Exelon (EXC) 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2018shares
Entity Registrant Name	EXELON CORP
Entity Central Index Key	1,109,357
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding	965,381,919
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	127,021,264
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 and Light Company [Member]
Entity Registrant Name	DELMARVA POWER & LIGHT CO/DE
Entity Central Index Key	27,879
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	1,000
Atlantic City Electric Company [Member]
Entity Registrant Name	ATLANTIC CITY ELECTRIC CO
Entity Central Index Key	8,192
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding	8,546,017

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Unaudited) - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Operating revenues [Abstract]
Operating Revenue		$ 5,113	$ 4,550
Regulated Operating Revenue		4,570	4,118
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs		10	79
Operating revenues from affiliates	[1]	0	0
Revenues		9,693	8,747
Operating expenses
Competitive businesses purchased power and fuel		3,289	2,795
Cost of Purchased Power		1,438	1,104
Operating and maintenance		2,384	2,438
Depreciation and amortization		1,091	896
Taxes other than income		446	436
Total operating expenses		8,648	7,669
Gain (Loss) on Disposition of Other Assets		56	4
Bargain purchase gain		0	226
Operating income		1,101	1,308
Other income and (deductions)
Interest expense, net		(365)	(363)
Interest expense to affiliates		(6)	(10)
Other, net		(28)	257
Total other income and (deductions)		(399)	(116)
Income before income taxes		702	1,192
Income taxes		59	211
Equity in losses of unconsolidated affiliates		(7)	(10)
Net income		636	971
Net income (loss) attributable to noncontrolling interests		51	(19)
Net income attributable to common shareholders		585	990
Other comprehensive income (loss), net of income taxes
Prior service benefit reclassified to periodic benefit cost		(17)	(13)
Actuarial loss reclassified to periodic benefit cost		61	49
Pension and non-pension postretirement benefit plan valuation adjustment		18	(59)
Unrealized gain on cash flow hedges		8	6
Other Comprehensive Income Unrealized Income Loss On Equity Investments Arising During Period Net Of Tax		1	3
Unrealized gain on foreign currency translation		1	1
Unrealized gain on marketable securities		0	1
Other comprehensive income (loss)		72	(12)
Comprehensive income		708	959
Comprehensive income (loss) attributable to noncontrolling interests		52	(21)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 656	$ 980
Average shares of common stock outstanding:
Weighted average common shares outstanding — basic		966	928
Weighted average common shares outstanding — diluted		968	930
Earnings per average common share:
Basic		$ 0.61	$ 1.07
Diluted		0.60	1.06
Dividends declared per common share		$ 0.35	$ 0.33
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Operating Revenue		$ 5,114	$ 4,548
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs			0
Operating revenues from affiliates		398	330
Revenues		5,512	4,878
Operating expenses
Cost of Purchased Power		3,289	2,796
Purchased power from affiliate		4	2
Operating and maintenance		1,178	1,313
Operating and maintenance from affiliates		161	179
Depreciation and amortization		448	302
Taxes other than income		138	143
Total operating expenses		5,218	4,735
Gain (Loss) on Disposition of Other Assets		53	4
Bargain purchase gain		0	226
Operating income		347	373
Other income and (deductions)
Interest expense, net		(91)	(90)
Interest expense to affiliates		(10)	(10)
Other, net		(44)	259
Total other income and (deductions)		(145)	159
Income before income taxes		202	532
Income taxes		9	123
Equity in losses of unconsolidated affiliates		(7)	(10)
Net income		186	399
Net income (loss) attributable to noncontrolling interests		50	(19)
Net income attributable to membership interest		136	418
Other comprehensive income (loss), net of income taxes
Unrealized gain on cash flow hedges		7	6
Other Comprehensive Income Unrealized Income Loss On Equity Investments Arising During Period Net Of Tax		1	4
Unrealized gain on foreign currency translation		(1)	1
Other comprehensive income (loss)		7	11
Comprehensive income		193	410
Comprehensive income (loss) attributable to noncontrolling interests		51	(21)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		142	431
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		1,493	1,279
Natural gas operating revenues			0
Revenues from alternative revenue programs		5	14
Operating revenues from affiliates		14	5
Revenues		1,512	1,298
Operating expenses
Purchased power		411	329
Purchased power from affiliate		194	5
Operating and maintenance		253	307
Operating and maintenance from affiliates		60	63
Depreciation and amortization		228	208
Taxes other than income		77	72
Total operating expenses		1,223	984
Gain (Loss) on Disposition of Other Assets		3	0
Operating income		292	314
Other income and (deductions)
Interest expense, net		(86)	(82)
Interest expense to affiliates		(3)	(3)
Other, net		8	4
Total other income and (deductions)		(81)	(81)
Income before income taxes		211	233
Income taxes		46	92
Net income		165	141
Other comprehensive income (loss), net of income taxes
Comprehensive income		165	141
PECO Energy Co [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		633	589
Natural gas operating revenues		232	206
Revenues from alternative revenue programs		(1)	0
Operating revenues from affiliates		2	1
Revenues		866	796
Operating expenses
Purchased power		199	156
Purchased fuel		98	86
Purchased power from affiliate		36	45
Operating and maintenance		233	174
Operating and maintenance from affiliates		42	34
Depreciation and amortization		75	71
Taxes other than income		41	38
Total operating expenses		724	604
Operating income		142	192
Other income and (deductions)
Interest expense, net		(30)	(28)
Interest expense to affiliates		(3)	(3)
Other, net		2	2
Total other income and (deductions)		(31)	(29)
Income before income taxes		111	163
Income taxes		(2)	36
Net income		113	127
Other comprehensive income (loss), net of income taxes
Comprehensive income		113	127
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		654	640
Natural gas operating revenues		330	271
Revenues from alternative revenue programs		(13)	35
Operating revenues from affiliates		6	5
Revenues		977	951
Operating expenses
Purchased power		192	133
Purchased fuel		123	83
Purchased power from affiliate		65	134
Operating and maintenance		184	148
Operating and maintenance from affiliates		37	35
Depreciation and amortization		134	128
Taxes other than income		65	62
Total operating expenses		800	723
Operating income		177	228
Other income and (deductions)
Interest expense, net		(25)	(23)
Interest expense to affiliates		0	(4)
Other, net		4	4
Total other income and (deductions)		(21)	(23)
Income before income taxes		156	205
Income taxes		28	80
Net income		128	125
Other comprehensive income (loss), net of income taxes
Comprehensive income		128	125
Pepco Holdings LLC [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		1,151	1,067
Natural gas operating revenues		78	66
Revenues from alternative revenue programs		18	30
Operating revenues from affiliates		4	12
Revenues		1,251	1,175
Operating expenses
Purchased power		374	288
Purchased fuel		41	29
Purchased power from affiliate		105	144
Operating and maintenance		271	223
Operating and maintenance from affiliates		38	33
Depreciation and amortization		183	167
Taxes other than income		113	111
Total operating expenses		1,125	995
Operating income		126	180
Other income and (deductions)
Interest expense, net		(63)	(62)
Other, net		11	13
Total other income and (deductions)		(52)	(49)
Income before income taxes		74	131
Income taxes		9	(9)
Net income		65	140
Other comprehensive income (loss), net of income taxes
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		65	140
Potomac Electric Power Company [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		536	514
Natural gas operating revenues			0
Revenues from alternative revenue programs		19	15
Operating revenues from affiliates		2	1
Revenues		557	530
Operating expenses
Purchased power		130	83
Purchased power from affiliate		52	83
Operating and maintenance		73	101
Operating and maintenance from affiliates		57	12
Depreciation and amortization		96	82
Taxes other than income		93	90
Total operating expenses		501	451
Operating income		56	79
Other income and (deductions)
Interest expense, net		(31)	(29)
Other, net		8	8
Total other income and (deductions)		(23)	(21)
Income before income taxes		33	58
Income taxes		2	0
Net income		31	58
Other comprehensive income (loss), net of income taxes
Comprehensive income		31	58
Delmarva Power and Light Company [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		303	285
Natural gas operating revenues		78	66
Revenues from alternative revenue programs		1	9
Operating revenues from affiliates		2	2
Revenues		384	362
Operating expenses
Purchased power		90	77
Purchased fuel		41	29
Purchased power from affiliate		46	51
Operating and maintenance		57	66
Operating and maintenance from affiliates		41	7
Depreciation and amortization		45	39
Taxes other than income		15	15
Total operating expenses		335	284
Operating income		49	78
Other income and (deductions)
Interest expense, net		(13)	(13)
Other, net		2	3
Total other income and (deductions)		(11)	(10)
Income before income taxes		38	68
Income taxes		7	11
Net income		31	57
Other comprehensive income (loss), net of income taxes
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		31	57
Atlantic City Electric Company [Member]
Operating revenues [Abstract]
Operating Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		311	268
Natural gas operating revenues			0
Revenues from alternative revenue programs		(2)	6
Operating revenues from affiliates		1	1
Revenues		310	275
Operating expenses
Purchased power		155	128
Purchased power from affiliate		6	9
Operating and maintenance		54	69
Operating and maintenance from affiliates		36	7
Depreciation and amortization		33	35
Taxes other than income		3	2
Total operating expenses		287	250
Operating income		23	25
Other income and (deductions)
Interest expense, net		(16)	(15)
Other, net		1	2
Total other income and (deductions)		(15)	(13)
Income before income taxes		8	12
Income taxes		1	(16)
Net income		7	28
Other comprehensive income (loss), net of income taxes
Comprehensive income		$ 7	$ 28
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 636	$ 971
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	1,501	1,274
Impairment of long-lived assets and losses on regulatory assets	0	10
Gain on sales of assets and businesses	(56)	(4)
Bargain purchase gain	0	(226)
Deferred income taxes and amortization of investment tax credits	(14)	185
Net fair value changes related to derivatives	259	47
Net realized and unrealized gains (losses) on nuclear decommissioning trust fund investments	68	(175)
Other non-cash operating activities	240	118
Changes in assets and liabilities:
Accounts receivable	133	291
Inventories	167	109
Accounts payable and accrued expenses	(451)	(728)
Option premiums paid, net	(27)	(6)
Collateral posted, net	(214)	(110)
Income taxes	86	50
Pension and non-pension postretirement benefit contributions	(331)	(307)
Other assets and liabilities	(495)	(425)
Net cash flows provided by (used in) operating activities	1,502	1,074
Cash flows from investing activities
Capital expenditures	(1,880)	(2,009)
Proceeds from nuclear decommissioning trust fund sales	1,189	1,767
Investment in nuclear decommissioning trust funds	(1,248)	(1,833)
Acquisition of businesses, net	0	(212)
Proceeds from sales of assets and businesses	79	22
Other investing activities	3	(18)
Net cash flows provided by (used in) investing activities	(1,857)	(2,283)
Cash flows from financing activities
Changes in short-term borrowings	726	721
Proceeds from short-term borrowings with maturities greater than 90 days	1	560
Repayments on short-term borrowings with maturities greater than 90 days	(1)	(500)
Issuance of long-term debt	1,130	763
Retirement of long-term debt	(1,241)	(65)
Dividends paid on common stock	(333)	(303)
Proceeds from employee stock plans	12	12
Other financing activities	(30)	(4)
Net cash flows provided by (used in) financing activities	264	1,184
Increase (Decrease) in cash and cash equivalents	(91)	(25)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	1,190	914
Cash, Cash Equivalents and Restricted Cash at End of Period	1,099	889
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	186	399
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	858	678
Impairment of long-lived assets and losses on regulatory assets	0	10
Gain on sales of assets and businesses	(53)	(4)
Bargain purchase gain	0	(226)
Deferred income taxes and amortization of investment tax credits	(68)	108
Net fair value changes related to derivatives	264	51
Net realized and unrealized gains (losses) on nuclear decommissioning trust fund investments	68	(175)
Other non-cash operating activities	45	(10)
Changes in assets and liabilities:
Accounts receivable	194	173
Receivables from and payables to affiliates, net	(15)	23
Inventories	122	81
Accounts payable and accrued expenses	(317)	(236)
Option premiums paid, net	(27)	(6)
Collateral posted, net	(214)	(102)
Income taxes	79	(81)
Pension and non-pension postretirement benefit contributions	(125)	(110)
Other assets and liabilities	(142)	(153)
Net cash flows provided by (used in) operating activities	855	420
Cash flows from investing activities
Capital expenditures	(628)	(625)
Proceeds from nuclear decommissioning trust fund sales	1,189	1,767
Investment in nuclear decommissioning trust funds	(1,248)	(1,833)
Acquisition of businesses, net	0	(212)
Proceeds from sales of assets and businesses	79	22
Other investing activities	(7)	(29)
Net cash flows provided by (used in) investing activities	(615)	(910)
Cash flows from financing activities
Changes in short-term borrowings	165	(42)
Proceeds from short-term borrowings with maturities greater than 90 days	1	60
Repayments on short-term borrowings with maturities greater than 90 days	(1)	0
Issuance of long-term debt	4	762
Retirement of long-term debt	(29)	(30)
Change in Exelon intercompany money pool	0	(1)
Distributions to member	(188)	(164)
Other financing activities	(9)	(3)
Net cash flows provided by (used in) financing activities	(57)	582
Increase (Decrease) in cash and cash equivalents	183	92
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	554	448
Cash, Cash Equivalents and Restricted Cash at End of Period	737	540
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	165	141
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	228	208
Deferred income taxes and amortization of investment tax credits	50	137
Other non-cash operating activities	46	31
Changes in assets and liabilities:
Accounts receivable	39	92
Receivables from and payables to affiliates, net	(19)	(16)
Inventories	5	4
Accounts payable and accrued expenses	(158)	(236)
Collateral posted, net	(3)	(7)
Income taxes	(5)	(34)
Pension and non-pension postretirement benefit contributions	(38)	(35)
Other assets and liabilities	(176)	(49)
Net cash flows provided by (used in) operating activities	134	236
Cash flows from investing activities
Capital expenditures	(531)	(626)
Other investing activities	8	7
Net cash flows provided by (used in) investing activities	(523)	(619)
Cash flows from financing activities
Changes in short-term borrowings	317	365
Issuance of long-term debt	800	0
Retirement of long-term debt	(700)	0
Dividends paid on common stock	(114)	(105)
Contributions from parent	113	100
Other financing activities	(9)	(1)
Net cash flows provided by (used in) financing activities	407	359
Increase (Decrease) in cash and cash equivalents	18	(24)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	144	58
Cash, Cash Equivalents and Restricted Cash at End of Period	162	34
PECO Energy Co [Member]
Cash flows from operating activities
Net income	113	127
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	75	71
Deferred income taxes and amortization of investment tax credits	(4)	24
Other non-cash operating activities	21	23
Changes in assets and liabilities:
Accounts receivable	(51)	(25)
Receivables from and payables to affiliates, net	7	(10)
Inventories	12	19
Accounts payable and accrued expenses	6	(40)
Income taxes	5	25
Pension and non-pension postretirement benefit contributions	(24)	(23)
Other assets and liabilities	(141)	(85)
Net cash flows provided by (used in) operating activities	19	106
Cash flows from investing activities
Capital expenditures	(217)	(201)
Changes in Exelon intercompany money pool	0	131
Other investing activities	2	1
Net cash flows provided by (used in) investing activities	(215)	(69)
Cash flows from financing activities
Changes in short-term borrowings	220	0
Issuance of long-term debt	325	0
Retirement of long-term debt	(500)	0
Dividends paid on common stock	(287)	(72)
Change in Exelon intercompany money pool	194	0
Other financing activities	(5)	0
Net cash flows provided by (used in) financing activities	(53)	(72)
Increase (Decrease) in cash and cash equivalents	(249)	(35)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	275	67
Cash, Cash Equivalents and Restricted Cash at End of Period	26	32
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	128	125
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	134	128
Deferred income taxes and amortization of investment tax credits	22	72
Other non-cash operating activities	20	24
Changes in assets and liabilities:
Accounts receivable	(32)	(7)
Receivables from and payables to affiliates, net	0	(7)
Inventories	20	17
Accounts payable and accrued expenses	(9)	(81)
Income taxes	14	33
Pension and non-pension postretirement benefit contributions	(45)	(44)
Other assets and liabilities	61	(52)
Net cash flows provided by (used in) operating activities	313	208
Cash flows from investing activities
Capital expenditures	(224)	(206)
Other investing activities	1	4
Net cash flows provided by (used in) investing activities	(223)	(202)
Cash flows from financing activities
Changes in short-term borrowings	(32)	50
Dividends paid on common stock	(52)	(49)
Net cash flows provided by (used in) financing activities	(84)	1
Increase (Decrease) in cash and cash equivalents	6	7
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	18	50
Cash, Cash Equivalents and Restricted Cash at End of Period	24	57
Pepco Holdings LLC [Member]
Cash flows from operating activities
Net income	65	140
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	183	167
Deferred income taxes and amortization of investment tax credits	17	13
Other non-cash operating activities	53	(8)
Changes in assets and liabilities:
Accounts receivable	(9)	68
Receivables from and payables to affiliates, net	10	(8)
Inventories	4	(11)
Accounts payable and accrued expenses	44	(81)
Income taxes	(9)	55
Pension and non-pension postretirement benefit contributions	(55)	(66)
Other assets and liabilities	(24)	(75)
Net cash flows provided by (used in) operating activities	279	194
Cash flows from investing activities
Capital expenditures	(258)	(320)
Other investing activities	0	(3)
Net cash flows provided by (used in) investing activities	(258)	(323)
Cash flows from financing activities
Changes in short-term borrowings	57	145
Repayments on short-term borrowings with maturities greater than 90 days	0	(500)
Issuance of long-term debt	0	1
Retirement of long-term debt	(12)	(24)
Change in Exelon intercompany money pool	13	13
Distributions to member	(71)	(69)
Contributions from member	0	500
Net cash flows provided by (used in) financing activities	(13)	66
Increase (Decrease) in cash and cash equivalents	8	(63)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	95	236
Cash, Cash Equivalents and Restricted Cash at End of Period	103	173
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net income	31	58
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	96	82
Deferred income taxes and amortization of investment tax credits	4	5
Other non-cash operating activities	10	(15)
Changes in assets and liabilities:
Accounts receivable	0	45
Receivables from and payables to affiliates, net	(18)	(6)
Inventories	(2)	(10)
Accounts payable and accrued expenses	36	(49)
Income taxes	(3)	20
Pension and non-pension postretirement benefit contributions	(7)	(64)
Other assets and liabilities	(21)	(37)
Net cash flows provided by (used in) operating activities	126	29
Cash flows from investing activities
Capital expenditures	(127)	(139)
Other investing activities	0	(5)
Net cash flows provided by (used in) investing activities	(127)	(144)
Cash flows from financing activities
Changes in short-term borrowings	34	144
Issuance of long-term debt	0	1
Dividends paid on common stock	(25)	(30)
Other financing activities	0	(1)
Net cash flows provided by (used in) financing activities	9	114
Increase (Decrease) in cash and cash equivalents	8	(1)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	40	42
Cash, Cash Equivalents and Restricted Cash at End of Period	48	41
Delmarva Power and Light Company [Member]
Cash flows from operating activities
Net income	31	57
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	45	39
Deferred income taxes and amortization of investment tax credits	10	13
Other non-cash operating activities	19	(7)
Changes in assets and liabilities:
Accounts receivable	(1)	6
Receivables from and payables to affiliates, net	(16)	1
Inventories	7	1
Accounts payable and accrued expenses	18	14
Income taxes	(5)	21
Other assets and liabilities	7	(23)
Net cash flows provided by (used in) operating activities	115	122
Cash flows from investing activities
Capital expenditures	(65)	(82)
Other investing activities	0	2
Net cash flows provided by (used in) investing activities	(65)	(80)
Cash flows from financing activities
Changes in short-term borrowings	(5)	0
Retirement of long-term debt	(4)	(14)
Dividends paid on common stock	(36)	(30)
Net cash flows provided by (used in) financing activities	(45)	(44)
Increase (Decrease) in cash and cash equivalents	5	(2)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	2	46
Cash, Cash Equivalents and Restricted Cash at End of Period	7	44
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net income	7	28
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	33	35
Deferred income taxes and amortization of investment tax credits	2	(7)
Other non-cash operating activities	9	2
Changes in assets and liabilities:
Accounts receivable	(5)	14
Receivables from and payables to affiliates, net	(4)	(5)
Inventories	0	(1)
Accounts payable and accrued expenses	30	(5)
Income taxes	0	3
Pension and non-pension postretirement benefit contributions	(6)	0
Other assets and liabilities	(7)	(6)
Net cash flows provided by (used in) operating activities	59	58
Cash flows from investing activities
Capital expenditures	(63)	(88)
Other investing activities	(1)	1
Net cash flows provided by (used in) investing activities	(64)	(87)
Cash flows from financing activities
Changes in short-term borrowings	28	0
Retirement of long-term debt	(8)	(10)
Dividends paid on common stock	(9)	(10)
Net cash flows provided by (used in) financing activities	11	(20)
Increase (Decrease) in cash and cash equivalents	6	(49)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	31	133
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 37	$ 84

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents		$ 787	$ 898
Restricted cash and cash equivalents		209	207
Accounts receivable, net
Customer		4,190	4,445
Other		1,103	1,132
Mark-to-market derivative assets, current		978	976
Unamortized energy contract assets		55	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		180	340
Inventory, Raw Materials and Supplies, Gross		1,291	1,311
Regulatory Assets, Current		1,245	1,267
Other		1,495	1,260
Total current assets		11,533	11,896
Property, plant and equipment, net		74,711	74,202
Deferred debits and other assets
Regulatory Assets, Noncurrent		8,063	8,021
Nuclear decommissioning trust funds		13,149	13,272
Investments		640	640
Goodwill		6,677	6,677
Mark-to-market derivative assets, noncurrent		527	337
Unamortized energy contract assets		385	395
Other		1,333	1,330
Total deferred debits and other assets		30,774	30,672
Total assets	[1]	117,018	116,770
Current Liabilities
Short-term borrowings		1,654	929
Long-term debt due within one year		1,203	2,088
Accounts payable		3,207	3,532
Accrued expenses		1,569	1,837
Payable to affiliates, current		5	5
Regulatory Liability, Current		522	523
Mark-to-market derivative liabilities		415	232
Unamortized energy contract liabilities		202	231
Energy Marketing Accounts Payable		333	352
Accounts Payable and Accrued Liabilities, Current		87	87
Other		956	982
Total current liabilities		10,153	10,798
Long-term debt		32,905	32,176
Long-term debt to financing trust		389	389
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		11,344	11,235
Asset Retirement Obligations, Noncurrent		10,126	10,029
Pension obligations		3,433	3,736
Non-pension postretirement benefit obligations		2,114	2,093
Spent nuclear fuel obligation		1,151	1,147
Regulatory Liability, Noncurrent		9,724	9,865
Mark-to-market derivative liabilities, noncurrent		468	409
Unamortized energy contract liabilities		579	609
Other		2,067	2,097
Total deferred credits and other liabilities		41,006	41,220
Total liabilities	[1]	84,453	84,583
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		18,973	18,964
Treasury stock, at cost (2 shares at March 31, 2018 and December 31, 2017)		(123)	(123)
Retained Earnings		14,346	14,081
Accumulated other comprehensive loss, net		(2,965)	(3,026)
Total shareholders’ equity		30,231	29,896
Member’s equity
Noncontrolling Interests		2,334	2,291
Total equity		32,565	32,187
Total liabilities and shareholders’ equity		117,018	116,770
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,556	3,618
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,727	9,597
Exelon Generation Co L L C [Member]
Current Assets
Cash and cash equivalents		610	416
Restricted cash and cash equivalents		127	138
Accounts receivable, net
Customer		2,478	2,697
Other		294	321
Mark-to-market derivative assets, current		978	976
Receivable from affiliates, current		153	140
Unamortized energy contract assets		55	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		151	264
Inventory, Raw Materials and Supplies, Gross		916	937
Other		1,122	933
Total current assets		6,884	6,882
Property, plant and equipment, net		24,714	24,906
Deferred debits and other assets
Nuclear decommissioning trust funds		13,149	13,272
Investments		431	433
Goodwill		47	47
Mark-to-market derivative assets, noncurrent		527	334
Prepaid pension asset		1,571	1,502
Unamortized energy contract assets		385	395
Deferred income taxes		10	16
Other		657	670
Total deferred debits and other assets		16,777	16,669
Total assets	[2]	48,375	48,457
Current Liabilities
Short-term borrowings		166	2
Long-term debt due within one year		373	346
Accounts payable		1,447	1,773
Accrued expenses		951	1,022
Payable to affiliates, current		114	123
Borrowings from Exelon intercompany money pool		54	54
Mark-to-market derivative liabilities		391	211
Unamortized energy contract liabilities		39	43
Energy Marketing Accounts Payable		333	352
Other		288	265
Total current liabilities		4,156	4,191
Long-term debt		7,685	7,734
Long-term debt to affiliate		907	910
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		3,749	3,811
Asset Retirement Obligations, Noncurrent		9,941	9,844
Non-pension postretirement benefit obligations		911	916
Spent nuclear fuel obligation		1,151	1,147
Payables to affiliates, noncurrent		2,970	3,065
Mark-to-market derivative liabilities, noncurrent		221	174
Unamortized energy contract liabilities		40	48
Other		686	658
Total deferred credits and other liabilities		19,669	19,663
Total liabilities	[2]	32,417	32,498
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Retained Earnings		4,303	4,349
Accumulated other comprehensive loss, net		(34)	(37)
Member’s equity
Membership Interest		9,357	9,357
Total members' equity		13,626	13,669
Noncontrolling Interests		2,332	2,290
Total equity		15,958	15,959
Total liabilities and shareholders’ equity		48,375	48,457
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,461	3,516
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,688	9,556
Commonwealth Edison Co [Member]
Current Assets
Cash and cash equivalents		70	76
Restricted cash and cash equivalents		9	5
Accounts receivable, net
Customer		485	559
Other		290	266
Receivable from affiliates, current		28	13
Inventories, net
Inventories, net		146	152
Regulatory Assets, Current		226	225
Other		82	68
Total current assets		1,336	1,364
Property, plant and equipment, net		21,010	20,723
Deferred debits and other assets
Regulatory Assets, Noncurrent		1,125	1,054
Investments		6	6
Goodwill		2,625	2,625
Receivable from affiliate, noncurrent		2,464	2,528
Prepaid pension asset		1,177	1,188
Other		259	238
Total deferred debits and other assets		7,656	7,639
Total assets		30,002	29,726
Current Liabilities
Short-term borrowings		317	0
Long-term debt due within one year		440	840
Accounts payable		491	568
Accrued expenses		198	327
Payable to affiliates, current		70	74
Regulatory Liability, Current		212	249
Mark-to-market derivative liabilities		24	21
Customer deposits		111	112
Other		82	103
Total current liabilities		1,945	2,294
Long-term debt		7,254	6,761
Long-term debt to financing trust		205	205
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		3,539	3,469
Asset Retirement Obligations, Noncurrent		111	111
Non-pension postretirement benefit obligations		215	219
Regulatory Liability, Noncurrent		6,212	6,328
Mark-to-market derivative liabilities, noncurrent		243	235
Other		572	562
Total deferred credits and other liabilities		10,892	10,924
Total liabilities		20,296	20,184
Stockholders' Equity Attributable to Parent
Common stock		1,588	1,588
Other paid-in capital		6,935	6,822
Retained Earnings, Unappropriated		(1,639)	(1,639)
Retained Earnings, Appropriated		2,822	2,771
Total shareholders’ equity		9,706	9,542
Member’s equity
Total liabilities and shareholders’ equity		30,002	29,726
PECO Energy Co [Member]
Current Assets
Cash and cash equivalents		21	271
Restricted cash and cash equivalents		5	4
Accounts receivable, net
Customer		349	327
Other		117	105
Inventories, net
Energy Related Inventory, Other Fossil Fuel		16	31
Inventory, Raw Materials and Supplies, Gross		33	30
Regulatory Assets, Current		78	29
Prepaid Taxes		97	8
Other		20	17
Total current assets		736	822
Property, plant and equipment, net		8,176	8,053
Deferred debits and other assets
Regulatory Assets, Noncurrent		408	381
Investments		25	25
Receivable from affiliate, noncurrent		505	537
Prepaid pension asset		359	340
Other		9	12
Total deferred debits and other assets		1,306	1,295
Total assets		10,218	10,170
Current Liabilities
Short-term borrowings		220	0
Long-term debt due within one year		0	500
Accounts payable		379	370
Accrued expenses		91	114
Payable to affiliates, current		59	53
Borrowings from Exelon intercompany money pool		194	0
Regulatory Liability, Current		117	141
Customer deposits		66	66
Other		29	23
Total current liabilities		1,155	1,267
Long-term debt		2,723	2,403
Long-term debt to financing trust		184	184
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,824	1,789
Asset Retirement Obligations, Noncurrent		27	27
Non-pension postretirement benefit obligations		288	288
Regulatory Liability, Noncurrent		529	549
Other		85	86
Total deferred credits and other liabilities		2,753	2,739
Total liabilities		6,815	6,593
Stockholders' Equity Attributable to Parent
Common stock		2,489	2,489
Retained Earnings		914	1,087
Accumulated other comprehensive loss, net		0	1
Total shareholders’ equity		3,403	3,577
Member’s equity
Total liabilities and shareholders’ equity		10,218	10,170
Baltimore Gas and Electric Company [Member]
Current Assets
Cash and cash equivalents		22	17
Restricted cash and cash equivalents		2	1
Accounts receivable, net
Customer		394	375
Other		91	94
Receivable from affiliates, current		0	1
Inventories, net
Energy Related Inventory, Natural Gas in Storage		12	37
Inventory, Raw Materials and Supplies, Gross		45	40
Regulatory Assets, Current		149	174
Prepaid Taxes		35	69
Other		5	3
Total current assets		755	811
Property, plant and equipment, net		7,725	7,602
Deferred debits and other assets
Regulatory Assets, Noncurrent		391	397
Investments		5	5
Prepaid pension asset		313	285
Other		6	4
Total deferred debits and other assets		715	691
Total assets		9,195	9,104
Current Liabilities
Short-term borrowings		45	77
Accounts payable		253	265
Accrued expenses		162	164
Payable to affiliates, current		51	52
Regulatory Liability, Current		102	62
Customer deposits		118	116
Other		26	24
Total current liabilities		757	760
Long-term debt		2,578	2,577
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,286	1,244
Asset Retirement Obligations, Noncurrent		22	23
Non-pension postretirement benefit obligations		199	202
Regulatory Liability, Noncurrent		1,083	1,101
Other		53	56
Total deferred credits and other liabilities		2,643	2,626
Total liabilities		5,978	5,963
Stockholders' Equity Attributable to Parent
Common stock		1,605	1,605
Retained Earnings		1,612	1,536
Total shareholders’ equity		3,217	3,141
Member’s equity
Total liabilities and shareholders’ equity		9,195	9,104
Pepco Holdings LLC [Member]
Current Assets
Cash and cash equivalents		43	30
Restricted cash and cash equivalents		40	42
Accounts receivable, net
Customer		484	486
Other		210	206
Inventories, net
Energy Related Inventory, Natural Gas in Storage		2	7
Inventory, Raw Materials and Supplies, Gross		152	151
Regulatory Assets, Current		507	554
Other		55	75
Total current assets		1,493	1,551
Property, plant and equipment, net		12,688	12,498
Deferred debits and other assets
Regulatory Assets, Noncurrent		2,453	2,493
Investments		132	132
Notes, Loans and Financing Receivable, Gross, Noncurrent		4	4
Goodwill		4,005	4,005
Prepaid pension asset		527	490
Deferred income taxes		4	4
Other		69	70
Total deferred debits and other assets		7,194	7,198
Total assets	[3]	21,375	21,247
Current Liabilities
Short-term borrowings		407	350
Long-term debt due within one year		385	396
Accounts payable		469	348
Accrued expenses		246	261
Payable to affiliates, current		100	90
Borrowings from Exelon intercompany money pool		13	0
Regulatory Liability, Current		77	56
Unamortized energy contract liabilities		162	188
Customer deposits		114	119
Merger related obligation		42	42
Other		52	81
Total current liabilities		2,067	1,931
Long-term debt		5,464	5,478
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		2,103	2,070
Asset Retirement Obligations, Noncurrent		16	16
Non-pension postretirement benefit obligations		102	105
Regulatory Liability, Noncurrent		1,888	1,872
Unamortized energy contract liabilities		539	561
Other		377	389
Total deferred credits and other liabilities		5,025	5,013
Total liabilities	[3]	12,556	12,422
Stockholders' Equity Attributable to Parent
Retained Earnings		(16)	(10)
Member’s equity
Membership Interest		8,835	8,835
Total members' equity		8,819	8,825
Total equity		8,819	8,825
Total liabilities and shareholders’ equity		21,375	21,247
Variable Interest Entity, Consolidated, Liabilities, No Recourse		95	102
Variable Interest Entity, Consolidated, Assets, Not Pledged			41
Potomac Electric Power Company [Member]
Current Assets
Cash and cash equivalents		15	5
Restricted cash and cash equivalents		33	35
Accounts receivable, net
Customer		246	250
Other		87	87
Inventories, net
Inventories, net		89	87
Regulatory Assets, Current		207	213
Other		19	33
Total current assets		696	710
Property, plant and equipment, net		6,095	6,001
Deferred debits and other assets
Regulatory Assets, Noncurrent		656	678
Investments		104	102
Prepaid pension asset		323	322
Other		22	19
Total deferred debits and other assets		1,105	1,121
Total assets		7,896	7,832
Current Liabilities
Short-term borrowings		60	26
Long-term debt due within one year		19	19
Accounts payable		181	139
Accrued expenses		145	137
Payable to affiliates, current		56	74
Regulatory Liability, Current		7	3
Customer deposits		52	54
Merger related obligation		42	42
Current portion of DC PLUG obligation		30	28
Other		8	28
Total current liabilities		600	550
Long-term debt		2,521	2,521
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		1,076	1,063
Non-pension postretirement benefit obligations		34	36
Regulatory Liability, Noncurrent		838	829
Other		288	300
Total deferred credits and other liabilities		2,236	2,228
Total liabilities		5,357	5,299
Stockholders' Equity Attributable to Parent
Common stock		1,470	1,470
Retained Earnings		1,069	1,063
Total shareholders’ equity		2,539	2,533
Member’s equity
Total liabilities and shareholders’ equity		7,896	7,832
Delmarva Power and Light Company [Member]
Current Assets
Cash and cash equivalents		7	2
Restricted cash and cash equivalents		0	0
Accounts receivable, net
Customer		141	146
Other		43	38
Receivable from affiliates, current		2	0
Inventories, net
Energy Related Inventory, Natural Gas in Storage		2	7
Inventory, Raw Materials and Supplies, Gross		34	36
Regulatory Assets, Current		63	69
Other		22	27
Total current assets		314	325
Property, plant and equipment, net		3,620	3,579
Deferred debits and other assets
Regulatory Assets, Noncurrent		242	245
Goodwill		8	8
Prepaid pension asset		192	193
Other		7	7
Total deferred debits and other assets		449	453
Total assets		4,383	4,357
Current Liabilities
Short-term borrowings		211	216
Long-term debt due within one year		79	83
Accounts payable		106	82
Accrued expenses		43	35
Payable to affiliates, current		32	46
Regulatory Liability, Current		48	42
Customer deposits		34	35
Other		5	8
Total current liabilities		558	547
Long-term debt		1,217	1,217
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		618	603
Non-pension postretirement benefit obligations		13	14
Regulatory Liability, Noncurrent		598	593
Other		49	48
Total deferred credits and other liabilities		1,278	1,258
Total liabilities		3,053	3,022
Stockholders' Equity Attributable to Parent
Common stock		764	764
Retained Earnings		566	571
Total shareholders’ equity		1,330	1,335
Member’s equity
Total liabilities and shareholders’ equity		4,383	4,357
Atlantic City Electric Company [Member]
Current Assets
Cash and cash equivalents		10	2
Restricted cash and cash equivalents		7	6
Accounts receivable, net
Customer		97	92
Other		51	56
Receivable from affiliates, current		1	0
Inventories, net
Inventories, net		29	29
Regulatory Assets, Current		64	71
Other		4	2
Total current assets		263	258
Property, plant and equipment, net		2,767	2,706
Deferred debits and other assets
Regulatory Assets, Noncurrent		377	359
Notes, Loans and Financing Receivable, Gross, Noncurrent		4	4
Prepaid pension asset		76	73
Other		43	45
Total deferred debits and other assets		500	481
Total assets	[4]	3,530	3,445
Current Liabilities
Short-term borrowings		136	108
Long-term debt due within one year		278	281
Accounts payable		166	118
Accrued expenses		41	33
Payable to affiliates, current		26	29
Regulatory Liability, Current		21	11
Customer deposits		28	31
Other		7	8
Total current liabilities		703	619
Long-term debt		836	840
Deferred credits and other liabilities
Deferred Income Taxes and Other Tax Liabilities, Noncurrent		496	493
Non-pension postretirement benefit obligations		14	14
Regulatory Liability, Noncurrent		416	411
Other		24	25
Total deferred credits and other liabilities		950	943
Total liabilities	[4]	2,489	2,402
Stockholders' Equity Attributable to Parent
Common stock		912	912
Retained Earnings		129	131
Total shareholders’ equity		1,041	1,043
Member’s equity
Total liabilities and shareholders’ equity		3,530	3,445
Variable Interest Entity, Consolidated, Liabilities, No Recourse		83	90
Variable Interest Entity, Consolidated, Assets, Not Pledged		$ 27	$ 29
[1]	Exelon’s consolidated assets include $9,727 million and $9,597 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,556 million and $3,618 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities.
[2]	Generation’s consolidated assets include $9,688 million and $9,556 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,461 million and $3,516 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities.
[3]	PHI’s consolidated total assets include $39 million and $41 million at March 31, 2018 and December 31, 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 $95 million and $102 million at March 31, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 — Variable Interest Entities.
[4]	ACE’s consolidated total assets include $27 million and $29 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $83 million and $90 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 3 — Variable Interest Entities.

