	0	0
Other, net				19	16	21
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				4	2
Interest income (expense) related to uncertain income tax positions				0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0
AFUDC—Equity				25	36
Other				14	16
Other, net				43	54
Pepco Holdings LLC [Member] | Successor [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)			$ 1
Long-term lease income			0
Interest income (expense) related to uncertain income tax positions			(1)
Benefit (penalty) related to uncertain income tax positions	[3]		0
AFUDC—Equity			23
Loss on debt extinguishment			0
Other			21
Other, net			$ 44
Pepco Holdings LLC [Member] | Predecessor [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)		$ 0
Long-term lease income		0
Interest income (expense) related to uncertain income tax positions		0
Benefit (penalty) related to uncertain income tax positions	[3]	0
AFUDC—Equity		7
Loss on debt extinguishment		0
Other		(11)
Other, net		$ (4)
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				2	1	1
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	1
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				22	23	19
Loss on debt extinguishment						0
Other				7	8	15
Other, net				31	32	36
Delmarva Power & Light Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				1	0	0
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				2	7	5
Loss on debt extinguishment						0
Other				7	7	8
Other, net				10	14	13
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Investment income (loss)				0	0	1
Long-term lease income						0
Interest income (expense) related to uncertain income tax positions				0	0	0
Benefit (penalty) related to uncertain income tax positions	[3]				0	0
AFUDC—Equity				1	6	6
Loss on debt extinguishment						0
Other				1	1	2
Other, net				$ 2	$ 7	$ 9
[1]	Includes investment income and realized gains and losses on sales of investments within the NDT funds.
[2]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246MTE0OEY2QkJBNTBGNUFBQ0IwMkE4RTI0QzY3MTNDRUEM}
[3]	See Note 14—Income Taxes for additional information on the penalty related to the Tax Court’s decision on Exelon’s like-kind exchange tax position.

Supplemental Financial Inform_5

Supplemental Financial Information Supplemental Financial Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended		12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 23, 2016	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Depreciation, amortization and accretion
Depreciation							$ 3,740		$ 3,293		$ 3,477
Amortization of Regulatory Asset							555		478		407
Amortization of Intangible Assets							(109)		(237)		(336)
Amortization of Nuclear Fuel Lease	[1]						1,115		1,096		1,159
Asset Retirement Obligation, Accretion Expense	[2]						489		468		446
Total depreciation, amortization and accretion							5,971		5,427		5,576
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							1,421		2,430		1,340
Income taxes (net of refunds)							95		540		(441)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							583		643		619
Gain (loss) on equity method investments							28		32		24
Provision for uncollectible accounts							159		125		155
Provision for excess and obsolete inventory							24		56		12
Stock-based compensation costs							75		88		111
Other decommissioning related-activity							(2)	[3]	(313)	[4]	(384)	[5]
Energy-related options							10	[6]	7	[7]	(11)	[8]
Amortization of regulatory asset related to debt costs							8		9		9
Amortization of rate stabilization deferral							14		(10)		76
Amortization of debt fair value adjustment							(15)		(18)		(11)
Merger-related commitments							0	[9]	0	[10]	558	[11],[12]
Severance costs							35		35		99
Amortization of debt costs							36		64		35
Discrete impacts from EIMA and FEJA							28	[13]	(52)	[14]	8	[15]
Vacation accrual adjustment	[16]								68
Long-term incentive plan							140		109		70
Change in environmental liabilities									44
Lower of cost or market inventory adjustment											37
Baltimore City conduit lease settlement											(28)
Cash Working Capital order											(13)
Asset Retirement Obligation, Revision of Estimate							20				2
Other							(19)		(30)		(35)
Total other non-cash operating activities							1,124		721		1,333
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(69)		42		(128)
Change in PPE related to ARO update		$ (107)				$ 191	(107)		29		191
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		95
Noncash or Part Noncash Divestiture, Amount of Consideration Received	[12]										37
Dividends on stock compensation							6		7		6
Acquisition of land							3
Assumption of member purchase liability							154		208		6,923
Dissolution of financing trust due to long-term debt retirement									8
Fair value adjustment of long-term debt due to retirement									(5)
Allowance for Doubtful Accounts Receivable, Write-offs											5
Fitzpatrick [Member]
Non-cash investing and financing activities:
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[17]										(54)
Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Depreciation							1,748		1,409		1,835
Amortization of Regulatory Asset							0		0		0
Amortization of Intangible Assets							63		83		79
Amortization of Nuclear Fuel Lease	[1]						1,115		1,096		1,159
Asset Retirement Obligation, Accretion Expense	[2]						489		468		446
Total depreciation, amortization and accretion							3,415		3,056		3,519
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							369		391		339
Income taxes (net of refunds)							746		337		435
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							204		227		218
Gain (loss) on equity method investments							30		33		25
Provision for uncollectible accounts							48		38		19
Provision for excess and obsolete inventory							20		51		6
Other decommissioning related-activity							(2)	[3]	(313)	[4]	(384)	[5]
Energy-related options							10	[6]	7	[7]	(11)	[8]
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)		(12)		(11)
Merger-related commitments							0	[9]	0	[10]	53	[11],[12]
Severance costs							9		31		22
Amortization of debt costs							14		37		17
Vacation accrual adjustment	[16]								35
Change in environmental liabilities									44
Lower of cost or market inventory adjustment											36
Asset Retirement Obligation, Revision of Estimate		203	$ 84		$ 138		0				0
Other							(23)		4		25
Total other non-cash operating activities							298		112		15
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(199)		73		50
Change in PPE related to ARO update		(130)				191	(130)		29		191
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									16		95
Noncash or Part Noncash Divestiture, Amount of Consideration Received	[12]										37
Acquisition of land							0
Assumption of member purchase liability							154		208		293
Fair value of pension and OPEB obligation transferred in connection with FitzPatrick									33
Exelon Generation Co L L C [Member] | noncash member [Member]
Non-cash investing and financing activities:
Fair value of net assets contributed (distributed) in connection with the PHI merger, net of cash											119
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Non-cash investing and financing activities:
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	[17]										(54)
Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Depreciation							820		777		708
Amortization of Regulatory Asset							120		73		67
Amortization of Intangible Assets							7		7		7
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							940		850		775
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							332		307		298
Income taxes (net of refunds)							(153)		83		(444)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							177		176		166
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							40		34		41
Provision for excess and obsolete inventory							3		3		4
Amortization of regulatory asset related to debt costs							3		4		4
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							5		5		4
Discrete impacts from EIMA and FEJA							28	[13]	(52)	[14]	8	[15]
Vacation accrual adjustment	[16]								12
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(14)		6		(12)
Total other non-cash operating activities							242		164		215
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							11		(61)		(91)
Change in PPE related to ARO update		7				0	7		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Contribution of Property									21	[18]	158	[19]
Acquisition of land							0
PECO Energy Co [Member]
Depreciation, amortization and accretion
Depreciation							274		261		244
Amortization of Regulatory Asset							27		25		26
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							301		286		270
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							125		103		104
Income taxes (net of refunds)							(2)		47		64
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							18		29		33
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							33		26		30
Provision for excess and obsolete inventory							0		0		0
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							2		2		3
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											1
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(3)		(4)		(3)
Total other non-cash operating activities							51		54		65
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							(12)		22		(11)
Change in PPE related to ARO update		0				0	0		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Depreciation							335		312		299
Amortization of Regulatory Asset							148		161		124
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							483		473		423
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							94		96		92
Income taxes (net of refunds)							14		(2)		31
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							59		62		67
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							10		8		1
Provision for excess and obsolete inventory							0		0		0
Amortization of regulatory asset related to debt costs							0		0		0
Amortization of rate stabilization deferral							0		7		81
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	0	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							1		2		1
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Baltimore City conduit lease settlement											(28)
Cash Working Capital order											(13)
Asset Retirement Obligation, Revision of Estimate							0				0
Other							(12)		(14)		(21)
Total other non-cash operating activities							58		65		88
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							50		23		(86)
Change in PPE related to ARO update		1				0	1		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Dissolution of financing trust due to long-term debt retirement									8
Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Depreciation							480		457
Amortization of Regulatory Asset							260		218
Asset Retirement Obligation, Accretion Expense	[2]						0		0
Total depreciation, amortization and accretion							740		675
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							250		236
Income taxes (net of refunds)							(32)		(144)
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							67		94
Gain (loss) on equity method investments							(1)		(1)
Provision for uncollectible accounts							28		19
Provision for excess and obsolete inventory							0		2
Amortization of regulatory asset related to debt costs							4		4
Amortization of rate stabilization deferral							14		(17)
Amortization of debt fair value adjustment							(3)		(6)
Merger-related commitments							5	[9]	(8)	[10]
Severance costs							0		3
Amortization of debt costs							3		4
Vacation accrual adjustment	[16]								8
Change in environmental liabilities									0
Other							6		(28)
Total other non-cash operating activities							143		58
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							93		(12)
Change in PPE related to ARO update		15					15		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0
Acquisition of land							3
Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, amortization and accretion
Depreciation						325
Amortization of Regulatory Asset						190
Asset Retirement Obligation, Accretion Expense	[2]					0
Total depreciation, amortization and accretion						515
Cash paid (refunded) during the year:
Interest (net of amount capitalized)						209
Income taxes (net of refunds)						258
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs						86
Gain (loss) on equity method investments						0
Provision for uncollectible accounts						65
Provision for excess and obsolete inventory						1
Amortization of regulatory asset related to debt costs						3
Amortization of rate stabilization deferral						(5)
Amortization of debt fair value adjustment						0
Merger-related commitments	[11],[12]					317
Severance costs						56
Amortization of debt costs						1
Lower of cost or market inventory adjustment						0
Asset Retirement Obligation, Revision of Estimate						2	20
Other						(11)
Total other non-cash operating activities						515
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid						21
Change in PPE related to ARO update						0					0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired						0
Fair value of net assets contributed (distributed) in connection with the PHI merger, net of cash	[12],[20]					127
Fair value of pension obligation transferred in connection with the PHI Merger, net of cash	[12],[20]					53
Pepco Holdings LLC [Member] | Successor [Member] | noncash member [Member]
Other non-cash operating activities:
Merger-related commitments						33
Non-cash investing and financing activities:
Assumption of member purchase liability						29
Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, amortization and accretion
Depreciation				$ 94
Amortization of Regulatory Asset				58
Asset Retirement Obligation, Accretion Expense	[2]			0
Total depreciation, amortization and accretion				152
Cash paid (refunded) during the year:
Interest (net of amount capitalized)				43
Income taxes (net of refunds)				11
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs				23
Gain (loss) on equity method investments				0
Provision for uncollectible accounts				16
Provision for excess and obsolete inventory				1
Stock-based compensation costs				3
Amortization of regulatory asset related to debt costs				1
Amortization of rate stabilization deferral				5
Amortization of debt fair value adjustment				0
Merger-related commitments	[11],[12]			0
Severance costs				0
Amortization of debt costs				0
Lower of cost or market inventory adjustment				0
Asset Retirement Obligation, Revision of Estimate				0
Other				(3)
Total other non-cash operating activities				46
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid				11
Change in PPE related to ARO update				0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Depreciation							218		203		175
Amortization of Regulatory Asset							167		118		120
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							385		321		295
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							123		114		118
Income taxes (net of refunds)							41		(104)		216
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							15		25		31
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							11		8		29
Provision for excess and obsolete inventory							0		1		3
Amortization of regulatory asset related to debt costs							2		2		2
Amortization of rate stabilization deferral							14		(17)		(12)
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	(6)	[10]	125	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							2		2		0
Vacation accrual adjustment	[16]								8
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							22				0
Other							(6)		(13)		(3)
Total other non-cash operating activities							60		(6)		175
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							20		5		27
Change in PPE related to ARO update		12				0	12		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Potomac Electric Power Company [Member] | noncash member [Member]
Other non-cash operating activities:
Merger-related commitments											33
Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Depreciation							131		124		110
Amortization of Regulatory Asset							51		43		47
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							182		167		157
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							56		49		47
Income taxes (net of refunds)							(6)		(49)		115
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							6		13		18
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							6		3		23
Provision for excess and obsolete inventory							0		1		1
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		2
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							5	[9]	(2)	[10]	82	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							0		0		0
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							(1)				1
Other							7		(7)		(14)
Total other non-cash operating activities							24		9		114
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							22		4		(12)
Change in PPE related to ARO update		2				0	2		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							0
Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Depreciation							94		89		82
Amortization of Regulatory Asset							42		57		83
Asset Retirement Obligation, Accretion Expense	[2]						0		0		0
Total depreciation, amortization and accretion							136		146		165
Cash paid (refunded) during the year:
Interest (net of amount capitalized)							61		59		62
Income taxes (net of refunds)							(12)		(2)		200
Other non-cash operating activities:
Pension and non-pension postretirement benefit costs							12		13		15
Gain (loss) on equity method investments							0		0		0
Provision for uncollectible accounts							11		8		32
Provision for excess and obsolete inventory							0		0		1
Amortization of regulatory asset related to debt costs							1		1		1
Amortization of rate stabilization deferral							0		0		0
Amortization of debt fair value adjustment							0		0		0
Merger-related commitments							0	[9]	0	[10]	110	[11],[12]
Severance costs							0		0		0
Amortization of debt costs							1		1		0
Vacation accrual adjustment	[16]								0
Change in environmental liabilities									0
Lower of cost or market inventory adjustment											0
Asset Retirement Obligation, Revision of Estimate							(1)				2
Other							0		(6)		(6)
Total other non-cash operating activities							24		17		155
Non-cash investing and financing activities:
Increase (decrease) in capital expenditures not paid							46		(13)		11
Change in PPE related to ARO update		$ 1				0	1		0		0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired									0		0
Acquisition of land							3
Other Intangible Assets [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							58		57		52
Other Intangible Assets [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							49		48		44
Other Intangible Assets [Member] | Commonwealth Edison Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | PECO Energy Co [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Baltimore Gas and Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets						$ 0
Other Intangible Assets [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets				$ 0
Other Intangible Assets [Member] | Potomac Electric Power Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Delmarva Power & Light Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Other Intangible Assets [Member] | Atlantic City Electric Company [Member]
Depreciation, amortization and accretion
Amortization of Intangible Assets							0		0		0
Unamortized Energy Contracts [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	[21]						14		35		35
Unamortized Energy Contracts [Member] | Exelon Generation Co L L C [Member]
Depreciation, amortization and accretion
Amortization of Power Contracts Emission Credits	[21]						$ 14		$ 35		$ 35
[1]	Included in Purchased power and fuel expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[3]	Includes the elimination of decommissioning-related activities 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]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVlYzRiNDIxOTkxNDRkN2ViNWYzYTRhOTVmMjFkNDYzfFRleHRTZWxlY3Rpb246ODE3Q0FGRTQ3ODgzNTMyQkFDNzc4ODYwRDFBNDI1OTMM}
[5]	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.
[6]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[7]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[8]	Includes option premiums reclassified to realized at the settlement of the underlying contracts and recorded to results of operations.
[9]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[10]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[11]	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.
[12]	See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[13]	Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 4 — Regulatory Matters for additional information.
[14]	Reflects the change in ComEd's distribution and energy efficiency formula rates . See Note 4 — Regulatory Matters for additional information.
[15]	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 4 — Regulatory Matters for additional information.
[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]	Reflects the transfer of nuclear fuel to Entergy under the cost reimbursement provisions of the FitzPatrick acquisition agreements. See Note 5 - Mergers, Acquisitions and Dispositions for additional information.
[18]	See Note 14 — Income Taxes for additional information on the like-kind exchange tax position
[19]	See Note 14 — Income Taxes for additional information on the like-kind exchange tax position.
[20]	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.
[21]	Included in Operating revenues or Purchased power and fuel in the Registrants’ Consolidated Statements of Operations and Comprehensive Income