Consolidated Balance Sheets (U5

Consolidated Balance Sheets (Unaudited) (Parenthetical) - shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common Stock, Shares Authorized	2,000,000,000	2,000,000,000
Common Stock, Shares, Outstanding	965,381,919	963,335,888
Treasury Stock, Shares held	1,832,457	1,832,457

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions		Total	Common Stock [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]		Noncontrolling Interest [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]Retained Earnings, Unappropriated [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]Common Stock [Member]	Baltimore Gas and Electric Company [Member]Retained Earnings [Member]	Pepco Holdings LLC [Member]	Pepco Holdings LLC [Member]Membership Interest [Member]	Pepco Holdings LLC [Member]Retained Earnings, Unappropriated [Member]	Potomac Electric Power Company [Member]	Potomac Electric Power Company [Member]Common Stock [Member]	Potomac Electric Power Company [Member]Retained Earnings [Member]	Delmarva Power and Light Company [Member]	Delmarva Power and Light Company [Member]Common Stock [Member]	Delmarva Power and Light Company [Member]Retained Earnings [Member]	Atlantic City Electric Company [Member]	Atlantic City Electric Company [Member]Common Stock [Member]	Atlantic City Electric Company [Member]Retained Earnings [Member]
Beginning balance at Dec. 31, 2016	[1]					$ (2,660)
Beginning Balance at Dec. 31, 2016	[1]											$ (54)
Beginning Balance at Dec. 31, 2016	[1]																						$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 971							$ 399						$ 141					$ 127					$ 125			$ 140			$ 58			$ 57			$ 28
Other Comprehensive Income (Loss), Net of Tax		$ (12)				(10)	[1]		11			13	[1]										0	[1]
Ending balance at Mar. 31, 2017	[1]					(2,670)
Ending Balance at Mar. 31, 2017	[1]											(41)
Ending Balance at Mar. 31, 2017	[1]																						1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															(2,771)
Beginning Balance (in shares) at Dec. 31, 2017		965,168
Beginning balance at Dec. 31, 2017		$ 32,187	$ 18,964	$ (123)	$ 14,081	(3,026)	[1]	$ 2,291
Beginning Balance at Dec. 31, 2017									15,959	$ 9,357	$ 4,349	(37)	[1]	$ 2,290														8,825	$ 8,835	$ (10)
Beginning Balance at Dec. 31, 2017		29,896													9,542	$ 1,588	$ 6,822	$ (1,639)	$ 2,771	3,577	$ 2,489	$ 1,087	1	[1]	3,141	$ 1,605	$ 1,536				2,533	$ 1,470	$ 1,063	1,335	$ 764	$ 571	1,043	$ 912	$ 131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		$ 636			585			51	186		136	0		50	165			165		113	0	113	0		128		128	65	0	65	31		31	31		31	7		7
Stock Issued During Period, Shares, Share-based Compensation, Gross		1,685
Stock Issued During Period, Value, Share-based Compensation, Gross		$ (3)	(3)	0	0	0		0
Stock Issued During Period, Shares, Employee Stock Purchase Plans		361
Stock Issued During Period, Value, Employee Stock Purchase Plan		$ 12	12	0	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(9)						(9)	(9)					(9)
Common stock dividends		(334)			(334)										(114)				(114)	(287)	0	(287)	0		(52)		(52)				(25)		(25)	(36)		(36)	(9)		(9)
Other Comprehensive Income (Loss), Net of Tax		72				71	[1]	1	7		0	6	[1]	1									0	[1]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		$ 4			14	(10)			3		6	(3)								0		1	(1)
Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared									(188)		(188)																	(71)	0	(71)
Adjustments to Additional Paid in Capital, Other															113		113
Ending Balance (in shares) at Mar. 31, 2018		967,214
Ending balance at Mar. 31, 2018		$ 32,565	$ 18,973	$ (123)	$ 14,346	$ (2,965)	[1]	$ 2,334
Ending Balance at Mar. 31, 2018									$ 15,958	$ 9,357	$ 4,303	$ (34)	[1]	$ 2,332														$ 8,819	$ 8,835	$ (16)
Ending Balance at Mar. 31, 2018		$ 30,231													9,706	$ 1,588	$ 6,935	(1,639)	2,822	$ 3,403	$ 2,489	$ 914	$ 0	[1]	$ 3,217	$ 1,605	$ 1,612				$ 2,539	$ 1,470	$ 1,069	$ 1,330	$ 764	$ 566	$ 1,041	$ 912	$ 129
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															$ (2,822)			$ (165)	$ (165)
[1]	All amounts are net of tax and noncontrolling interest. Amounts in parenthesis represent a decrease in AOCI.

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Significant Accounting Policies (All Registrants) Description of Business (All Registrants) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy distribution and transmission businesses. 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) Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. The accompanying consolidated financial statements as of March 31, 2018 and 2017 and for the three months then ended are unaudited but, in the opinion of the management of each Registrant include all adjustments that are considered necessary for a fair statement of the Registrants’ respective financial statements in accordance with GAAP. All adjustments are of a normal, recurring nature, except as otherwise disclosed. The December 31, 2017 revised Consolidated Balance Sheets were derived from audited financial statements. Financial results for interim periods are not necessarily indicative of results that may be expected for any other interim period or for the fiscal year ending December 31, 2018 . These Combined Notes to Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Prior Period Adjustments and Reclassifications (All Registrants) In the second quarter of 2017, errors were identified related to the Exelon, Generation, ComEd, PECO and BGE Consolidated Statements of Cash Flows for the three months ended March 31, 2017. These classification errors related to the presentation of changes in Accounts payable and accrued expenses and Accounts receivable within Cash flows provided by operating activities and Capital expenditures and Proceeds from sale of long-lived assets within Cash flows used in investing activities. These errors have been corrected in Exelon's, Generation's, ComEd's, PECO's, and BGE's Consolidated Statements of Cash Flows for the three months ended March 31, 2017 that are presented in this first quarter 2018 Form 10-Q. As revised, the Cash flows provided by operating activities for the three months ended March 31, 2017 are $1,074 million , $420 million , $236 million , $106 million and $208 million for Exelon, Generation, ComEd, PECO and BGE, respectively, an increase (decrease) of $(127) million , $(320) million , $91 million , $42 million and $40 million for Exelon, Generation, ComEd, PECO and BGE, respectively, from the originally reported amounts. As revised, the Cash flows used in investing activities are $2,283 million , $910 million , $619 million , $69 million and $202 million for Exelon, Generation, ComEd, PECO and BGE, respectively, an increase (decrease) of $(127) million , $(320) million , $91 million , $42 million and $40 million for Exelon, Generation, ComEd, PECO and BGE, respectively, from the originally reported amounts. Management concluded that the errors are not material to the previously issued financial statements. Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. Beginning on January 1, 2018, Exelon adopted the following new accounting standards requiring reclassification or adjustments to previously reported information as follows: • Statement of Cash Flows: Classification of Restricted Cash. 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 18 — Supplemental Financial Information for further information. • Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . Exelon early adopted and retrospectively applied the new guidance to when the effects of the TCJA were recognized and, accordingly, recasted its December 31, 2017 AOCI and retained earnings in its Consolidated Balance Sheet and Consolidated Statement of Changes in Shareholders' Equity. 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 2 — New Accounting Standards for further information. • Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. Exelon applied this guidance retrospectively for the presentation of the service and other non-service costs components of net benefit cost and, accordingly, have recasted those amounts, which were not material, in its Consolidated Statement of Operations and Comprehensive Income in prior periods presented. As part of the adoption, 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. See Note 14 — Retirement Benefits for further information. • Revenue from Contracts with Customers . 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' 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 Financial Statements were not material. See Note 5 — Revenue from Contracts with Customers for further information. Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 4,560 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,197 — — — — — — — — Operating revenues — 4,558 — — — — — — — Electric operating revenues — — 1,293 589 665 1,097 529 294 274 Natural gas operating revenues — — — 206 281 66 — 66 — Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,757 $ 4,888 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 Operating Revenues - Adjustments Competitive business revenues $ (10 ) $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (79 ) — — — — — — — — Operating revenues — (10 ) — — — — — — — Electric operating revenues — — (14 ) — (25 ) (30 ) (15 ) (9 ) (6 ) Natural gas operating revenues — — — — (10 ) — — — — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — — — — — — — — — Total operating revenues $ (10 ) $ (10 ) $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 4,550 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,118 — — — — — — — — Operating revenues — 4,548 — — — — — — — Electric operating revenues — — 1,279 589 640 1,067 514 285 268 Natural gas operating revenues — — — 206 271 66 — 66 — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,747 $ 4,878 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 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 5 — Revenue from Contracts with Customers and Note 6 — Regulatory Matters for further information. RTOs and ISOs . In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly sale or purchase position. In addition, capacity revenue and expense classification is based on the net sale or purchase position of the Registrants in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives . Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 6 — Regulatory Matters and Note 10 — Derivative Financial Instruments for further 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 natural gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed directly on the Registrants. The Registrants do not recognize revenue or expense in their Consolidated Statements of Operations and Comprehensive Income when these taxes are imposed on the customer, such as sales taxes. However, when these taxes are imposed directly on the Registrants, such as gross receipts taxes or other surcharges or fees, the Registrants recognize revenue for the taxes collected from customers along with an offsetting expense. See Note 18 — 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.

New Accounting Standards (All R

New Accounting Standards (All Registrants)	3 Months Ended
	Mar. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	New Accounting Standards Issued and Not Yet Adopted as of March 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 March 31, 2018. Unless otherwise indicated, the Registrants are currently assessing the impacts such guidance may have (which could be material) on 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. 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 standard is effective January 1, 2019. Early adoption is permitted, however the Registrants will not early adopt the standard. The issued guidance required a modified retrospective transition approach, which requires lessees and lessors to recognize and measure leases at the beginning of the earliest period presented (January 1, 2017). In January 2018, the FASB proposed amending the standard to give entities another option for transition. The proposed transition method would allow entities to initially apply the requirements of the standard in the period of adoption (January 1, 2019). The Registrants will assess this transition option when the FASB issues the standard. The new guidance requires lessees to recognize both the right-of-use assets and lease liabilities in the balance sheet for most leases, whereas today only finance lease liabilities (referred to as capital leases) are 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 guidance, 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 current 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 current disclosures relate only to lessees. Significant changes to lease systems, processes and procedures are required to implement the requirements of the new standard. The recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee have not significantly changed from current GAAP. Lessor accounting is also largely unchanged. The standard provides a number of transition practical expedients that entities may elect. These include 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. The Registrants expect to elect this practical expedient. In January 2018, the FASB issued additional guidance which provides another optional transition practical expedient. This practical expedient allows entities to not evaluate land easements under the new guidance at adoption if they were not previously accounted for as leases. The Registrants have assessed the lease standard and are executing a detailed implementation plan in preparation for adoption on January 1, 2019. Key activities in the implementation plan include: • Developing a complete lease inventory and abstracting the required data attributes into a lease accounting system that supports the Registrants' lease portfolios and integrates with existing systems. • Evaluating the transition practical expedients available under the guidance. • Identifying, assessing and documenting technical accounting issues, policy considerations and financial reporting implications which includes completing a detailed contract assessment for a sample of transactions to determine whether they are leases under the new guidance. • Identifying and implementing changes to processes and controls to ensure all impacts of the new guidance are effectively addressed. 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. 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 March 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. Derivatives and Hedging (Issued September 2017): Allows more financial and nonfinancial hedging strategies to be eligible for hedge accounting. The amendments are intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. There are also amendments related to effectiveness testing and disclosure requirements. The guidance is effective January 1, 2019 and early adoption is permitted with a modified retrospective transition approach. The Registrants are currently assessing this standard but do not currently expect a significant impact given the limited activity for which the Registrants elect hedge accounting and because the Registrants do not anticipate increasing their use of hedge accounting as a result of this standard.
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	New Accounting Standards (All Registrants) New Accounting Standards Adopted: In 2018, the Registrants have adopted the following new authoritative accounting guidance issued by the FASB. 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 during the first quarter 2018 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 related to deferred income taxes associated with Exelon’s pension and OPEB obligations. There was no impact for Generation, ComEd, PECO, BGE, PHI, Pepco, DPL or ACE. See Note 1 — Significant Accounting Policies of the Exelon 2017 Form 10-K for information on other new accounting standards issued and adopted as of January 1, 2018.

Variable Interest Entities (All

Variable Interest Entities (All Registrants)	3 Months Ended
	Mar. 31, 2018
Variable Interest Entity [Abstract]
Variable Interest Entity Disclosure (All Registrants)	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 March 31, 2018 and December 31, 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 March 31, 2018 and December 31, 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 As of March 31, 2018 and December 31, 2017 , Exelon's and Generation's consolidated VIEs consist of: • energy related companies involved in distributed generation, backup generation and energy development • renewable energy project companies formed by Generation to build, own and operate renewable power facilities • certain retail power and gas companies for which Generation is the sole supplier of energy, and • CENG. As of March 31, 2018 and December 31, 2017 , Exelon's, PHI's and ACE's consolidated VIE consist of: • ATF , 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. As of March 31, 2018 and December 31, 2017 , ComEd, PECO, BGE, Pepco and DPL did not have any material consolidated VIEs. As of March 31, 2018 and December 31, 2017 , Exelon and Generation provided the following support to their respective consolidated VIEs: • Generation provides operating and capital funding to the renewable energy project companies and there is limited recourse to Generation related to certain renewable energy project companies. • Generation provides operating and capital funding to one of the energy related companies involved in backup generation. • Generation provides approximately $30 million in credit support for the retail power and gas companies for which Generation is the sole supplier of energy. • Exelon and Generation, where indicated, provide the following support to CENG (see Note 26 — Related Party Transactions of the Exelon 2017 Form 10-K for additional information regarding Generation's and Exelon’s transactions with CENG): • under power purchase agreements with CENG, Generation purchased or will purchase 50.01% of the available output generated by the CENG nuclear plants not subject to other contractual agreements from January 2015 through the end of the operating life of each respective plant. However, pursuant to amendments dated March 31, 2015, the energy obligations under the Ginna Nuclear Power Plant (Ginna) PPAs were suspended during the term of the Reliability Support Services Agreement (RSSA), through the end of March 31, 2017. With the expiration of the RSSA, the PPA was reinstated beginning April 1, 2017 (see Note 6 — Regulatory Matters for additional details), • Generation provided a $400 million loan to CENG. As of March 31, 2018 , the remaining obligation is $337 million , including accrued interest, which reflects the principal payment made in January 2015, • Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF against third-party claims that may arise from any future nuclear incident (as defined in the Price-Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this Indemnity Agreement. (See Note 17 — Commitments and Contingencies for more details), • Generation and EDF share in the $637 million of contingent payment obligations for the payment of contingent retrospective premium adjustments for the nuclear liability insurance, • 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 March 31, 2018 and December 31, 2017 , Exelon, PHI and ACE provided the following support to their respective consolidated VIE: • In the case of ATF, 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 months ended March 31, 2018 , ACE transferred $8 million to ATF. During the three months ended March 31, 2017 , ACE transferred $19 million to ATF. For each of the consolidated VIEs, except as otherwise noted: • the assets of the VIEs are restricted and can only be used to settle obligations of the respective VIE; • Exelon, Generation, PHI and ACE did not provide any additional material financial support to the VIEs; • Exelon, Generation, PHI and ACE did not have any material contractual commitments or obligations to provide financial support to the VIEs; and • the creditors of the VIEs did not have recourse to Exelon’s, Generation’s, PHI's or ACE's general credit. The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at March 31, 2018 and December 31, 2017 are as follows: March 31, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 823 $ 812 $ 11 $ 7 $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,279 9,251 28 20 9,317 9,286 31 23 Total assets $ 10,102 $ 10,063 $ 39 $ 27 $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 269 $ 236 $ 33 $ 29 $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,292 3,230 62 54 3,316 3,250 66 58 Total liabilities $ 3,561 $ 3,466 $ 95 $ 83 $ 3,624 $ 3,522 $ 102 $ 90 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. 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 March 31, 2018 and December 31, 2017 , these assets and liabilities primarily consisted of the following: March 31, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 280 $ 280 $ — $ — $ 126 $ 126 $ — $ — Restricted cash 73 66 7 7 64 58 6 6 Accounts receivable, net Customer 154 154 — — 170 170 — — Other 29 29 — — 25 25 — — Inventory Materials and supplies 202 202 — — 205 205 — — Other current assets 55 51 4 — 45 41 4 — Total current assets 793 782 11 7 635 625 10 6 Property, plant and equipment, net 6,181 6,181 — — 6,186 6,186 — — Nuclear decommissioning trust funds 2,483 2,483 — — 2,502 2,502 — — Other noncurrent assets 270 242 28 20 274 243 31 23 Total noncurrent assets 8,934 8,906 28 20 8,962 8,931 31 23 Total assets $ 9,727 $ 9,688 $ 39 $ 27 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 102 $ 70 $ 32 $ 28 $ 102 $ 67 $ 35 $ 31 Accounts payable 93 93 — — 114 114 — — Accrued expenses 52 51 1 1 67 66 1 1 Unamortized energy contract liabilities 17 17 — — 18 18 — — Other current liabilities 5 5 — — 7 7 — — Total current liabilities 269 236 33 29 308 272 36 32 Long-term debt 1,125 1,063 62 54 1,154 1,088 66 58 Asset retirement obligations 2,062 2,062 — — 2,035 2,035 — — Unamortized energy contract liabilities 1 1 — — 5 5 — — Other noncurrent liabilities 99 99 — — 116 116 — — Total noncurrent liabilities 3,287 3,225 62 54 3,310 3,244 66 58 Total liabilities $ 3,556 $ 3,461 $ 95 $ 83 $ 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 on Exelon’s and Generation’s Consolidated Balance Sheets in Investments. For the energy purchase and sale contracts (commercial agreements), the carrying amount of assets and liabilities in Exelon’s and Generation’s Consolidated Balance Sheets that relate to their involvement with the VIEs are predominately related to working capital accounts and generally represent the amounts owed by, or owed to, Exelon and Generation for the deliveries associated with the current billing cycles under the commercial agreements. Further, Exelon and Generation have not provided material debt or equity support, liquidity arrangements or performance guarantees associated with these commercial agreements. As of March 31, 2018 and December 31, 2017 , Exelon's and Generation's unconsolidated VIEs consist of: • Energy purchase and sale agreements with VIEs for which Generation has concluded that consolidation is not required. • Asset sale agreement with ZionSolutions, LLC and EnergySolutions, Inc. in which Generation has a variable interest but has concluded that consolidation is not required. • Equity investments in distributed energy companies for which Generation has concluded that consolidation is not required. As of March 31, 2018 and December 31, 2017 , ComEd, PECO, BGE, PHI, Pepco, ACE and DPL did not have any material unconsolidated VIEs. As of March 31, 2018 and December 31, 2017 , Exelon and Generation had significant unconsolidated variable interests in seven VIEs for which Exelon or Generation, as applicable, was not the primary beneficiary; including certain equity investments and certain commercial agreements. Exelon and Generation only include unconsolidated VIEs that are individually material in the tables below. However, Generation has several individually immaterial VIEs that in aggregate represent a total investment of $9 million . These immaterial VIEs are equity and debt securities in energy development companies. The maximum exposure to loss related to these securities is limited to the $9 million included in Investments on Exelon’s and Generation’s Consolidated Balance Sheets . The risk of a loss was assessed to be remote and, accordingly, Exelon and Generation have not recognized a liability associated with any portion of the maximum exposure to loss. The following tables present summary information about Exelon's and Generation’s significant unconsolidated VIE entities: March 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 626 $ 501 $ 1,127 Total liabilities (a) 37 225 262 Exelon's ownership interest in VIE (a) — 246 246 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 246 246 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) 2 — 2 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 on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $30 million and $39 million as of March 31, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions, LLC of $28 million and $37 million as of March 31, 2018 and December 31, 2017 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. See Note 13 — Nuclear Decommissioning for additional details. 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 affect the fair value or risk of their variable interests in these VIEs.

Mergers, Acquisitions, and Disp

Mergers, Acquisitions, and Dispositions	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Mergers, Acquisitions and Dispositions (Exelon and Generation) Acquisition of Handley Generating Station (Exelon and Generation) 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. 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 was approved by the Bankruptcy Court in January 2018 and 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. Acquisition of James A. FitzPatrick Nuclear Generating Station (Exelon and Generation) On March 31, 2017, Generation acquired the 842 MW single-unit James A. FitzPatrick (FitzPatrick) nuclear generating station located in Scriba, New York from Entergy Nuclear FitzPatrick LLC (Entergy) for a total purchase price of $289 million , which consisted of a cash purchase price of $110 million and a net cost reimbursement to and on behalf of Entergy of $179 million . As part of the acquisition agreements, Generation provided nuclear fuel and reimbursed Entergy for incremental costs to prepare for and conduct a plant refueling outage; and Generation reimbursed Entergy for incremental costs to operate and maintain the plant for the period after the refueling outage through the acquisition closing date. These reimbursements covered costs that Entergy otherwise would have avoided had it shut down the plant as originally intended in January 2017. The amounts reimbursed by Generation were offset by FitzPatrick's electricity and capacity sales revenues for this same post-outage period. As part of the transaction, Generation received the FitzPatrick NDT fund assets and assumed the obligation to decommission FitzPatrick. The NRC license for FitzPatrick expires in 2034. The fair values of FitzPatrick’s assets and liabilities were determined based on significant estimates and assumptions that are judgmental in nature, including projected future cash flows (including timing), discount rates reflecting risk inherent in the future cash flows and future power and fuel market prices. The valuations performed in the first quarter of 2017 to determine the fair value of the FitzPatrick assets acquired and liabilities assumed were updated in the third quarter of 2017. The purchase price allocation is now final. For the three months ended March 31, 2017, an after-tax bargain purchase gain of $226 million is included within Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income and primarily reflects differences in strategies between Generation and Entergy for the intended use and ultimate decommissioning of the plant. During the third quarter of 2017, Exelon and Generation recorded an additional after-tax bargain purchase gain of $7 million for the three months ended September 30, 2017. The total after-tax bargain purchase gain recorded at Exelon and Generation was $233 million for the twelve months ended December 31, 2017. See Note 13 — Nuclear Decommissioning and Note 14 — Retirement Benefits for additional information regarding the FitzPatrick decommissioning ARO and pension and OPEB updates. The following table summarizes the 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 23 - Commitments and Contingencies of the Exelon 2017 Form 10-K for additional background regarding SNF obligations to the DOE. Exelon and Generation incurred $32 million of merger and integration costs related to FitzPatrick for the three months ended March 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 three months ended March 31, 2018 . Asset Dispositions 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 on Exelon's and Generations' 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 in Gain on sales of assets and businesses on Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2018 .

Revenue from Contracts with Cus

Revenue from Contracts with Customers Revenue from Contracts with Customers (All Registrants)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 4,560 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,197 — — — — — — — — Operating revenues — 4,558 — — — — — — — Electric operating revenues — — 1,293 589 665 1,097 529 294 274 Natural gas operating revenues — — — 206 281 66 — 66 — Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,757 $ 4,888 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 Operating Revenues - Adjustments Competitive business revenues $ (10 ) $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (79 ) — — — — — — — — Operating revenues — (10 ) — — — — — — — Electric operating revenues — — (14 ) — (25 ) (30 ) (15 ) (9 ) (6 ) Natural gas operating revenues — — — — (10 ) — — — — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — — — — — — — — — Total operating revenues $ (10 ) $ (10 ) $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 4,550 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,118 — — — — — — — — Operating revenues — 4,548 — — — — — — — Electric operating revenues — — 1,279 589 640 1,067 514 285 268 Natural gas operating revenues — — — 206 271 66 — 66 — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,747 $ 4,878 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 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. Revenues related to such contracts are generally recognized over time as the power is generated and simultaneously delivered to the customer. However, revenues related to the sale of any goods or services that are not simultaneously received and consumed by the customer are recognized as the performance obligations are satisfied at a point in time. 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, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) 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, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) 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 $25 million and $26 million as of March 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 $5 million and $9 million for the three months ended March 31, 2018 and 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 on Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to March 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 28 Amounts reclassified to receivables (9 ) Balance at March 31, 2018 $ 302 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. 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 on Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to March 31, 2018: Contract Liabilities Exelon and Generation Balance as of January 1, 2018 $ 35 Increases as a result of additional cash received or due 227 Amounts recognized into revenues (216 ) Balance at March 31, 2018 $ 46 The Utility Registrants also record contract liabilities when consideration is received prior to the satisfaction of the performance obligations. As of March 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 March 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 $ 544 $ 264 $ 104 $ 46 $ 128 $ 1,086 Generation 544 264 104 46 128 $ 1,086 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 19 — Segment Information for the presentation of the Registrant's revenue disaggregation.

Regulatory Matters (All Registr

Regulatory Matters (All Registrants)	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Regulatory Matters (All Registrants)	Regulatory Matters (All Registrants) Except for the matters noted below, the disclosures set forth in Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K reflect, in all material respects, the current status of regulatory and legislative proceedings of the Registrants. The following is an update to that discussion. Illinois Regulatory Matters Tax Cuts and Jobs Act (Exelon and ComEd). On January 18, 2018, the ICC approved ComEd's petition filed on January 5, 2018 seeking approval to pass back to customers beginning February 1, 2018 $201 million in tax savings resulting from the enactment of the TCJA through a reduction in electric distribution rates. The amounts being passed back to customers reflect the benefit of lower income tax rates beginning January 1, 2018 and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. Refer to Note 12 — Income Taxes for more detail on Corporate Tax Reform. Electric Distribution Formula Rate (Exelon and ComEd). On April 16, 2018, ComEd filed its annual distribution formula rate update with the ICC. The filing establishes the revenue requirement used to set the rates that will take effect in January 2019 after the ICC’s review and approval, which is due by December 2018. The revenue requirement requested is based on 2017 actual costs plus projected 2018 capital additions as well as an annual reconciliation of the revenue requirement in effect in 2017 to the actual costs incurred that year. ComEd's 2018 filing request includes a total decrease to the revenue requirement of $23 million , reflecting a decrease of $58 million for the initial revenue requirement for 2018 and an increase of $35 million related to the annual reconciliation for 2017. The revenue requirement for 2018 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. The annual reconciliation for 2017 provided 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. For additional information on ComEd's distribution formula rate filings see Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K. During the first quarter 2018, ComEd revised its electric distribution formula rate, as provided for by FEJA, to reduce the ROE collar calculation from plus or minus 50 basis points to 0 basis points beginning with the reconciliation filed in 2018 for the 2017 calendar year. This revision effectively offsets the favorable or unfavorable impacts to ComEd's electric distribution formula rate revenues associated with variations in delivery volumes associated with above or below normal weather, numbers of customers or usage per customer. ComEd began reflecting the impacts of this change in its electric distribution services costs regulatory asset in the first quarter 2017. Zero Emission Standard (Exelon, Generation and ComEd). Pursuant to FEJA, on January 25, 2018, the ICC announced that Generation’s Clinton Unit 1, Quad Cities Unit 1 and Quad Cities Unit 2 nuclear plants were selected as the winning bidders through the IPA's ZEC procurement event. Generation executed the ZEC procurement contracts with Illinois utilities, including ComEd, effective January 26, 2018 and began recognizing revenue. Winning bidders are entitled to compensation for the sale of ZECs retroactive to the June 1, 2017 effective date of FEJA. In the first quarter of 2018, Generation recognized approximately $202 million of revenue, of which $150 million related to ZECs generated from June 1, 2017 through December 31, 2017. ComEd recovers all costs associated with purchasing ZECs through a rate rider that provides for an annual reconciliation and true-up to actual costs incurred by ComEd to purchase ZECs, with any difference to be credited to or collected from ComEd’s retail customers in subsequent periods with interest. ComEd began billing its retail customers under its new ZEC rate rider on June 1, 2017. On February 14, 2017, two lawsuits were filed in the Northern District of Illinois against the IPA alleging that the state’s ZEC program violates certain provisions of the U.S. Constitution. One lawsuit was filed by customers of ComEd, led by the Village of Old Mill Creek, and the other was brought by the EPSA and three other electric suppliers. Both lawsuits argue that the Illinois ZEC program will distort PJM's FERC-approved energy and capacity market auction system of setting wholesale prices, and seek a permanent injunction preventing the implementation of the program. Exelon intervened and filed motions to dismiss in both lawsuits. In addition, on March 31, 2017, plaintiffs in both lawsuits filed motions for preliminary injunction with the court; the court stayed briefing on the motions for preliminary injunction until the resolution of the motions to dismiss. On July 14, 2017, the district court granted the motions to dismiss. On July 17, 2017, the plaintiffs appealed the decision to the Seventh Circuit. Briefs were fully submitted on December 12, 2017, the Court heard oral argument on January 3, 2018. At the argument, the Court asked for supplemental briefing, which was filed on January 26, 2018. On February 21, 2018, the Seventh Circuit issued an order inviting the Solicitor General to express the views of the United States on the matter, however the timing of that response is currently uncertain. Exelon cannot predict the outcome of these lawsuits. It is possible that resolution of these matters could have a material, unfavorable impact on Exelon’s and Generation’s results of operations, cash flows, and financial positions. See Note 8 — Early Plant Retirements for additional information regarding the economic challenges facing Generation’s Clinton and Quad Cities nuclear plants and the expected benefits of the ZES. Pennsylvania Regulatory Matters 2018 Pennsylvania Electric Distribution Base Rate Case (Exelon and PECO). On March 29, 2018, PECO filed a request with the PAPUC seeking approval to increase its electric distribution base rates by $82 million beginning January 1, 2019. This requested amount includes the effect of an approximately $71 million reduction as a result of the ongoing annual tax savings beginning January 1, 2019 associated with the TCJA. The requested ROE is 10.95% . PECO expects a decision on its electric distribution rate case proceeding in the fourth quarter of 2018 but cannot predict what increase, if any, the PAPUC will approve. Tax Cuts and Jobs Act (Exelon and PECO). As part of the rate case filing referenced above, PECO is seeking approval to pass back to electric distribution customers $68 million in 2018 TCJA tax savings, which would be an additional offset to the proposed increase to its electric distribution rates. PECO will file with the PAPUC in 2018 seeking approval to pass back to gas distribution customers $4 million in TCJA tax savings beginning January 1, 2019. The amounts being proposed to be passed back to customers reflect the annual benefit of lower income tax rates established upon enactment of the TCJA . PECO cannot predict the amount or timing of the refunds the PAPUC will ultimately approve. See Note 12 — Income Taxes for more detail on Corporate Tax Reform and the table below for regulatory liabilities recognized during 2018 associated with TCJA tax savings that will be passed through future customer rates. Maryland Regulatory Matters Tax Cuts and Jobs Act (Exelon, BGE, PHI, Pepco and DPL). On January 12, 2018, the MDPSC issued an order that directed each of BGE, Pepco and DPL to track the impacts of the TCJA beginning January 1, 2018 and file by February 15, 2018 how and when they expect to pass through such impacts to their customers. On January 31, 2018, the MDPSC approved BGE’s petition to pass back to customers $103 million in ongoing annual tax savings resulting from the enactment of the TCJA through a reduction in distribution base rates beginning February 1, 2018, of which $72 million and $31 million were related to electric and natural gas, respectively. The amounts being passed back to customers reflect the ongoing annual benefit of lower income tax rates and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. It is expected that the MDPSC will address later in 2018 the treatment of BGE's TCJA tax savings for the period January 1, 2018 through February 1, 2018. On April 20, 2018, Pepco entered into a settlement agreement with several parties to resolve all issues in its pending electric distribution base rate case, including the treatment of the annual ongoing TCJA tax savings as well as the TCJA tax savings from January 1, 2018 through the expected effective date of the rate change. See discussion below for further details. On February 9, 2018, DPL filed with the MDPSC seeking approval to pass back to customers $13 million in ongoing annual TCJA tax savings through a reduction in electric distribution base rates beginning in 2018. On April 18, 2018, the MDPSC approved a settlement agreement to pass back to customers $14 million in ongoing annual TCJA tax savings through a reduction in electric distribution base rates beginning April 20, 2018. The amounts being passed back to customers reflect the ongoing annual benefit of lower income tax rates and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. In addition, the MDPSC separately ordered DPL to provide a one-time bill credit to customers of $2 million in June 2018 representing the TCJA tax savings from January 1, 2018 through March 31, 2018. See Note 12 — Income Taxes for more detail on Corporate Tax Reform and the table below for regulatory liabilities recognized during 2018 associated with TCJA tax savings that will be passed through future customer rates. 2018 Maryland Electric Distribution Base Rates (Exelon, PHI and Pepco). On January 2, 2018, Pepco filed an application with the MDPSC to increase its annual electric distribution base rates by $41 million , reflecting a requested ROE of 10.1% . On February 5, 2018, Pepco filed with the MDPSC an update to its current distribution base rate case to reflect $31 million in ongoing annual TCJA tax savings, thereby reducing the requested annual base rate increase to $11 million . On March 8, 2018, Pepco filed with the MDPSC a subsequent update to its electric distribution base rate case, which further reduced the requested annual base rate increase to $3 million . On April 20, 2018, Pepco entered into a settlement agreement with several parties to resolve all issues in the rate case and filed the settlement agreement with the MDPSC. The settlement agreement provides for a net decrease to annual electric distribution base rates of $15 million , which includes annual ongoing TCJA tax savings, and reflects a ROE of 9.5% . The parties to the settlement agreement have requested that Pepco’s new rates be effective on June 1, 2018. In addition, the settlement agreement separately provides a one-time bill credit to customers of approximately $10 million representing the TCJA tax savings from January 1, 2018 through the expected rate effective date of June 1, 2018. Pepco expects a decision in the matter in the second quarter of 2018. 2017 Maryland Electric Distribution Base Rates (Exelon, PHI and DPL). On July 14, 2017, DPL filed an application with the MDPSC to increase its annual electric distribution base rates by $27 million , which was updated to $19 million on November 16, 2017, reflecting a requested ROE of 10.1% . On December 18, 2017, a settlement agreement was filed with the MDPSC wherein DPL will be granted a base rate increase of $13 million , and a ROE of 9.5% solely for purposes of calculating AFUDC and regulatory asset carrying costs. On February 9, 2018, the MDPSC approved the settlement agreement and the new rates became effective. Delaware Regulatory Matters Tax Cuts and Jobs Act (Exelon, PHI and DPL). On January 16, 2018, the DPSC opened a docket indicating that DPL’s TCJA tax savings would be addressed in its pending rate cases. See discussion below for more details. 2017 Delaware Electric and Natural Gas Distribution Base Rates (Exelon, PHI and DPL). On August 17, 2017, DPL filed applications with the DPSC to increase its annual electric and natural gas distribution base rates by $24 million and $13 million , respectively, reflecting a requested ROE of 10.1% . DPL filed updated testimony on October 18, 2017, to request a $31 million increase in electric distribution base rates, and updated testimony on November 7, 2017, to request an $11 million increase in natural gas distribution base rates. On October 16, 2017 and November 1, 2017, $2.5 million of the proposed rate increases for electric and natural gas, respectively, were put into effect, subject to refund, based on the final DPSC order. On February 9, 2018, DPL filed with the DPSC updates to its distribution base rate cases to reflect $26 million in ongoing annual TCJA tax savings, of which $19 million and $7 million is related to electric and natural gas, respectively. The proposed distribution base rate increase in each rate case were lowered by those amounts, which reflect the ongoing annual benefit of lower income tax rates and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. It is expected that the DPSC will address in a future rate proceeding DPL's treatment of the TCJA tax savings for the period February 1, 2018 through the effective date of any final customer rate adjustments in the pending rate proceedings. On March 17, 2018, an additional $3 million of the proposed rate increase in the electric distribution base rate case and $1 million in the natural gas distribution base rate case was put into effect subject to refund based on the final DPSC order. DPL expects decisions on its electric and natural gas distribution base rate proceedings in the third and fourth quarters of 2018, respectively, but cannot predict how much of the requested increases the DPSC will approve. See Note 12 — Income Taxes for more detail on Corporate Tax Reform and the table below for regulatory liabilities recognized during 2018 associated with TCJA tax savings that will be passed through future customer rates. District of Columbia Regulatory Matters Tax Cuts and Jobs Act (Exelon, PHI and Pepco) . On January 23, 2018, the DCPSC opened a rate proceeding directing Pepco to track the impacts of the TCJA beginning January 1, 2018 and file its plan to reduce the current revenue requirement by customer class by February 12, 2018. The DCPSC stated it will address the impact of the TCJA on future rates within Pepco's pending electric distribution base rate case discussed below. On February 6, 2018, Pepco filed with the DCPSC seeking approval to pass back to customers $39 million in ongoing annual tax savings resulting from the enactment of the TCJA through a reduction to existing electric distribution base rates beginning in 2018. On April 17, 2018, Pepco entered into a settlement agreement with several parties to resolve all issues in its pending electric distribution base rate case, including the treatment of the annual ongoing TCJA tax savings as well as the TCJA tax savings from January 1, 2018 through the expected effective date of the rate change. See discussion below for more details. 2017 District of Columbia Electric Distribution Base Rates (Exelon, PHI and Pepco). On December 19, 2017 (and updated on February 9, 2018), Pepco filed an application with the DCPSC to increase its annual electric distribution base rates by $66 million , reflecting a requested ROE of 10.1% . On April 17, 2018, Pepco entered into a settlement agreement with several parties to resolve both the pending electric distribution base rate case and the $39 million rate reduction request in the TCJA proceeding discussed above, and filed the settlement agreement with the DCPSC. The settlement agreement provides for a net decrease to annual electric distribution rates of $24 million , which includes annual ongoing TCJA tax savings, and a ROE of 9.525% . The parties to the settlement agreement have requested that Pepco’s new rates be effective on July 1, 2018. In addition, the settlement agreement separately provides a one-time bill credit to customers of approximately $19 million representing the TCJA benefits for the period January 1, 2018 through the expected rate effective date of July 1, 2018. Pepco expects a decision in the matter in the second quarter of 2018. See Note 12 — Income Taxes for more detail on Corporate Tax Reform and the table below for regulatory liabilities recognized during 2018 associated with TCJA tax savings that will be passed through future customer rates. New Jersey Regulatory Matters Tax Cuts and Jobs Act (Exelon, PHI and ACE). On January 31, 2018, the NJBPU issued an order mandating that New Jersey utility companies, including ACE, pass any economic benefit from the TCJA to rate payers. The order directed New Jersey utility companies to file by March 2, 2018 proposed tariff sheets reflecting TCJA benefits, with new rates to be implemented in two phases effective April 1, 2018 and July 1, 2018. In addition, the NJBPU directed New Jersey utility companies to file by March 2, 2018 a Petition with the NJBPU outlining how they propose to refund any over-collection associated with revised rates not being in place from January 1, 2018 through March 31, 2018, with interest. On March 2, 2018, ACE filed with the NJBPU seeking approval to pass back to customers $23 million in ongoing annual TCJA tax savings through a reduction in electric distribution base rates beginning in 2018. The amounts being passed back to customers would reflect the ongoing annual benefit of lower income tax rates and the settlement of a portion of deferred income tax regulatory liabilities established upon enactment of the TCJA. On March 26, 2018, the NJBPU issued an order accepting ACE’s proposed bill reduction. A portion of the annual decrease in electric distribution base rates totaling approximately $13 million was effective as of April 1, 2018, but considered interim, with the proposed final electric distribution base rates, representing the full $23 million decrease to be effective on July 1, 2018. It is expected that the NJBPU will address in a future rate proceeding ACE's treatment of the TCJA tax savings for the period January 1, 2018 through the effective date of any final customer rate adjustments. See Note 12 — Income Taxes for more detail on Corporate Tax Reform and the table below for regulatory liabilities recognized during 2018 associated with TCJA tax savings that will be passed through future customer rates. 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 through a new rider mechanism a series of investments, 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. An NJBPU decision has been requested by the fourth quarter of 2018. Update and Reconciliation of Certain Under-Recovered Balances (Exelon, PHI and ACE). On February 5, 2018, ACE submitted its 2018 annual petition with the NJBPU seeking to reconcile and update (i) charges related to the recovery of above-market costs associated with ACE’s long-term power purchase contracts with the non-utility generators and (ii) costs related to surcharges for the New Jersey Societal Benefit Program (a statewide public interest program that is intended to benefit low income customers and address other public policy goals) and ACE’s uncollectible accounts. The net impact of adjusting the charges as proposed is an overall annual rate decrease of approximately $19 million , including New Jersey sales and use tax. The matter is pending at the NJBPU. ACE has requested that the NJBPU place the new rates into effect by June 1, 2018. An NJBPU decision has been requested by the fourth quarter of 2018. New York Regulatory Matters New York Clean Energy Standard (Exelon and Generation). On August 1, 2016, the New York Public Service Commission (NYPSC) issued an order establishing the New York CES, a component of which is a Tier 3 ZEC program targeted at preserving the environmental attributes of zero-emissions nuclear-powered generating facilities that meet the criteria demonstrating public necessity as determined by the NYPSC. The ZEC price for the first tranche has been set at $17.48 per MWh of production. Following the first tranche, the price will be updated bi-annually. On October 19, 2016, a coalition of fossil-generation companies filed a complaint in federal district court against the NYPSC alleging that the ZEC program violates certain provisions of the U.S. Constitution; specifically, that the ZEC program interferes with FERC’s jurisdiction over wholesale rates and that it discriminates against out of state competitors. On December 9, 2016, Generation and CENG filed a motion to intervene in the case and to dismiss the lawsuit. The State also filed a motion to dismiss. On July 25, 2017, the court granted both motions to dismiss. On August 24, 2017, plaintiffs appealed the decision to the Second Circuit. Plaintiffs-Appellants' initial brief was filed on October 13, 2017. Briefing in the appeal was completed in December 2017 and oral argument was held on March 12, 2018. In addition, on November 30, 2016, a group of parties, including certain environmental groups and individuals, filed a Petition in New York State court seeking to invalidate the ZEC program. The Petition, which was amended on January 13, 2017, argued that the NYPSC did not have authority to establish the program, that it violated state environmental law and that it violated certain technical provisions of the State Administrative Procedures Act (SAPA) when adopting the ZEC program. On February 15, 2017, Generation and CENG filed a motion to dismiss the state court action. The NYPSC also filed a motion to dismiss the state court action. On March 24, 2017, the plaintiffs filed a memorandum of law opposing the motions to dismiss, and Generation and CENG filed a reply brief on April 28, 2017. Oral argument was held on June 19, 2017. On January 22, 2018, the court dismissed the environmental claims and the majority of the plaintiffs from the case, but denied the motions to dismiss with respect to the remaining five plaintiffs and claims, without commenting on the merits of the case. The case is now proceeding to summary judgment with the full record. Exelon’s and the state’s answers and briefs were filed on March 30, 2018. Plaintiffs’ responses are due on May 11, 2018. Other legal challenges remain possible, the outcomes of which remain uncertain. See Note 8 — Early Plant Retirements for additional information relative to Ginna and Nine Mile Point. Federal Regulatory Matters Tax Cuts and Jobs Act and Transmission-Related Income Tax Regulatory Assets (Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE). Pursuant to their respective transmission formula rates, ComEd, BGE, Pepco, DPL and ACE will begin passing back to customers on June 1, 2018, the benefit of lower income tax rates effective January 1, 2018. 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 (and 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. 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. 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. 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 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. ComEd, Pepco, DPL and ACE have similar transmission-related income tax regulatory liabilities and assets also requiring FERC approval separate from their transmission formula rate mechanisms. On February 23, 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. The companies requested the revisions be effective as of April 24, 2018. On April 24, 2018, the FERC issued a letter order neither approving or rejecting the filings, but rather indicating that the filings were deficient and requiring the parties to file additional information within 30 days. 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. As discussed below, PECO is currently in settlement discussions regarding its transmission formula rate and expects to pass back TCJA benefits to customers through its annual formula rate update. Each of BGE, ComEd, Pepco, DPL and ACE believe there is sufficient basis to support full recovery of their existing transmission-related income tax regulatory assets, as evidenced by the further pursuit of full recovery with FERC. However, upon further consideration of the November 16, 2017 FERC 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 charges to Income tax expense within their Consolidated Statements of Operations and Comprehensive Income in the fourth quarter 2017, reducing their associated transmission-related income tax regulatory assets. If any of the companies are ultimately successful with FERC allowing future recovery of these amounts, the associated regulatory assets will be reestablished, with corresponding decreases to Income tax expense. To the extent all or a portion of the prospective amortization amounts were no longer considered probable of recovery, Exelon, ComEd, BGE, PHI, Pepco, DPL and ACE would record additional charges to Income tax expense, which could be up to approximately $82 million , $41 million , $22 million , $19 million , $9 million , $7 million and $3 million , respectively, as of March 31, 2018 . The Utility Registrants cannot predict the outcome of these FERC proceedings. 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 would 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. PECO cannot predict the final outcome of the settlement or hearing proceedings, or the transmission formula FERC may approve. DOE Notice of Proposed Rulemaking (Exelon and Generation). On August 23, 2017, the DOE staff released its report on the reliability of the electric grid. One aspect of the wide-ranging report is the DOE’s recognition that the electricity markets do not currently value the resiliency provided by baseload generation, such as nuclear plants. On September 28, 2017, the DOE issued a Notice of Proposed Rulemaking (NOPR) that would entitle certain eligible resilient generating units (i.e., those located in organized markets, with a 90-day supply of fuel on site, not already subject to state cost of service regulation and satisfying certain other requirements) to recover fully allocated costs and earn a fair return on equity on their investment. The DOE's NOPR recommended that the FERC take comments for 45 days after publication in the Federal Register and issue a final order 60 days after such publication. On January 8, 2018, the FERC issued an order terminating the rulemaking docket that was initiated to address the proposed rule in the DOE NOPR, concluding the proposed rule did not sufficiently demonstrate there is a resiliency issue and that it proposed a remedy that did not appear to be just, reasonable and nondiscriminatory as required under the Federal Power Act. At the same time, the FERC initiated a new proceeding to consider resiliency challenges to the bulk power system and evaluate whether additional FERC action to address resiliency would be appropriate. The FERC directed each RTO and ISO to respond within 60 days to 24 specific questions about how they assess and mitigate threats to resiliency. Interested parties may submit reply comments through May 9, 2018. Exelon has been and will continue to be an active participant in these proceedings, but cannot predict the final outcome or its potential financial impact, if any, on Exelon or Generation. Operating License Renewals (Exelon and Generation). On August 29, 2012, Generation submitted a hydroelectric license application to FERC for a 46 -year license for the Conowingo Hydroelectric Project (Conowingo). In connection with Generation’s efforts to obtain a water quality certification pursuant to Section 401 of the Clean Water Act (401 certification) with Maryland Department of the Environment (MDE) for Conowingo, Generation continues to work with MDE and other stakeholders to resolve water quality licensing issues, including: (1) water quality, (2) fish habitat, and (3) sediment. On April 21, 2016, Exelon and the US Fish and Wildlife Service of the US Department of the Interior executed a Settlement Agreement resolving all fish passage issues between the parties. The financial impact of the Settlement Agreement is estimated to be $3 million to $7 million per year, on average, over the 46-year life of the new license, including both capital and operating costs. The actual timing and amount of these costs are not currently fixed and may vary significantly from year to year throughout the life of the new license. On April 27, 2018, MDE issued its 401 certification for Conowingo. As issued, the 401 certification imposes requirements and conditions which could have a material, unfavorable impact on Exelon’s and Generation’s results of operations, cash flows and financial positions through an increase in capital expenditures and operating costs if implemented. Generation is reviewing the certification and will determine next steps to ensure the long-term viability of the Conowingo Dam. As of March 31, 2018 , $32 million of direct costs associated with Conowingo licensing efforts have been capitalized. See Note 3 — Regulatory Matters of

Impairment of Long-lived Assets

Impairment of Long-lived Assets (Exelon and Generation)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Asset Impairment Charges [Text Block]	7 . Impairment of Long-Lived Assets (Exelon and Generation) 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 announced it had formally 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 interim and 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 on the early retirement of the Mystic Generating Station assets.

Early Nuclear Plant Retirements

Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Exelon, Generation)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	8 . Early Plant Retirements (Exelon and Generation) Exelon and Generation continue to evaluate the current and expected economic value of each of Generation’s plants. Factors that will continue to affect the economic value of Generation’s plants include, but are not limited to: market power prices, results of capacity auctions, potential legislative and regulatory solutions to ensure plants are fairly compensated for 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 decommissioning trust 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. 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. Assuming the continued effectiveness of 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 results of operations, cash flows and financial positions. Refer to Note 6 — Regulatory Matters for additional discussion on the New York CES and the Illinois ZES. In Pennsylvania, the TMI nuclear plant did not clear in the May 2017 PJM capacity auction for the 2020-2021 planning year, the third consecutive year that TMI failed to clear the PJM base residual capacity auction. The plant is currently committed to operate through May 2019 and is licensed to operate through 2034. On May 30, 2017, based on these capacity auction results, prolonged periods of low wholesale power prices, and the absence of federal or state policies that place a value on nuclear energy for its ability to produce electricity without air pollution, Exelon announced that Generation will permanently cease generation operations at TMI on or about September 30, 2019. Generation has filed the required market and regulatory notifications to shut down the plant. PJM has subsequently notified Generation that it has not identified any reliability issues and has approved the deactivation of TMI as proposed. On February 2, 2018, Exelon announced that Generation will permanently cease generation operations at Oyster Creek at the end of its current operating cycle by October 2018. In 2010, Generation announced that Oyster Creek would retire by the end of 2019 as part of an agreement with the State of New Jersey to avoid significant costs associated with the construction of cooling towers to meet the State’s then new environmental regulations. Since then, like other nuclear sites, Oyster Creek has continued to face rising operating costs amid a historically low wholesale power price environment. The decision to retire Oyster Creek in 2018 at the end of its current operating cycle involved consideration of several factors, including economic and operating efficiencies, and avoids a refueling outage scheduled for the fall of 2018 that would have required advanced purchasing of fuel fabrication and materials beginning in late February 2018. Generation has filed the required market and regulatory notifications to shut down the plant. PJM has subsequently notified Generation that it has not identified any reliability issues and has approved the deactivation of Oyster Creek as proposed. As a result of these plant retirement decisions, Exelon and Generation recognized one-time charges in Operating and maintenance expense related to materials and supplies inventory reserve adjustments, employee-related costs and CWIP impairments, among other items. In addition to these one-time charges, annual incremental non-cash charges to earnings stemming from shortening the expected economic useful lives primarily related to accelerated depreciation of plant assets (including any ARC), accelerated amortization of nuclear fuel, and additional ARO accretion expense associated with the changes in decommissioning timing and cost assumptions were also recorded. See Note 13 — Nuclear Decommissioning for additional detail on changes to the nuclear decommissioning ARO balance. Exelon's and Generation's first quarter 2018 results included a net incremental $178 million of total pre-tax expense associated with the early retirement decisions for TMI and Oyster Creek, as summarized in the table below. Income statement expense (pre-tax) Q1 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 137 Accelerated nuclear fuel amortization 15 Operating and maintenance (c) 26 Total $ 178 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI for the quarter ended March 31, 2018 , and for Oyster Creek from February 2, 2018 through March 31, 2018 . (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Exelon's and Generation's 2017 results included a net incremental $339 million of total pre-tax expense associated with the early retirement decision for TMI, as summarized in the table below. Income statement expense (pre-tax) Q2 2017 Q3 2017 Q4 2017 YTD 2017 Depreciation and amortization (a) Accelerated depreciation (b) $ 35 $ 106 $ 109 $ 250 Accelerated Nuclear Fuel amortization 2 6 4 12 Operating and maintenance (c) 71 5 1 77 Total $ 108 $ 117 $ 114 $ 339 _________ (a) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. 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. Although Salem is committed to operate through May 2021, the plant faces continued economic challenges and PSEG, as the operator of the plant, is exploring all options. On April 12, 2018, a bill was passed by both Houses of the New Jersey legislature that would 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. The program provides transparency and includes robust customer protections. The New Jersey Governor has up to 45 days to sign the bill, with the bill becoming effective immediately upon signing. The NJBPU then has 180 days from the effective date to establish procedures for implementation of the ZEC program and 330 days from the effective date to determine which nuclear power plants are selected to receive ZECs under the program. Selected nuclear plants will receive ZEC payments for each energy year (12-month period from June 1 through May 31) within 90 days after the completion of such energy year. Exelon and Generation continue to work with stakeholders. The following table provides the balance sheet amounts as of March 31, 2018 for Generation’s ownership share of the significant assets and liabilities associated with Salem. March 31, 2018 Asset Balances Materials and supplies inventory $ 45 Nuclear fuel inventory, net 102 Completed plant, net 618 Construction work in progress 27 Liability Balances Asset retirement obligation (446 ) NRC License Renewal Term 2036 (Unit 1) 2040 (Unit 2) On March 29, 2018, Generation announced it had formally 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 & 8. Mystic Unit 9 is currently committed through May 2021. Absent any regulatory reforms to properly value reliability and regional fuel security, these units will not participate in the Forward Capacity Auction (FCA) scheduled for February 2019 for the 2022 - 2023 planning year. The ISO-NE recently announced that it would take a three-step approach to fuel security. First, ISO-NE will make a filing soon to obtain tariff waivers to allow it to retain Mystic 8 and 9 for fuel security for the 2022 - 2024 planning years. Second, ISO-NE will file tariff revisions to allow it to retain other resources for fuel security in the capacity market if necessary in the future. Third, ISO-NE will 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. On April 3, 2018, ISO-NE issued a memorandum to the NEPOOL Participants’ Committee announcing its intention to seek FERC approval for waiver of certain tariff provisions in order to allow it to retain Mystic Units 8 and 9 for fuel security reasons. On April 4, 2018, Generation issued a letter indicating its willingness to cooperate and submit to full cost-of-service compensation for the Mystic Units 8 and 9, provided that the cost-of-service rate is determined before it commits to any future capacity obligation. The following table provides the balance sheet amounts as of March 31, 2018 for Generation’s significant assets and liabilities associated with the Mystic Generating Station assets. March 31, 2018 Asset Balances Materials and supplies inventory $ 26 Fuel inventory 18 Completed plant, net 896 Construction work in progress 4 Prepaid expense (a) 9 Liability Balances Asset retirement obligation (5 ) Accrued expense (a) (2 ) _________ (a) Reflects ending balances only as they relate to Mystic's Long-term Service Agreement.