Supplemental Financial Inform_6

Supplemental Financial Information Supplemental Financial Information - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 24, 2016	Mar. 23, 2016	Dec. 31, 2015
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		$ 1,349	$ 898	$ 635			$ 6,502
Restricted cash		247	207	253			205
Restricted cash included in other long-term assets		185	85	26			5
Total cash, cash equivalents and restricted cash		1,781	1,190	914			6,712
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	1,656	1,858
Allowance for uncollectible accounts	[2]	(319)	(322)
Purchased Receivables [Abstract]
Purchased receivables		313	298
Allowance for uncollectible accounts	[3]	(34)	(31)
Purchased receivables, net		279	267
Investments [Abstract]
Total equity method investments		267	297
Equity investments without readily determinable fair values		72	62
Other Investments		2
Total Investments		625	640
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	1,191	978
Taxes accrued		412	373
Interest accrued		334	328
Severance accrued		44	58
Other accrued expenses		131	100
Total accrued expenses		2,112	1,837
Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	14	14
Bloom Energy
Investments [Abstract]
Equity Method Investments		180	206
NET Power
Investments [Abstract]
Equity Method Investments		70	76
Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		3	1
Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	244	244
Other available for sale investments
Investments [Abstract]
Available for sale investments		40	37
Exelon Generation Co L L C [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		750	416	290			431
Restricted cash		153	138	158			123
Restricted cash included in other long-term assets		0	0	0			2
Total cash, cash equivalents and restricted cash		903	554	448			556
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	965	1,017
Allowance for uncollectible accounts	[2]	(104)	(114)
Investments [Abstract]
Total equity method investments		251	283
Equity investments without readily determinable fair values		72	62
Other Investments		2
Total Investments		414	433
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	479	407
Taxes accrued		226	444
Interest accrued		77	78
Severance accrued		26	30
Other accrued expenses		90	63
Total accrued expenses		898	1,022
Exelon Generation Co L L C [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Exelon Generation Co L L C [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		180	206
Exelon Generation Co L L C [Member] | NET Power
Investments [Abstract]
Equity Method Investments		70	76
Exelon Generation Co L L C [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		1	1
Exelon Generation Co L L C [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	49	51
Exelon Generation Co L L C [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		40	37
Commonwealth Edison Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		135	76	56			67
Restricted cash		29	5	2			2
Restricted cash included in other long-term assets		166	63	0			0
Total cash, cash equivalents and restricted cash		330	144	58			69
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	223	242
Allowance for uncollectible accounts	[2]	(81)	(73)
Purchased Receivables [Abstract]
Purchased receivables		94	87
Allowance for uncollectible accounts	[3]	(17)	(14)
Purchased receivables, net		77	73
Investments [Abstract]
Total equity method investments		6	6
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		6	6
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	187	158
Taxes accrued		71	60
Interest accrued		105	102
Severance accrued		2	2
Other accrued expenses		8	5
Total accrued expenses		373	327
Commonwealth Edison Co [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	6	6
Commonwealth Edison Co [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Commonwealth Edison Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Commonwealth Edison Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
PECO Energy Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		130	271	63			295
Restricted cash		5	4	4			3
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		135	275	67			298
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	114	162
Allowance for uncollectible accounts	[2]	(61)	(56)
Purchased Receivables [Abstract]
Purchased receivables		74	70
Allowance for uncollectible accounts	[3]	(5)	(5)
Purchased receivables, net		69	65
Investments [Abstract]
Total equity method investments		8	8
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		25	25
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	49	64
Taxes accrued		28	15
Interest accrued		33	33
Severance accrued		0	0
Other accrued expenses		3	2
Total accrued expenses		113	114
PECO Energy Co [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	8	8
PECO Energy Co [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
PECO Energy Co [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	17	17
PECO Energy Co [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Baltimore Gas and Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7	17	23			9
Restricted cash		6	1	24			24
Restricted cash included in other long-term assets		0	0	3			3
Total cash, cash equivalents and restricted cash		13	18	50			36
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	168	205
Allowance for uncollectible accounts	[2]	(20)	(24)
Purchased Receivables [Abstract]
Purchased receivables		61	58
Allowance for uncollectible accounts	[3]	(3)	(3)
Purchased receivables, net		58	55
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		5	5
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	68	58
Taxes accrued		46	71
Interest accrued		39	34
Severance accrued		0	0
Other accrued expenses		2	1
Total accrued expenses		155	164
Baltimore Gas and Electric Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Baltimore Gas and Electric Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Baltimore Gas and Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	5	5
Baltimore Gas and Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Pepco Holdings LLC [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		124	30
Restricted cash		43	42
Restricted cash included in other long-term assets		19	23
Total cash, cash equivalents and restricted cash		186	95	236
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	186	232
Allowance for uncollectible accounts	[2]	(53)	(55)
Purchased Receivables [Abstract]
Purchased receivables		84	83
Allowance for uncollectible accounts	[3]	(9)	(9)
Purchased receivables, net		75	74
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		130	132
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	99	106
Taxes accrued		74	61
Interest accrued		50	48
Severance accrued		5	17
Other accrued expenses		28	29
Total accrued expenses		256	261
Pepco Holdings LLC [Member] | Successor [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents				170
Restricted cash				43
Restricted cash included in other long-term assets				23
Total cash, cash equivalents and restricted cash				236	$ 348
Pepco Holdings LLC [Member] | Predecessor [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents						$ 319	26
Restricted cash						11	14
Restricted cash included in other long-term assets						18	18
Total cash, cash equivalents and restricted cash						$ 348	58
Pepco Holdings LLC [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Pepco Holdings LLC [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Pepco Holdings LLC [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	130	132
Pepco Holdings LLC [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Potomac Electric Power Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		16	5	9			5
Restricted cash		37	35	33			2
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		53	40	42			7
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	97	133
Allowance for uncollectible accounts	[2]	(21)	(21)
Purchased Receivables [Abstract]
Purchased receivables		57	56
Allowance for uncollectible accounts	[3]	(5)	(5)
Purchased receivables, net		52	51
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		105	102
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	29	29
Taxes accrued		58	68
Interest accrued		25	23
Severance accrued		0	0
Other accrued expenses		14	17
Total accrued expenses		126	137
Potomac Electric Power Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Potomac Electric Power Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Potomac Electric Power Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	105	102
Potomac Electric Power Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Delmarva Power & Light Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		23	2	46			5
Restricted cash		1	0	0			0
Restricted cash included in other long-term assets		0	0	0			0
Total cash, cash equivalents and restricted cash		24	2	46			5
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	59	68
Allowance for uncollectible accounts	[2]	(13)	(16)
Purchased Receivables [Abstract]
Purchased receivables		8	9
Allowance for uncollectible accounts	[3]	(1)	(1)
Purchased receivables, net		7	8
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		0	0
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	19	17
Taxes accrued		4	4
Interest accrued		8	8
Severance accrued		0	0
Other accrued expenses		8	6
Total accrued expenses		39	35
Delmarva Power & Light Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Delmarva Power & Light Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Delmarva Power & Light Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Delmarva Power & Light Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		0	0
Atlantic City Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7	2	101			3
Restricted cash		4	6	9			12
Restricted cash included in other long-term assets		19	23	23			18
Total cash, cash equivalents and restricted cash		30	31	$ 133			$ 33
Contracts Receivable [Abstract]
Unbilled customer revenues	[1]	30	31
Allowance for uncollectible accounts	[2]	(19)	(18)
Purchased Receivables [Abstract]
Purchased receivables		19	18
Allowance for uncollectible accounts	[3]	(3)	(3)
Purchased receivables, net		16	15
Investments [Abstract]
Total equity method investments		0	0
Equity investments without readily determinable fair values		0	0
Other Investments		0
Total Investments		0	0
Accrued Expenses [Abstract]
Compensation-related accruals	[4]	12	11
Taxes accrued		5	5
Interest accrued		12	12
Severance accrued		0	0
Other accrued expenses		6	5
Total accrued expenses		35	33
Atlantic City Electric Company [Member] | Financing Trusts
Investments [Abstract]
Equity Method Investments	[5]	0	0
Atlantic City Electric Company [Member] | Bloom Energy
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | NET Power
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Other Equity Method Investments
Investments [Abstract]
Equity Method Investments		0	0
Atlantic City Electric Company [Member] | Employee benefit trusts and investments
Investments [Abstract]
Available for sale investments	[6]	0	0
Atlantic City Electric Company [Member] | Other available for sale investments
Investments [Abstract]
Available for sale investments		$ 0	$ 0
[1]	Represents unbilled portion of receivables estimated under Exelon’s unbilled critical accounting policy.
[2]	Includes the estimated allowance for uncollectible accounts on billed customer and other accounts receivable.
[3]	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 a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.
[4]	Primarily includes accrued payroll, bonuses and other incentives, vacation and benefits.
[5]	Includes investments in affiliated financing trusts, which were not consolidated within the financial statements of Exelon and are shown as investments in the Consolidated Balance Sheets. See Note 1 — Significant Accounting Policies for additional information.
[6]	The Registrants’ debt and equity security investments are recorded at fair market value.