Intangibles Intangibles (Exelon

Intangibles Intangibles (Exelon and Generation)	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets (Exelon and PHI) 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 . The specific sponsorship rights were to be determined over time through future negotiations. As of March 31, 2018 , PHI has recorded the sponsorship agreement as a finite-lived intangible asset with a $25 million carrying amount.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	9 . Fair Value of Financial Assets and Liabilities (All Registrants) Fair Value of Financial Liabilities Recorded at Amortized Cost 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 March 31, 2018 and December 31, 2017 : Exelon March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 1,654 $ — $ 1,654 $ — $ 1,654 Long-term debt (including amounts due within one year) (b)(c) 34,108 — 33,091 1,893 34,984 Long-term debt to financing trusts (d) 389 — — 421 421 SNF obligation 1,151 — 922 — 922 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 929 $ — $ 929 $ — $ 929 Long-term debt (including amounts due within one year) (b)(c) 34,264 — 34,735 1,970 36,705 Long-term debt to financing trusts (d) 389 — — 431 431 SNF obligation 1,147 — 936 — 936 Generation March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 166 $ — $ 166 $ — $ 166 Long-term debt (including amounts due within one year) (b)(c) 8,965 — 7,585 1,610 9,195 SNF obligation 1,151 — 922 — 922 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 2 $ — $ 2 $ — $ 2 Long-term debt (including amounts due within one year) (b)(c) 8,990 — 7,839 1,673 9,512 SNF obligation 1,147 — 936 — 936 ComEd March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 317 $ — $ 317 $ — $ 317 Long-term debt (including amounts due within one year) (b)(c) 7,694 — 8,061 — 8,061 Long-term debt to financing trusts (d) 205 — — 222 222 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 7,601 $ — $ 8,418 $ — $ 8,418 Long-term debt to financing trusts (d) 205 — — 227 227 PECO March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 220 $ — $ 220 $ — $ 220 Long-term debt (including amounts due within one year) (b)(c) 2,723 — 2,870 — 2,870 Long-term debt to financing trusts (d) 184 — — 199 199 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 2,903 $ — $ 3,194 $ — $ 3,194 Long-term debt to financing trusts (d) 184 — — 204 204 BGE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 45 $ — $ 45 $ — $ 45 Long-term debt (including amounts due within one year) (b)(c) $ 2,578 $ — $ 2,689 $ — $ 2,689 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 77 $ — $ 77 $ — $ 77 Long-term debt (including amounts due within one year) (b)(c) 2,577 — 2,825 — 2,825 PHI March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 407 $ — $ 407 $ — $ 407 Long-term debt (including amounts due within one year) (b)(c) 5,849 — 5,423 283 5,706 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 350 $ — $ 350 $ — $ 350 Long-term debt (including amounts due within one year) (b)(c) 5,874 — 5,722 297 6,019 Pepco March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 60 $ — $ 60 $ — $ 60 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 2,933 9 2,942 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 26 $ — $ 26 $ — $ 26 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 3,114 9 3,123 DPL March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 211 $ — $ 211 $ — $ 211 Long-term debt (including amounts due within one year) (b)(c) 1,296 — 1,320 — 1,320 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (b)(c) 1,300 — 1,393 — 1,393 ACE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 136 $ — $ 136 $ — $ 136 Long-term debt (including amounts due within one year) (b)(c) 1,114 — 916 274 1,190 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 108 $ — $ 108 $ — $ 108 Long-term debt (including amounts due within one year) (b)(c) 1,121 — 949 288 1,237 _________ (a) Level 1 securities consist of dividends payable (included in other current liabilities). Level 2 securities consist of short term borrowings. (b) Includes unamortized debt issuance costs which are not fair valued of $213 million , $57 million , $60 million , $20 million , $16 million , $6 million , $32 million , $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 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 . (c) Level 2 securities consist of fixed-rate taxable debt securities, fixed-rate tax-exempt debt, variable rate tax-exempt debt and variable rate non-recourse debt. Level 3 securities consist of fixed-rate private placement taxable debt securities, fixed rate nonrecourse debt and government-backed fixed rate non-recourse debt. (d) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2018 and December 31, 2017 . Recurring Fair Value Measurements Exelon records the fair value of assets and liabilities in accordance with the hierarchy established by the authoritative guidance for fair value measurements. The hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three levels as follows: • Level 1 — quoted prices (unadjusted) in active markets for identical assets or liabilities that the Registrants have the ability to liquidate as of the reporting date. • Level 2 — inputs other than quoted prices included within Level 1 that are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. • Level 3 — unobservable inputs, such as internally developed pricing models or third-party valuations for the asset or liability due to little or no market activity for the asset or liability. Transfers in and out of levels are recognized as of the end of the reporting period when the transfer occurred. Given derivatives categorized within Level 1 are valued using exchange-based quoted prices within observable periods, transfers between Level 2 and Level 1 were not material. Additionally, there were no material transfers between Level 1 and Level 2 during the three months ended March 31, 2018 for cash equivalents, nuclear decommissioning trust fund investments, Pledged assets for Zion Station decommissioning, Rabbi trust investments, and Deferred compensation obligations. For derivative contracts, transfers into Level 2 from Level 3 generally occur when the contract tenor becomes more observable and due to changes in market liquidity or assumptions for certain commodity contracts. Generation and Exelon In accordance with the applicable guidance on fair value measurement, certain investments that are measured at fair value using the NAV per share as a practical expedient are no longer classified within the fair value hierarchy and are included under "Not subject to leveling" in the table below. The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : Generation Exelon As of March 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) 343 — — — 343 517 — — — 517 NDT fund investments Cash equivalents (b) 222 105 — — 327 222 105 — — 327 Equities 4,002 983 — 2,119 7,104 4,002 983 — 2,119 7,104 Fixed income Corporate debt — 1,583 240 — 1,823 — 1,583 240 — 1,823 U.S. Treasury and agencies 1,869 88 — — 1,957 1,869 88 — — 1,957 Foreign governments — 86 — — 86 — 86 — — 86 State and municipal debt — 254 — — 254 — 254 — — 254 Other (c) — 39 — 532 571 — 39 — 532 571 Fixed income subtotal 1,869 2,050 240 532 4,691 1,869 2,050 240 532 4,691 Middle market lending — — 369 127 496 — — 369 127 496 Private equity — — — 253 253 — — — 253 253 Real estate — — — 488 488 — — — 488 488 NDT fund investments subtotal (d) 6,093 3,138 609 3,519 13,359 6,093 3,138 609 3,519 13,359 Pledged assets for Zion Station decommissioning Cash equivalents 13 — — — 13 13 — — — 13 Generation Exelon As of March 31, 2018 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 — — 16 — 16 — — 16 — 16 Pledged assets for Zion Station (e) 13 — 16 — 29 13 — 16 — 29 Rabbi trust investments Cash equivalents 5 — — — 5 77 — — — 77 Mutual funds 24 — — — 24 59 — — — 59 Fixed income — — — — — — 10 — — 10 Life insurance contracts — 22 — — 22 — 71 23 — 94 Rabbi trust investments subtotal (f) 29 22 — — 51 136 81 23 — 240 Commodity derivative assets Economic hedges 286 2,923 1,892 — 5,101 286 2,923 1,892 — 5,101 Proprietary trading — 151 58 — 209 — 151 58 — 209 Effect of netting and allocation of collateral (g) (h) (335 ) (2,589 ) (895 ) — (3,819 ) (335 ) (2,589 ) (895 ) — (3,819 ) Commodity derivative assets subtotal (49 ) 485 1,055 — 1,491 (49 ) 485 1,055 — 1,491 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 12 — — 12 — 12 — — 12 Economic hedges — 6 — — 6 — 6 — — 6 Effect of netting and allocation of collateral (1 ) (3 ) — — (4 ) (1 ) (3 ) — — (4 ) Interest rate and foreign currency derivative assets subtotal (1 ) 15 — — 14 (1 ) 15 — — 14 Other investments — — 36 — 36 — — 36 — 36 Total assets 6,428 3,660 1,716 3,519 15,323 6,709 3,719 1,739 3,519 15,686 Liabilities Commodity derivative liabilities Economic hedges (415 ) (3,317 ) (1,203 ) — (4,935 ) (415 ) (3,317 ) (1,470 ) — (5,202 ) Proprietary trading — (164 ) (15 ) — (179 ) — (164 ) (15 ) — (179 ) Effect of netting and allocation of collateral (g) (h) 415 3,007 1,081 — 4,503 415 3,007 1,081 — 4,503 Commodity derivative liabilities subtotal — (474 ) (137 ) — (611 ) — (474 ) (404 ) — (878 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Generation Exelon As of March 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Economic hedges (1 ) (4 ) — — (5 ) (1 ) (4 ) — — (5 ) Effect of netting and allocation of collateral 1 3 — — 4 1 3 — — 4 Interest rate and foreign currency derivative liabilities subtotal — (1 ) — — (1 ) — (5 ) — — (5 ) Deferred compensation obligation — (35 ) — — (35 ) — (138 ) — — (138 ) Total liabilities — (510 ) (137 ) — (647 ) — (617 ) (404 ) — (1,021 ) Total net assets $ 6,428 $ 3,150 $ 1,579 $ 3,519 $ 14,676 $ 6,709 $ 3,102 $ 1,335 $ 3,519 $ 14,665 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 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 (e) 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 collateral (g) (h) (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 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 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of collateral (g) (h) 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 $371 million and $259 million at March 31, 2018 and December 31, 2017 and restricted cash of $23 million and $127 million at March 31, 2018 and December 31, 2017 . Exelon excludes cash of $531 million and $389 million at March 31, 2018 and December 31, 2017 and restricted cash of $51 million and $145 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $103 million and $85 million at March 31, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $53 million and $77 million of cash received from outstanding repurchase agreements at March 31, 2018 and December 31, 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 $2 million and less than $1 million , which have a total notional amount of $949 million and $811 million at March 31, 2018 and December 31, 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 $84 million and $82 million at March 31, 2018 and December 31, 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 $1 million at March 31, 2018 . 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 three months ended March 31, 2018 and March 31, 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million and $2 million for the three months ended March 31, 2018 and March 31, 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $80 million , $418 million and $186 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2018 . Collateral posted/(received) from counterparties, net of collateral paid to 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), $156 million represents variation margin on the exchanges as of March 31, 2018 . Of the collateral posted/(received), $(117) million represents variation margin on the exchanges as of December 31, 2017 . Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $68 million as of March 31, 2018 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three months ended March 31, 2018 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : ComEd PECO BGE As of March 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) $ 93 $ — $ — $ 93 $ 6 $ — $ — $ 6 $ — $ — $ — $ — 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 93 — — 93 13 10 — 23 6 — — 6 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (c) — — (267 ) (267 ) — — — — — — — — Total liabilities — (8 ) (267 ) (275 ) — (11 ) — (11 ) — (4 ) — (4 ) Total net assets (liabilities) $ 93 $ (8 ) $ (267 ) $ (182 ) $ 13 $ (1 ) $ — $ 12 $ 6 $ (4 ) $ — $ 2 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 $69 million and $45 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $83 million and $62 million at March 31, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $20 million and $47 million at March 31, 2018 and December 31, 2017 . BGE excludes cash of $22 million and $17 million at March 31, 2018 and December 31, 2017 and restricted cash of $2 million and $1 million at March 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 three months ended March 31, 2018 and March 31, 2017 , respectively. (c) The Level 3 balance consists of the current and noncurrent liability of $24 million and $243 million , respectively, at March 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 on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : As of March 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) $ 67 $ — $ — $ 67 $ 83 $ — $ — $ 83 Rabbi trust investments Cash equivalents 72 — — 72 72 — — 72 Fixed income — 10 — 10 — 12 — 12 Life insurance contracts — 23 23 46 — 23 22 45 Rabbi trust investments subtotal (b) 72 33 23 128 72 35 22 129 Total assets 139 33 23 195 155 35 22 212 Liabilities Deferred compensation obligation — (23 ) — (23 ) — (25 ) — (25 ) Mark-to-market derivative liabilities (c) — — — — (1 ) — — (1 ) Effect of netting and allocation of collateral — — — — 1 — — 1 Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (23 ) — (23 ) — (25 ) — (25 ) Total net assets $ 139 $ 10 $ 23 $ 172 $ 155 $ 10 $ 22 $ 187 Pepco DPL ACE As of March 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) $ 33 $ — $ — $ 33 $ — $ — $ — $ — $ 27 $ — $ — $ 27 Rabbi trust investments Cash equivalents 44 — — 44 — — — — — — — — Fixed income — 10 — 10 — — — — — — — — Life insurance contracts — 23 23 46 — — — — — — — — Rabbi trust investments subtotal (b) 44 33 23 100 — — — — — — — — Total assets 77 33 23 133 — — — — 27 — — 27 Liabilities Deferred compensation obligation — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total liabilities — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 77 $ 29 $ 23 $ 129 $ — $ (1 ) $ — $ (1 ) $ 27 $ — $ — $ 27 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 (c) — — — — (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 $36 million and $12 million at March 31, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $15 million and $4 million at March 31, 2018 and December 31, 2017 , respectively. DPL excludes cash of $7 million and $2 million at March 31, 2018 and December 31, 2017 , respectively. ACE excludes cash of $10 million and $2 million at March 31, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) The amount of unrealized gains/(losses) at PHI, Pepco, DPL and ACE totaled less than $1 million for the three months ended March 31, 2018 and March 31, 2017 . (c) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the three months ended March 31, 2018 and 2017 : Generation ComEd PHI Exelon Three Months Ended March 31, 2018 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 December 31, 2017 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 Total realized / unrealized gains (losses) Included in net income — — 184 (a) 1 185 — 1 — 186 Included in noncurrent payables to affiliates 7 — — — 7 — — (7 ) — Included in payable for Zion Station decommissioning — 4 — — 4 — — — 4 Included in regulatory assets/liabilities — — — — — (11 ) (b) — 7 (4 ) Change in collateral — — 105 — 105 — — — 105 Purchases, sales, issuances and settlements Purchases 2 — 88 — 90 — — — 90 Sales — — (3 ) — (3 ) — — — (3 ) Settlements (48 ) — — — (48 ) — — — (48 ) Transfers into Level 3 — — (8 ) — (8 ) — — — (8 ) Transfers out of Level 3 — — — (2 ) (2 ) — — — (2 ) Balance at March 31, 2018 $ 609 $ 16 $ 918 $ 36 $ 1,579 $ (267 ) $ 23 $ — $ 1,335 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2018 $ — $ — $ 256 $ 1 $ 257 $ — $ 1 $ — $ 258 Generation ComEd PHI Exelon Three Months Ended March 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 December 31, 2016 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 Total realized / unrealized gains (losses) Included in net income 3 — (43 ) (a) 1 (39 ) — 1 — (38 ) Included in noncurrent payables to affiliates 9 — — — 9 — — (9 ) — Included in regulatory assets/liabilities — — — — — (24 ) (b) — 9 (15 ) Change in collateral — — 38 — 38 — — — 38 Purchases, sales, issuances and settlements Purchases 17 1 69 2 89 — — — 89 Sales — — (2 ) — (2 ) — — — (2 ) Issuances — — — — — — (1 ) — (1 ) Settlements (23 ) — — — (23 ) — — — (23 ) Transfers into Level 3 — — (1 ) — (1 ) — — — (1 ) Transfers out of Level 3 — — 11 (5 ) 6 — — — 6 Balance as of March 31, 2017 $ 683 $ 20 $ 565 $ 40 $ 1,308 $ (282 ) $ 20 $ — $ 1,046 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2017 $ 2 $ — $ 59 $ — $ 61 $ — $ 1 $ — $ 62 ________ (a) Includes a reduction for the reclassification of $72 million and $102 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2018 and March 31, 2017 , respectively. (b) Includes $ 17 million of decreases in fair value and an increase for realized losses due to settlements of $ 6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018 . Includes $30 million of decreases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2017 . (c) The amounts represented are life insurance contracts at Pepco. 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 three months ended March 31, 2018 and 2017 : Generation PHI Exelon Operating Purchased Other, net (a) Operating and Maintenance Operating Purchased Operating and Maintenance Other, net (a) Total gains (losses) included in net income for the three months ended March 31, 2018 $ 335 $ (151 ) $ 1 $ 1 $ 335 $ (151 ) $ 1 $ 1 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2018 309 (53 ) 1 1 309 (53 ) 1 1 Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the three months ended March 31, 2017 $ 88 $ (131 ) $ 3 $ 1 $ 88 $ (131 ) $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2017 140 (81 ) 2 1 140 (81 ) 3 _________ (a) Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco. Valuation Techniques Used to Determine Fair Value The following describes the valuation techniques used to measure the fair value of the assets and liabilities shown in the tables above. Cash Equivalents (Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE). The Registrants’ cash equivalents include investments with original maturities of three months or less when purchased. The cash equivalents shown in the fair value tables are comprised of investments in mutual and money market funds. The fair values of the shares of these funds are based on observable market prices and, therefore, have been categorized in Level 1 in the fair value hierarchy. Nuclear Decommissioning Trust Fund Investments and Pledged Assets for Zion Station Decommissioning (Exelon and Generation). The trust fund investments have been established to satisfy Generation’s and CENG's nuclear decommissioning obligations as required by the NRC. The NDT funds hold debt and equity securities directly and indirectly through commingled funds and mutual funds, which are included in Equities and Fixed Income. Generation’s and CENG's NDT fund investments policies outline investment guidelines for the trusts and limit the trust funds’ exposures to investments in highly illiquid markets and other alternative investments. Investments with maturities of three months or less when purchased, including certain short-term fixed income securities are considered cash equivalents and included in the recurring fair value measurements hierarchy as Level 1 or Level 2. With respect to individually held equity securities, the trustees obtain prices from pricing services, whose prices are generally obtained from direct feeds from market exchanges, which Generation is able to independently corroborate. The fair values of equity securities held directly by the trust funds which are based on quoted prices in active markets are categorized in Level 1. Certain equity securities have been categorized as Level 2 because they are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities. Equity securities held individually are primarily traded on the New York Stock Exchange and NASDAQ-Global Select Market, which contain only actively traded securities due to the volume trading requirements imposed by these exchanges. For fixed income securities, multiple prices from pricing services are obtained whenever possible, which enables cross-provider validations in addition to checks for unusual daily movements. A primary price source is identified based on asset type, class or issue for each security. With respect to individually held fixed income securities, the trustees monitor prices supplied by pricing services and may use a supplemental price source or change the primary price source of a given security if the portfolio managers challenge an assigned price and the trustees determine that another price source is conside

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments (All Registrants)	10 . 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 March 31, 2018 and December 31, 2017 , $8 million and $4 million of cash collateral held, respectively, was not offset against derivative positions because such collateral was not associated with any energy-related derivatives, were associated with accrual positions, or had no positions to offset as of the balance sheet date. Excluded from the tables below are economic hedges that qualify for the NPNS scope exception and other non-derivative contracts that are accounted for under the accrual method of accounting. ComEd’s use of cash collateral is generally unrestricted unless ComEd is downgraded below investment grade (i.e., to BB+ or Ba1). Cash collateral held by 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 recorded by the Registrants as of March 31, 2018 : Generation ComEd DPL Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,343 $ 166 $ (2,533 ) $ 976 $ — $ — $ — $ — $ 976 Mark-to-market derivative assets (noncurrent assets) 1,758 43 (1,286 ) 515 — — — — 515 Total mark-to-market derivative assets 5,101 209 (3,819 ) 1,491 — — — — 1,491 Mark-to-market derivative liabilities (current liabilities) (3,185 ) (151 ) 2,945 (391 ) (24 ) — — — (415 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,750 ) (28 ) 1,558 (220 ) (243 ) — — — (463 ) Total mark-to-market derivative liabilities (4,935 ) (179 ) 4,503 (611 ) (267 ) — — — (878 ) Total mark-to-market derivative net assets (liabilities) $ 166 $ 30 $ 684 $ 880 $ (267 ) $ — $ — $ — $ 613 _________ (a) Exelon, Generation and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $192 million and $103 million , respectively, and current and noncurrent liabilities are shown net of collateral of $220 million and $169 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $684 million at March 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $156 million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2017 : Generation ComEd DPL Exelon Description Economic Proprietary Collateral (a)(e) Subtotal (b) Economic (c) Economic (d) Collateral and (a) Subtotal Total Mark-to-market derivative assets (current assets) $ 3,061 $ 56 $ (2,144 ) $ 973 $ — $ — $ — $ — $ 973 Mark-to-market derivative assets (noncurrent assets) 1,164 12 (845 ) 331 — — — — 331 Total mark-to-market derivative assets 4,225 68 (2,989 ) 1,304 — — — — 1,304 Mark-to-market derivative liabilities (current liabilities) (2,646 ) (43 ) 2,480 (209 ) (21 ) (1 ) 1 — (230 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,137 ) (10 ) 975 (172 ) (235 ) — — — (407 ) Total mark-to-market derivative liabilities (3,783 ) (53 ) 3,455 (381 ) (256 ) (1 ) 1 — (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ (1 ) $ 1 $ — $ 667 _________ (a) Exelon, Generation and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, and letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $169 million and $53 million , respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(117) million represents variation margin on the exchanges. 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 three months ended March 31, 2018 and 2017 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ (100 ) $ 46 Purchased power and fuel (167 ) (93 ) Total Exelon and Generation $ (267 ) $ (47 ) 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 March 31, 2018 , the percentage of expected generation hedged is 91% - 94% , 63% - 66% and 33% - 36% for 2018 , 2019 and 2020 , 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 3 — Regulatory Matters of the Exelon 2017 Form 10-K 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 2016 PAPUC PGC settlement and to reduce the exposure of PECO and its customers to natural gas price volatility, PECO has continued its program to purchase natural gas for both winter and summer supplies using a layered approach of locking-in prices ahead of each season with long-term gas purchase agreements (those with primary terms of at least twelve months). Under the terms of the 2016 PGC settlement, PECO is required to lock in (i.e., economically hedge) the price of a minimum volume of its long-term gas commodity purchases. PECO’s gas-hedging program is designed to cover about 20% of planned natural gas purchases in support of projected firm sales. The hedging program for natural gas procurement has no direct impact on PECO’s results of operations and financial position as natural gas costs are fully recovered from customers under the PGC. BGE has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC. The SOS rates charged recover BGE's wholesale power supply costs and include an administrative fee. BGE’s commodity price risk related to electric supply procurement is limited. BGE locks in fixed prices for all of its SOS requirements through full requirements contracts. Certain of BGE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other BGE full requirements contracts are not derivatives. BGE provides natural gas to its customers under a MBR mechanism approved by the MDPSC. Under this mechanism, BGE’s actual cost of gas is compared to a market index (a measure of the market price of gas in a given period). The difference between BGE’s actual cost and the market index is shared equally between shareholders and customers. BGE must also secure fixed price contracts for at least 10% , but not more than 20% , of forecasted system supply requirements for flowing (i.e., non-storage) gas for the November through March period. These fixed-price contracts are not subject to sharing under the MBR mechanism. BGE also ensures it has sufficient pipeline transportation capacity to meet customer requirements. BGE’s natural gas supply and asset management agreements qualify for the NPNS scope exception and result in physical delivery. Pepco has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and DCPSC. The SOS rates charged recover Pepco's wholesale power supply costs and include an administrative fee. The administrative fee includes an incremental cost component and a shareholder return component for residential and commercial rate classes. Pepco’s commodity price risk related to electric supply procurement is limited. Pepco locks in fixed prices for its SOS requirements through full requirements contracts. Certain of Pepco’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other Pepco full requirements contracts are not derivatives. DPL has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and the DPSC. The SOS rates charged recover DPL's wholesale power supply costs. In Delaware, DPL is also entitled to recover a Reasonable Allowance for Retail Margin (RARM). The RARM includes a fixed annual margin of approximately $2.75 million , plus an incremental cost component and a cash working capital allowance. In Maryland, DPL charges an administrative fee intended to allow it to recover its administrative costs. DPL locks in fixed prices for its SOS requirements through full requirements contracts. DPL’s commodity price risk related to electric supply procurement is limited. Certain of DPL’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. DPL provides natural gas to its customers under an Annual GCR mechanism approved by the DPSC. Under this mechanism, DPL’s Annual GCR Filing establishes a future GCR for firm bundled sales customers by using a forecast of demand and commodity costs. The actual costs are trued up against forecasts 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 all of 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 three months ended March 31, 2018 and 2017 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ 2 $ (1 ) Interest Rate and Foreign Exchange Risk (All Registrants) The Registrants use a combination of fixed-rate and variable-rate debt to manage interest rate exposure. The Registrants utilize fixed-to-floating interest rate swaps, which are typically designated as fair value hedges, to manage their interest rate exposure. In addition, the Registrants may utilize interest rate derivatives to lock in rate levels, which are typically designated as cash flow hedges to manage interest rate risk. To manage foreign exchange rate exposure associated with international commodity purchases in currencies other than U.S. dollars, Generation utilizes foreign currency derivatives, which are treated as economic hedges. Below is a summary of the interest rate and foreign exchange hedge balances as of March 31, 2018 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Collateral and Netting (a) Subtotal Derivatives Designated as Hedging Instruments Total Mark-to-market derivative assets (current assets) $ — $ 5 $ (3 ) $ 2 $ — $ 2 Mark-to-market derivative assets (noncurrent assets) 12 1 (1 ) 12 — 12 Total mark-to-market derivative assets 12 6 (4 ) 14 — 14 Mark-to-market derivative liabilities (current liabilities) — (3 ) 3 — — — Mark-to-market derivative liabilities (noncurrent liabilities) — (2 ) 1 (1 ) (4 ) (5 ) Total mark-to-market derivative liabilities — (5 ) 4 (1 ) (4 ) (5 ) Total mark-to-market derivative net assets (liabilities) $ 12 $ 1 $ — $ 13 $ (4 ) $ 9 __________ (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 Designated as Hedging Instruments 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. Fair Value Hedges (Interest Rate Risk) For derivative instruments that qualify and are designated as fair value hedges, the gain or loss on the derivative as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in earnings immediately. Exelon and Generation include the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps as follows: Three Months Ended March 31, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (7 ) $ (4 ) $ 13 $ 8 The table below provides the notional amounts of fixed-to-floating hedges outstanding held by Exelon at March 31, 2018 and December 31, 2017 : As of March 31, 2018 December 31, 2017 Fixed-to-floating hedges $ 800 $ 800 During the three months ended March 31, 2018 and 2017 , the impact on the results of operations as a result of ineffectiveness from fair value hedges was a $6 million gain and a $4 million gain, respectively. Cash Flow Hedges (Interest Rate Risk) For derivative instruments that qualify and are designated as cash flow hedges, the gain or loss on the effective portion of the derivative will be deferred in AOCI and reclassified into earnings when the underlying transaction occurs. To mitigate interest rate risk, Exelon and Generation enter into floating-to-fixed interest rate swaps to manage a portion of interest rate exposure associated with debt issuances. The table below provides the notional amounts of floating-to-fixed hedges outstanding held by Exelon and Generation as of March 31, 2018 . As of March 31, 2018 December 31, 2017 Floating-to-fixed hedges $ 636 $ 636 The tables below provide the activity of OCI related to cash flow hedges for the three months ended March 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 OCI, 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 OCI Activity, Net of Income Tax Generation Exelon Three Months Ended March 31, 2018 Income Statement Location Total Cash Total Cash AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Effective portion of changes in fair value 7 8 AOCI derivative loss at March 31, 2018 $ (9 ) $ (6 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Three Months Ended March 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 2 2 Reclassifications from AOCI to net income Interest Expense 4 (a) 4 (a) AOCI derivative loss at March 31, 2017 $ (13 ) $ (11 ) _________ (a) Amount is net of related income tax expense of $3 million for the three months ended March 31, 2017 . During the three months ended March 31, 2018 and 2017 , the impact on the results of operations as a result of ineffectiveness from cash flow hedges in continuing designated hedge relationships was immaterial. The estimated amount of existing gains and losses that are reported in AOCI at the reporting date that are expected to be reclassified into earnings within the next twelve months is immaterial. Economic Hedges (Interest Rate and Foreign Exchange Risk) Exelon and Generation executes these instruments to mitigate exposure to fluctuations in interest rates or foreign exchange but for which the fair value or cash flow hedge elections were not made. Generation also enters into interest rate derivative contracts and foreign exchange currency swaps ("treasury") to manage the exposure related to the interest rate component of commodity positions and international purchases of commodities in currencies other than U.S. Dollars. At March 31, 2018 and December 31, 2017 , Generation had immaterial notional amounts of interest rate derivative contracts to economically hedge risk associated with the interest rate component of commodity positions. The following table provides notional amounts outstanding held by Exelon and Generation at March 31, 2018 and December 31, 2017 related to foreign currency exchange rate swaps that are marked-to-market to manage the exposure associated with international purchases of commodities in currencies other than U.S. dollars. As of March 31, 2018 December 31, 2017 Foreign currency exchange rate swaps $ 87 $ 94 For the three months ended March 31, 2018 and 2017 , 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. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Generation Operating Revenues $ 2 $ (2 ) Generation Purchased Power and Fuel (1 ) — Total Generation $ 1 $ (2 ) Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Exelon Operating Revenues $ 2 $ (2 ) Exelon Purchased Power and Fuel (1 ) — Total Exelon $ 1 $ (2 ) 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 three months ended March 31, 2018 and 2017 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses). Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating Revenues $ — $ (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 scoring model, leverage, liquidity, profitability, credit ratings by credit rating agencies, and risk management capabilities. To the extent that a counterparty’s margining thresholds are exceeded, the counterparty is required to post collateral with Generation a

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt and Credit Agreements (All Registrants)	11 . 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 Registrants had the following amounts of commercial paper borrowings outstanding as of March 31, 2018 and December 31, 2017 : Commercial Paper Borrowings March 31, 2018 December 31, 2017 Exelon $ 1,154 $ 427 Generation 165 — ComEd 317 — PECO 220 — BGE 45 77 PHI (a) 407 350 Pepco 60 26 DPL 211 216 ACE 136 108 _________ (a) PHI reflects the commercial paper borrowings outstanding of Pepco, DPL and ACE. 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 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 As of March 15, 2018, the credit agreement for Generation’s $30 million bilateral credit facility was amended to increase the overall facility size to $95 million . This facility will solely be used by Generation to issue letters of credit. Long-Term Debt Issuance of Long-Term Debt During the three months ended March 31, 2018 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.72 % April 30, 2018 $ 1 Funding to install energy conservation measures for the Smithsonian Zoo project. Generation Energy Efficiency Project Financing 3.17 % April 30, 2018 $ 1 Funding to install energy conservation measures in Brooklyn, NY. Generation Energy Efficiency Project Financing 2.61 % September 30, 2018 $ 2 Funding to install energy conservation measures for the Pensacola project. ComEd First Mortgage Bonds, Series 124 4.00 % March 1, 2048 $ 800 Refinance one series of maturing first mortgage bonds, to repay a portion of ComEd’s outstanding commercial paper obligations and to fund general corporate purposes. PECO First and Refunding Mortgage Bonds 3.90 % March 1, 2048 $ 325 Refinance a portion of maturing mortgage bonds.

Income Taxes (All Registrants)

Income Taxes (All Registrants)	3 Months Ended
	Mar. 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 will be determined by the Utility Registrants’ respective rate regulators, subject to certain IRS “normalization” rules. See Note 6 — Regulatory Matters for further information. The Registrants have completed their assessment of the majority of the applicable provisions in the TCJA and have recorded the associated impacts as of December 31, 2017. As discussed further below, under SAB 118 issued by the SEC in December 2017, the Registrants have recorded provisional income tax amounts as of December 31, 2017 for changes pursuant to the TCJA related to depreciation for which the impacts could not be finalized upon issuance of the Registrants’ financial statements, but for which reasonable estimates could be determined. For property acquired and placed-in-service after September 27, 2017, the TCJA repeals 50% bonus depreciation for all taxpayers and in addition provides for 100% expensing for taxpayers other than regulated utilities. As a result, Generation will be required to evaluate the contractual terms of its fourth quarter 2017 capital additions and determine if they qualify for 100% expensing under the TCJA as compared to 50% bonus depreciation under prior tax law. Similarly, the Utility Registrants will be required to evaluate the contractual terms of their fourth quarter 2017 capital additions to determine whether they still qualify for the prior tax law’s 50% bonus depreciation as compared to no bonus depreciation pursuant to the TCJA. At Generation, any required changes to the provisional estimates during the measurement period related to the above item would result in an adjustment to current income tax expense at 35% and a corresponding adjustment to deferred income tax expense at 21% and such changes could be material to Generation’s future results of operations. At the Utility Registrants, any required changes to the provisional estimates would result in the recording of regulatory assets or liabilities to the extent such amounts are probable of settlement or recovery through customer rates and a net change to income tax expense for any other amounts. The Registrants expect any final adjustments to the provisional amounts to be recorded by the third quarter of 2018, which could be material to the Registrants’ future results of operations or financial positions. The accounting for all other applicable provisions of the TCJA is considered complete based on our current interpretation of the provisions of the TCJA as enacted as of December 31, 2017. While the Registrants have recorded the impacts of the TCJA based on their interpretation of the provisions as enacted, it is expected that technical corrections or other forms of guidance will be issued during 2018, which could result in material changes to previously finalized provisions. At this time, most states have not provided guidance regarding TCJA impacts and may issue guidance in 2018 which may impact estimates. The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: 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 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 Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Deferred Income Tax Benefit/(Expense) Recorded $ 1,309 $ 1,895 $ 1 $ 13 $ (4 ) $ (35 ) $ (8 ) $ (5 ) $ (2 ) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information. The net regulatory liabilities above include (1) amounts subject to IRS “normalization” rules that are required to be passed back to customers generally over the remaining useful life of the underlying assets giving rise to the associated deferred income taxes, and (2) amounts for which the timing of settlement with customers is subject to determinations by the rate regulators. The table below sets forth the Registrants’ estimated categorization of their net regulatory liabilities as of December 31, 2017. The amounts in the table below are shown on an after-tax basis reflecting future net cash outflows after taking into consideration the income tax benefits associated with the ultimate settlement with customers. Exelon ComEd PECO (a) BGE PHI PEPCO DPL ACE Subject to IRS Normalization Rules $ 3,040 $ 1,400 $ 533 $ 459 $ 648 $ 299 $ 195 $ 153 Subject to Rate Regulator Determination 1,694 573 43 324 754 391 194 170 Net Regulatory Liabilities $ 4,734 $ 1,973 $ 576 $ 783 $ 1,402 $ 690 $ 389 $ 323 __________ (a) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information. The net regulatory liability amounts subject to the IRS normalization rules generally relate to property, plant and equipment with remaining useful lives ranging from 30 to 40 years across the Utility Registrants. For the other amounts, rate regulators could require the passing back of amounts to customers over shorter time frames. Rate Reconciliation The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Three Months Ended March 31, 2018 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 4.1 2.4 8.2 (3.9) 6.3 4.6 1.7 6.3 6.6 Qualified nuclear decommissioning trust fund income (0.4) (1.3) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.3) (4.3) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (2.7) — 0.1 (14.2) (0.7) (2.6) (3.4) (1.3) (2.6) Production tax credits and other credits (2.8) (9.5) (0.1) — — — — — — Noncontrolling interests (0.7) (2.5) — — — — — — — Excess deferred tax amortization (6.0) — (7.5) (4.8) (8.6) (10.6) (12.8) (7.9) (8.7) Other (2.8) (1.3) 0.3 0.2 — — (0.3) 0.5 (3.5) Effective income tax rate 8.4% 4.5% 21.8% (1.8)% 17.9% 12.2% 6.1% 18.4% 12.5% Three Months Ended March 31, 2017 (a) 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 0.9 1.0 4.9 0.1 5.2 4.9 4.6 5.3 5.6 Qualified nuclear decommissioning trust fund income 3.5 7.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.4) (0.7) (0.2) (0.1) (0.1) (0.2) (0.1) (0.3) (0.4) Plant basis differences (2.4) — (0.2) (13.2) (0.9) (3.8) (5.8) (1.9) (3.4) Production tax credits and other credits (0.7) (1.5) — — — — — — — Noncontrolling interest — 0.1 — — — — — — — Merger expenses (b) (11.5) (3.4) — — — (42.4) (34.2) (21.9) (167.1) Fitzpatrick bargain purchase gain (6.6) (14.8) — — — — — — — Other (0.1) (0.4) — 0.3 (0.2) (0.4) 0.5 — (3.0) Effective income tax rate 17.7% 23.1% 39.5% 22.1% 39.0% (6.9)% 0.0% 16.2% (133.3)% _________ (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 a remeasurement of uncertain state income tax positions for Pepco and DPL. Accounting for Uncertainty in Income Taxes The Registrants have the following unrecognized tax benefits as of March 31, 2018 and December 31, 2017 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE March 31, 2018 $ 733 $ 464 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 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 March 31, 2018 , Exelon and ComEd have approximately $ 33 million and $2 million , respectively, of unrecognized federal and state income tax benefits that could significantly decrease within the 12 months after the reporting date due to a final resolution of the like-kind exchange litigation described below. The recognition of these unrecognized tax benefits would decrease Exelon and ComEd's effective tax rate. Settlement of Income Tax Audits, Refund Claims, and Litigation As of March 31, 2018 , Exelon, Generation, BGE, PHI, Pepco, DPL, and ACE have approximately $679 million , $ 465 million , $120 million , $ 94 million , $ 59 million , $ 21 million , and $ 14 million 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, and the outcomes of pending court cases. Of the above unrecognized tax benefits, Exelon and Generation have $ 458 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefits related to BGE, Pepco, DPL, and ACE, if recognized, may be included in future regulated base rates and that portion would have no impact to the effective tax rate. Other Income Tax Matters Like-Kind Exchange (Exelon and ComEd) 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 and a decision is expected in 2018. 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 by 2022. In the second quarter of 2018, Exelon, Generation, PHI, DPL, and Pepco expect to record an estimated one-time increase to deferred income taxes of approximately $17 million , $5 million , $18 million , $1 million and $17 million , respectively. At PHI, DPL and Pepco, the increase to the Maryland deferred income tax liability will be 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, DPL's or Pepco's future results of operations.

Nuclear Decommissioning (Exelon

Nuclear Decommissioning (Exelon and Generation)	3 Months Ended
	Mar. 31, 2018
Environmental Remediation Obligations [Abstract]
Nuclear Decommissioning (Exelon and Generation)	Nuclear Decommissioning (Exelon and Generation) Nuclear Decommissioning Asset Retirement Obligations Generation has a legal obligation to decommission its nuclear power plants following the expiration of their operating licenses. To estimate its decommissioning obligation related to its nuclear generating stations for financial accounting and reporting purposes, Generation uses a probability-weighted, discounted cash flow model which, on a unit-by-unit basis, considers multiple outcome scenarios that include significant estimates and assumptions, and are based on decommissioning cost studies, cost escalation rates, probabilistic cash flow models and discount rates. Generation updates its ARO annually, unless circumstances warrant more frequent updates, based on its review of updated cost studies and its annual evaluation of cost escalation factors and probabilities assigned to various scenarios. The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets from December 31, 2017 to March 31, 2018 : Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 Accretion expense 117 Net increase due to changes in, and timing of, estimated future cash flows 32 Costs incurred related to decommissioning plants (4 ) Nuclear decommissioning ARO at March 31, 2018 (a) $ 9,807 _________ (a) Includes $64 million and $13 million for the current portion of the ARO at March 31, 2018 and December 31, 2017 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. During the three months ended March 31, 2018 , Generation’s total nuclear ARO increased by approximately $145 million , p rimarily reflecting the accretion of the ARO liability due to the passage of time and the impact of the February 2, 2018 announcement to retire Oyster Creek at the end of its current operating cycle by October 2018. Refer to Note 8 — Early Plant Retirements for additional information regarding the announced early retirement of Oyster Creek. Nuclear Decommissioning Trust Fund Investments NDT funds have been established for each generation station unit to satisfy Generation’s nuclear decommissioning obligations. Generally, NDT funds established for a particular unit may not be used to fund the decommissioning obligations of any other unit. The NDT funds associated with Generation’s nuclear units have been funded with amounts collected from the previous owners and their respective utility customers. PECO is authorized to collect funds, in revenues, for decommissioning the former PECO nuclear plants through regulated rates, and these collections are scheduled through the operating lives of the former PECO plants. The amounts collected from PECO customers are remitted to Generation and deposited into the NDT funds for the unit for which funds are collected. Every five years, PECO files a rate adjustment with the PAPUC that reflects PECO’s calculations of the estimated amount needed to decommission each of the former PECO units based on updated fund balances and estimated decommissioning costs. The rate adjustment is used to determine the amount collectible from PECO customers. The most recent rate adjustment occurred on January 1, 2018, and the effective rates currently yield annual collections of approximately $4 million . The next five-year adjustment is expected to be reflected in rates charged to PECO customers effective January 1, 2023. See Note 15 — Asset Retirement Obligations of Exelon's 2017 Form 10-K, for information regarding the amount collected from PECO ratepayers for decommissioning costs. Exelon and Generation had NDT fund investments totaling $13,275 million and $13,349 million at March 31, 2018 and December 31, 2017 , respectively. The following table provides net unrealized gains (losses) on NDT funds for the three months ended March 31, 2018 and 2017 : Exelon and Generation Three Months Ended 2018 2017 Net unrealized gains (losses) on decommissioning trust funds — Regulatory Agreement Units (a) $ (75 ) $ 222 Net unrealized gains (losses) on decommissioning trust funds — Non-Regulatory Agreement Units (b)(c) (96 ) 166 _________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $(2) million and $(1) million of net unrealized losses related to the Zion Station pledged assets for the three months ended March 31, 2018 and 2017 , respectively. Net unrealized losses related to Zion Station pledged assets are included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets in 2018 and 2017 , respectively. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends on NDT fund investments are recognized when earned and are included in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income. Interest and dividends earned on the NDT fund investments for the Regulatory Agreement Units are eliminated in Other, net on Exelon’s and Generation’s Consolidated Statement of Operations and Comprehensive Income. Refer to Note 3 — Regulatory Matters and Note 26 — Related Party Transactions of the Exelon 2017 Form 10-K for information regarding regulatory liabilities at ComEd and PECO and intercompany balances between Generation, ComEd and PECO reflecting the obligation to refund to customers any decommissioning-related assets in excess of the related decommissioning obligations. Zion Station Decommissioning On September 1, 2010, Generation completed an Asset Sale Agreement (ASA) with EnergySolutions Inc. and its wholly owned subsidiaries, EnergySolutions, LLC (EnergySolutions) and ZionSolutions, under which ZionSolutions has assumed responsibility for decommissioning Zion Station, which is located in Zion, Illinois and ceased operation in 1998. See Note 15 — Asset Retirement Obligations of the Exelon 2017 Form 10-K for information regarding the specific treatment of assets, including NDT funds, and decommissioning liabilities transferred in the transaction. ZionSolutions is subject to certain restrictions on its ability to request reimbursements from the Zion Station NDT funds as defined within the ASA. Therefore, the transfer of the Zion Station assets did not qualify for asset sale accounting treatment and, as a result, the related NDT funds were reclassified to Pledged assets for Zion Station decommissioning within Generation’s and Exelon’s Consolidated Balance Sheets and will continue to be measured in the same manner as prior to the completion of the transaction. Additionally, the transferred ARO for decommissioning was replaced with a Payable for Zion Station decommissioning in Generation’s and Exelon’s Consolidated Balance Sheets. Changes in the value of the Zion Station NDT assets, net of applicable taxes, 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 approximately $115 million which is included within the nuclear decommissioning ARO at March 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 the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at March 31, 2018 and December 31, 2017 : Exelon and Generation March 31, 2018 December 31, 2017 Carrying value of Zion Station pledged assets (a) $ 30 $ 39 Payable to Zion Solutions (b)(c) 28 37 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 949 942 _________ (a) Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets. (b) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized. (c) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (d) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings. 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. 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). The status report demonstrated adequate decommissioning funding assurance for all units except for Peach Bottom Unit 1. As a former PECO plant, financial assurance for decommissioning Peach Bottom Unit 1 is provided by the NDT fund in addition to collections from PECO ratepayers. As discussed under Nuclear Decommissioning Trust Fund Investments above, the amount collected from PECO ratepayers has been adjusted effective January 1, 2018. On March 28, 2018, Generation submitted its annual decommissioning funding status report with the NRC for shutdown reactors, reactors within five years of shut down 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.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Retirement Benefits (Exelon, Generation, ComEd, PECO and BGE)	Retirement Benefits (All Registrants) Exelon sponsors defined benefit pension plans and other postretirement benefit plans for essentially all current employees. Substantially all non-union employees and electing union employees hired on or after January 1, 2001 participate in cash balance pension plans. Effective January 1, 2009, substantially all newly-hired union-represented employees participate in cash balance pension plans. Effective February 1, 2018, most newly-hired Generation and BSC non-represented employees are not eligible for pension benefits, and will instead be eligible to receive an enhanced non-discretionary employer contribution in an Exelon defined contribution savings plan. Effective January 1, 2018, most newly-hired non-represented employees are not eligible for OPEB benefits and employees represented by Local 614 are not eligible for retiree health care benefits. During the first quarter of 2017, in connection with the acquisition of Fitzpatrick, Exelon established a new qualified pension plan and a new OPEB plan, and recorded a provisional obligation for Fitzpatrick employees based on information available at the merger date of $38 million and $11 million , respectively. As permitted by business combinations authoritative guidance, during the third quarter of 2017, Exelon updated those obligations based on a final valuation for Fitzpatrick employees as of the merger date of March 31, 2017. The updated obligations for pension and OPEB were $ 16 million and $ 17 million , respectively. Refer to Note 4 — Mergers, Acquisitions and Dispositions for additional discussion of the acquisition of FitzPatrick. Defined Benefit Pension and Other Postretirement Benefits 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. The majority of the 2018 pension benefit cost for 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 table presents the components of Exelon's net periodic benefit costs, prior to capitalization, for the three months ended March 31, 2018 and 2017 . Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 101 $ 95 $ 28 $ 26 Interest cost 201 210 43 45 Expected return on assets (312 ) (299 ) (43 ) (41 ) Amortization of: Prior service benefit — — (46 ) (47 ) Actuarial loss 157 152 16 16 Net periodic benefit cost $ 147 $ 158 $ (2 ) $ (1 ) _________ (a) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017. The amounts below represent Exelon's, Generation's, ComEd's, PECO's, BGE's, BSC's, PHI's, Pepco's, DPL's, ACE's, and PHISCO's allocated portion of the pension and postretirement benefit plan 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 three months ended March 31, 2017. The amounts below represent the Registrants’ as well as BSC's and PHISCO's pension and postretirement benefit plan net periodic benefit costs. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment for the three months ended March 31, 2018 and 2017, while the non-service cost components are included in Other, net and Regulatory assets for the three months ended March 31, 2018 and in Other, net and Property, plant and equipment for the three months ended March 31, 2017. For the Registrants other than Exelon, the service cost and non-service cost components are included in Operating and maintenance expense and Property, plant and equipment on their consolidated financial statements for the three months ended March 31, 2018 and 2017. Three Months Ended March 31, Pension and Other Postretirement Benefit Costs 2018 2017 Exelon (a)(b) $ 145 $ 157 Generation (b) 51 54 ComEd 45 44 PECO 5 7 BGE 15 16 BSC (c) 14 12 PHI (a)(d) 15 24 Pepco 4 7 DPL — 3 ACE 3 3 PHISCO (d) 8 11 _________ (a) Exelon reflects the consolidated pension and other postretirement benefit costs of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated pension and other postretirement benefit costs of Pepco, DPL, ACE, and PHISCO. (b) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017. (c) 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. (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. Defined Contribution Savings Plans The Registrants participate in various 401(k) defined contribution savings plans that are sponsored by Exelon. The plans are qualified under applicable sections of the IRC and allow employees to contribute a portion of their pre-tax and/or after-tax income in accordance with specified guidelines. All Registrants match a percentage of the employee contributions up to certain limits. The following table presents the matching contributions to the savings plans during the three months ended March 31, 2018 and 2017 , respectively. Three Months Ended March 31, Savings Plan Matching Contributions 2018 2017 Exelon (a)(b) $ 32 $ 30 Generation (b) 15 14 ComEd 7 7 PECO 2 2 BGE 2 2 BSC (c) 3 2 PHI (a)(d) 3 3 Pepco 1 1 DPL 1 1 PHISCO (d) 1 1 _________ (a) Exelon reflects the consolidated savings plan matching contributions of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated savings plan matching contributions of Pepco, DPL, and PHISCO. (b) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017. (c) 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 or DPL amounts above. (d) These amounts represent amounts billed to Pepco and DPL through intercompany allocations. These amounts are not included in Pepco or DPL amounts above.

Severance (All Registrants)

Severance (All Registrants)	3 Months Ended
	Mar. 31, 2018
Restructuring Charges [Abstract]
Severance (All Registrants)	Severance (All Registrants) The Registrants have an ongoing severance plan under which, in general, the longer an employee worked prior to termination the greater the amount of severance benefits. The Registrants record a liability and expense or regulatory asset for severance once terminations are probable of occurrence and the related severance benefits can be reasonably estimated. For severance benefits that are incremental to its ongoing severance plan (“one-time termination benefits”), the Registrants measure the obligation and record the expense at fair value at the communication date if there are no future service requirements, or, if future service is required to receive the termination benefit, ratably over the required service period. Ongoing Severance Plans The Registrants provide severance and health and welfare benefits under Exelon’s ongoing severance benefit plans to terminated employees in the normal course of business. These benefits are accrued for when the benefits are considered probable and can be reasonably estimated. For the three months ended March 31, 2018 and 2017 , the Registrants recorded the following severance costs associated with these ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Exelon Generation (a) ComEd (a) PECO (a) BGE (a) PHI (a) Pepco (a) DPL (a) ACE (a) Three Months Ended March 31, 2018 $ 8 $ 2 $ 1 $ — $ 1 $ 4 $ 2 $ 1 $ 1 March 31, 2017 4 3 1 — — — — — — _________ (a) The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017 . Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017 . Cost Management Program-Related Severance In August 2015, Exelon announced a cost management program focused on cost savings of approximately $400 million at BSC and Generation. Additionally, in November 2017, Exelon announced a new commitment for an additional $250 million of cost savings, primarily at Generation, to be achieved by 2020. These actions are in response to the continuing economic challenges confronting all parts of Exelon’s business and industry, necessitating continued focus on cost management through enhanced efficiency and productivity. In connection with the program, certain positions have been identified for elimination and severance costs were recognized as both probable and estimable. While there may be additional position eliminations identified leading to potential severance or other termination benefit changes, Exelon, Generation and BSC intend to manage any staff reductions through natural attrition to the extent possible to minimize impacts on employees. Any additional severance or other termination benefit charges related to this commitment will be recognized when such amounts are considered probable and can be reasonably estimated. For the three months ended March 31, 2018 and 2017 , these costs were immaterial. Early Plant Retirement-Related Severance (Exelon and Generation) As a result of the Three Mile Island and Oyster Creek plant retirement decision, Exelon and Generation have recognized severance costs as both probable and estimable. Severance costs will be provided to management employees that are eligible under Exelon’s severance policy and to union employees if specified within the respective collective bargaining agreements, to the extent that those employees are not redeployed to other locations. The final amount of the severance cost will ultimately depend on the specific employees severed. See Note 8 - Early Plant Retirements for additional information regarding the announced early retirement of TMI and Oyster Creek. For the three months ended March 31, 2018 and 2017 , these costs were immaterial. Severance Liability Amounts included in the table below represent the severance liability recorded for employees of each Registrant and exclude amounts included at Exelon and billed through intercompany allocations: Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — Severance charges (a) 9 3 1 — 1 2 1 — — Payments (16 ) (5 ) (1 ) — — (6 ) (1 ) — — Balance at March 31, 2018 $ 87 $ 56 $ 3 $ — $ 1 $ 16 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon, Generation, PECO and PHI)	3 Months Ended
	Mar. 31, 2018
Changes in Accumulated Other Comprehensive Income [Abstract]
Comprehensive Income (Loss) Note [Text Block]	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 three months ended March 31, 2018 and 2017 : Three Months Ended March 31, 2018 Gains Unrealized Gains and (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) (d) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 8 — 18 1 — 27 Amounts reclassified from AOCI (b) — — 44 — — 44 Net current-period OCI 8 — 62 1 — 71 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (10 ) (c) — — — (10 ) Ending balance $ (6 ) $ — $ (2,936 ) $ (22 ) $ (1 ) $ (2,965 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 7 — — (1 ) — 6 Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI 7 — — (1 ) — 6 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (3 ) (c) — — — (3 ) Ending balance $ (9 ) $ — $ — $ (24 ) $ (1 ) $ (34 ) 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 Liabilities standard — (1 ) (c) — — — (1 ) Ending balance $ — $ — $ — $ — $ — $ — Three Months Ended March 31, 2017 Gains Unrealized Gains and (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications 2 1 (59 ) 1 5 (50 ) Amounts reclassified from AOCI (b) 4 — 36 — — 40 Net current-period OCI 6 1 (23 ) 1 5 (10 ) Ending balance $ (11 ) $ 5 $ (2,633 ) $ (29 ) $ (2 ) $ (2,670 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications 2 — — 1 6 9 Amounts reclassified from AOCI (b) 4 — — — — 4 Net current-period OCI 6 — — 1 6 13 Ending balance $ (13 ) $ 2 $ — $ (29 ) $ (1 ) $ (41 ) 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 interest. 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 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 2 — New Accounting Standards 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 2 — New Accounting Standards for additional information. ComEd, PECO, BGE, PHI, Pepco, DPL and ACE did not have any reclassifications out of AOCI to Net income during the three months ended March 31, 2018 and 2017 . The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 Actuarial losses (b) (83 ) Total before tax (60 ) Tax benefit 16 Net of tax $ (44 ) Total Reclassifications $ (44 ) Comprehensive income Three Months Ended March 31, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Other cash flow hedges $ (7 ) $ (7 ) Interest expense Total before tax (7 ) (7 ) Tax benefit 3 3 Net of tax $ (4 ) $ (4 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (81 ) — Total before tax (58 ) — Tax benefit 22 — Net of tax $ (36 ) $ — Total Reclassifications $ (40 ) $ (4 ) Comprehensive income _________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional details). The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the three months ended March 31, 2018 and 2017 : Three Months Ended 2018 2017 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 10 Actuarial loss reclassified to periodic benefit cost (22 ) (32 ) Pension and non-pension postretirement benefit plans valuation adjustment (7 ) — Change in unrealized (loss) on cash flow hedges (3 ) (1 ) Change in unrealized (loss) on investments in unconsolidated affiliates (1 ) (4 ) Change in unrealized (loss) on marketable securities — (1 ) Total $ (27 ) $ (28 ) Generation Change in unrealized (loss) on cash flow hedges $ (3 ) $ (1 ) Change in unrealized (loss) on investments in unconsolidated affiliates (1 ) (3 ) Total $ (4 ) $ (4 )

Earnings Per Share and Equity (

Earnings Per Share and Equity (Exelon)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share and Equity (Exelon)	Earnings Per Share and Equity (Exelon) Earnings per Share 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: Three Months Ended March 31, 2018 2017 Exelon Net income attributable to common shareholders $ 585 $ 990 Weighted average common shares outstanding — basic 966 928 Assumed exercise and/or distributions of stock-based awards 2 2 Weighted average common shares outstanding — diluted 968 930 The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 5 million and 9 million for the three months ended March 31, 2018 and 2017 , respectively. 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 three months ended March 31, 2018 and 2017 . Refer to Note 19 — Shareholders' Equity of the Exelon 2017 Form 10-K for further information regarding the equity units. Under share repurchase programs, 2 million shares of common stock are held as treasury stock with a cost of $123 million as of March 31, 2018 .