Segment Information Segment Inf

Segment Information Segment Information - Narrative (Details)	12 Months Ended
	Dec. 31, 2018Reportable_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 I_2

Segment Information Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended									9 Months Ended		12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Rate-regulated electric revenues														$ 0	$ 0
Rate-regulated natural gas revenues														0	0
Revenues		$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747				$ 35,985	33,565	31,366
Operating revenues from affiliates														0	0
Depreciation and amortization													4,353	3,828	3,936
Operating Expenses	[1]												32,143	29,619	28,106
Interest expense, net													1,554	1,560	1,536
Income (loss) before income taxes													2,232	3,782	1,973
Income taxes		26											120	(126)	753
Net income (loss)													2,084	3,876	1,196
Capital expenditures													7,594	7,584	8,553
Assets	[2]	119,666				116,770							119,666	116,770
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues													4,609	4,428
Rate-regulated natural gas revenues													181	161
Revenues		1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175				4,805	4,679
Operating revenues from affiliates													15	50
Income (loss) before income taxes													432	578
Income taxes													35	217
Net income (loss)													398	362
Capital expenditures													1,375	1,396
Assets	[3]	21,984				21,247							21,984	21,247
Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues												$ 3,463		4,428
Rate-regulated natural gas revenues												92		161
Revenues												3,643		4,679
Operating revenues from affiliates												45	15	50
Income (loss) before income taxes												(58)
Income taxes												3
Net income (loss)											$ (61)	(61)
Capital expenditures												1,008
Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues										$ 1,122
Rate-regulated natural gas revenues										57
Revenues										1,153
Operating revenues from affiliates										0
Income (loss) before income taxes										36
Income taxes										17
Net income (loss)										19
Capital expenditures										273
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues														0	0
Rate-regulated natural gas revenues														0	0
Revenues		5,069	$ 5,278	$ 4,579	$ 5,512	4,657	$ 4,750	$ 4,216	$ 4,878				20,437	18,500	17,757
Operating revenues from affiliates													1,268	1,115	1,439
Income (loss) before income taxes													365	1,455	857
Income taxes													(108)	(1,376)	282
Net income (loss)													443	2,798	550
Capital expenditures													2,242	2,259	3,078
Assets	[4]	47,556				48,457							47,556	48,457
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]												16,155	14,227	13,970
Competitive businesses natural gas revenues	[1]												2,710	2,575	2,146
Competitive businesses other revenues	[1]												303	592	207
Rate-regulated electric revenues	[1]												15,344	14,840	13,869
Rate-regulated natural gas revenues	[1]												1,470	1,333	1,166
Shared service and other revenues	[1]												3	0	7
Revenues	[1]												35,985	33,567	31,365
Operating Segments [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues	[5]													47
Operating Segments [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Revenues	[5]											43
Operating Segments [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Revenues	[5]									0
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													(1)	7	10
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1]												(1,256)	(1,105)	(1,430)
Competitive businesses natural gas revenues	[1]												(8)	0	0
Competitive businesses other revenues	[1]												(5)	(1)	(4)
Rate-regulated electric revenues	[1]												(45)	(29)	(31)
Rate-regulated natural gas revenues	[1]												(20)	(10)	(13)
Shared service and other revenues	[1]												(1,960)	(1,880)	(1,686)
Revenues	[1]												(3,294)	(3,025)	(3,164)
Operating revenues from affiliates	[6]												1	2	5
Depreciation and amortization													0	0	0
Operating Expenses	[1]												(3,341)	(3,026)	(3,164)
Interest expense, net													0	0	0
Income (loss) before income taxes													(1)	(2)	(5)
Income taxes													0	0	0
Net income (loss)													(1)	(2)	(5)
Capital expenditures													0	0	0
Assets		(9,800)				(10,552)							(9,800)	(10,552)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]												(17)	(14)
Rate-regulated natural gas revenues	[7]												0	0
Shared service and other revenues	[7]												(420)	(3)
Revenues	[7]												(437)	(17)
Operating revenues from affiliates													(437)	(19)
Depreciation and amortization													0	(1)
Operating Expenses													(435)	(17)
Interest expense, net													0	(1)
Income (loss) before income taxes													(408)	(404)
Income taxes													(2)	0
Net income (loss)													15	50
Capital expenditures													0	0
Assets		(5,421)				(4,987)							(5,421)	(4,987)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]											(13)
Rate-regulated natural gas revenues	[7]											0
Shared service and other revenues	[7]											0
Revenues	[7]											(13)
Operating revenues from affiliates												(13)
Depreciation and amortization												0
Operating Expenses												(13)
Interest expense, net												0
Income (loss) before income taxes												71
Income taxes												0
Net income (loss)												45
Capital expenditures												0
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]									(4)
Rate-regulated natural gas revenues	[7]									0
Shared service and other revenues	[7]									0
Revenues	[7]									(4)
Operating revenues from affiliates										(4)
Depreciation and amortization										(4)
Operating Expenses										(3)
Interest expense, net										(2)
Income (loss) before income taxes										(118)
Income taxes										0
Net income (loss)										0
Capital expenditures										0
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[8]												17,411	15,332	15,400
Competitive businesses natural gas revenues	[1],[8]												2,718	2,575	2,146
Competitive businesses other revenues	[1],[8]												308	593	211
Rate-regulated electric revenues	[1],[8]												0	0	0
Rate-regulated natural gas revenues	[1],[8]												0	0	0
Shared service and other revenues	[1],[8]												0	0	0
Revenues	[1],[8]												20,437	18,500	17,757
Depreciation and amortization	[8]												1,797	1,457	1,879
Operating Expenses	[1],[8]												19,510	18,001	16,878
Interest expense, net	[8]												432	440	364
Income (loss) before income taxes	[8]												365	1,455	857
Income taxes	[8]												(108)	(1,376)	282
Net income (loss)	[8]												443	2,798	550
Capital expenditures	[8]												2,242	2,259	3,078
Assets	[8]	47,556				48,457							47,556	48,457
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6],[8]												1,269	1,110	1,428
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]												5,882	5,536	5,254
Rate-regulated natural gas revenues	[1]												0	0	0
Shared service and other revenues	[1]												0	0	0
Revenues	[1]												5,882	5,536	5,254
Depreciation and amortization													940	850	775
Operating Expenses	[1]												4,741	4,214	4,056
Interest expense, net													347	361	461
Income (loss) before income taxes													832	984	679
Income taxes													168	417	301
Net income (loss)													664	567	378
Capital expenditures													2,126	2,250	2,734
Assets		31,213				29,726							31,213	29,726
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]												27	15	15
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]												2,470	2,375	2,531
Rate-regulated natural gas revenues	[1]												568	495	463
Shared service and other revenues	[1]												0	0	0
Revenues	[1]												3,038	2,870	2,994
Depreciation and amortization													301	286	270
Operating Expenses	[1]												2,452	2,215	2,292
Interest expense, net													129	126	123
Income (loss) before income taxes													466	538	587
Income taxes													6	104	149
Net income (loss)													460	434	438
Capital expenditures													849	732	686
Assets		10,642				10,170							10,642	10,170
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]												8	7	8
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]												2,428	2,489	2,609
Rate-regulated natural gas revenues	[1]												741	687	624
Shared service and other revenues	[1]												0	0	0
Revenues	[1]												3,169	3,176	3,233
Depreciation and amortization													483	473	423
Operating Expenses	[1]												2,696	2,562	2,683
Interest expense, net													106	105	103
Income (loss) before income taxes													387	525	468
Income taxes													74	218	174
Net income (loss)													313	307	294
Capital expenditures													959	882	934
Assets		9,716				9,104							9,716	9,104
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]												29	16	21
Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Revenues												3,643
Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Revenues										1,153
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[9]												0	0
Competitive businesses natural gas revenues	[1],[9]												0	0
Competitive businesses other revenues	[1],[9]												0	0
Rate-regulated electric revenues	[1],[7],[9]												4,609	4,469
Rate-regulated natural gas revenues	[1],[7],[9]												181	161
Shared service and other revenues	[1],[7],[9]												15	49
Revenues	[1],[7],[9]												4,805	4,679
Depreciation and amortization	[9]												740	675
Operating Expenses	[1],[9]												4,156	3,911
Interest expense, net	[9]												261	245
Income (loss) before income taxes	[9]												432	578
Income taxes	[9]												35	217
Net income (loss)	[9]												398	362
Capital expenditures	[9]												1,375	1,396
Assets		21,984				21,247							21,984	21,247
Pepco Holdings LLC [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[9]											0
Competitive businesses natural gas revenues	[1],[9]											0
Competitive businesses other revenues	[1],[9]											0
Rate-regulated electric revenues	[1],[7],[9]											3,506
Rate-regulated natural gas revenues	[1],[7],[9]											92
Shared service and other revenues	[1],[7],[9]											45
Revenues	[1],[7],[9]											3,643
Depreciation and amortization	[9]											515
Operating Expenses	[1],[9]											3,549
Interest expense, net	[9]											195
Income (loss) before income taxes	[9]											(58)
Income taxes	[9]											3
Net income (loss)	[9]											(61)
Capital expenditures	[9]											1,008
Assets	[9]	21,984				21,247							21,984	21,247
Pepco Holdings LLC [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]									1,096
Rate-regulated natural gas revenues	[7]									57
Shared service and other revenues	[7]									0
Revenues	[7]									1,153
Depreciation and amortization										152
Operating Expenses										1,048
Interest expense, net										65
Income (loss) before income taxes										36
Income taxes										17
Net income (loss)										19
Capital expenditures										273
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6],[9]												15	50
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6],[9]											45
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										0
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]												2,239	2,158
Rate-regulated natural gas revenues	[7]												0	0
Shared service and other revenues	[7]												0	0
Revenues	[7]												2,239	2,158
Depreciation and amortization													385	321
Operating Expenses													1,919	1,760
Interest expense, net													128	121
Income (loss) before income taxes													223	310
Income taxes													13	105
Net income (loss)													210	205
Capital expenditures													656	628
Assets		8,299				7,832							8,299	7,832
Potomac Electric Power Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]											1,675
Rate-regulated natural gas revenues	[7]											0
Shared service and other revenues	[7]											0
Revenues	[7]											1,675
Depreciation and amortization												224
Operating Expenses												1,577
Interest expense, net												98
Income (loss) before income taxes												36
Income taxes												26
Net income (loss)												10
Capital expenditures												489
Potomac Electric Power Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]									511
Rate-regulated natural gas revenues	[7]									0
Shared service and other revenues	[7]									0
Revenues	[7]									511
Depreciation and amortization										71
Operating Expenses										443
Interest expense, net										29
Income (loss) before income taxes										47
Income taxes										15
Net income (loss)										32
Capital expenditures										97
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													6	6
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates												4
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										1
Delmarva Power & Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]												1,151	1,139
Rate-regulated natural gas revenues	[7]												181	161
Shared service and other revenues	[7]												0	0
Revenues	[7]												1,332	1,300
Depreciation and amortization													182	167
Operating Expenses													1,143	1,071
Interest expense, net													58	51
Income (loss) before income taxes													142	192
Income taxes													22	71
Net income (loss)													120	121
Capital expenditures													364	428
Assets		4,588				4,357							4,588	4,357
Delmarva Power & Light Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]											850
Rate-regulated natural gas revenues	[7]											92
Shared service and other revenues	[7]											0
Revenues	[7]											942
Depreciation and amortization												120
Operating Expenses												952
Interest expense, net												38
Income (loss) before income taxes												(30)
Income taxes												5
Net income (loss)												(35)
Capital expenditures												277
Delmarva Power & Light Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]									279
Rate-regulated natural gas revenues	[7]									56
Shared service and other revenues	[7]									0
Revenues	[7]									335
Depreciation and amortization										37
Operating Expenses										284
Interest expense, net										12
Income (loss) before income taxes										43
Income taxes										17
Net income (loss)										26
Capital expenditures										72
Delmarva Power & Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													8	8
Delmarva Power & Light Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates												5
Delmarva Power & Light Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]												1,236	1,186
Rate-regulated natural gas revenues	[7]												0	0
Shared service and other revenues	[7]												0	0
Revenues	[7]												1,236	1,186
Depreciation and amortization													136	146
Operating Expenses													1,087	1,029
Interest expense, net													64	61
Income (loss) before income taxes													87	103
Income taxes													12	26
Net income (loss)													75	77
Capital expenditures													335	312
Assets		3,699				3,445							3,699	3,445
Atlantic City Electric Company [Member] | Operating Segments [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]											989
Rate-regulated natural gas revenues	[7]											0
Shared service and other revenues	[7]											0
Revenues	[7]											989
Depreciation and amortization												128
Operating Expenses												1,000
Interest expense, net												47
Income (loss) before income taxes												(51)
Income taxes												(5)
Net income (loss)												(47)
Capital expenditures												218
Atlantic City Electric Company [Member] | Operating Segments [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]									268
Rate-regulated natural gas revenues	[7]									0
Shared service and other revenues	[7]									0
Revenues	[7]									268
Depreciation and amortization										37
Operating Expenses										251
Interest expense, net										15
Income (loss) before income taxes										5
Income taxes										1
Net income (loss)										5
Capital expenditures										93
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													3	2
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates												2
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates										1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[1],[10]												0	0	0
Competitive businesses natural gas revenues	[1],[10]												0	0	0
Competitive businesses other revenues	[1],[10]												0	0	0
Rate-regulated electric revenues	[1],[10]												0	0	0
Rate-regulated natural gas revenues	[1],[10]												0	0	0
Shared service and other revenues	[1],[10]												1,948	1,831	1,648
Revenues	[1],[10]												1,948	1,831	1,648
Depreciation and amortization	[10]												92	87	74
Operating Expenses	[1],[10]												1,929	1,742	1,812
Interest expense, net	[10]												279	283	290
Income (loss) before income taxes	[10]												(249)	(296)	(555)
Income taxes	[10]												(55)	294	(156)
Net income (loss)	[10]												(193)	(590)	(398)
Capital expenditures	[10]												43	65	113
Assets	[10]	8,355				8,618							8,355	8,618
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7],[11]												0	0
Rate-regulated natural gas revenues	[7],[11]												0	0
Shared service and other revenues	[7],[11]												435	52
Revenues	[7],[11]												435	52
Depreciation and amortization	[11]												37	42
Operating Expenses	[11]												442	68
Interest expense, net	[11]												11	13
Income (loss) before income taxes	[11]												388	377
Income taxes	[11]												(10)	15
Net income (loss)	[11]												(22)	(91)
Capital expenditures	[11]												20	28
Assets	[11]	$ 10,819				$ 10,600							10,819	10,600
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7],[11]											5
Rate-regulated natural gas revenues	[7],[11]											0
Shared service and other revenues	[7],[11]											45
Revenues	[7],[11]											50
Depreciation and amortization	[11]											43
Operating Expenses	[11]											33
Interest expense, net	[11]											12
Income (loss) before income taxes	[11]											(84)
Income taxes	[11]											(23)
Net income (loss)	[11]											(34)
Capital expenditures	[11]											24
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7],[11]									42
Rate-regulated natural gas revenues	[7],[11]									1
Shared service and other revenues	[7],[11]									0
Revenues	[7],[11]									43
Depreciation and amortization	[11]									11
Operating Expenses	[11]									73
Interest expense, net	[11]									11
Income (loss) before income taxes	[11]									59
Income taxes	[11]									(16)
Net income (loss)	[11]									(44)
Capital expenditures	[11]									11
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6],[10]												1,942	1,824	1,647
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]												435	53
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]											$ 47
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[11]									$ 0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues													5,487	5,540	6,179
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[12]												5,474	5,515	6,212
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													13	25	(33)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues													4,706	4,181	4,412
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[12]												4,717	4,206	4,402
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates													(11)	(25)	10
Segment Elimination [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[6]												$ (3,289)	$ (3,020)	$ (3,159)
[1]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[2]	Exelon’s consolidated assets include $9,667 million and $9,597 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,548 million and $3,618 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities for additional information.
[3]	PHI’s consolidated total assets include $33 million and $41 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE that can only be used to settle the liabilities of the VIE. PHI’s consolidated total liabilities include $69 million and $102 million at December 31, 2018 and 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 2 - Variable Interest Entities for additional information.
[4]	Generation’s consolidated assets include $9,634 million and $9,556 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,480 million and $3,516 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 2–Variable Interest Entities for additional information.
[5]	Includes operating revenues from affiliates of $47 million and $43 million at PHI in 2017 and 2016, respectively.
[6]	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 authoritative guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[7]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[8]	See Note 25 — Related Party Transactions for additional information on intersegment revenues.
[9]	Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2018.
[10]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[11]	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.
[12]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants

Segment Information Segment I_3

Segment Information Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues		$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747	$ 35,985	$ 33,565	$ 31,366
Revenue from Related Parties											0	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues										5,487	5,540	6,179
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues										4,706	4,181	4,412
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues										2,841	2,002	1,769
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues										1,687	1,550	1,166
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues										1,133	962	837
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues										1,494	1,049	907
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues										17,348	15,284	15,270
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues										2,780	2,628	2,281
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1]									309	588	206
Unrealized Gain (Loss) on Securities										(262)	(131)	(500)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues										20,437	18,500	17,757
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									35,985	33,567	31,365
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,474	5,515	6,212
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,717	4,206	4,402
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,845	2,010	1,778
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,687	1,567	1,208
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,132	958	831
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,556	1,076	969
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									17,411	15,332	15,400
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,718	2,575	2,146
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts											(38)	52
Unrealized Gain (Loss) on Securities										(319)	(175)	(41)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									20,437	18,500	17,757
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(1)	7	10
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									308	593	211
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[2]									(3,294)	(3,025)	(3,164)
Revenue from Related Parties	[4]									1	2	5
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										13	25	(33)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(11)	(25)	10
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(4)	(8)	(9)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										0	(17)	(42)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										1	4	6
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(62)	(27)	(62)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										(63)	(48)	(130)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										62	53	135
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties	[1]									1	(5)	(5)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties										0	0	0
Contracts with Customers [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									5,241	5,523	6,182
Contracts with Customers [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									4,527	3,923	4,007
Contracts with Customers [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									2,660	2,064	1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,723	1,605	1,198
Contracts with Customers [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									572	641	810
Contracts with Customers [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									870	594	670
Contracts with Customers [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									15,593	14,350	14,820
Contracts with Customers [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									1,524	1,658	1,953
Contracts with Customers [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3]									17,627	16,752	17,529
Contracts with Customers [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3]									510	744	756
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									233	(8)	30
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									190	283	395
Other [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									185	(54)	(175)
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									(36)	(38)	10
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									560	317	21
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									686	482	299
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									1,818	982	580
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									1,194	917	193
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[3],[5]									2,810	1,748	228
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[1],[3],[5]									$ (202)	$ (151)	$ (545)
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $38 million and $52 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value in 2017 and 2016, respectively, unrealized mark-to-market losses of $262 million, $131 million, and $500 million in 2018, 2017, and 2016, respectively, and elimination of intersegment revenues.
[2]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[3]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants
[4]	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 authoritative guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[5]	Includes revenues from derivatives and leases.

Segment Information Segment I_4

Segment Information Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 3,073	$ 3,214	$ 3,317
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		3,135	2,820	2,971
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		354	514	438
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		1,122	1,008	752
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		258	332	281
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		375	305	336
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		8,317	8,193	8,095
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	427	617	832
Unrealized Gain (Loss) on Securities		(262)	(131)	(500)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		8,744	8,810	8,927
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	3,022	3,105	3,282
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	3,112	2,810	2,969
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	368	538	467
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	1,112	1,007	771
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	501	575	412
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	515	476	483
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	8,630	8,511	8,384
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[1],[2]	114	299	543
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			54	57
Unrealized Gain (Loss) on Securities		(319)	(175)	(41)
Nuclear Fuel Amortization		(57)	(12)	(60)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
RNF from external customers	[2]	8,744	8,810	8,927
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		51	109	35
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		23	10	2
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(14)	(24)	(29)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		10	1	(19)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(243)	(243)	(131)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(140)	(171)	(147)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(313)	(318)	(289)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	313	318	289
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		$ 0	$ 0	$ 0
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $54 million and $57 million decrease in RNF for the amortization of intangible assets and liabilities related to commodity contracts in 2017 and 2016, respectively, unrealized mark-to-market losses of $319 million, $175 million, and $41 million in 2018, 2017, and 2016, respectively, accelerated nuclear fuel amortization associated with the announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $57 million, $12 million and $60 million for the year ended December 31, 2018, 2017, and 2016 and the elimination of intersegment RNF.
[2]	Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.