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies (All Registrants)	Commitments and Contingencies (All Registrants) The following is an update to the current status of commitments and contingencies set forth in Note 23 of the Exelon 2017 Form 10-K. See Note 4 — Mergers, Acquisitions and Dispositions of the Exelon 2017 Form 10-K for further discussion on the PHI Merger commitments. Commitments PHI Merger Commitments (Exelon, PHI, Pepco, DPL and ACE) The merger of Exelon and PHI was approved in Delaware, New Jersey, Maryland and the District of Columbia. Exelon and PHI agreed 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. The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date and the remaining obligations as of March 31, 2018 : Description Expected Payment Period Pepco DPL ACE PHI Exelon Rate credits 2016 - 2017 $ 91 $ 67 $ 101 $ 259 $ 259 Energy efficiency 2016 - 2021 — — — — 122 Charitable contributions 2016 - 2026 28 12 10 50 50 Delivery system modernization Q2 2017 — — — — 22 Green sustainability fund Q2 2017 — — — — 14 Workforce development 2016 - 2020 — — — — 17 Other 1 5 — 6 29 Total commitments $ 120 $ 84 $ 111 $ 315 $ 513 Remaining commitments $ 75 $ 12 $ 8 $ 95 $ 165 In addition, Exelon is committed to develop or to assist in the commercial development of approximately 37 MWs of new generation in Maryland, District of Columbia, and Delaware, 27 MWs of which are expected to be completed by 2018. These investments are expected to total approximately $137 million, are expected to be primarily capital in nature, and will generate future earnings at Exelon and Generation. Investment costs will be recognized as incurred and recorded on Exelon's and Generation's financial statements. Exelon has also committed to purchase 100 MWs of wind energy in PJM, to procure 120 MWs of wind RECs for the purpose of meeting Delaware's renewable portfolio standards, and to maintain and promote energy efficiency and demand response programs in the PHI jurisdictions. Pursuant to the various jurisdictions' merger approval conditions, over specified periods Pepco, DPL and ACE are not permitted to reduce employment levels due to involuntary attrition associated with the merger integration process and have made other commitments regarding hiring and relocation of positions. 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 develop or assist in the development of 285 - 300 MWs of new generation. Exelon and Generation have incurred $ 458 million towards satisfying the commitment for new generation development in the State of Maryland, with 220 MW of new generation in operations to date and 10 MW of this commitment satisfied through a liquidated damages payment made in the fourth quarter of 2016. The remaining 55 MW 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, as of March 31, 2018 Exelon’s and Generation’s Consolidated Balance Sheets include a $ 50 million liability within Deferred credits and other liabilities for this remaining commitment, to be paid on or before January 15, 2023 unless the period is extended by consent of Exelon and the State. Refer to Note 23 - Commitments and Contingencies of the Combined Notes to Consolidated Financial Statements in the Exelon 2017 Form 10-K for additional information regarding the Constellation Merger Commitments. Commercial Commitments (All Registrants) The Registrants’ commercial commitments as of March 31, 2018 , representing commitments potentially triggered by future events were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Letters of credit (non-debt) (a) $ 1,586 $ 1,533 $ 2 $ 1 $ 5 $ 1 $ 1 $ — $ — Surety bonds (b) 1,651 1,463 9 9 10 66 32 4 5 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (c) 22 — — — — 22 7 9 6 Total commercial commitments $ 3,637 $ 2,996 $ 211 $ 188 $ 15 $ 89 $ 40 $ 13 $ 11 _________ (a) Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. Includes letters of credits issued under credit facility agreements arranged at minority and community banks and nonrecourse debt letters of credits. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $58 million , $17 million of which is a guarantee by Pepco, $24 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. 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 also to limit the liability of nuclear reactor owners for such claims from any single incident. As of March 31, 2018 , the current liability limit per incident is $13.2 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors at least once every five years with the last adjustment effective September 10, 2013. In accordance with the Price-Anderson Act, Generation maintains financial protection at levels equal to the amount of liability insurance available from private sources through the purchase of private nuclear energy liability insurance for public liability claims that could arise in the event of an incident. Effective January 1, 2017, the required amount of nuclear energy liability insurance purchased is $450 million for each operating site. Claims exceeding that amount are covered through mandatory participation in a financial protection pool, as required by the Price Anderson-Act, which provides the additional $13.0 billion per incident in funds available for public liability claims. Participation in this secondary financial protection pool requires the operator of each reactor to fund its proportionate share of costs for any single incident that exceeds the primary layer of financial protection. Exelon’s share of this secondary layer would be approximately $2.8 billion , however any amounts payable under this secondary layer would be capped at $ 420 million per year. In addition, the U.S. Congress could impose revenue-raising measures on the nuclear industry to pay public liability claims exceeding the $13.2 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 of the Exelon 2017 Form 10-K 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. In March 2018, NEIL declared a supplemental distribution. Generation's portion of the supplemental distribution declared by NEIL is estimated to be $31 million and was recorded as a reduction to Operating and maintenance expense within Exelon and Generation’s Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2018, with cash expected to be received during the second quarter 2018. Premiums paid to NEIL by its members are also subject to a potential assessment for adverse loss experience in the form of a retrospective premium obligation. NEIL has never assessed this retrospective premium since its formation in 1973, and Generation cannot predict the level of future assessments if any. The current maximum aggregate annual retrospective premium obligation for Generation is approximately $ 360 million . NEIL requires its members to maintain an investment grade credit rating or to ensure collectability of their annual retrospective premium obligation by providing a financial guarantee, letter of credit, deposit premium, or some other means of assurance. NEIL provides “all risk” property damage, decontamination and premature decommissioning insurance for each station for losses resulting from damage to its nuclear plants, either due to accidents or acts of terrorism. If the decision is made to decommission the facility, a portion of the insurance proceeds will be allocated to a fund, which Generation is required by the NRC to maintain, to provide for decommissioning the facility. In the event of an insured loss, Generation is unable to predict the timing of the availability of insurance proceeds to Generation and the amount of such proceeds that would be available. In the event that one or more acts of terrorism cause accidental property damage within a twelve-month period from the first accidental property damage under one or more policies for all insured plants, the maximum recovery by Exelon will be an aggregate of $3.2 billion plus such additional amounts as the insurer may recover for all such losses from reinsurance, indemnity and any other source, applicable to such losses. For its insured losses, Generation is self-insured to the extent that losses are within the policy deductible or exceed the amount of insurance maintained. Uninsured losses and other expenses, to the extent not recoverable from insurers or the nuclear industry, could also be borne by Generation. Any such losses could have a material adverse effect on Exelon’s and Generation’s financial condition, results of operations and cash flows. Environmental Remediation Matters General. The Registrants’ operations have in the past, and may in the future, require substantial expenditures to comply with environmental laws. Additionally, under Federal and state environmental laws, the Registrants are generally liable for the costs of remediating environmental contamination of property now or formerly owned by them and of property contaminated by hazardous substances generated by them. The Registrants own or lease a number of real estate parcels, including parcels on which their operations or the operations of others may have resulted in contamination by substances that are considered hazardous under environmental laws. In addition, the Registrants are currently involved in a number of proceedings relating to sites where hazardous substances have been deposited and may be subject to additional proceedings in the future. Unless otherwise disclosed, the Registrants cannot reasonably estimate whether they will incur significant liabilities for additional investigation and remediation costs at these or additional sites identified by the Registrants, environmental agencies or others, or whether such costs will be recoverable from third parties, including customers. Additional costs could have a material, unfavorable impact on the Registrants' financial conditions, results of operations and cash flows. MGP Sites ComEd, PECO, BGE and DPL have identified sites where former MGP activities have or may have resulted in actual site contamination. For almost all of these sites, there are additional PRPs that may share responsibility for the ultimate remediation of each location. • ComEd has identified 42 sites, 20 of which have been remediated and approved by the Illinois EPA or the U.S. EPA and 22 that are currently under some degree of active study and/or remediation. ComEd expects the majority of the remediation at these sites to continue through at least 2022. • PECO has identified 26 sites, 17 of which have been remediated in accordance with applicable PA DEP regulatory requirements and 9 that are currently under some degree of active study and/or remediation. PECO expects the majority of the remediation at these sites to continue through at least 2022. • BGE has identified 13 former gas manufacturing or purification sites, 9 of which the remediation has been completed and approved by the MDE and 4 that require some level of remediation and/or ongoing activity. BGE has determined that a loss associated with these sites is probable and has recorded an estimated liability, which is included in the table below. However, it is reasonably possible that BGE’s cost of remediation for one of its sites could be up to $13 million . • DPL has identified 3 sites, 2 of which remediation has been completed and approved by the MDE or the Delaware Department of Natural Resources and Environmental Control. The remaining site is under study and the required cost at the site is not expected to be material. The historical nature of the MGP sites and the fact that many of the sites have been buried and built over, impacts the ability to determine a precise estimate of the ultimate costs prior to initial sampling and determination of the exact scope and method of remedial activity. Management determines its best estimate of remediation costs using all available information at the time of each study, including probabilistic and deterministic modeling for ComEd and PECO, and the remediation standards currently required by the applicable state environmental agency. Prior to completion of any significant clean up, each site remediation plan is approved by the appropriate state environmental agency. ComEd, pursuant to an ICC order, and PECO, pursuant to settlements of natural gas distribution rate cases with the PAPUC, are currently recovering environmental remediation costs of former MGP facility sites through customer rates. See Note 6 — Regulatory Matters for additional information regarding the associated regulatory assets. While BGE and DPL do not have riders for MGP clean-up costs, they have historically received recovery of actual clean-up costs in distribution rates. As of March 31, 2018 and December 31, 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: March 31, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 462 $ 313 Generation 117 — ComEd 283 281 PECO 29 28 BGE 5 4 PHI 28 — Pepco 26 — 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 — Solid and Hazardous Waste Cotter Corporation. The EPA has advised Cotter Corporation (Cotter), a former ComEd subsidiary, that it is potentially liable in connection with radiological contamination at a site known as the West Lake Landfill in Missouri. In 2000, ComEd sold Cotter to an unaffiliated third-party. As part of the sale, ComEd agreed to indemnify Cotter for any liability arising in connection with the West Lake Landfill. In connection with Exelon’s 2001 corporate restructuring, this responsibility to indemnify Cotter was transferred to Generation. On May 29, 2008, the EPA issued a Record of Decision (ROD) approving a landfill cover remediation approach. Generation had previously recorded an estimated liability for its anticipated share of a landfill cover remedy that was estimated to cost approximately $90 million in total. By letter dated January 11, 2010, the EPA requested that the PRPs perform a supplemental feasibility study for a remediation alternative that would involve complete excavation of the radiological contamination. On September 30, 2011, the PRPs submitted the supplemental feasibility study to the EPA for review. Since June 2012, the EPA has requested that the PRPs perform a series of additional analyses and groundwater and soil sampling as part of the supplemental feasibility study. This further analysis was focused on a partial excavation remedial option. The PRPs provided the draft final Remedial Investigation and Feasibility Study (RI/FS) to the EPA in January 2018, which formed the basis for EPA’s proposed remedy selection, as further discussed below. There are currently three PRPs participating in the West Lake Landfill remediation proceeding. Investigation by Generation has identified a number of other parties who also may be PRPs and could be liable to contribute to the final remedy. Further investigation is ongoing. On February 1, 2018, the EPA announced its proposed remedy involving partial excavation of the site with an enhanced landfill cover. The proposed remedy was open for public comment through April 23, 2018 and Generation currently expects that a ROD will be issued during the third quarter of 2018. Thereafter, the EPA will seek to enter into a Consent Decree with the PRPs to effectuate the remedy, which Generation currently expects will occur in late 2018 or early 2019. The estimated cost of the remedy, taking into account the current EPA technical requirements and the total costs expected to be incurred by the PRPs in fully executing the remedy, is approximately $340 million , including cost escalation on an undiscounted basis, which would be allocated among the final group of PRPs. Generation has determined that a loss associated with the EPA’s partial excavation and enhanced landfill cover remedy is probable and has recorded a liability included in the table above, that reflects management’s best estimate of Cotter’s allocable share of the ultimate cost for the entire remediation effort. Given the joint and several nature of this liability, the magnitude of Generation’s ultimate liability will depend on the actual costs incurred to implement the ultimate required remediation remedy as well as on the nature and terms of any cost-sharing arrangements with the final group of PRPs. Therefore, it is reasonably possible that the ultimate cost and Generation’s associated allocable share could differ significantly once these uncertainties are resolved, which could have a material impact on Exelon's and Generation's future financial conditions, results of operations and cash flows. On January 16, 2018, the PRPs were advised by the EPA that it will begin an additional investigation and evaluation of groundwater conditions at the West Lake Landfill. The PRPs have been provided with a draft statement of work that will form the basis of an Administrative Settlement Agreement and Order on Consent for the performance by the PRPs of the groundwater RI/FS and reimbursement of EPA’s oversight costs. The purposes of this new RI/FS are to define the nature and extent of any groundwater contamination from the West Lake Landfill site, determine the potential risk posed to human health and the environment, and evaluate remedial alternatives. Generation estimates the undiscounted cost for the groundwater RI/FS for West Lake to be approximately $20 million and Generation has recorded a liability included in the table above, that reflects management’s best estimate of Cotter’s allocable share of the cost among the PRPs. At this time Generation cannot predict the likelihood or the extent to which, if any, remediation activities will be required and cannot estimate a reasonably possible range of loss for response costs beyond those associated with the RI/FS component. It is reasonably possible, however, that resolution of this matter could have a material, unfavorable impact on Exelon’s and Generation’s future results of operations and cash flows. During December 2015, the EPA took two actions related to the West Lake Landfill designed to abate what it termed as imminent and dangerous conditions at the landfill. The first involved installation by the PRPs of a non-combustible surface cover to protect against surface fires in areas where radiological materials are believed to have been disposed. Generation has accrued what it believes to be an adequate amount to cover its anticipated liability for this interim action, and the work is expected to be completed in 2018. The second action involved EPA's public statement that it will require the PRPs to construct a barrier wall in an adjacent landfill to prevent a subsurface fire from spreading to those areas of the West Lake Landfill where radiological materials are believed to have been disposed. At this time, Generation believes that the requirement to build a barrier wall is remote in light of other technologies that have been employed by the adjacent landfill owner. Finally, one of the other PRPs, the landfill owner and operator of the adjacent landfill, has indicated that it will be making a contribution claim against Cotter for costs that it has incurred to prevent the subsurface fire from spreading to those areas of the West Lake Landfill where radiological materials are believed to have been disposed. At this time, Exelon and Generation do not possess sufficient information to assess this claim and therefore are unable to estimate a range of loss, if any. As such, no liability has been recorded for the potential contribution claim. It is reasonably possible, however, that resolution of this matter could have a material, unfavorable impact on Exelon’s and Generation's financial conditions, results of operations and cash flows. On August 8, 2011, Cotter was notified by the DOJ that Cotter is considered a PRP with respect to the government’s clean-up costs for contamination attributable to low level radioactive residues at a former storage and reprocessing facility named Latty Avenue near St. Louis, Missouri. The Latty Avenue site is included in ComEd’s indemnification responsibilities discussed above as part of the sale of Cotter. The radioactive residues had been generated initially in connection with the processing of uranium ores as part of the U.S. Government’s Manhattan Project. Cotter purchased the residues in 1969 for initial processing at the Latty Avenue facility for the subsequent extraction of uranium and metals. In 1976, the NRC found that the Latty Avenue site had radiation levels exceeding NRC criteria for decontamination of land areas. Latty Avenue was investigated and remediated by the United States Army Corps of Engineers pursuant to funding under FUSRAP. The DOJ has not yet formally advised the PRPs of the amount that it is seeking, but it is believed to be approximately $90 million from all PRPs. The DOJ and the PRPs agreed to toll the statute of limitations until August 2018 so that settlement discussions could proceed. Generation has determined that a loss associated with this matter is probable under its indemnification agreement with Cotter and has recorded an estimated liability, which is included in the table above. Commencing in February 2012, a number of lawsuits have been filed in the U.S. District Court for the Eastern District of Missouri. Among the defendants were Exelon, Generation and ComEd, all of which were subsequently dismissed from the case, as well as Cotter, which remains a defendant. The suits allege that individuals living in the North St. Louis area developed some form of cancer or other serious illness due to Cotter's negligent or reckless conduct in processing, transporting, storing, handling and/or disposing of radioactive materials. Plaintiffs are asserting public liability claims under the Price-Anderson Act. Their state law claims for negligence, strict liability, emotional distress, and medical monitoring have been dismissed. The complaints do not contain specific damage claims. In the event of a finding of liability against Cotter, it is reasonably possible that Generation would be financially responsible due to its indemnification responsibilities of Cotter described above. The court has dismissed a number of the lawsuits as untimely, and that has been upheld on appeal. The parties have engaged in settlement discussions pursuant to court-ordered mediation and it is expected that resolution of this matter will not have a material, unfavorable impact on Exelon’s and Generation's financial conditions, results of operations and cash flows. Benning Road Site. In September 2010, PHI received a letter from EPA identifying the Benning Road site as one of six land-based sites potentially contributing to contamination of the lower Anacostia River. A portion of the site was formerly the location of a Pepco Energy Services electric generating facility. That generating facility was deactivated in June 2012 and plant structure demolition was completed in July 2015. The remaining portion of the site consists of a Pepco transmission and distribution service center that remains in operation. In December 2011, the U.S. District Court for the District of Columbia approved a Consent Decree entered into by Pepco and Pepco Energy Services with the DOEE, which requires Pepco and Pepco Energy Services to conduct a Remediation Investigation (RI)/ Feasibility Study (FS) for the Benning Road site and an approximately 10 to 15-acre portion of the adjacent Anacostia River. The RI/FS will form the basis for the remedial actions for the Benning Road site and for the Anacostia River sediment associated with the site. The Consent Decree does not obligate Pepco or Pepco Energy Services to pay for or perform any remediation work, but it is anticipated that DOEE will look to Pepco and Pepco Energy Services to assume responsibility for cleanup of any conditions in the river that are determined to be attributable to past activities at the Benning Road site. Pursuant to Exelon's March 23, 2016 acquisition of PHI, Pepco Energy Services was transferred to Generation. Since 2013, Pepco and Pepco Energy Services (now Generation) have been performing RI work and have submitted multiple draft RI reports to the DOEE. Once the RI work is completed, Pepco and Generation will issue a draft “final” RI report for review and comment by DOEE and the public. Pepco and Generation will then proceed to develop an FS to evaluate possible remedial alternatives for submission to DOEE. The Court has established a schedule for completion of the RI and FS, and approval by the DOEE, by May 6, 2019. Upon DOEE’s approval of the final RI and FS Reports, Pepco and Generation will have satisfied their obligations under the Consent Decree. At that point, DOEE will prepare a Proposed Plan regarding further response actions. After considering public comment on the Proposed Plan, DOEE will issue a Record of Decision identifying any further response actions determined to be necessary. PHI, Pepco and Generation have determined that a loss associated with this matter is probable and have accrued an estimated liability, which is included in the table above. Anacostia River Tidal Reach . Contemporaneous with the Benning RI/FS being performed by Pepco and Generation, DOEE and certain federal agencies have been conducting a separate RI/FS focused on the entire tidal reach of the Anacostia River extending from just north of the Maryland-D.C. boundary line to the confluence of the Anacostia and Potomac Rivers. In March 2016, DOEE released a draft of the river-wide RI Report for public review and comment. The river-wide RI incorporated the results of the river sampling performed by Pepco and Pepco Energy Services as part of the Benning RI/FS, as well as similar sampling efforts conducted by owners of other sites adjacent to this segment of the river and supplemental river sampling conducted by DOEE’s contractor. DOEE asked Pepco, along with parties responsible for other sites along the river, to participate in a “Consultative Working Group” to provide input into the process for future remedial actions addressing the entire tidal reach of the river and to ensure proper coordination with the other river cleanup efforts currently underway, including cleanup of the river segment adjacent to the Benning Road site resulting from the Benning RI/FS. Pepco responded that it will participate in the Consultative Working Group but its participation is not an acceptance of any financial responsibility beyond the work that will be performed at the Benning Road site described above. DOEE has advised the Consultative Working Group that the federal and DOEE authorities conducted the remedial investigation and a draft of that report was released to the public on April 1, 2018. Written comments will be accepted by the Agencies until May 14, 2018 and a Public Meeting to present the finding of the RI is scheduled for April 24, 2018. Pepco intends to submit comments, participate in the Public Hearing, and continue its outreach efforts as appropriate to the agencies, governmental officials, community organizations and other key stakeholders. A feasibility study of potential remedies is being prepared by the Agencies and is scheduled to be released in the late summer or early fall of this year. DOEE currently is working under a statutorily mandated date to complete the Record of Decision selecting the final remedy for the project by June 30, 2018. However, on January 11, 2018 the DOEE requested at a hearing of the District of Columbia Council Committee of the Environment that this statutory deadline be extended until December 31, 2019 to reflect the time necessary to complete the investigation. A recommendation by the Committee to the DC Council is expected in the near future. The District of Columbia Council will make the final determination to extend the deadline. An appropriate liability for Pepco’s share of investigation costs has been accrued and is included in the table above. Although Pepco has determined that it is probable that costs for remediation will be incurred , Pepco cannot estimate the reasonably possible range of loss at this time and no liability has been accrued for those future costs. It is anticipated that Pepco will likely be in a better position to estimate that range of loss when the draft Feasibility Study for the Project is released. The timing for that release is currently scheduled for late this summer or early fall. Conectiv Energy Wholesale Power Generation Sites. In July 2010, PHI sold the wholesale power generation business of Conectiv Energy Holdings, Inc. and substantially all of its subsidiaries (Conectiv Energy) to Calpine Corporation (Calpine). Under New Jersey’s Industrial Site Recovery Act (ISRA), the transfer of ownership triggered an obligation on the part of Conectiv Energy to remediate any environmental contamination at each of the nine Conectiv Energy generating facility sites located in New Jersey. Under the terms of the sale, Calpine has assumed responsibility for performing the ISRA-required remediation and for the payment of all related ISRA compliance cos

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	3 Months Ended
	Mar. 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 three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 46 $ 46 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 56 56 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (75 ) (75 ) — — — — — — — Non-regulatory agreement units (96 ) (96 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (2 ) (2 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) 24 24 — — — — — — — Total decommissioning-related activities (47 ) (47 ) — — — — — — — Investment income 4 2 — — — — — — — Interest income related to uncertain income tax positions 2 1 — — — — — — — AFUDC — Equity 18 — 6 2 4 6 5 1 — Non-service net periodic benefit cost (10 ) — — — — — — — — Other 5 — 2 — — 5 3 1 1 Other, net $ (28 ) $ (44 ) $ 8 $ 2 $ 4 $ 11 $ 8 $ 2 $ 1 Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 68 $ 68 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 32 32 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 222 222 — — — — — — — Non-regulatory agreement units 166 166 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (1 ) (1 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (234 ) (234 ) — — — — — — — Total decommissioning-related activities 253 253 — — — — — — — Investment income 2 2 — — — — — — — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 17 — 2 2 4 9 5 2 2 Non-service net periodic benefit cost (26 ) — — — — — — — — Other 10 4 2 — — 4 3 1 — Other, net $ 257 $ 259 $ 4 $ 2 $ 4 $ 13 $ 8 $ 3 $ 2 _________ (a) Includes investment income and realized gains and losses on sales of investments of the trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2017 Form 10-K for additional information regarding the accounting for nuclear decommissioning. The following utility taxes are included in revenues and expenses for the three months ended March 31, 2018 and 2017 . Generation’s utility tax expense represents gross receipts tax related to its retail operations, and the Utility Registrants' utility tax expense represents municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 235 $ 32 $ 61 $ 33 $ 26 $ 83 $ 77 $ 6 $ — Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 224 $ 32 $ 59 $ 31 $ 26 $ 76 $ 71 $ 5 $ — Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 926 $ 436 $ 201 $ 68 $ 82 $ 117 $ 53 $ 32 $ 23 Amortization of regulatory assets (a) 152 — 27 7 52 66 43 13 10 Amortization of intangible assets, net (a) 13 12 — — — — — — — Amortization of energy contract assets and liabilities (b) 3 3 — — — — — — — Nuclear fuel (c) 287 287 — — — — — — — ARO accretion (d) 120 120 — — — — — — — Total depreciation, amortization and accretion $ 1,501 $ 858 $ 228 $ 75 $ 134 $ 183 $ 96 $ 45 $ 33 Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 754 $ 289 $ 190 $ 64 $ 80 $ 112 $ 50 $ 30 $ 21 Amortization of regulatory assets (a) 128 — 18 7 48 55 32 9 14 Amortization of intangible assets, net (a) 14 13 — — — — — — — Amortization of energy contract assets and liabilities (b) 2 2 — — — — — — — Nuclear fuel (c) 264 264 — — — — — — — ARO accretion (d) 112 110 — — — — — — — Total depreciation, amortization and accretion $ 1,274 $ 678 $ 208 $ 71 $ 128 $ 167 $ 82 $ 39 $ 35 _________ (a) Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income. (b) Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (d) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 145 $ 51 $ 45 $ 5 $ 14 $ 15 $ 4 $ — $ 3 Loss from equity method investments 7 7 — — — — — — — Provision for uncollectible accounts 64 11 8 17 8 20 6 8 5 Stock-based compensation costs 29 — — — — — — — — Other decommissioning-related activity (a) (31 ) (31 ) — — — — — — — Energy-related options (b) (7 ) (7 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral 7 — — — — 7 1 6 — Amortization of debt fair value adjustment (3 ) (3 ) — — — — — — — Discrete impacts from EIMA and FEJA (c) (4 ) — (4 ) — — — — — — Amortization of debt costs 9 3 1 — — 1 — — — Provision for excess and obsolete inventory 13 12 1 — — — — — — Other 9 2 (6 ) (1 ) (2 ) 9 (1 ) 5 1 Total other non-cash operating activities $ 240 $ 45 $ 46 $ 21 $ 20 $ 53 $ 10 $ 19 $ 9 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (177 ) $ (131 ) $ (48 ) $ (25 ) $ (11 ) $ 61 $ 19 $ 14 $ 27 Increase in PPE related to ARO update 32 32 — — — — — — — Dividends on stock compensation 1 — — — — — — — — Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 157 $ 54 $ 44 $ 7 $ 16 $ 24 $ 7 $ 3 $ 3 Loss from equity method investments 10 10 — — — — — — — Provision for uncollectible accounts 34 9 7 17 5 (4 ) (5 ) (1 ) 1 Stock-based compensation costs 31 — — — — — — — — Other decommissioning-related activity (a) (84 ) (84 ) — — — — — — — Energy-related options (b) (4 ) (4 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral (14 ) — — — 7 (21 ) (15 ) (6 ) — Amortization of debt fair value adjustment (5 ) (3 ) — — — (2 ) — — — Discrete impacts from EIMA and FEJA (c) (24 ) — (24 ) — — — — — — Amortization of debt costs 9 4 1 — — — — — — Provision for excess and obsolete inventory 2 1 1 — — — — — — Other 4 3 1 (1 ) (4 ) (6 ) (2 ) (3 ) (2 ) Total other non-cash operating activities $ 118 $ (10 ) $ 31 $ 23 $ 24 $ (8 ) $ (15 ) $ (7 ) $ 2 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (193 ) $ (56 ) $ (66 ) $ (42 ) $ 1 $ (5 ) $ (6 ) $ 9 $ — Non-cash financing of capital projects 10 10 — — — — — — — Dividends on stock compensation 2 — — — — — — — — _________ (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 of the Exelon 2017 Form 10-K 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 in Operating revenues. (c) Reflects the change in distribution rates pursuant to EIMA and FEJA, which allows for the recovery of distribution costs by a utility through a pre-established performance-based formula rate tariff. Beginning June 1, 2017, also reflects the change in energy efficiency rates pursuant to FEJA, which allows for the recovery of energy efficiency costs by a utility through a pre-established performance-based formula rate tariff. See Note 6 — Regulatory Matters for more 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. March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 787 $ 610 $ 70 $ 21 $ 22 $ 43 $ 15 $ 7 $ 10 Restricted cash 209 127 9 5 2 40 33 — 7 Restricted cash included in other long-term assets 103 — 83 — — 20 — — 20 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 1,099 $ 737 $ 162 $ 26 $ 24 $ 103 $ 48 $ 7 $ 37 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 shown in the statement of cash flows $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 609 $ 400 $ 31 $ 28 $ 11 $ 109 $ 8 $ 44 $ 54 Restricted cash 254 140 3 4 43 41 33 — 7 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 889 $ 540 $ 34 $ 32 $ 57 $ 173 $ 41 $ 44 $ 84 December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 170 $ 9 $ 46 $ 101 Restricted cash 253 158 2 4 24 43 33 — 9 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 914 $ 448 $ 58 $ 67 $ 50 $ 236 $ 42 $ 46 $ 133 For additional information on restricted cash see Note 1 — Significant Accounting Policies of the Exelon 2017 Form 10-K. Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants as of March 31, 2018 and December 31, 2017 . March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 21,905 (a) $ 11,936 (a) $ 4,391 $ 3,445 $ 3,471 $ 575 $ 3,224 $ 1,273 $ 1,086 Accounts receivable: Allowance for uncollectible accounts $ 369 $ 115 $ 89 $ 68 $ 31 $ 66 $ 24 $ 22 $ 20 December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 21,064 (b) $ 11,428 (b) $ 4,269 $ 3,411 $ 3,405 $ 487 $ 3,177 $ 1,247 $ 1,066 Accounts receivable: Allowance for uncollectible accounts $ 322 $ 114 $ 73 $ 56 $ 24 $ 55 $ 21 $ 16 $ 18 _________ (a) Includes accumulated amortization of nuclear fuel in the reactor core of $3,263 million . (b) Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million . PECO Installment Plan Receivables (Exelon and PECO) PECO enters into payment agreements with certain delinquent customers, primarily residential, seeking to restore their service, as required by the PAPUC. Customers with past due balances that meet certain income criteria are provided the option to enter into an installment payment plan, some of which have terms greater than one year. The receivable balance for these payment agreement receivables is recorded in accounts receivable for the current portion and other deferred debits and other assets for the noncurrent portion. The net receivable balance for installment plans with terms greater than one year was $8 million and $11 million as of March 31, 2018 and December 31, 2017 , respectively. The allowance for uncollectible accounts balance associated with these receivables at March 31, 2018 of $10 million consists of $3 million and $7 million for medium risk and high risk segments, respectively. The allowance for uncollectible accounts balance at December 31, 2017 of $11 million consists of $3 million and $8 million for medium risk and high risk segments, respectively. For further information regarding uncollectible accounts reserve methodology and assessment of the credit quality of the installment plan receivables, refer to Note 1 — Significant Accounting Policies of the Exelon 2017 Form 10-K.

Segment Information (All Regist

Segment Information (All Registrants)	3 Months Ended
	Mar. 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 ComEd, PECO, BGE, PHI's three reportable segments consisting of Pepco, DPL, and ACE, and Generation’s six reportable segments consisting of the Mid-Atlantic, Midwest, New England, New York, ERCOT and all other power regions referred to collectively as “Other Power Regions”, which includes activities in the South, West and Canada. ComEd, PECO, BGE, Pepco, DPL and ACE each represent a single reportable segment, and as such, no separate segment information is provided for these Registrants. Exelon, ComEd, PECO, BGE, Pepco, DPL and ACE's CODMs evaluate the performance of and allocate resources to ComEd, PECO, BGE, Pepco, DPL and ACE based on net income and return on equity. The basis for Generation's reportable segments is the integrated management of its electricity business that is located in different geographic regions, and largely representative of the footprints of ISO/RTO and/or NERC regions, which utilize multiple supply sources to provide electricity through various distribution channels (wholesale and retail). Generation's hedging strategies and risk metrics are also aligned to these same geographic regions. Descriptions of each of Generation’s six reportable segments are as follows: • Mid-Atlantic represents operations in the eastern half of PJM, which includes New Jersey, Maryland, Virginia, West Virginia, Delaware, the District of Columbia and parts of Pennsylvania and North Carolina. • Midwest represents operations in the western half of PJM, which includes portions of Illinois, Pennsylvania, Indiana, Ohio, Michigan, Kentucky and Tennessee, and the United States footprint of MISO, excluding MISO’s Southern Region, which covers all or most of North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, the remaining parts of Illinois, Indiana, Michigan and Ohio not covered by PJM, and parts of Montana, Missouri and Kentucky. • New England represents the operations within ISO-NE covering the states of Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont. • New York represents operations within ISO-NY, which covers the state of New York in its entirety. • ERCOT represents operations within Electric Reliability Council of Texas, covering most of the state of Texas. • Other Power Regions : • South represents operations in the FRCC, MISO’s Southern Region, and the remaining portions of the SERC not included within MISO or PJM, which includes all or most of Florida, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Tennessee, North Carolina, South Carolina and parts of Missouri, Kentucky and Texas. Generation’s South region also includes operations in the SPP, covering Kansas, Oklahoma, most of Nebraska and parts of New Mexico, Texas, Louisiana, Missouri, Mississippi and Arkansas. • West represents operations in the WECC, which includes California ISO, and covers the states of California, Oregon, Washington, Arizona, Nevada, Utah, Idaho, Colorado and parts of New Mexico, Wyoming and South Dakota. • Canada represents operations across the entire country of Canada and includes AESO, OIESO and the Canadian portion of MISO. The CODMs for Exelon and Generation evaluate the performance of Generation’s electric business activities and allocate resources based on revenues net of purchased power and fuel expense (RNF). Generation believes that RNF is a useful measurement of operational performance. RNF is not a presentation defined under GAAP and may not be comparable to other companies’ presentations or deemed more useful than the GAAP information provided elsewhere in this report. Generation’s operating revenues include all sales to third parties and affiliated sales to the Utility Registrants. Purchased power costs include all costs associated with the procurement and supply of electricity including capacity, energy and ancillary services. Fuel expense includes the fuel costs for Generation’s owned generation and fuel costs associated with tolling agreements. The results of Generation's other business activities are not regularly reviewed by the CODM and are therefore not classified as operating segments or included in the regional reportable segment amounts. These activities include natural gas, as well as other miscellaneous business activities that are not significant to Generation's overall operating revenues or results of operations. Further, Generation’s unrealized mark-to-market gains and losses on economic hedging activities and its amortization of certain intangible assets and liabilities relating to commodity contracts recorded at fair value from mergers and acquisitions are also excluded from the regional reportable segment amounts. Exelon and Generation do not use a measure of total assets in making decisions regarding allocating resources to or assessing the performance of these reportable segments. An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the three months ended March 31, 2018 and 2017 is as follows: Three Months Ended March 31, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 4,509 $ — $ — $ — $ — $ — $ (391 ) $ 4,118 Competitive businesses natural gas revenues 955 — — — — — (8 ) 947 Competitive businesses other revenues 48 — — — — — — 48 Rate-regulated electric revenues — 1,512 634 658 1,169 — (18 ) 3,955 Rate-regulated natural gas revenues — — 232 319 78 — (4 ) 625 Shared service and other revenues — — — — 4 451 (455 ) — Total operating revenues 5,512 1,512 866 977 1,251 451 (876 ) 9,693 2017 Competitive businesses electric revenues $ 3,710 $ — $ — $ — $ — $ — $ (328 ) $ 3,382 Competitive businesses natural gas revenues 918 — — — — — — 918 Competitive businesses other revenues 250 — — — — — — 250 Rate-regulated electric revenues — 1,298 590 667 1,097 — (8 ) 3,644 Rate-regulated natural gas revenues — — 206 284 66 — (3 ) 553 Shared service and other revenues — — — — 12 419 (431 ) — Total operating revenues 4,878 1,298 796 951 1,175 419 (770 ) 8,747 Shared service and other revenues Intersegment revenues (d) : 2018 $ 400 $ 14 $ 2 $ 6 $ 4 $ 450 $ (876 ) $ — 2017 328 5 1 5 12 419 (770 ) — Net income (loss): 2018 $ 186 $ 165 $ 113 $ 128 $ 65 $ (21 ) $ — $ 636 2017 399 141 127 125 140 39 — 971 Total assets: March 31, 2018 $ 48,375 $ 30,002 $ 10,218 $ 9,195 $ 21,375 $ 8,833 $ (10,980 ) $ 117,018 December 31, 2017 48,457 29,726 10,170 9,104 21,247 8,618 (10,552 ) 116,770 __________ (a) Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the three months ended March 31, 2018 include revenue from sales to PECO of $37 million , sales to BGE of $65 million , sales to Pepco of $52 million , sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation. For the three months ended March 31, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $45 million , sales to BGE of $134 million , sales to Pepco of $83 million , sales to DPL of $51 million and sales to ACE of $9 million in the Mid-Atlantic region, and sales to ComEd of $5 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017 . (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income. PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : Three Months Ended March 31, 2018 Rate-regulated electric revenues $ 557 $ 306 $ 310 $ — $ (4 ) $ 1,169 Rate-regulated natural gas revenues — 78 — — — 78 Shared service and other revenues — — — 113 (109 ) 4 Total operating revenues 557 384 310 113 (113 ) 1,251 Three Months Ended March 31, 2017 Rate-regulated electric revenues $ 530 $ 296 $ 275 $ — $ (4 ) $ 1,097 Rate-regulated natural gas revenues — 66 — — — 66 Shared service and other revenues — — — 12 — 12 Total operating revenues 530 362 275 12 (4 ) 1,175 Intersegment revenues: Three Months Ended March 31, 2018 $ 2 $ 2 $ 1 $ 112 $ (113 ) $ 4 Three Months Ended March 31, 2017 1 2 1 13 (5 ) 12 Net income (loss): Three Months Ended March 31, 2018 $ 31 $ 31 $ 7 $ (8 ) $ 4 $ 65 Three Months Ended March 31, 2017 58 57 28 (15 ) 12 140 Total assets: March 31, 2018 $ 7,896 $ 4,383 $ 3,530 $ 10,514 $ (4,948 ) $ 21,375 December 31, 2017 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 on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017 . (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities. 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 three months ended March 31, 2018 and 2017 . 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): Three Months Ended March 31, 2018 Revenues from external parties (a) Intersegment Revenues Total Revenues Contracts with customers Other (b) Total Mid-Atlantic $ 1,355 $ 80 $ 1,435 $ 5 $ 1,440 Midwest 1,273 71 1,344 2 1,346 New England 725 68 793 (1 ) 792 New York 439 (29 ) 410 (1 ) 409 ERCOT 149 59 208 1 209 Other Power Regions 210 109 319 (31 ) 288 Total Competitive Businesses Electric Revenues 4,151 358 4,509 (25 ) 4,484 Competitive Businesses Natural Gas Revenues 522 433 955 25 980 Competitive Businesses Other Revenues (c) 134 (86 ) 48 — 48 Total Generation Consolidated Operating Revenues $ 4,807 $ 705 $ 5,512 $ — $ 5,512 Three Months Ended March 31, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,494 $ (65 ) $ 1,429 $ (4 ) $ 1,425 Midwest 980 71 1,051 2 1,053 New England 589 (40 ) 549 (2 ) 547 New York 303 (3 ) 300 (3 ) 297 ERCOT 168 24 192 (1 ) 191 Other Power Regions 128 61 189 (5 ) 184 Total Competitive Businesses Electric Revenues 3,662 48 3,710 (13 ) 3,697 Competitive Businesses Natural Gas Revenues 768 150 918 12 930 Competitive Businesses Other Revenues (c) 206 44 250 1 251 Total Generation Consolidated Operating Revenues $ 4,636 $ 242 $ 4,878 $ — $ 4,878 __________ (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 $3 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the three months ended March 31, 2017 , unrealized mark-to-market losses of $98 million and gains of $44 million for the three months ended March 31, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 RNF from external customers (a) Intersegment RNF Total RNF RNF from external customers (a) Intersegment RNF Total RNF Mid-Atlantic $ 836 $ 14 $ 850 $ 755 $ 18 $ 773 Midwest 847 13 860 704 11 715 New England 122 (3 ) 119 115 (4 ) 111 New York 282 1 283 143 — 143 ERCOT 106 (70 ) 36 94 (25 ) 69 Other Power Regions 157 (40 ) 117 108 (44 ) 64 Total Revenues net of purchased power and fuel expense for Reportable Segments 2,350 (85 ) 2,265 1,919 (44 ) 1,875 Other (b) (131 ) 85 (46 ) 161 44 205 Total Generation Revenues net of purchased power and fuel expense $ 2,219 $ — $ 2,219 $ 2,080 $ — $ 2,080 __________ (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 $3 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended March 31, 2017 , unrealized mark-to-market losses of $266 million and $49 million for the three months ended March 31, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 7 - Early Nuclear Plant Retirements of the Combined Notes to Consolidated Financial Statements of $15 million decrease to revenue net of purchased power and fuel expense for the three months ended March 31, 2018 , and the elimination of intersegment revenue net of purchased power and fuel expense. Electric and Gas Revenue by Customer Class (ComEd, PECO, BGE, PHI, PECO, DPL, ACE): Three Months Ended March 31, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 717 $ 403 $ 393 $ 610 $ 259 $ 191 $ 160 Small commercial & industrial 385 101 68 115 32 46 37 Large commercial & industrial 152 58 106 259 190 23 46 Public authorities & electric railroads 14 8 7 14 7 4 3 Other (a) 230 62 78 156 49 41 66 Total rate-regulated electric revenues (b) $ 1,498 $ 632 $ 652 $ 1,154 $ 537 $ 305 $ 312 Rate-regulated natural gas revenues Residential $ — $ 161 $ 224 $ 47 $ — $ 47 $ — Small commercial & industrial — 62 34 18 — 18 — Large commercial & industrial — 1 47 4 — 4 — Transportation — 6 — 5 — 5 — Other (c) — 2 27 4 — 4 — Total rate-regulated natural gas revenues (d) $ — $ 232 $ 332 $ 78 $ — $ 78 $ — Total rate-regulated revenues from contracts with customers $ 1,498 $ 864 $ 984 $ 1,232 $ 537 $ 383 $ 312 Other revenues Revenues from alternative revenue programs 5 (1 ) (13 ) 18 19 1 (2 ) Other rate-regulated electric revenues (e) 9 3 4 1 1 — — Other rate-regulated natural gas revenues (e) — — 2 — — — — Total other revenues 14 2 (7 ) 19 20 1 (2 ) Total rate-regulated revenues for reportable segments $ 1,512 $ 866 $ 977 $ 1,251 $ 557 $ 384 $ 310 Three Months Ended March 31, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 611 $ 382 $ 386 $ 554 $ 236 $ 176 $ 142 Small commercial & industrial 328 97 69 114 34 44 36 Large commercial & industrial 107 52 108 257 188 24 45 Public authorities & electric railroads 12 8 7 15 8 4 3 Other (a) 218 48 68 126 48 38 43 Total rate-regulated electric revenues (b) $ 1,276 $ 587 $ 638 $ 1,066 $ 514 $ 286 $ 269 Rate-regulated natural gas revenues Residential $ — $ 142 $ 185 $ 40 $ — $ 40 $ — Small commercial & industrial — 55 30 17 — 17 — Large commercial & industrial — — 44 2 — 2 — Transportation — 6 — 5 — 5 — Other (c) — 3 14 2 — 2 — Total rate-regulated natural gas revenues (d) $ — $ 206 $ 273 $ 66 $ — $ 66 $ — Total rate-regulated revenues from contracts with customers $ 1,276 $ 793 $ 911 $ 1,132 $ 514 $ 352 $ 269 Other revenues Revenues from alternative revenue programs 14 — 35 30 15 9 6 Other rate-regulated electric revenues (e) 8 3 4 2 1 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Other revenues (f) — — — 11 — — — Total other revenues 22 3 40 43 16 10 6 Total rate-regulated revenues for reportable segments $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $14 million , $2 million , $2 million , $4 million , $2 million , $2 million , and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2018 and $5 million , $1 million , $2 million , $1 million , $1 million , $2 million , and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2017. (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, for the three months ended March 31, 2018 and less than $1 million and $3 million at PECO and BGE, respectively, for the three months ended March 31, 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $11 million at PHI for the three months ended March 31, 2017 .