Segment Information Segment I_5

Segment Information Segment Information - Electric and Gas Revenue by Customer Class (Details) - USD ($) $ in Millions		3 Months Ended									9 Months Ended	12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Major Customer [Line Items]
Operating revenues from affiliates													$ 0	$ 0
Electric operating revenues													0	0
Natural gas operating revenues													0	0
Revenues		$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747			$ 35,985	33,565	31,366
Revenues from alternative revenue programs												(62)	207	48
Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[1]											15,344	14,840	13,869
Natural gas operating revenues	[1]											1,470	1,333	1,166
Revenues	[1]											35,985	33,567	31,365
Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[1],[2],[3]											4,609	4,469
Natural gas operating revenues	[1],[2],[3]											181	161
Revenues	[1],[2],[3]											4,805	4,679
Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												27	15	15
Electric operating revenues												5,884	5,478	5,263
Natural gas operating revenues													0	0
Revenues		1,373	1,598	1,398	1,512	1,309	1,571	1,357	1,298			5,882	5,536	5,254
Revenues from alternative revenue programs												(29)	43	(24)
Commonwealth Edison Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												(29)	43	(24)
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]											5,881	5,463	5,248
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												2,942	2,715	2,603
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												1,487	1,363	1,318
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												538	455	462
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												47	44	45
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											867	886	820
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											30	30	30
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											0	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											0	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											0	0	0
Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												5,881	5,463	5,248
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												1	73	6
PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												8	7	8
Electric operating revenues												2,469	2,369	2,524
Natural gas operating revenues												568	494	462
Revenues		765	757	653	866	729	715	630	796			3,038	2,870	2,994
Revenues from alternative revenue programs												(7)	0	0
PECO Energy Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												(7)	0	0
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]											2,464	2,363	2,519
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												1,566	1,505	1,631
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												404	401	430
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												223	223	234
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												28	30	32
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											243	204	192
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											12	12	12
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											568	494	463
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												395	331	309
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												143	131	121
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												1	1	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											6	8	9
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												23	23	24
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											1	1	0
PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												3,032	2,857	2,982
PECO Energy Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												6	13	12
Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												29	16	21
Electric operating revenues												2,428	2,384	2,531
Natural gas operating revenues												738	652	628
Revenues		799	731	662	977	813	738	674	951			3,169	3,176	3,233
Revenues from alternative revenue programs												(26)	124	53
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												(26)	124	53
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												8	5	7
Electric operating revenues	[5]											2,423	2,376	2,525
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												1,382	1,365	1,504
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												257	254	276
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												429	427	434
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												28	31	35
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											327	299	276
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											13	13	13
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												21	11	14
Natural gas operating revenues	[8]											755	659	640
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												491	437	432
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												77	75	66
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												124	119	114
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											63	28	28
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											4	4	2
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												3,178	3,035	3,165
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												(9)	141	68
Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												15	50
Electric operating revenues												4,609	4,428
Natural gas operating revenues												181	161
Revenues		1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175			4,805	4,679
Revenues from alternative revenue programs												0	40
Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												47
Revenues from alternative revenue programs												0	40
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates													3	2
Electric operating revenues	[5]											4,614	4,423
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												2,351	2,246
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												488	490
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												1,124	1,086
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												58	60
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											593	541
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											10	8
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											180	160
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												99	90
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												44	38
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												8	8
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											13	9
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												16	15
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											1	1
Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												4,794	4,583
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												15
Revenues												11	96
Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												6	6	5
Electric operating revenues												2,233	2,126	2,167
Natural gas operating revenues													0	0
Revenues		531	628	523	557	510	604	514	530			2,239	2,158	2,186
Revenues from alternative revenue programs												0	26	14
Potomac Electric Power Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												0	26	14
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]											2,232	2,127	2,166
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												1,021	964	1,004
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												140	137	150
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												846	794	790
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												32	33	32
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											193	199	190
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											7	5	6
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											0	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0		0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											0	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											0	0	0
Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												2,232	2,127	2,166
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												7	31	20
Delmarva Power & Light Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												8	8	7
Electric operating revenues												1,139	1,125	1,128
Natural gas operating revenues												181	161	148
Revenues		331	328	289	384	330	327	282	362			1,332	1,300	1,277
Revenues from alternative revenue programs												4	6	(6)
Delmarva Power & Light Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												4	6	(6)
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]											1,144	1,130	1,132
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												669	663	672
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												186	187	188
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												100	103	99
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												14	14	13
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											175	163	160
Delmarva Power & Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											3	3	3
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											180	160	148
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												99	90	86
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												44	38	35
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												8	8	6
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											13	9	8
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												16	15	13
Delmarva Power & Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											1	1	0
Delmarva Power & Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												1,324	1,290	1,280
Delmarva Power & Light Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												8	10	(3)
Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates												3	2	3
Electric operating revenues												1,237	1,176	1,245
Natural gas operating revenues													0	0
Revenues		$ 254	$ 406	$ 265	$ 310	$ 271	$ 370	$ 270	$ 275			1,236	1,186	1,257
Revenues from alternative revenue programs												(4)	8	9
Atlantic City Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]												0	0
Revenues from alternative revenue programs												(4)	8	9
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]											1,240	1,178	1,248
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												661	619	664
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												162	166	183
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												178	189	201
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues												12	13	13
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]											227	191	187
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]											0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]											0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0		0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]											0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues												0	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]											0	0	0
Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues												1,240	1,178	1,248
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues												(4)	8	$ 9
Successor [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenues											$ 3,643
Successor [Member] | Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[1],[2],[3]										3,506
Natural gas operating revenues	[1],[2],[3]										92
Revenues	[1],[2],[3]										3,643
Successor [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates											45	$ 15	50
Electric operating revenues											3,463		4,428
Natural gas operating revenues											92		161
Revenues											3,643		4,679
Revenues from alternative revenue programs											43		$ 40
Successor [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]										43
Revenues from alternative revenue programs											43
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]										3,459
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues											1,779
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues											400
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues											835
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues											45
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]										400
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]										6
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]										92
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues											50
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues											21
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues											4
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]										7
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues											10
Successor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]										0
Successor [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues											3,551
Successor [Member] | Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues											$ 92
Predecessor [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Revenues										$ 1,153
Predecessor [Member] | Operating Segments [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[3]									1,096
Natural gas operating revenues	[3]									57
Revenues	[3]									1,153
Predecessor [Member] | Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Operating revenues from affiliates										0
Electric operating revenues										1,122
Natural gas operating revenues										57
Revenues										1,153
Revenues from alternative revenue programs										(26)
Predecessor [Member] | Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues	[4]									0
Revenues from alternative revenue programs										(26)
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[5]									1,119
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues										561
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues										121
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues										255
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues										13
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[6]									169
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Electric operating revenues	[7]									3
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[8]									57
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues										36
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues										14
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues										2
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[9]									2
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues										3
Predecessor [Member] | Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Natural gas operating revenues	[7]									0
Predecessor [Member] | Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues										1,176
Predecessor [Member] | Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues										$ (23)
[1]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[2]	Amounts included represent activity for PHI's successor period, March 24, 2016 through December 31, 2018.
[3]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[4]	Includes operating revenues from affiliates of $47 million and $43 million at PHI in 2017 and 2016, respectively.
[5]	Includes operating revenues from affiliates of $27 million, $7 million, $8 million, $15 million, $6 million, $8 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2018, $15 million, $6 million, $5 million, $3 million, $6 million, $8 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, in 2017, and $15 million, $7 million, $7 million, $2 million, $5 million, $7 million and $3 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, in 2016.
[6]	Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue.
[7]	Includes late payment charge revenues.
[8]	Includes operating revenues from affiliates of $1 million and $21 million at PECO and BGE, respectively, in 2018, $1 million and $11 million at PECO and BGE, respectively, in 2017, and $1 million and $14 million at PECO and BGE, respectively, in 2016.
[9]	Includes revenues from off-system natural gas sales.

Related Party Transactions - Re

Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Operating revenues from affiliates				$ 0	$ 0
Interest expense to affiliates, net			$ 25	36	41
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			(28)	(32)	(24)
Equity in earnings (losses) of unconsolidated affiliates			(28)	(32)	(24)
Cash dividends paid to parent			1,332	1,236	1,166
Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			(1)	7	10
Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		(2)	0
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	1	1
Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	4	4
Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[1]		0	0	0
ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			13	14	13
PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
PECO Trust IV 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			0	10	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			(29)	(33)	(25)
Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	2	5
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			1	1	1
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1,268	1,115	1,439
Related Party Transaction, Purchases from Related Party			14	19	12
Operating and maintenance from affiliates			661	697	663
Interest expense to affiliates, net			36	39	39
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			(30)	(33)	(25)
Equity in earnings (losses) of unconsolidated affiliates			(30)	(33)	(25)
Cash distribution paid to member			1,001	659	922
Cash contributions received from affiliates			155	102	142
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[2]		523	121	47
Related Party Transaction, Purchases from Related Party			(6)	13	0
Operating and maintenance from affiliates	[3]		7	7	7
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[4]		128	138	290
Operating and maintenance from affiliates	[3]		2	1	3
Interest expense to affiliates, net			0	1	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]		260	388	608
Related Party Transaction, Purchases from Related Party			20	9	12
Operating and maintenance from affiliates	[3]		2	1	1
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[6]		206	255	295
Operating and maintenance from affiliates			1	0	1
Exelon Generation Co L L C [Member] | Delmarva Power & Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[7]		120	179	154
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[8]		29	29	37
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates			1	1	1
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net	[9]		36	37	39
Cash distribution paid to member			1,001	659	922
Cash contributions received from affiliates			155	102	142
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			2	1	2
Operating and maintenance from affiliates	[10]		652	689	650
Capitalized costs	[10]		67	98	98
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			0	1	0
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			(30)	(33)	(25)
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			0	4	6
Related Party Transaction, Purchases from Related Party			0	(3)	0
Operating and maintenance from affiliates			(4)	(2)	0
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			27	15	15
Related Party Transaction, Purchases from Related Party			529	108	47
Operating and maintenance from affiliates			267	270	227
Interest expense to affiliates, net			13	13	13
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			459	422	369
Proceeds from Contributions from Parent			500	651	315
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			9	9	7
Related Party Transaction, Purchases from Related Party	[11]		529	108	47
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			10	0	1
Operating and maintenance from affiliates			1	0	1
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			1	0	1
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			459	422	369
Proceeds from Contributions from Parent			500	651	315
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			7	6	6
Operating and maintenance from affiliates	[12]		265	270	225
Capitalized costs	[12]		135	118	112
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			13	13	13
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			8	7	8
Related Party Transaction, Purchases from Related Party			126	135	287
Operating and maintenance from affiliates			156	149	146
Interest expense to affiliates, net			14	11	12
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			306	288	277
Proceeds from Contributions from Parent			89	16	18
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[13]		2	1	3
Related Party Transaction, Purchases from Related Party	[14]		126	135	287
Operating and maintenance from affiliates			2	2	2
Interest income from affiliates, net			0	(1)	0
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			7	0	1
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			1	1	1
PECO Energy Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			2	0	0
Cash dividends paid to parent			306	288	277
Proceeds from Contributions from Parent			89	16	18
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			3	5	3
Operating and maintenance from affiliates	[15]		146	146	142
Capitalized costs	[15]		64	59	57
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			6	6	6
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			29	16	21
Related Party Transaction, Purchases from Related Party			257	384	604
Operating and maintenance from affiliates			162	153	132
Interest expense to affiliates, net			0	10	16
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			209	198	179
Proceeds from Contributions from Parent			109	184	61
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[16]		22	10	13
Related Party Transaction, Purchases from Related Party	[17]		257	384	604
Operating and maintenance from affiliates			3	0	0
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	1
Operating and maintenance from affiliates			1	0	1
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			1	1	1
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			209	198	179
Proceeds from Contributions from Parent			109	184	61
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			5	5	6
Operating and maintenance from affiliates	[18]		157	152	130
Capitalized costs	[18]		79	54	36
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II Affiliate [Member]
Related Party Transaction [Line Items]
Interest expense to affiliates, net			0	10	16
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			15	50
Related Party Transaction, Purchases from Related Party			355	463
Operating and maintenance from affiliates			152	150
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions			1	1
Equity in earnings (losses) of unconsolidated affiliates			1	1
Cash distribution paid to member			326	311
Proceeds from Contributions from Parent			385	758
Pepco Holdings LLC [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		$ 45	15	50
Related Party Transaction, Purchases from Related Party		486
Operating and maintenance from affiliates		89	152	150
Capitalized costs		0	181	0
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		0
Equity in earnings (losses) of unconsolidated affiliates		0
Cash distribution paid to member		273
Proceeds from Contributions from Parent		1,251
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		1	2	0
Related Party Transaction, Purchases from Related Party		486	355	463
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		0	1	2
Capitalized costs	[19]	0	79	0
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent		1,251	326	311
Proceeds from Contributions from Parent		273	385	758
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates		44	12	48
Operating and maintenance from affiliates	[19]	86	147	145
Capitalized costs	[19]	0	102	0
Pepco Holdings LLC [Member] | Other Affiliate [Member] | Successor [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates		3	5	5
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions		$ 0	1	0
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			6	6	5
Related Party Transaction, Purchases from Related Party			206	255	295
Operating and maintenance from affiliates			226	58	35
Capitalized costs			72	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			169	133	136
Proceeds from Contributions from Parent			166	161	187
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance			0	248	302
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates	[20]		1	0	1
Related Party Transaction, Purchases from Related Party	[21]		206	255	295
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			4	6	4
Operating and maintenance from affiliates	[22],[23]		137	5	4
Operating and maintenance	[22],[23]		0	219	263
Capitalized costs	[23]		32	0	0
Potomac Electric Power Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			169	133	136
Proceeds from Contributions from Parent			166	161	187
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Operating and maintenance from affiliates	[23]		89	53	31
Capitalized costs	[23]		40	0	0
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[24]		0	29	39
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			8	8	7
Related Party Transaction, Purchases from Related Party			120	179	154
Operating and maintenance from affiliates			162	32	19
Capitalized costs			53	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			96	112	54
Proceeds from Contributions from Parent			150	0	152
Delmarva Power & Light Company [Member] | Corporate, Non-Segment [Member]
Related Party Transaction [Line Items]
Operating and maintenance			0	174	202
Delmarva Power & Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[25]		120	179	154
Delmarva Power & Light Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Delmarva Power & Light Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Delmarva Power & Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			4	6	5
Operating and maintenance from affiliates	[26],[27]		111	0	0
Operating and maintenance	[26],[27]		0	165	194
Capitalized costs	[26]		25	0	0
Delmarva Power & Light Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			96	112	54
Proceeds from Contributions from Parent			150	0	152
Delmarva Power & Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	0	0
Operating and maintenance from affiliates	[26]		51	31	18
Capitalized costs	[26]		28	0	0
Delmarva Power & Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance	[28]		0	9	8
Delmarva Power & Light Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	2	2
Operating and maintenance from affiliates			0	1	1
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			3	2	3
Related Party Transaction, Purchases from Related Party			29	29	37
Operating and maintenance from affiliates			142	28	18
Capitalized costs			41	0	0
Equity in earnings (losses) of unconsolidated affiliates			0	0	0
Cash dividends paid to parent			59	68	63
Proceeds from Contributions from Parent			67	0	139
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Purchases from Related Party	[29]		29	29	37
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			2	1	2
Operating and maintenance from affiliates	[30],[31]		98	0	0
Operating and maintenance	[30],[31]		0	135	155
Capitalized costs	[30]		21	0	0
Atlantic City Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Cash dividends paid to parent			59	68	63
Cash contributions received from affiliates			67	0	139
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[30]		42	25	15
Capitalized costs	[30]		20	0	0
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates			1	1	1
Operating and maintenance from affiliates			$ 2	$ 3	$ 3
[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 authoritative guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statements of Operations. See Note 4—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 and ZECs to ComEd.
[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.
[5]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs.
[6]	Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC.
[7]	Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs.
[8]	Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process.
[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]	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.
[11]	ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs and ZECs from Generation.
[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.
[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.
[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 supply requirements from Generation under its MDPSC and DCPSC approved market based SOS commodity programs.
[22]	Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.
[23]	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.
[24]	PES performed underground transmission, distribution construction and maintenance services, including services that are treated as capital costs, for Pepco.
[25]	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.
[26]	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.
[27]	Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.
[28]	PES performed underground transmission construction services, including services that are treated as capital costs, for DPL.
[29]	ACE purchases electric supply from Generation under contracts executed through its competitive procurement process.
[30]	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.
[31]	Due to the PHI entities' system conversion to Exelon's accounting systems on January 1, 2018, corporate support services received from PHISCO are reported in Operating and maintenance from affiliates in 2018.