Significant Accounting Polici28

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Business Description and Basis of Presentation [Text Block]	Description of Business (All Registrants) Exelon is a utility services holding company engaged through its principal subsidiaries in the energy generation and energy distribution and transmission businesses. 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) Each of the Registrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. The accompanying consolidated financial statements as of March 31, 2018 and 2017 and for the three months then ended are unaudited but, in the opinion of the management of each Registrant include all adjustments that are considered necessary for a fair statement of the Registrants’ respective financial statements in accordance with GAAP. All adjustments are of a normal, recurring nature, except as otherwise disclosed. The December 31, 2017 revised Consolidated Balance Sheets were derived from audited financial statements. Financial results for interim periods are not necessarily indicative of results that may be expected for any other interim period or for the fiscal year ending December 31, 2018 . These Combined Notes to Consolidated Financial Statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations.
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.
Reclassifications [Text Block]	Prior Period Adjustments and Reclassifications (All Registrants) In the second quarter of 2017, errors were identified related to the Exelon, Generation, ComEd, PECO and BGE Consolidated Statements of Cash Flows for the three months ended March 31, 2017. These classification errors related to the presentation of changes in Accounts payable and accrued expenses and Accounts receivable within Cash flows provided by operating activities and Capital expenditures and Proceeds from sale of long-lived assets within Cash flows used in investing activities. These errors have been corrected in Exelon's, Generation's, ComEd's, PECO's, and BGE's Consolidated Statements of Cash Flows for the three months ended March 31, 2017 that are presented in this first quarter 2018 Form 10-Q. As revised, the Cash flows provided by operating activities for the three months ended March 31, 2017 are $1,074 million , $420 million , $236 million , $106 million and $208 million for Exelon, Generation, ComEd, PECO and BGE, respectively, an increase (decrease) of $(127) million , $(320) million , $91 million , $42 million and $40 million for Exelon, Generation, ComEd, PECO and BGE, respectively, from the originally reported amounts. As revised, the Cash flows used in investing activities are $2,283 million , $910 million , $619 million , $69 million and $202 million for Exelon, Generation, ComEd, PECO and BGE, respectively, an increase (decrease) of $(127) million , $(320) million , $91 million , $42 million and $40 million for Exelon, Generation, ComEd, PECO and BGE, respectively, from the originally reported amounts. Management concluded that the errors are not material to the previously issued financial statements. Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Income, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. Beginning on January 1, 2018, Exelon adopted the following new accounting standards requiring reclassification or adjustments to previously reported information as follows: • Statement of Cash Flows: Classification of Restricted Cash. 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 18 — Supplemental Financial Information for further information. • Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income . Exelon early adopted and retrospectively applied the new guidance to when the effects of the TCJA were recognized and, accordingly, recasted its December 31, 2017 AOCI and retained earnings in its Consolidated Balance Sheet and Consolidated Statement of Changes in Shareholders' Equity. 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 2 — New Accounting Standards for further information. • Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. Exelon applied this guidance retrospectively for the presentation of the service and other non-service costs components of net benefit cost and, accordingly, have recasted those amounts, which were not material, in its Consolidated Statement of Operations and Comprehensive Income in prior periods presented. As part of the adoption, 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. See Note 14 — Retirement Benefits for further information. • Revenue from Contracts with Customers . 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' 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 Financial Statements were not material. See Note 5 — Revenue from Contracts with Customers for further information.
Revenues [Policy Text Block]	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 5 — Revenue from Contracts with Customers and Note 6 — Regulatory Matters for further information. RTOs and ISOs . In RTO and ISO markets that facilitate the dispatch of energy and energy-related products, the Registrants generally report sales and purchases conducted on a net hourly basis in either revenues or purchased power on their Consolidated Statements of Operations and Comprehensive Income, the classification of which depends on the net hourly sale or purchase position. In addition, capacity revenue and expense classification is based on the net sale or purchase position of the Registrants in the different RTOs and ISOs. Option Contracts, Swaps and Commodity Derivatives . Certain option contracts and swap arrangements that meet the definition of derivative instruments are recorded at fair value with subsequent changes in fair value recognized as revenue or expense. The classification of revenue or expense is based on the intent of the transaction. For example, gas transactions may be used to hedge the sale of power. This will result in the change in fair value recorded through revenue. To the extent a Utility Registrant receives full cost recovery for energy procurement and related costs from retail customers, it records the fair value of its energy swap contracts with unaffiliated suppliers as well as an offsetting regulatory asset or liability on its Consolidated Balance Sheets. Refer to Note 6 — Regulatory Matters and Note 10 — Derivative Financial Instruments for further 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 natural gas and electricity. Some of these taxes are imposed on the customer, but paid by the Registrants, while others are imposed directly on the Registrants. The Registrants do not recognize revenue or expense in their Consolidated Statements of Operations and Comprehensive Income when these taxes are imposed on the customer, such as sales taxes. However, when these taxes are imposed directly on the Registrants, such as gross receipts taxes or other surcharges or fees, the Registrants recognize revenue for the taxes collected from customers along with an offsetting expense. See Note 18 — 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.
Fair Value of Financial Instruments, Policy [Policy Text Block]	Valuation Techniques Used to Determine Fair Value The following describes the valuation techniques used to measure the fair value of the assets and liabilities shown in the tables above. Cash Equivalents (Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE). The Registrants’ cash equivalents include investments with original maturities of three months or less when purchased. The cash equivalents shown in the fair value tables are comprised of investments in mutual and money market funds. The fair values of the shares of these funds are based on observable market prices and, therefore, have been categorized in Level 1 in the fair value hierarchy. Nuclear Decommissioning Trust Fund Investments and Pledged Assets for Zion Station Decommissioning (Exelon and Generation). The trust fund investments have been established to satisfy Generation’s and CENG's nuclear decommissioning obligations as required by the NRC. The NDT funds hold debt and equity securities directly and indirectly through commingled funds and mutual funds, which are included in Equities and Fixed Income. Generation’s and CENG's NDT fund investments policies outline investment guidelines for the trusts and limit the trust funds’ exposures to investments in highly illiquid markets and other alternative investments. Investments with maturities of three months or less when purchased, including certain short-term fixed income securities are considered cash equivalents and included in the recurring fair value measurements hierarchy as Level 1 or Level 2. With respect to individually held equity securities, the trustees obtain prices from pricing services, whose prices are generally obtained from direct feeds from market exchanges, which Generation is able to independently corroborate. The fair values of equity securities held directly by the trust funds which are based on quoted prices in active markets are categorized in Level 1. Certain equity securities have been categorized as Level 2 because they are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities. Equity securities held individually are primarily traded on the New York Stock Exchange and NASDAQ-Global Select Market, which contain only actively traded securities due to the volume trading requirements imposed by these exchanges. For fixed income securities, multiple prices from pricing services are obtained whenever possible, which enables cross-provider validations in addition to checks for unusual daily movements. A primary price source is identified based on asset type, class or issue for each security. With respect to individually held fixed income securities, the trustees monitor prices supplied by pricing services and may use a supplemental price source or change the primary price source of a given security if the portfolio managers challenge an assigned price and the trustees determine that another price source is considered to be preferable. Generation has obtained an understanding of how these prices are derived, including the nature and observability of the inputs used in deriving such prices. Additionally, Generation selectively corroborates the fair values of securities by comparison to other market-based price sources. U.S. Treasury securities are categorized as Level 1 because they trade in a highly liquid and transparent market. The fair values of fixed income securities, excluding U.S. Treasury securities, are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities, adjusted for observable differences and are categorized in Level 2. The fair values of private placement fixed income securities, which are included in Corporate debt, are determined using a third party valuation that contains significant unobservable inputs and are categorized in Level 3. Equity and fixed income commingled funds and mutual funds are maintained by investment companies and hold certain investments in accordance with a stated set of fund objectives such as holding short-term fixed income securities or tracking the performance of certain equity indices by purchasing equity securities to replicate the capitalization and characteristics of the indices. The values of some of these funds are publicly quoted. For mutual funds which are publicly quoted, the funds are valued based on quoted prices in active markets and have been categorized as Level 1. For commingled funds and mutual funds, which are not publicly quoted, the funds are valued using NAV as a practical expedient for fair value, which is primarily derived from the quoted prices in active markets on the underlying securities, and are not classified within the fair value hierarchy. These investments typically can be redeemed monthly with 30 or less days of notice and without further restrictions. Derivative instruments consisting primarily of futures and interest rate swaps to manage risk are recorded at fair value. Over the counter derivatives are valued daily based on quoted prices in active markets and trade in open markets, and have been categorized as Level 1. Derivative instruments other than over the counter derivatives are valued based on external price data of comparable securities and have been categorized as Level 2. Middle market lending are investments in loans or managed funds which lend to private companies. Generation elected the fair value option for its investments in certain limited partnerships that invest in middle market lending managed funds. The fair value of these loans is determined using a combination of valuation models including cost models, market models and income models. Investments in loans are categorized as Level 3 because the fair value of these securities is based largely on inputs that are unobservable and utilize complex valuation models. Managed funds are valued using NAV or its equivalent as a practical expedient, and therefore, are not classified within the fair value hierarchy. Investments in middle market lending typically cannot be redeemed until maturity of the term loan. Private equity and real estate investments include those in limited partnerships that invest in operating companies and real estate holding companies that are not publicly traded on a stock exchange, such as, leveraged buyouts, growth capital, venture capital, distressed investments, investments in natural resources, and direct investments in pools of real estate properties. The fair value of private equity and real estate investments is determined using NAV or its equivalent as a practical expedient, and therefore, are not classified within the fair value hierarchy. These investments typically cannot be redeemed and are generally liquidated over a period of 8 to 10 years from the initial investment date. Private equity and real estate valuations are reported by the fund manager and are based on the valuation of the underlying investments, which include inputs such as cost, operating results, discounted future cash flows, market based comparable data, and independent appraisals from sources with professional qualifications. These valuation inputs are unobservable. As of March 31, 2018 , Generation has outstanding commitments to invest in equities, fixed income, middle market lending, private equity and real estate investments of approximately $208 million , $65 million , $386 million , $194 million , and $107 million , respectively. These commitments will be funded by Generation’s existing nuclear decommissioning trust funds. Concentrations of Credit Risk . Generation evaluated its NDT portfolios for the existence of significant concentrations of credit risk as of March 31, 2018 . Types of concentrations that were evaluated include, but are not limited to, investment concentrations in a single entity, type of industry, foreign country, and individual fund. As of March 31, 2018 , there were no significant concentrations (generally defined as greater than 10 percent) of risk in Generation's NDT assets. See Note 13 — Nuclear Decommissioning for further discussion on the NDT fund investments. Rabbi Trust Investments (Exelon, Generation, PECO, BGE, PHI, Pepco, DPL and ACE). The Rabbi trusts were established to hold assets related to deferred compensation plans existing for certain active and retired members of Exelon’s executive management and directors. The Rabbi trusts assets are included in investments in the Registrants’ Consolidated Balance Sheets and consist primarily of money market funds, mutual funds, fixed income securities and life insurance policies. The mutual funds are maintained by investment companies and hold certain investments in accordance with a stated set of fund objectives, which are consistent with Exelon’s overall investment strategy. Money market funds and mutual funds are publicly quoted and have been categorized as Level 1 given the clear observability of the prices. The fair values of fixed income securities are based on evaluated prices that reflect observable market information, such as actual trade information or similar securities, adjusted for observable differences and are categorized in Level 2. The life insurance policies are valued using the cash surrender value of the policies, net of loans against those policies, which is provided by a third-party. Certain life insurance policies, which consist primarily of mutual funds that are priced based on observable market data, have been categorized as Level 2 because the life insurance policies can be liquidated at the reporting date for the value of the underlying assets. Life insurance policies that are valued using unobservable inputs have been categorized as Level 3. Mark-to-Market Derivatives (Exelon, Generation, ComEd, PHI and DPL) . Derivative contracts are traded in both exchange-based and non-exchange-based markets. Exchange-based derivatives that are valued using unadjusted quoted prices in active markets are categorized in Level 1 in the fair value hierarchy. Certain derivatives’ pricing is verified using indicative price quotations available through brokers or over-the-counter, on-line exchanges and are categorized in Level 2. These price quotations reflect the average of the bid-ask, mid-point prices and are obtained from sources that the Registrants believe provide the most liquid market for the commodity. The price quotations are reviewed and corroborated to ensure the prices are observable and representative of an orderly transaction between market participants. This includes consideration of actual transaction volumes, market delivery points, bid-ask spreads and contract duration. The remainder of derivative contracts are valued using the Black model, an industry standard option valuation model. The Black model takes into account inputs such as contract terms, including maturity, and market parameters, including assumptions of the future prices of energy, interest rates, volatility, credit worthiness and credit spread. For derivatives that trade in liquid markets, such as generic forwards, swaps and options, model inputs are generally observable. Such instruments are categorized in Level 2. The Registrants’ derivatives are predominantly at liquid trading points. For derivatives that trade in less liquid markets with limited pricing information model inputs generally would include both observable and unobservable inputs. These valuations may include an estimated basis adjustment from an illiquid trading point to a liquid trading point for which active price quotations are available. Such instruments are categorized in Level 3. Exelon may utilize fixed-to-floating interest rate swaps, which are typically designated as fair value hedges, as a means to achieve its targeted level of variable-rate debt as a percent of total debt. In addition, the Registrants may utilize interest rate derivatives to lock in interest rate levels in anticipation of future financings. These interest rate derivatives are typically designated as cash flow hedges. Exelon determines the current fair value by calculating the net present value of expected payments and receipts under the swap agreement, based on and discounted by the market's expectation of future interest rates. Additional inputs to the net present value calculation may include the contract terms, counterparty credit risk and other market parameters. As these inputs are based on observable data and valuations of similar instruments, the interest rate swaps are categorized in Level 2 in the fair value hierarchy. See Note 10 — Derivative Financial Instruments for further discussion on mark-to-market derivatives. Deferred Compensation Obligations (Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE). The Registrants’ deferred compensation plans allow participants to defer certain cash compensation into a notional investment account. The Registrants include such plans in other current and noncurrent liabilities in their Consolidated Balance Sheets. The value of the Registrants’ deferred compensation obligations is based on the market value of the participants’ notional investment accounts. The underlying notional investments are comprised primarily of equities, mutual funds, commingled funds, and fixed income securities which are based on directly and indirectly observable market prices. Since the deferred compensation obligations themselves are not exchanged in an active market, they are categorized as Level 2 in the fair value hierarchy. The value of certain employment agreement obligations (which are included with the Deferred Compensation Obligation in the tables above) are based on a known and certain stream of payments to be made over time and are categorized as Level 2 within the fair value hierarchy.

Significant Accounting Polici29

Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from Contract with Customer [Text Block]	Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 4,560 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,197 — — — — — — — — Operating revenues — 4,558 — — — — — — — Electric operating revenues — — 1,293 589 665 1,097 529 294 274 Natural gas operating revenues — — — 206 281 66 — 66 — Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,757 $ 4,888 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 Operating Revenues - Adjustments Competitive business revenues $ (10 ) $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (79 ) — — — — — — — — Operating revenues — (10 ) — — — — — — — Electric operating revenues — — (14 ) — (25 ) (30 ) (15 ) (9 ) (6 ) Natural gas operating revenues — — — — (10 ) — — — — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — — — — — — — — — Total operating revenues $ (10 ) $ (10 ) $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 4,550 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,118 — — — — — — — — Operating revenues — 4,548 — — — — — — — Electric operating revenues — — 1,279 589 640 1,067 514 285 268 Natural gas operating revenues — — — 206 271 66 — 66 — Revenues from alternative revenue programs 79 — 14 — 35 30 15 9 6 Operating revenues from affiliates — 330 5 1 5 12 1 2 1 Total operating revenues $ 8,747 $ 4,878 $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 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. Revenues related to such contracts are generally recognized over time as the power is generated and simultaneously delivered to the customer. However, revenues related to the sale of any goods or services that are not simultaneously received and consumed by the customer are recognized as the performance obligations are satisfied at a point in time. 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, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) 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, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE) 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 $25 million and $26 million as of March 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 $5 million and $9 million for the three months ended March 31, 2018 and 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 on Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to March 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 28 Amounts reclassified to receivables (9 ) Balance at March 31, 2018 $ 302 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. 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 on Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to March 31, 2018: Contract Liabilities Exelon and Generation Balance as of January 1, 2018 $ 35 Increases as a result of additional cash received or due 227 Amounts recognized into revenues (216 ) Balance at March 31, 2018 $ 46 The Utility Registrants also record contract liabilities when consideration is received prior to the satisfaction of the performance obligations. As of March 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 March 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 $ 544 $ 264 $ 104 $ 46 $ 128 $ 1,086 Generation 544 264 104 46 128 $ 1,086 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 19 — Segment Information for the presentation of the Registrant's revenue disaggregation.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
	Mar. 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 March 31, 2018 and December 31, 2017 are as follows: March 31, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 823 $ 812 $ 11 $ 7 $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,279 9,251 28 20 9,317 9,286 31 23 Total assets $ 10,102 $ 10,063 $ 39 $ 27 $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 269 $ 236 $ 33 $ 29 $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,292 3,230 62 54 3,316 3,250 66 58 Total liabilities $ 3,561 $ 3,466 $ 95 $ 83 $ 3,624 $ 3,522 $ 102 $ 90 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. As of March 31, 2018 and December 31, 2017 , these assets and liabilities primarily consisted of the following: March 31, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 280 $ 280 $ — $ — $ 126 $ 126 $ — $ — Restricted cash 73 66 7 7 64 58 6 6 Accounts receivable, net Customer 154 154 — — 170 170 — — Other 29 29 — — 25 25 — — Inventory Materials and supplies 202 202 — — 205 205 — — Other current assets 55 51 4 — 45 41 4 — Total current assets 793 782 11 7 635 625 10 6 Property, plant and equipment, net 6,181 6,181 — — 6,186 6,186 — — Nuclear decommissioning trust funds 2,483 2,483 — — 2,502 2,502 — — Other noncurrent assets 270 242 28 20 274 243 31 23 Total noncurrent assets 8,934 8,906 28 20 8,962 8,931 31 23 Total assets $ 9,727 $ 9,688 $ 39 $ 27 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 102 $ 70 $ 32 $ 28 $ 102 $ 67 $ 35 $ 31 Accounts payable 93 93 — — 114 114 — — Accrued expenses 52 51 1 1 67 66 1 1 Unamortized energy contract liabilities 17 17 — — 18 18 — — Other current liabilities 5 5 — — 7 7 — — Total current liabilities 269 236 33 29 308 272 36 32 Long-term debt 1,125 1,063 62 54 1,154 1,088 66 58 Asset retirement obligations 2,062 2,062 — — 2,035 2,035 — — Unamortized energy contract liabilities 1 1 — — 5 5 — — Other noncurrent liabilities 99 99 — — 116 116 — — Total noncurrent liabilities 3,287 3,225 62 54 3,310 3,244 66 58 Total liabilities $ 3,556 $ 3,461 $ 95 $ 83 $ 3,618 $ 3,516 $ 102 $ 90 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. The following tables present summary information about Exelon's and Generation’s significant unconsolidated VIE entities: March 31, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 626 $ 501 $ 1,127 Total liabilities (a) 37 225 262 Exelon's ownership interest in VIE (a) — 246 246 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 246 246 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) 2 — 2 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 on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs. (b) These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $30 million and $39 million as of March 31, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions, LLC of $28 million and $37 million as of March 31, 2018 and December 31, 2017 , respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. See Note 13 — Nuclear Decommissioning for additional details.

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (Tables)	3 Months Ended
	Mar. 31, 2018
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The following table summarizes the 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 23 - Commitments and Contingencies of the Exelon 2017 Form 10-K for additional background regarding SNF obligations to the DOE.

Revenue from Contracts with C32

Revenue from Contracts with Customers Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract with Customer, Asset and Liability [Table Text Block]	The following table provides a rollforward of the contract assets reflected on Exelon's and Generation's Consolidated Balance Sheets from January 1, 2018 to March 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 28 Amounts reclassified to receivables (9 ) Balance at March 31, 2018 $ 302 The following table provides a rollforward of the contract liabilities reflected on Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to March 31, 2018: Contract Liabilities Exelon and Generation Balance as of January 1, 2018 $ 35 Increases as a result of additional cash received or due 227 Amounts recognized into revenues (216 ) Balance at March 31, 2018 $ 46
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	2019 2020 2021 2022 2023 and thereafter Total Exelon $ 544 $ 264 $ 104 $ 46 $ 128 $ 1,086 Generation 544 264 104 46 128 $ 1,086

Regulatory Matters (Tables)