Related Party Transactions - _2

Related Party Transactions - Related Party Transactions included in Consolidated Balance Sheet (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Payables to affiliates, current		$ 5,000,000	$ 5,000,000
Long-term debt to financing trusts		390,000,000	389,000,000
ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		4,000,000	4,000,000
Long-term debt to financing trusts		206,000,000	205,000,000
PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	1,000,000
Long-term debt to financing trusts		81,000,000	81,000,000
PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts		103,000,000	103,000,000
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		173,000,000	140,000,000
Borrowings from Exelon intercompany money pool		100,000,000	54,000,000
Payables to affiliates, current		139,000,000	123,000,000
Long-term debt due to affiliates		898,000,000	910,000,000
Payables to affiliates, noncurrent		2,606,000,000	3,065,000,000
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[1]	30,000,000	26,000,000
Payables to affiliates, current	[1]	0	4,000,000
Payables to affiliates, noncurrent	[2]	389,000,000	537,000,000
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[3]	69,000,000	28,000,000
Payables to affiliates, current		19,000,000	12,000,000
Due to Related Parties, Current	[3]	14,000,000	0
Payables to affiliates, noncurrent	[2]	2,217,000,000	2,528,000,000
Exelon Generation Co L L C [Member] | Delmarva Power & Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[4]	7,000,000	12,000,000
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[5]	28,000,000	36,000,000
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[6]	5,000,000	6,000,000
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[7]	24,000,000	24,000,000
Exelon Generation Co L L C [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[8]	0	1,000,000
Exelon Generation Co L L C [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Borrowings from Exelon intercompany money pool		0	54,000,000
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		10,000,000	7,000,000
Payables to affiliates, current		8,000,000	12,000,000
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Borrowings from Exelon intercompany money pool		100,000,000	0
Payables to affiliates, current	[9]	17,000,000	21,000,000
Long-term debt due to affiliates	[10]	898,000,000	910,000,000
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[8]	95,000,000	74,000,000
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		20,000,000	13,000,000
Receivable from affiliates, noncurrent		2,217,000,000	2,528,000,000
Payables to affiliates, current		119,000,000	74,000,000
Long-term debt to financing trusts		205,000,000	205,000,000
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		19,000,000	12,000,000
Receivable from affiliates, noncurrent	[11]	2,217,000,000	2,528,000,000
Payables to affiliates, current	[12]	55,000,000	28,000,000
Commonwealth Edison Co [Member] | ComEd Financing III Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		4,000,000	4,000,000
Long-term debt to financing trusts		205,000,000	205,000,000
Commonwealth Edison Co [Member] | Voluntary Employee Beneficiary Association Trust Affiliate [Member]
Related Party Transaction [Line Items]
Prepaid voluntary employee beneficiary association trust	[13]	5,000,000	2,000,000
Receivables from affiliates, current		1,000,000	1,000,000
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		4,000,000	3,000,000
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[14]	56,000,000	39,000,000
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Receivable from affiliates, noncurrent		389,000,000	537,000,000
Payables to affiliates, current		59,000,000	53,000,000
Long-term debt to financing trusts	[15]	184,000,000	184,000,000
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Receivable from affiliates, noncurrent	[16]	389,000,000	537,000,000
Payables to affiliates, current	[17]	30,000,000	22,000,000
PECO Energy Co [Member] | PECO Trust III Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	1,000,000
Long-term debt to financing trusts		81,000,000	81,000,000
PECO Energy Co [Member] | PECO Trust IV Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts		103,000,000	103,000,000
PECO Energy Co [Member] | Voluntary Employee Beneficiary Association Trust Affiliate [Member]
Related Party Transaction [Line Items]
Prepaid voluntary employee beneficiary association trust	[18]	1,000,000	0
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		2,000,000	1,000,000
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[19]	26,000,000	29,000,000
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	1,000,000
Payables to affiliates, current		65,000,000	52,000,000
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[20]	24,000,000	24,000,000
Baltimore Gas and Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	1,000,000
Payables to affiliates, current		1,000,000	2,000,000
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		2,000,000	1,000,000
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[21]	38,000,000	25,000,000
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		94,000,000	90,000,000
Pepco Holdings LLC [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		40,000,000	54,000,000
Pepco Holdings LLC [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		0	1,000,000
Pepco Holdings LLC [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		7,000,000	5,000,000
Pepco Holdings LLC [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		6,000,000	6,000,000
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[22]	41,000,000	24,000,000
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	0
Payables to affiliates, current		62,000,000	74,000,000
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[23]	28,000,000	36,000,000
Potomac Electric Power Company [Member] | Delmarva Power & Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	0
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[24]	14,000,000	27,000,000
Potomac Electric Power Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	0
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[24]	19,000,000	11,000,000
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		33,000,000	46,000,000
Delmarva Power & Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[25]	7,000,000	12,000,000
Delmarva Power & Light Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	0
Delmarva Power & Light Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	0
Delmarva Power & Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[26]	12,000,000	27,000,000
Delmarva Power & Light Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		1,000,000	0
Delmarva Power & Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[26]	11,000,000	7,000,000
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	0
Payables to affiliates, current		28,000,000	29,000,000
Atlantic City Electric Company [Member] | Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		1,000,000	0
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[27]	5,000,000	6,000,000
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[28]	13,000,000	18,000,000
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current		2,000,000	0
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Payables to affiliates, current	[28]	8,000,000	5,000,000
Parent Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		44,000,000	33,000,000
Note receivable from affiliates, current		216,000,000	217,000,000
Payables to affiliates, current		360,000,000	360,000,000
Parent Company [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		17,000,000	21,000,000
Note receivable from affiliates, current	[29]	100,000,000	0
Parent Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current		6,000,000	6,000,000
Parent Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	[30]	13,000,000	1,000,000
Note receivable from affiliates, current	[30]	$ 116,000,000	$ 217,000,000
[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.
[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 for additional information.
[3]	Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs and ZECs to ComEd.
[4]	Generation provides a portion of DPL's energy requirements under its MDPSC and DPSC approved market based SOS and gas commodity programs.
[5]	Generation provides electric supply to Pepco under contracts executed through Pepco's competitive procurement process approved by the MDPSC and DCPSC.
[6]	Generation provides electric supply to ACE under contracts executed through ACE's competitive procurement process.
[7]	Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs.
[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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in 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 and ZECs from Generation.
[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]	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.
[15]	Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.
[16]	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.
[17]	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.
[18]	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.
[19]	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.
[20]	BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs.
[21]	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.
[22]	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.
[23]	Pepco procures a portion of its electricity supply requirements from Generation under its MDPSC and DCPSC approved market based SOS commodity programs.
[24]	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.
[25]	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.
[26]	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.
[27]	ACE purchases electric supply from Generation under contracts executed through its competitive procurement process.
[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.
[29]	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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in Exelon’s Consolidated Balance Sheets.
[30]	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.

Quarterly Data (Unaudited) - Qu

Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747	$ 35,985	$ 33,565	$ 31,366
Operating income (loss)	708	1,146	942	1,101	1,288	1,499	300	1,308	3,898	4,395	3,212
Net income attributable to common shareholders	152	733	539	585	1,880	823	95	990	2,010	3,786	1,121
Net income (loss)									2,084	3,876	1,196
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878	20,437	18,500	17,757
Operating income (loss)	35	311	282	347	504	497	(427)	373	975	947	820
Net income (loss) attributable to membership interest	(178)	234	178	136	2,224	304	(235)	418	370	2,710	483
Net income (loss)									443	2,798	550
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,373	1,598	1,398	1,512	1,309	1,571	1,357	1,298	5,882	5,536	5,254
Operating income (loss)	242	323	288	292	286	404	319	314	1,146	1,323	1,205
Net income (loss)	141	193	164	165	120	189	118	141	664	567	378
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	765	757	653	866	729	715	630	796	3,038	2,870	2,994
Operating income (loss)	165	154	127	142	157	169	137	192	587	655	702
Net income (loss)	124	126	96	113	107	112	88	127	460	434	438
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	799	731	662	977	813	738	674	951	3,169	3,176	3,233
Operating income (loss)	109	103	85	177	163	124	98	228	474	614	550
Net income attributable to common shareholders									313	307	286
Net income (loss)	71	63	51	128	76	62	45	125	313	307	294
Pepco Holdings LLC [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175	4,805	4,679
Operating income (loss)	126	245	153	126	159	285	148	180	650	769
Net income (loss) attributable to membership interest	62	187	84	65	4	153	66	140	398	362
Net income (loss)									398	362
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	531	628	523	557	510	604	514	530	2,239	2,158	2,186
Operating income (loss)	65	112	85	56	87	149	84	79	320	399	174
Net income (loss)	36	89	54	31	17	87	43	58	210	205	42
Delmarva Power & Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	331	328	289	384	330	327	282	362	1,332	1,300	1,277
Operating income (loss)	48	51	42	49	52	59	41	78	190	229	50
Net income (loss)	30	33	26	31	14	31	19	57	120	121	(9)
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	254	406	265	310	271	370	270	275	1,236	1,186	1,257
Operating income (loss)	14	84	25	23	28	79	25	25	149	157	7
Net income (loss)	$ (1)	$ 61	$ 8	$ 7	$ 0	$ 41	$ 8	$ 28	$ 75	$ 77	$ (42)

Quarterly Data (Unaudited) - _2

Quarterly Data (Unaudited) - Quarterly Per Share Information (Details) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Net Income per Basic Share	$ 0.16	$ 0.76	$ 0.56	$ 0.61	$ 1.95	$ 0.86	$ 0.10	$ 1.07	$ 2.08	$ 4	$ 1.21
Net Income per Diluted Share	$ 0.16	$ 0.76	$ 0.56	$ 0.60	$ 1.94	$ 0.85	$ 0.10	$ 1.06	$ 2.07	$ 3.99	$ 1.21

Subsequent Events Subsequent _2

Subsequent Events Subsequent Events - Narrative (Details) - Exelon Generation Co L L C [Member] - Subsequent Event [Member] $ in Millions	Dec. 31, 2018USD ($)
Subsequent Event [Line Items]
Net long-lived assets	$ 750
Non-recourse debt	510
Antelope Valley [Member]
Subsequent Event [Line Items]
Net long-lived assets	1,990
Antelope Valley [Member] | ExGenRenewablesIVNov2024 [Member]
Subsequent Event [Line Items]
Non-recourse debt	$ 830

Schedule I - Condensed Financ_2

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Operations and Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Expenses [Abstract]
Total operating expenses										$ 32,143	$ 29,619	$ 28,106
Operating income (loss)		$ 708	$ 1,146	$ 942	$ 1,101	$ 1,288	$ 1,499	$ 300	$ 1,308	3,898	4,395	3,212
Other income and (deductions)
Interest expense, net										(1,529)	(1,524)	(1,495)
Equity in earnings (losses) of unconsolidated affiliates										(28)	(32)	(24)
Other, net										(112)	947	297
Total other income and (deductions)										(1,666)	(613)	(1,239)
Income taxes		$ 26								120	(126)	753
Net income (loss)										2,084	3,876	1,196
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost										(66)	(56)	(48)
Actuarial loss reclassified to periodic cost, net of tax										247	197	184
Unrealized gain on cash flow hedges										12	3	2
Unrealized gain on marketable securities										0	6	1
Unrealized (loss) gain on foreign currency translation										(10)	7	10
Other comprehensive income (loss)										42	171	(36)
Comprehensive Income										2,051	3,959	1,085
Exelon Corporate [Member]
Operating Expenses [Abstract]
Operating and maintenance										(5)	10	221
Operating and maintenance from affiliates	[1]									9	25	51
Other										4	4	4
Total operating expenses										8	39	276
Operating income (loss)										(8)	(39)	(276)
Other income and (deductions)
Interest expense, net										(312)	(315)	(312)
Equity in earnings (losses) of unconsolidated affiliates										2,188	4,414	1,508
Interest income from affiliates, net										42	40	39
Other, net										3	1	7
Total other income and (deductions)										1,921	4,140	1,242
Income before income taxes										1,913	4,101	966
Income taxes										(97)	315	(155)
Net income (loss)										2,010	3,786	1,121
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost										(66)	(56)	(48)
Actuarial loss reclassified to periodic cost, net of tax										247	197	184
Other Comprehensive Income (Loss), Defined Benefit Plan, Settlement and Curtailment Gain (Loss), after Tax										(143)	10	(181)
Unrealized gain on cash flow hedges										12	3	2
Unrealized gain (loss) on equity investments										1	6	(4)
Unrealized gain on marketable securities										0	6	1
Unrealized (loss) gain on foreign currency translation										(10)	7	10
Other comprehensive income (loss)										41	173	(36)
Comprehensive Income										$ 2,051	$ 3,959	$ 1,085
[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 Financ_3

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net cash flows provided by (used in) operating activities	$ 8,644	$ 7,480	$ 8,461
Cash flows from investing activities
Other investing activities	58	(43)	(153)
Net cash flows provided by (used in) investing activities	(7,834)	(7,971)	(15,450)
Cash flows from financing activities
Issuance of long-term debt	3,115	3,470	4,716
Proceeds from short-term borrowings with maturities greater than 90 days	126	621	240
Retirement of long-term debt	(1,786)	(2,490)	(1,936)
Common stock issued from treasury stock	0	1,150	0
Dividends paid on common stock	(1,332)	(1,236)	(1,166)
Proceeds from employee stock plans	105	150	55
Other financing activities	(108)	(83)	(85)
Net cash flows provided by (used in) financing activities	(219)	767	1,191
Increase (Decrease) in cash, cash equivalents and restricted cash	591	276	(5,798)
Cash, cash equivalents and restricted cash at beginning of period	898	635	6,502
Cash, cash equivalents and restricted cash at end of period	1,349	898	635
Exelon Corporate [Member]
Net cash flows provided by (used in) operating activities	2,581	1,921	1,029
Cash flows from investing activities
Changes in Exelon intercompany money pool	1	(129)	1,390
Investment in affiliates	(1,236)	(1,717)	(1,757)
Acquisition of business	0	0	6,962
Other investing activities	0	(5)	5
Net cash flows provided by (used in) investing activities	(1,235)	(1,851)	(7,324)
Cash flows from financing activities
Issuance of long-term debt	0	0	1,800
Proceeds from short-term borrowings with maturities greater than 90 days	0	500	0
Retirement of long-term debt	0	(569)	(46)
Common stock issued from treasury stock	0	1,150	0
Dividends paid on common stock	(1,332)	(1,236)	(1,166)
Proceeds from employee stock plans	105	150	55
Other financing activities	(4)	(9)	(20)
Net cash flows provided by (used in) financing activities	(1,231)	(14)	623
Increase (Decrease) in cash, cash equivalents and restricted cash	115	56	(5,672)
Cash, cash equivalents and restricted cash at beginning of period	74	18	5,690
Cash, cash equivalents and restricted cash at end of period	$ 189	$ 74	$ 18

Schedule I - Condensed Financ_4

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 17, 2012
Current assets
Cash and cash equivalents		$ 1,349	$ 898	$ 635	$ 6,502
Accounts receivable, net
Other accounts receivable		1,256	1,132
Regulatory assets, current		1,222	1,267
Other		1,238	1,260
Total current assets		13,360	11,896
Property, plant and equipment, net		76,707	74,202
Deferred debits and other assets
Regulatory assets, noncurrent		8,237	8,021
Other		1,575	1,330
Total assets	[1]	119,666	116,770
Current liabilities
Short-term borrowings		714	929
Long-term debt due within one year		1,349	2,088
Accounts payable		3,800	3,532
Accrued expenses		2,112	1,837
Payables to affiliates, current		5	5
Regulatory Liability, Current		644	523
Other		1,035	1,069
Total current liabilities		11,404	10,798
Long-term debt		34,075	32,176
Deferred credits and other liabilities
Regulatory liabilities, noncurrent		9,559	9,865
Pension obligations		3,988	3,736
Non-pension postretirement benefit obligations		1,928	2,093
Other		2,130	2,097
Total deferred credits and other liabilities		40,727	41,220
Total liabilities	[1]	86,596	84,583
Commitments and Contingencies						$ 1,000
Shareholders’ equity
Common stock		19,116	18,964
Treasury stock, at cost		(123)	(123)
Retained earnings		14,766	14,081
Accumulated other comprehensive income (loss), net		(2,995)	(3,026)
Total shareholders’ equity		30,764	29,896
Total liabilities and equity		119,666	116,770
Exelon Corporate [Member]
Current assets
Cash and cash equivalents		189	74	$ 18	$ 5,690
Accounts receivable, net
Other accounts receivable		48	431
Accounts receivable from affiliates, current		44	33
Note receivable from affiliates, current		216	217
Regulatory assets, current		182	284
Other		4	4
Total current assets		683	1,043
Property, plant and equipment, net		48	50
Deferred debits and other assets
Regulatory assets, noncurrent		3,742	3,697
Investments in affiliates		40,448	39,311
Deferred income taxes		1,455	1,431
Notes receivable from affiliates, noncurrent		898	910
Other		235	234
Total deferred debits and other assets		46,778	45,583
Total assets		47,509	46,676
Current liabilities
Short-term borrowings		500	500
Accounts payable		1	2
Accrued expenses		184	99
Payables to affiliates, current		360	360
Regulatory Liability, Current		15	16
Pension obligations		63	65
Other		14	46
Total current liabilities		1,137	1,088
Long-term debt		7,147	7,161
Deferred credits and other liabilities
Regulatory liabilities, noncurrent		32	15
Pension obligations		7,795	7,792
Non-pension postretirement benefit obligations		199	322
Deferred income taxes		233	220
Other		202	180
Total deferred credits and other liabilities		8,461	8,529
Total liabilities		16,745	16,778
Commitments and Contingencies
Shareholders’ equity
Common stock		19,116	18,966
Treasury stock, at cost		(123)	(123)
Retained earnings		14,766	14,081
Accumulated other comprehensive income (loss), net		(2,995)	(3,026)
Total shareholders’ equity		30,764	29,898
Total liabilities and equity		$ 47,509	$ 46,676
[1]	Exelon’s consolidated assets include $9,667 million and $9,597 million at December 31, 2018 and 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,548 million and $3,618 million at December 31, 2018 and 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 2–Variable Interest Entities for additional information.

Schedule I - Condensed Financ_5

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Condensed Balance Sheet - Parenthetical (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	2,000,000,000	2,000,000,000
Common stock, shares outstanding	968,187,955	963,335,888
Treasury stock, shares held	2,000,000	2,000,000
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 Financ_6

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Basis of Presentation - Narrative (Details) - Exelon Corporate [Member]	Dec. 31, 2018
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 Financ_7

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Line of Credit Facility [Line Items]
Maximum Program Size	$ 9,704	[1]
Line of Credit Facility, Capacity Available for Trade Purchases	7,687
Revolving Credit Facility [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Maximum Program Size	600	[1]
Line of Credit Facility, Capacity Available for Trade Purchases	591
Corporate, Non-Segment [Member] | Exelon Corporate [Member]
Line of Credit Facility [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
Debt Instrument, Interest Rate Terms	LIBOR plus 1%
[1]	Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

Schedule I - Condensed Financ_8

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, 2018	Dec. 31, 2017	Jun. 30, 2014
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 34,911	$ 33,657
Unamortized debt discount and premium, net		(66)	(57)
Unamortized debt issuance costs		216	201
Long-term debt		34,075	32,176
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	$ 11,285
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%
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	7,039
Unamortized debt discount and premium, net		(7)	(8)
Unamortized debt issuance costs		(47)	(49)
Fair value adjustment of consolidated subsidiary		162	179
Long-term debt		7,147	7,161
Exelon Corporate [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		1,150	1,150
Exelon Corporate [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	[1]	$ 5,889	$ 5,889
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.50%
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[1]	7.60%
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	[1]	2.45%
[1]	Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets.

Schedule I - Condensed Financ_9

Schedule I - Condensed Financial Information of Parent (Exelon Corporate) - Debt and Credit Agreements - Schedule of Debt Maturities (Details) $ in Millions	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
2,019	$ 1,349
2,020	3,528
2,021	1,511
2,022	3,084
2,023	850
Thereafter	24,979	[1]
Total	35,301
Exelon Corporate [Member]
Debt Instrument [Line Items]
2,019	0
2,020	1,450
2,021	300
2,022	1,150
2,023	0
Thereafter	4,139
Total	$ 7,039
[1]	Includes $390 million due to ComEd and PECO financing trusts.

Schedule I - Condensed Finan_10

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		$ (28)	$ (32)	$ (24)
Payables to affiliates, current		5	5
Exelon Corporate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[1]	9	25	51
Interest income from affiliates, net		42	40	39
Equity in earnings (losses) of unconsolidated affiliates		2,188	4,414	1,508
Cash contributions received from affiliates		2,302	1,879	1,912
Accounts receivable from affiliates, current		44	33
Note receivable from affiliates, current		216	217
Investments in affiliates		40,448	39,311
Notes receivable from affiliates, noncurrent		898	910
Payables to affiliates, current		360	360
Exelon Corporate [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates	[1]	11	23	51
Interest income from affiliates, net		4	3	0
Equity in earnings (losses) of unconsolidated affiliates		0	1	1
Accounts receivable from affiliates, current	[1]	13	1
Note receivable from affiliates, current	[1]	116	217
Investments in affiliates	[1]	197	196
Exelon Corporate [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates		(2)	2	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		36	37	39
Equity in earnings (losses) of unconsolidated affiliates		369	2,710	483
Accounts receivable from affiliates, current		17	21
Note receivable from affiliates, current	[2]	100	0
Investments in affiliates		13,204	13,674
Notes receivable from affiliates, noncurrent	[2]	898	910
Exelon Corporate [Member] | Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current		4	3
Exelon Corporate [Member] | PECO Energy Co [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current		2	1
Exelon Corporate [Member] | Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current		2	1
Exelon Corporate [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Accounts receivable from affiliates, current		6	6
Exelon Corporate [Member] | Exelon Energy Delivery Company LLC [Member]
Related Party Transaction [Line Items]
Interest income from affiliates, net	[3]	2	0	0
Equity in earnings (losses) of unconsolidated affiliates	[3]	1,835	1,670	1,041
Investments in affiliates	[3]	26,702	25,082
Exelon Corporate [Member] | Potomac Capital Investment Affiliate [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		(17)	1	6
Investments in affiliates		61	78
Exelon Corporate [Member] | UII LLC [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		0	41	(9)
Investments in affiliates		268	268
Payables to affiliates, current		360	360
Exelon Corporate [Member] | Exelon Transmission Company LLC [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		1	(10)	(13)
Investments in affiliates		1	1
Exelon Corporate [Member] | VEBA [Member]
Related Party Transaction [Line Items]
Investments in affiliates		(1)	(4)
Exelon Corporate [Member] | Exelon Enterprise [Member]
Related Party Transaction [Line Items]
Equity in earnings (losses) of unconsolidated affiliates		0	1	$ (1)
Investments in affiliates		$ 22	$ 22
[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 affiliates in Generation’s Consolidated Balance Sheets and intercompany notes receivable at Exelon Corporate, which are eliminated in consolidation in 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 Q_2

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, 2018		Dec. 31, 2017	Dec. 31, 2016
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 284		$ 322		$ 334	$ 284
Charged to Costs and Expenses	[1]			159		126	162
Charged to Other Accounts	[1],[2]			35		27	99	[3]
Deductions	[1],[4]			197		165	211
Balance at End of Period	[1]		$ 334	319		322	334
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		13		37		20	13
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				5		17	10	[3]
Deductions				7		0	3
Balance at End of Period			20	35		37	20
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		105		174		113	105
Charged to Costs and Expenses				25		56	12
Charged to Other Accounts				(31)	[5]	10	1	[3]
Deductions				12		5	5
Balance at End of Period			113	156		174	113
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		114		91	77
Charged to Costs and Expenses				44		34	19
Charged to Other Accounts				4		0	3
Deductions				58		11	8
Balance at End of Period			91	104		114	91
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		23		9	11
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				3		14	0
Deductions				0		0	2
Balance at End of Period			9	26		23	9
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		166		106	102
Charged to Costs and Expenses				20		51	6
Charged to Other Accounts				(32)	[6]	9	0
Deductions				9		0	2
Balance at End of Period			106	145		166	106
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		75		73		70	75
Charged to Costs and Expenses				44		39	45
Charged to Other Accounts	[7]			23		20	23
Deductions	[8]			59		56	73
Balance at End of Period			70	81		73	70
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		3		5		4	3
Charged to Costs and Expenses				3		3	4
Charged to Other Accounts				1		1	1
Deductions				3		3	4
Balance at End of Period			4	6		5	4
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[9]	83		56		61	83
Charged to Costs and Expenses	[9]			33		26	32
Charged to Other Accounts	[9],[10]			3		4	7
Deductions	[9],[11]			31		35	61
Balance at End of Period	[9]		61	61		56	61
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		2		2	1
Charged to Costs and Expenses				0		0	1
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			2	2		2	2
PECO Energy Co [Member] | Allowance for Doubtful Accounts, Noncurrent [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period				15		23
Balance at End of Period			23	13		15	23
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		24		32	49
Charged to Costs and Expenses				10		8	1
Charged to Other Accounts				(2)		(3)	9
Deductions	[12]			12		13	27
Balance at End of Period			32	20		24	32
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				1		0	0
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			0	1		0	0
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	55		80
Charged to Costs and Expenses			65	28		19
Charged to Other Accounts	[13]		5	7		6
Deductions	[14]		42	37		50
Balance at End of Period		52	80	53		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
Charged to Costs and Expenses		16
Charged to Other Accounts	[13]	2
Deductions	[14]	22
Balance at End of Period		52
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	13		10
Charged to Costs and Expenses			0	0		0
Charged to Other Accounts			(53)	2		3
Deductions			0	7		0
Balance at End of Period		63	10	8		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
Charged to Costs and Expenses		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		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		2
Charged to Costs and Expenses			1	0		2
Charged to Other Accounts			0	0		0
Deductions			(1)	0		2
Balance at End of Period		0	2	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
Charged to Costs and Expenses		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		0
Potomac Electric Power Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		21		29	17
Charged to Costs and Expenses				11		8	29
Charged to Other Accounts	[15]			3		2	3
Deductions	[16]			14		18	20
Balance at End of Period			29	21		21	29
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		1	0
Charged to Costs and Expenses				0		1	3
Charged to Other Accounts				0		0	0
Deductions				0		1	2
Balance at End of Period			1	1		1	1
Delmarva Power & Light Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		16		24	17
Charged to Costs and Expenses				6		3	23
Charged to Other Accounts	[17]			2		2	2
Deductions	[18]			11		13	18
Balance at End of Period			24	13		16	24
Delmarva Power & 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				0		1	1
Charged to Other Accounts				0		0	0
Deductions				0		1	1
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		18		27	17
Charged to Costs and Expenses				11		8	32
Charged to Other Accounts	[19]			2		2	2
Deductions	[20]			12		19	24
Balance at End of Period			27	19		18	27
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		1	0
Charged to Costs and Expenses				0		0	1
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			$ 1	$ 1		$ 1	$ 1
[1]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017 and 2016, 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 reflects the reclassification of assets as held for sale.
[6]	Primarily reflects the reclassification of assets as held for sale.
[7]	Primarily charges for late payments and non-service receivables.
[8]	Write-off of individual accounts receivable.
[9]	Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017, and 2016, respectively.
[10]	Primarily charges for late payments.
[11]	Write-off of individual accounts receivable.
[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.
[19]	Primarily charges for late payments.
[20]	Write-off of individual accounts receivable.

Uncategorized Items - exc-20181

Label	Element	Value
Pepco Holdings LLC [Member] | Predecessor [Member]
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	$ 2,000,000
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	290,000,000
Repayments of Short-term Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths	0
Impairment of Long-Lived Assets Held-for-use	us-gaap_ImpairmentOfLongLivedAssetsHeldForUse	0
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	19,000,000
Increase (Decrease) in Due to Affiliates, Current	us-gaap_IncreaseDecreaseInDueToAffiliatesCurrent	0
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	18,000,000
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	(121,000,000)
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	46,000,000
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	264,000,000
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	372,000,000
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	(4,000,000)
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	(28,000,000)
Proceeds from Contributions from Parent	us-gaap_ProceedsFromContributionsFromParent	0
Proceeds from Short-term Debt, Maturing in More than Three Months	us-gaap_ProceedsFromShortTermDebtMaturingInMoreThanThreeMonths	500,000,000
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	11,000,000
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	42,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	5,000,000
Payments of Distributions to Affiliates	us-gaap_PaymentsOfDistributionsToAffiliates	0
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	2,000,000
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	68,000,000
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	(8,000,000)
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	0
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	0
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	12,000,000
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	(346,000,000)
Pepco Holdings LLC [Member] | Successor [Member]
Proceeds from Stock Plans	us-gaap_ProceedsFromStockPlans	0
Cash and Cash Equivalents, Period Increase (Decrease)	us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease	(112,000,000)
Repayments of Short-term Debt, Maturing in More than Three Months	us-gaap_RepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths	300,000,000
Deferred Income Taxes and Tax Credits	us-gaap_DeferredIncomeTaxesAndTaxCredits	295,000,000
Increase (Decrease) in Due to Affiliates, Current	us-gaap_IncreaseDecreaseInDueToAffiliatesCurrent	(6,000,000)
Unrealized Gain (Loss) on Derivatives	us-gaap_UnrealizedGainLossOnDerivatives	0
Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less	us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess	(515,000,000)
Other Noncash Income (Expense)	us-gaap_OtherNoncashIncomeExpense	515,000,000
Net Cash Provided by (Used in) Operating Activities	us-gaap_NetCashProvidedByUsedInOperatingActivities	888,000,000
Net Cash Provided by (Used in) Financing Activities	us-gaap_NetCashProvidedByUsedInFinancingActivities	(7,000,000)
Increase (Decrease) in Inventories	us-gaap_IncreaseDecreaseInInventories	3,000,000
Increase (Decrease) in Receivables	us-gaap_IncreaseDecreaseInReceivables	(21,000,000)
Proceeds from Short-term Debt, Maturing in More than Three Months	us-gaap_ProceedsFromShortTermDebtMaturingInMoreThanThreeMonths	0
Repayments of Long-term Debt	us-gaap_RepaymentsOfLongTermDebt	338,000,000
Increase (Decrease) in Accounts Payable and Accrued Liabilities	us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities	19,000,000
Payments for (Proceeds from) Other Investing Activities	us-gaap_PaymentsForProceedsFromOtherInvestingActivities	(15,000,000)
Proceeds from (Payments for) Other Financing Activities	us-gaap_ProceedsFromPaymentsForOtherFinancingActivities	(5,000,000)
Payments to Acquire Marketable Securities	us-gaap_PaymentsToAcquireMarketableSecurities	0
Increase (Decrease) in Other Operating Assets and Liabilities, Net	us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet	(311,000,000)
Proceeds from Issuance of Long-term Debt	us-gaap_ProceedsFromIssuanceOfLongTermDebt	179,000,000
Change Receivables Payables From Affiliates	exc_ChangeReceivablesPayablesFromAffiliates	42,000,000
Increase (Decrease) in Income Taxes Payable	us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable	(22,000,000)
Net Cash Provided by (Used in) Investing Activities	us-gaap_NetCashProvidedByUsedInInvestingActivities	$ (993,000,000)