Regulatory Matters (Tables)	3 Months Ended
	Mar. 31, 2018
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	The following table illustrates our authorized amounts capitalized for ratemaking purposes related to earnings on shareholders’ investment that are not recognized for financial reporting purposes on our Consolidated Balance Sheets. These amounts will be recognized as revenues in our Consolidated Statements of Operations and Comprehensive Income in the periods they are billable to our customers. Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE March 31, 2018 $ 69 $ 7 $ — $ 52 $ 10 $ 6 $ 4 $ — Exelon ComEd (a) PECO BGE (b) PHI Pepco (c) DPL (c) ACE 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 Assets	he following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE as of March 31, 2018 and December 31, 2017 . For additional information on the specific regulatory assets and liabilities, refer to Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K. March 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,844 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 336 — 327 — 9 9 — — AMI programs (c) 621 151 33 208 229 154 75 — Electric distribution formula rate (d) 256 256 — — — — — — Energy efficiency costs 220 220 — — — — — — Debt costs 108 36 1 11 71 15 7 5 Fair value of long-term debt 745 — — — 607 — — — Fair value of PHI's unamortized energy contracts 701 — — — 701 — — — Asset retirement obligations 111 75 22 14 — — — — MGP remediation costs 284 263 21 — — — — — Under-recovered uncollectible accounts 69 69 — — — — — — Renewable energy 268 267 — — 1 — — 1 Energy and transmission programs (e)(f)(g)(h)(i)(j) 117 8 43 21 45 7 14 24 Deferred storm costs 46 — — — 46 12 5 29 Energy efficiency and demand response programs 559 — 1 269 289 212 77 — Merger integration costs (k)(l)(m) 46 — — 5 41 20 11 10 Under-recovered revenue decoupling (n) 44 — — 6 38 38 — — COPCO acquisition adjustment 5 — — — 5 — 5 — Workers compensation and long-term disability costs 33 — — — 33 33 — — Vacation accrual 27 — 14 — 13 — 8 5 Securitized stranded costs 71 — — — 71 — — 71 CAP arrearage 12 — 12 — — — — — Removal costs 535 — — — 535 150 94 292 DC PLUG charge 187 — — — 187 187 — — Other 63 6 12 6 39 26 9 4 Total regulatory assets 9,308 1,351 486 540 2,960 863 305 441 Less: current portion 1,245 226 78 149 507 207 63 64 Total noncurrent regulatory assets $ 8,063 $ 1,125 $ 408 $ 391 $ 2,453 $ 656 $ 242 $ 377 March 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 26 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,189 2,458 — 1,011 1,720 804 506 410 Nuclear decommissioning 2,969 2,464 505 — — — — — Removal costs 1,570 1,348 — 92 130 20 110 — Deferred rent 35 — — — 35 — — — Energy efficiency and demand response programs 16 4 11 — 1 — — 1 DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 27 — 27 — — — — — Gas distribution tax repairs 8 — 8 — — — — — Energy and transmission programs (e)(f)(g)(h)(i)(j) 153 53 56 22 22 4 6 12 Over-recovered revenue decoupling (n) 14 — — 11 3 — 3 — Renewable portfolio standards costs 81 81 — — — — — — Zero emission credit costs 8 8 — — — — — — Over-recovered uncollectible accounts 4 — — — 4 — — 4 Merger integration costs (l) 1 — — — 1 — 1 — TCJA income tax benefit over-recoveries (o) 54 — 10 17 27 14 7 6 Other 84 8 22 32 22 3 13 4 Total regulatory liabilities 10,246 6,424 646 1,185 1,965 845 646 437 Less: current portion 522 212 117 102 77 7 48 21 Total noncurrent regulatory liabilities $ 9,724 $ 6,212 $ 529 $ 1,083 $ 1,888 $ 838 $ 598 $ 416 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,848 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 306 — 297 — 9 9 — — AMI programs (c) 640 155 36 214 235 158 77 — Electric distribution formula rate (d) 244 244 — — — — — — Energy efficiency costs 166 166 — — — — — — Debt costs 116 37 1 11 73 15 8 5 Fair value of long-term debt 758 — — — 619 — — — Fair value of PHI's unamortized energy contracts 750 — — — 750 — — — Asset retirement obligations 109 73 22 14 — — — — MGP remediation costs 295 273 22 — — — — — Under-recovered uncollectible accounts 61 61 — — — — — — Renewable energy 258 256 — — 2 — 1 1 Energy and transmission programs (e)(g)(h)(i)(j) 82 6 1 23 52 11 15 26 Deferred storm costs 27 — — — 27 7 5 15 Energy efficiency and demand response programs 596 — 1 285 310 229 81 — Merger integration costs (k)(l)(m) 45 — — 6 39 20 10 9 Under-recovered revenue decoupling (n) 55 — — 14 41 38 3 — COPCO acquisition adjustment 5 — — — 5 — 5 — Workers compensation and long-term disability costs 35 — — — 35 35 — — Vacation accrual 19 — 6 — 13 — 8 5 Securitized stranded costs 79 — — — 79 — — 79 CAP arrearage 8 — 8 — — — — — Removal costs 529 — — — 529 150 93 286 DC PLUG charge 190 — — — 190 190 — — Other 67 8 16 4 39 29 8 4 Total regulatory assets 9,288 1,279 410 571 3,047 891 314 430 Less: current portion 1,267 225 29 174 554 213 69 71 Total noncurrent regulatory assets $ 8,021 $ 1,054 $ 381 $ 397 $ 2,493 $ 678 $ 245 $ 359 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 30 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,241 2,479 — 1,032 1,730 809 510 411 Nuclear decommissioning 3,064 2,528 536 — — — — — Removal costs 1,573 1,338 — 105 130 20 110 — Deferred rent 36 — — — 36 — — — Energy efficiency and demand response programs 23 4 19 — — — — — DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 35 — 35 — — — — — Gas distribution tax repairs 9 — 9 — — — — — Energy and transmission programs (e)(f)(i)(j) 111 47 60 — 4 — 1 3 Renewable portfolio standard costs 63 63 — — — — — — Zero emission credit costs 112 112 — — — — — — Over-recovered uncollectible accounts 2 — — — 2 — — 2 Other 82 6 24 26 26 3 14 6 Total regulatory liabilities 10,388 6,577 690 1,163 1,928 832 635 422 Less: current portion 523 249 141 62 56 3 42 11 Total noncurrent regulatory liabilities $ 9,865 $ 6,328 $ 549 $ 1,101 $ 1,872 $ 829 $ 593 $ 411 _________ (a) Includes regulatory regulatory assets established at the Constellation and PHI merger dates of $427 million and $934 million , respectively, as of March 31, 2018 and $440 million and $953 million , respectively, as of December 31, 2017 related to the rate regulated portions of the deferred costs associated with legacy Constellation’s and PHI’s pension and other postretirement benefit plans that are being amortized and recovered over approximately 12 years and 3 to 15 years, respectively (as established at the respective acquisition dates). The Utility Registrants are not earning or paying a return on these amounts. (b) As of March 31, 2018 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $479 million , $135 million , $146 million , $147 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively. As of December 31, 2017 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $484 million , $ 137 million , $147 million , $148 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively. (c) As of March 31, 2018 , BGE's regulatory asset of $208 million includes $125 million of unamortized incremental deployment costs under the program, $51 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. As of December 31, 2017 , BGE's regulatory asset of $214 million includes $129 million of unamortized incremental deployment costs under the program, $53 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. Recovery of the post-test year incremental deployment costs will be addressed in a future base rate proceeding. (d) As of March 31, 2018 , ComEd’s regulatory asset of $256 million was comprised of $195 million for the 2016, 2017 and 2018 annual reconciliations and $61 million related to significant one-time events. As of December 31, 2017 , ComEd’s regulatory asset of $244 million was comprised of $186 million for the 2016 and 2017 annual reconciliations and $58 million related to significant one-time events. (e) As of March 31, 2018 , ComEd’s regulatory asset of $8 million represents transmission costs recoverable through its FERC approved formula rate. As of March 31, 2018 , ComEd’s regulatory liability of $53 million included $21 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2017 , ComEd’s regulatory asset of $6 million represents transmission costs recoverable through its FERC approved formula rate. As of December 31, 2017 , ComEd’s regulatory liability of $47 million included $14 million related to over-recovered energy costs and $33 million associated with revenues received for renewable energy requirements. (f) As of March 31, 2018 , PECO's regulatory liability of $56 million included $44 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $9 million related to over-recovered non-bypassable transmission service charges. As of December 31, 2017 , PECO's regulatory liability of $60 million included $36 million related to over-recovered costs under the DSP program, $12 million related to over-recovered non-bypassable transmission service charges and $12 million related to the over-recovered natural gas costs under the PGC. (g) As of March 31, 2018 , BGE's regulatory asset of $21 million included $13 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of March 31, 2018 , BGE's regulatory liability of $22 million related to over-recovered natural gas costs. As of December 31, 2017 , BGE’s regulatory asset of $23 million included $7 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval and $8 million of under-recovered natural gas costs. (h) As of March 31, 2018 , Pepco's regulatory asset of $7 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018 , Pepco's regulatory liability of $4 million related to over-recovered electric energy costs. As of December 31, 2017 , Pepco's regulatory asset of $11 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $8 million of under-recovered electric energy costs. (i) As of March 31, 2018 , DPL's regulatory asset of $14 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018 , DPL's regulatory liability of $6 million related to over-recovered electric energy and gas fuel costs. As of December 31, 2017 , DPL's regulatory asset of $15 million included $8 million of transmission costs recoverable through its FERC approved formula rate and $7 million related to under-recovered electric energy costs. As of December 31, 2017 , DPL's regulatory liability of $1 million related to over-recovered electric energy costs. (j) As of March 31, 2018 , ACE's regulatory asset of $24 million included $9 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of March 31, 2018 , ACE's regulatory liability of $12 million related to over-recovered electric energy costs. As of December 31, 2017 , ACE's regulatory asset of $26 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of December 31, 2017 , ACE's regulatory liability of $3 million related to over-recovered electric energy costs. (k) As of March 31, 2018 and December 31, 2017 , Pepco’s regulatory asset of $20 million represents previously incurred PHI integration costs, including $11 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. (l) As of March 31, 2018 , DPL’s regulatory asset of $11 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates and $2 million authorized for recovery in Delaware gas rates. As of March 31, 2018 , DPL’s regulatory liability of $1 million represents net synergy savings incurred related to PHI integration costs that are expected to be returned in electric and gas rates in the Delaware service territory. As of December 31, 2017 , DPL’s regulatory asset of $10 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, and $1 million expected to be recovered in electric and gas rates in the Maryland and Delaware service territories. (m) As of March 31, 2018 and December 31, 2017 , ACE’s regulatory asset of $10 million and $9 million , respectively, represents previously incurred PHI integration costs expected to be recovered in the New Jersey service territory. (n) Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of March 31, 2018 , BGE had a regulatory asset of $6 million related to under-recovered electric revenue decoupling and a regulatory liability of $11 million related to over-recovered natural gas revenue decoupling. As of December 31, 2017 , BGE had a regulatory asset of $10 million related to under-recovered electric revenue decoupling and $4 million related to under-recovered natural gas revenue decoupling.
Schedule of Regulatory Liabilities	he following tables provide information about the regulatory assets and liabilities of Exelon, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE as of March 31, 2018 and December 31, 2017 . For additional information on the specific regulatory assets and liabilities, refer to Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K. March 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,844 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 336 — 327 — 9 9 — — AMI programs (c) 621 151 33 208 229 154 75 — Electric distribution formula rate (d) 256 256 — — — — — — Energy efficiency costs 220 220 — — — — — — Debt costs 108 36 1 11 71 15 7 5 Fair value of long-term debt 745 — — — 607 — — — Fair value of PHI's unamortized energy contracts 701 — — — 701 — — — Asset retirement obligations 111 75 22 14 — — — — MGP remediation costs 284 263 21 — — — — — Under-recovered uncollectible accounts 69 69 — — — — — — Renewable energy 268 267 — — 1 — — 1 Energy and transmission programs (e)(f)(g)(h)(i)(j) 117 8 43 21 45 7 14 24 Deferred storm costs 46 — — — 46 12 5 29 Energy efficiency and demand response programs 559 — 1 269 289 212 77 — Merger integration costs (k)(l)(m) 46 — — 5 41 20 11 10 Under-recovered revenue decoupling (n) 44 — — 6 38 38 — — COPCO acquisition adjustment 5 — — — 5 — 5 — Workers compensation and long-term disability costs 33 — — — 33 33 — — Vacation accrual 27 — 14 — 13 — 8 5 Securitized stranded costs 71 — — — 71 — — 71 CAP arrearage 12 — 12 — — — — — Removal costs 535 — — — 535 150 94 292 DC PLUG charge 187 — — — 187 187 — — Other 63 6 12 6 39 26 9 4 Total regulatory assets 9,308 1,351 486 540 2,960 863 305 441 Less: current portion 1,245 226 78 149 507 207 63 64 Total noncurrent regulatory assets $ 8,063 $ 1,125 $ 408 $ 391 $ 2,453 $ 656 $ 242 $ 377 March 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 26 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,189 2,458 — 1,011 1,720 804 506 410 Nuclear decommissioning 2,969 2,464 505 — — — — — Removal costs 1,570 1,348 — 92 130 20 110 — Deferred rent 35 — — — 35 — — — Energy efficiency and demand response programs 16 4 11 — 1 — — 1 DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 27 — 27 — — — — — Gas distribution tax repairs 8 — 8 — — — — — Energy and transmission programs (e)(f)(g)(h)(i)(j) 153 53 56 22 22 4 6 12 Over-recovered revenue decoupling (n) 14 — — 11 3 — 3 — Renewable portfolio standards costs 81 81 — — — — — — Zero emission credit costs 8 8 — — — — — — Over-recovered uncollectible accounts 4 — — — 4 — — 4 Merger integration costs (l) 1 — — — 1 — 1 — TCJA income tax benefit over-recoveries (o) 54 — 10 17 27 14 7 6 Other 84 8 22 32 22 3 13 4 Total regulatory liabilities 10,246 6,424 646 1,185 1,965 845 646 437 Less: current portion 522 212 117 102 77 7 48 21 Total noncurrent regulatory liabilities $ 9,724 $ 6,212 $ 529 $ 1,083 $ 1,888 $ 838 $ 598 $ 416 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,848 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 306 — 297 — 9 9 — — AMI programs (c) 640 155 36 214 235 158 77 — Electric distribution formula rate (d) 244 244 — — — — — — Energy efficiency costs 166 166 — — — — — — Debt costs 116 37 1 11 73 15 8 5 Fair value of long-term debt 758 — — — 619 — — — Fair value of PHI's unamortized energy contracts 750 — — — 750 — — — Asset retirement obligations 109 73 22 14 — — — — MGP remediation costs 295 273 22 — — — — — Under-recovered uncollectible accounts 61 61 — — — — — — Renewable energy 258 256 — — 2 — 1 1 Energy and transmission programs (e)(g)(h)(i)(j) 82 6 1 23 52 11 15 26 Deferred storm costs 27 — — — 27 7 5 15 Energy efficiency and demand response programs 596 — 1 285 310 229 81 — Merger integration costs (k)(l)(m) 45 — — 6 39 20 10 9 Under-recovered revenue decoupling (n) 55 — — 14 41 38 3 — COPCO acquisition adjustment 5 — — — 5 — 5 — Workers compensation and long-term disability costs 35 — — — 35 35 — — Vacation accrual 19 — 6 — 13 — 8 5 Securitized stranded costs 79 — — — 79 — — 79 CAP arrearage 8 — 8 — — — — — Removal costs 529 — — — 529 150 93 286 DC PLUG charge 190 — — — 190 190 — — Other 67 8 16 4 39 29 8 4 Total regulatory assets 9,288 1,279 410 571 3,047 891 314 430 Less: current portion 1,267 225 29 174 554 213 69 71 Total noncurrent regulatory assets $ 8,021 $ 1,054 $ 381 $ 397 $ 2,493 $ 678 $ 245 $ 359 December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 30 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,241 2,479 — 1,032 1,730 809 510 411 Nuclear decommissioning 3,064 2,528 536 — — — — — Removal costs 1,573 1,338 — 105 130 20 110 — Deferred rent 36 — — — 36 — — — Energy efficiency and demand response programs 23 4 19 — — — — — DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 35 — 35 — — — — — Gas distribution tax repairs 9 — 9 — — — — — Energy and transmission programs (e)(f)(i)(j) 111 47 60 — 4 — 1 3 Renewable portfolio standard costs 63 63 — — — — — — Zero emission credit costs 112 112 — — — — — — Over-recovered uncollectible accounts 2 — — — 2 — — 2 Other 82 6 24 26 26 3 14 6 Total regulatory liabilities 10,388 6,577 690 1,163 1,928 832 635 422 Less: current portion 523 249 141 62 56 3 42 11 Total noncurrent regulatory liabilities $ 9,865 $ 6,328 $ 549 $ 1,101 $ 1,872 $ 829 $ 593 $ 411 _________ (a) Includes regulatory regulatory assets established at the Constellation and PHI merger dates of $427 million and $934 million , respectively, as of March 31, 2018 and $440 million and $953 million , respectively, as of December 31, 2017 related to the rate regulated portions of the deferred costs associated with legacy Constellation’s and PHI’s pension and other postretirement benefit plans that are being amortized and recovered over approximately 12 years and 3 to 15 years, respectively (as established at the respective acquisition dates). The Utility Registrants are not earning or paying a return on these amounts. (b) As of March 31, 2018 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $479 million , $135 million , $146 million , $147 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively. As of December 31, 2017 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $484 million , $ 137 million , $147 million , $148 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively. (c) As of March 31, 2018 , BGE's regulatory asset of $208 million includes $125 million of unamortized incremental deployment costs under the program, $51 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. As of December 31, 2017 , BGE's regulatory asset of $214 million includes $129 million of unamortized incremental deployment costs under the program, $53 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. Recovery of the post-test year incremental deployment costs will be addressed in a future base rate proceeding. (d) As of March 31, 2018 , ComEd’s regulatory asset of $256 million was comprised of $195 million for the 2016, 2017 and 2018 annual reconciliations and $61 million related to significant one-time events. As of December 31, 2017 , ComEd’s regulatory asset of $244 million was comprised of $186 million for the 2016 and 2017 annual reconciliations and $58 million related to significant one-time events. (e) As of March 31, 2018 , ComEd’s regulatory asset of $8 million represents transmission costs recoverable through its FERC approved formula rate. As of March 31, 2018 , ComEd’s regulatory liability of $53 million included $21 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2017 , ComEd’s regulatory asset of $6 million represents transmission costs recoverable through its FERC approved formula rate. As of December 31, 2017 , ComEd’s regulatory liability of $47 million included $14 million related to over-recovered energy costs and $33 million associated with revenues received for renewable energy requirements. (f) As of March 31, 2018 , PECO's regulatory liability of $56 million included $44 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $9 million related to over-recovered non-bypassable transmission service charges. As of December 31, 2017 , PECO's regulatory liability of $60 million included $36 million related to over-recovered costs under the DSP program, $12 million related to over-recovered non-bypassable transmission service charges and $12 million related to the over-recovered natural gas costs under the PGC. (g) As of March 31, 2018 , BGE's regulatory asset of $21 million included $13 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of March 31, 2018 , BGE's regulatory liability of $22 million related to over-recovered natural gas costs. As of December 31, 2017 , BGE’s regulatory asset of $23 million included $7 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval and $8 million of under-recovered natural gas costs. (h) As of March 31, 2018 , Pepco's regulatory asset of $7 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018 , Pepco's regulatory liability of $4 million related to over-recovered electric energy costs. As of December 31, 2017 , Pepco's regulatory asset of $11 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $8 million of under-recovered electric energy costs. (i) As of March 31, 2018 , DPL's regulatory asset of $14 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018 , DPL's regulatory liability of $6 million related to over-recovered electric energy and gas fuel costs. As of December 31, 2017 , DPL's regulatory asset of $15 million included $8 million of transmission costs recoverable through its FERC approved formula rate and $7 million related to under-recovered electric energy costs. As of December 31, 2017 , DPL's regulatory liability of $1 million related to over-recovered electric energy costs. (j) As of March 31, 2018 , ACE's regulatory asset of $24 million included $9 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of March 31, 2018 , ACE's regulatory liability of $12 million related to over-recovered electric energy costs. As of December 31, 2017 , ACE's regulatory asset of $26 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of December 31, 2017 , ACE's regulatory liability of $3 million related to over-recovered electric energy costs. (k) As of March 31, 2018 and December 31, 2017 , Pepco’s regulatory asset of $20 million represents previously incurred PHI integration costs, including $11 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. (l) As of March 31, 2018 , DPL’s regulatory asset of $11 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates and $2 million authorized for recovery in Delaware gas rates. As of March 31, 2018 , DPL’s regulatory liability of $1 million represents net synergy savings incurred related to PHI integration costs that are expected to be returned in electric and gas rates in the Delaware service territory. As of December 31, 2017 , DPL’s regulatory asset of $10 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, and $1 million expected to be recovered in electric and gas rates in the Maryland and Delaware service territories. (m) As of March 31, 2018 and December 31, 2017 , ACE’s regulatory asset of $10 million and $9 million , respectively, represents previously incurred PHI integration costs expected to be recovered in the New Jersey service territory. (n) Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of March 31, 2018 , BGE had a regulatory asset of $6 million related to under-recovered electric revenue decoupling and a regulatory liability of $11 million related to over-recovered natural gas revenue decoupling. As of December 31, 2017 , BGE had a regulatory asset of $10 million related to under-recovered electric revenue decoupling and $4 million related to under-recovered natural gas revenue decoupling.
Purchase Of Receivables	The following tables provide information about the purchased receivables of those companies as of March 31, 2018 and December 31, 2017 . As of March 31, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 317 $ 88 $ 73 $ 64 $ 92 $ 55 $ 17 $ 20 Allowance for uncollectible accounts (a) (35 ) (16 ) (6 ) (4 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 282 $ 72 $ 67 $ 60 $ 83 $ 50 $ 16 $ 17 As of December 31, 2017 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 298 $ 87 $ 70 $ 58 $ 83 $ 56 $ 9 $ 18 Allowance for uncollectible accounts (a) (31 ) (14 ) (5 ) (3 ) (9 ) (5 ) (1 ) (3 ) Purchased receivables, net $ 267 $ 73 $ 65 $ 55 $ 74 $ 51 $ 8 $ 15 _________ (a) For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing tariff.

Early Nuclear Plant Retiremen34

Early Nuclear Plant Retirements Early Nuclear Plant Retirements (Tables)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Exelon's and Generation's 2017 results included a net incremental $339 million of total pre-tax expense associated with the early retirement decision for TMI, as summarized in the table below. Income statement expense (pre-tax) Q2 2017 Q3 2017 Q4 2017 YTD 2017 Depreciation and amortization (a) Accelerated depreciation (b) $ 35 $ 106 $ 109 $ 250 Accelerated Nuclear Fuel amortization 2 6 4 12 Operating and maintenance (c) 71 5 1 77 Total $ 108 $ 117 $ 114 $ 339 _________ (a) Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017. (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. Exelon's and Generation's first quarter 2018 results included a net incremental $178 million of total pre-tax expense associated with the early retirement decisions for TMI and Oyster Creek, as summarized in the table below. Income statement expense (pre-tax) Q1 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 137 Accelerated nuclear fuel amortization 15 Operating and maintenance (c) 26 Total $ 178 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI for the quarter ended March 31, 2018 , and for Oyster Creek from February 2, 2018 through March 31, 2018 . (b) Reflects incremental accelerated depreciation of plant assets, including any ARC. (c) Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments. The following table provides the balance sheet amounts as of March 31, 2018 for Generation’s significant assets and liabilities associated with the Mystic Generating Station assets. March 31, 2018 Asset Balances Materials and supplies inventory $ 26 Fuel inventory 18 Completed plant, net 896 Construction work in progress 4 Prepaid expense (a) 9 Liability Balances Asset retirement obligation (5 ) Accrued expense (a) (2 ) In 2017, PSEG made public similar financial challenges facing its New Jersey nuclear plants including Salem, of which Generation owns a 42.59% ownersh

Fair Value of Financial Asset35

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Tables [Line Items]
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 March 31, 2018 and December 31, 2017 : Exelon March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 1,654 $ — $ 1,654 $ — $ 1,654 Long-term debt (including amounts due within one year) (b)(c) 34,108 — 33,091 1,893 34,984 Long-term debt to financing trusts (d) 389 — — 421 421 SNF obligation 1,151 — 922 — 922 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 929 $ — $ 929 $ — $ 929 Long-term debt (including amounts due within one year) (b)(c) 34,264 — 34,735 1,970 36,705 Long-term debt to financing trusts (d) 389 — — 431 431 SNF obligation 1,147 — 936 — 936 Generation March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 166 $ — $ 166 $ — $ 166 Long-term debt (including amounts due within one year) (b)(c) 8,965 — 7,585 1,610 9,195 SNF obligation 1,151 — 922 — 922 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 2 $ — $ 2 $ — $ 2 Long-term debt (including amounts due within one year) (b)(c) 8,990 — 7,839 1,673 9,512 SNF obligation 1,147 — 936 — 936 ComEd March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 317 $ — $ 317 $ — $ 317 Long-term debt (including amounts due within one year) (b)(c) 7,694 — 8,061 — 8,061 Long-term debt to financing trusts (d) 205 — — 222 222 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 7,601 $ — $ 8,418 $ — $ 8,418 Long-term debt to financing trusts (d) 205 — — 227 227 PECO March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 220 $ — $ 220 $ — $ 220 Long-term debt (including amounts due within one year) (b)(c) 2,723 — 2,870 — 2,870 Long-term debt to financing trusts (d) 184 — — 199 199 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 2,903 $ — $ 3,194 $ — $ 3,194 Long-term debt to financing trusts (d) 184 — — 204 204 BGE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 45 $ — $ 45 $ — $ 45 Long-term debt (including amounts due within one year) (b)(c) $ 2,578 $ — $ 2,689 $ — $ 2,689 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 77 $ — $ 77 $ — $ 77 Long-term debt (including amounts due within one year) (b)(c) 2,577 — 2,825 — 2,825 PHI March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 407 $ — $ 407 $ — $ 407 Long-term debt (including amounts due within one year) (b)(c) 5,849 — 5,423 283 5,706 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 350 $ — $ 350 $ — $ 350 Long-term debt (including amounts due within one year) (b)(c) 5,874 — 5,722 297 6,019 Pepco March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 60 $ — $ 60 $ — $ 60 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 2,933 9 2,942 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 26 $ — $ 26 $ — $ 26 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 3,114 9 3,123 DPL March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 211 $ — $ 211 $ — $ 211 Long-term debt (including amounts due within one year) (b)(c) 1,296 — 1,320 — 1,320 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (b)(c) 1,300 — 1,393 — 1,393 ACE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 136 $ — $ 136 $ — $ 136 Long-term debt (including amounts due within one year) (b)(c) 1,114 — 916 274 1,190 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 108 $ — $ 108 $ — $ 108 Long-term debt (including amounts due within one year) (b)(c) 1,121 — 949 288 1,237 _________ (a) Level 1 securities consist of dividends payable (included in other current liabilities). Level 2 securities consist of short term borrowings. (b) Includes unamortized debt issuance costs which are not fair valued of $213 million , $57 million , $60 million , $20 million , $16 million , $6 million , $32 million , $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 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 . (c) Level 2 securities consist of fixed-rate taxable debt securities, fixed-rate tax-exempt debt, variable rate tax-exempt debt and variable rate non-recourse debt. Level 3 securities consist of fixed-rate private placement taxable debt securities, fixed rate nonrecourse debt and government-backed fixed rate non-recourse debt. (d) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2018
Assets and liabilities measured and recorded at fair value on recurring basis	PHI, Pepco, DPL and ACE The following tables present assets and liabilities measured and recorded at fair value on PHI's, Pepco's, DPL's and ACE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : As of March 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) $ 67 $ — $ — $ 67 $ 83 $ — $ — $ 83 Rabbi trust investments Cash equivalents 72 — — 72 72 — — 72 Fixed income — 10 — 10 — 12 — 12 Life insurance contracts — 23 23 46 — 23 22 45 Rabbi trust investments subtotal (b) 72 33 23 128 72 35 22 129 Total assets 139 33 23 195 155 35 22 212 Liabilities Deferred compensation obligation — (23 ) — (23 ) — (25 ) — (25 ) Mark-to-market derivative liabilities (c) — — — — (1 ) — — (1 ) Effect of netting and allocation of collateral — — — — 1 — — 1 Mark-to-market derivative liabilities subtotal — — — — — — — — Total liabilities — (23 ) — (23 ) — (25 ) — (25 ) Total net assets $ 139 $ 10 $ 23 $ 172 $ 155 $ 10 $ 22 $ 187 Pepco DPL ACE As of March 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) $ 33 $ — $ — $ 33 $ — $ — $ — $ — $ 27 $ — $ — $ 27 Rabbi trust investments Cash equivalents 44 — — 44 — — — — — — — — Fixed income — 10 — 10 — — — — — — — — Life insurance contracts — 23 23 46 — — — — — — — — Rabbi trust investments subtotal (b) 44 33 23 100 — — — — — — — — Total assets 77 33 23 133 — — — — 27 — — 27 Liabilities Deferred compensation obligation — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total liabilities — (4 ) — (4 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 77 $ 29 $ 23 $ 129 $ — $ (1 ) $ — $ (1 ) $ 27 $ — $ — $ 27 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 (c) — — — — (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 $36 million and $12 million at March 31, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $15 million and $4 million at March 31, 2018 and December 31, 2017 , respectively. DPL excludes cash of $7 million and $2 million at March 31, 2018 and December 31, 2017 , respectively. ACE excludes cash of $10 million and $2 million at March 31, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) The amount of unrealized gains/(losses) at PHI, Pepco, DPL and ACE totaled less than $1 million for the three months ended March 31, 2018 and March 31, 2017 . (c) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : Generation Exelon As of March 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) 343 — — — 343 517 — — — 517 NDT fund investments Cash equivalents (b) 222 105 — — 327 222 105 — — 327 Equities 4,002 983 — 2,119 7,104 4,002 983 — 2,119 7,104 Fixed income Corporate debt — 1,583 240 — 1,823 — 1,583 240 — 1,823 U.S. Treasury and agencies 1,869 88 — — 1,957 1,869 88 — — 1,957 Foreign governments — 86 — — 86 — 86 — — 86 State and municipal debt — 254 — — 254 — 254 — — 254 Other (c) — 39 — 532 571 — 39 — 532 571 Fixed income subtotal 1,869 2,050 240 532 4,691 1,869 2,050 240 532 4,691 Middle market lending — — 369 127 496 — — 369 127 496 Private equity — — — 253 253 — — — 253 253 Real estate — — — 488 488 — — — 488 488 NDT fund investments subtotal (d) 6,093 3,138 609 3,519 13,359 6,093 3,138 609 3,519 13,359 Pledged assets for Zion Station decommissioning Cash equivalents 13 — — — 13 13 — — — 13 Generation Exelon As of March 31, 2018 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 — — 16 — 16 — — 16 — 16 Pledged assets for Zion Station (e) 13 — 16 — 29 13 — 16 — 29 Rabbi trust investments Cash equivalents 5 — — — 5 77 — — — 77 Mutual funds 24 — — — 24 59 — — — 59 Fixed income — — — — — — 10 — — 10 Life insurance contracts — 22 — — 22 — 71 23 — 94 Rabbi trust investments subtotal (f) 29 22 — — 51 136 81 23 — 240 Commodity derivative assets Economic hedges 286 2,923 1,892 — 5,101 286 2,923 1,892 — 5,101 Proprietary trading — 151 58 — 209 — 151 58 — 209 Effect of netting and allocation of collateral (g) (h) (335 ) (2,589 ) (895 ) — (3,819 ) (335 ) (2,589 ) (895 ) — (3,819 ) Commodity derivative assets subtotal (49 ) 485 1,055 — 1,491 (49 ) 485 1,055 — 1,491 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 12 — — 12 — 12 — — 12 Economic hedges — 6 — — 6 — 6 — — 6 Effect of netting and allocation of collateral (1 ) (3 ) — — (4 ) (1 ) (3 ) — — (4 ) Interest rate and foreign currency derivative assets subtotal (1 ) 15 — — 14 (1 ) 15 — — 14 Other investments — — 36 — 36 — — 36 — 36 Total assets 6,428 3,660 1,716 3,519 15,323 6,709 3,719 1,739 3,519 15,686 Liabilities Commodity derivative liabilities Economic hedges (415 ) (3,317 ) (1,203 ) — (4,935 ) (415 ) (3,317 ) (1,470 ) — (5,202 ) Proprietary trading — (164 ) (15 ) — (179 ) — (164 ) (15 ) — (179 ) Effect of netting and allocation of collateral (g) (h) 415 3,007 1,081 — 4,503 415 3,007 1,081 — 4,503 Commodity derivative liabilities subtotal — (474 ) (137 ) — (611 ) — (474 ) (404 ) — (878 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (4 ) — — (4 ) Generation Exelon As of March 31, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Economic hedges (1 ) (4 ) — — (5 ) (1 ) (4 ) — — (5 ) Effect of netting and allocation of collateral 1 3 — — 4 1 3 — — 4 Interest rate and foreign currency derivative liabilities subtotal — (1 ) — — (1 ) — (5 ) — — (5 ) Deferred compensation obligation — (35 ) — — (35 ) — (138 ) — — (138 ) Total liabilities — (510 ) (137 ) — (647 ) — (617 ) (404 ) — (1,021 ) Total net assets $ 6,428 $ 3,150 $ 1,579 $ 3,519 $ 14,676 $ 6,709 $ 3,102 $ 1,335 $ 3,519 $ 14,665 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 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 (e) 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 collateral (g) (h) (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 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 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of collateral (g) (h) 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 $371 million and $259 million at March 31, 2018 and December 31, 2017 and restricted cash of $23 million and $127 million at March 31, 2018 and December 31, 2017 . Exelon excludes cash of $531 million and $389 million at March 31, 2018 and December 31, 2017 and restricted cash of $51 million and $145 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $103 million and $85 million at March 31, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $53 million and $77 million of cash received from outstanding repurchase agreements at March 31, 2018 and December 31, 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 $2 million and less than $1 million , which have a total notional amount of $949 million and $811 million at March 31, 2018 and December 31, 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 $84 million and $82 million at March 31, 2018 and December 31, 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 $1 million at March 31, 2018 . 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 three months ended March 31, 2018 and March 31, 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million and $2 million for the three months ended March 31, 2018 and March 31, 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $80 million , $418 million and $186 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2018 . Collateral posted/(received) from counterparties, net of collateral paid to 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), $156 million represents variation margin on the exchanges as of March 31, 2018 . Of the collateral posted/(received), $(117) million represents variation margin on the exchanges as of December 31, 2017 . Exelon and Generation hold investments without readily determinable fair values with carrying amounts of $68 million as of March 31, 2018 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three months ended March 31, 2018 . ComEd, PECO and BGE The following tables present assets and liabilities measured and recorded at fair value on ComEd's, PECO's and BGE's Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of March 31, 2018 and December 31, 2017 : ComEd PECO BGE As of March 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) $ 93 $ — $ — $ 93 $ 6 $ — $ — $ 6 $ — $ — $ — $ — 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 93 — — 93 13 10 — 23 6 — — 6 Liabilities Deferred compensation obligation — (8 ) — (8 ) — (11 ) — (11 ) — (4 ) — (4 ) Mark-to-market derivative liabilities (c) — — (267 ) (267 ) — — — — — — — — Total liabilities — (8 ) (267 ) (275 ) — (11 ) — (11 ) — (4 ) — (4 ) Total net assets (liabilities) $ 93 $ (8 ) $ (267 ) $ (182 ) $ 13 $ (1 ) $ — $ 12 $ 6 $ (4 ) $ — $ 2 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 $69 million and $45 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $83 million and $62 million at March 31, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $20 million and $47 million at March 31, 2018 and December 31, 2017 . BGE excludes cash of $22 million and $17 million at March 31, 2018 and December 31, 2017 and restricted cash of $2 million and $1 million at March 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 three months ended March 31, 2018 and March 31, 2017 , respectively. (c) The Level 3 balance consists of the current and noncurrent liability of $24 million and $243 million , respectively, at March 31, 2018 , and $21 million and $235 million , respectively, at December 31, 2017 , related to floating-to-fixed energy swap contracts with unaffiliated suppliers.
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis	The following tables present the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis during the three months ended March 31, 2018 and 2017 : Generation ComEd PHI Exelon Three Months Ended March 31, 2018 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 December 31, 2017 $ 648 $ 12 $ 552 $ 37 $ 1,249 $ (256 ) $ 22 $ — $ 1,015 Total realized / unrealized gains (losses) Included in net income — — 184 (a) 1 185 — 1 — 186 Included in noncurrent payables to affiliates 7 — — — 7 — — (7 ) — Included in payable for Zion Station decommissioning — 4 — — 4 — — — 4 Included in regulatory assets/liabilities — — — — — (11 ) (b) — 7 (4 ) Change in collateral — — 105 — 105 — — — 105 Purchases, sales, issuances and settlements Purchases 2 — 88 — 90 — — — 90 Sales — — (3 ) — (3 ) — — — (3 ) Settlements (48 ) — — — (48 ) — — — (48 ) Transfers into Level 3 — — (8 ) — (8 ) — — — (8 ) Transfers out of Level 3 — — — (2 ) (2 ) — — — (2 ) Balance at March 31, 2018 $ 609 $ 16 $ 918 $ 36 $ 1,579 $ (267 ) $ 23 $ — $ 1,335 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2018 $ — $ — $ 256 $ 1 $ 257 $ — $ 1 $ — $ 258 Generation ComEd PHI Exelon Three Months Ended March 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 December 31, 2016 $ 677 $ 19 $ 493 $ 42 $ 1,231 $ (258 ) $ 20 $ — $ 993 Total realized / unrealized gains (losses) Included in net income 3 — (43 ) (a) 1 (39 ) — 1 — (38 ) Included in noncurrent payables to affiliates 9 — — — 9 — — (9 ) — Included in regulatory assets/liabilities — — — — — (24 ) (b) — 9 (15 ) Change in collateral — — 38 — 38 — — — 38 Purchases, sales, issuances and settlements Purchases 17 1 69 2 89 — — — 89 Sales — — (2 ) — (2 ) — — — (2 ) Issuances — — — — — — (1 ) — (1 ) Settlements (23 ) — — — (23 ) — — — (23 ) Transfers into Level 3 — — (1 ) — (1 ) — — — (1 ) Transfers out of Level 3 — — 11 (5 ) 6 — — — 6 Balance as of March 31, 2017 $ 683 $ 20 $ 565 $ 40 $ 1,308 $ (282 ) $ 20 $ — $ 1,046 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of March 31, 2017 $ 2 $ — $ 59 $ — $ 61 $ — $ 1 $ — $ 62 ________ (a) Includes a reduction for the reclassification of $72 million and $102 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2018 and March 31, 2017 , respectively. (b) Includes $ 17 million of decreases in fair value and an increase for realized losses due to settlements of $ 6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018 . Includes $30 million of decreases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2017 . (c) The amounts represented are life insurance contracts at Pepco.
Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis	The following tables present the income statement classification of the total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis during the three months ended March 31, 2018 and 2017 : Generation PHI Exelon Operating Purchased Other, net (a) Operating and Maintenance Operating Purchased Operating and Maintenance Other, net (a) Total gains (losses) included in net income for the three months ended March 31, 2018 $ 335 $ (151 ) $ 1 $ 1 $ 335 $ (151 ) $ 1 $ 1 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2018 309 (53 ) 1 1 309 (53 ) 1 1 Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net (a) Other, net (a) Operating Revenues Purchased Power and Fuel Other, net (a) Total gains (losses) included in net income for the three months ended March 31, 2017 $ 88 $ (131 ) $ 3 $ 1 $ 88 $ (131 ) $ 4 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended March 31, 2017 140 (81 ) 2 1 140 (81 ) 3 _________ (a) Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco.
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis, valuation technique	isk. The table below discloses the significant inputs to the forward curve used to value these positions. Type of trade Fair Value at March 31, 2018 Valuation Technique Unobservable Input Range Mark-to-market derivatives — Economic Hedges (Exelon and Generation) (a)(b) $ 689 Discounted Forward power $1 - $202 Forward gas $1.12 - $12.80 Option Model Volatility 10% - 227% Mark-to-market derivatives — Proprietary trading (Exelon and Generation) (a)(b) $ 43 Discounted Forward power $4 - $202 Mark-to-market derivatives (Exelon and ComEd) $ (267 ) Discounted Forward heat (c) 9x - 10x Marketability 4% - 8% Renewable 87% - 122% Type of trade Fair Value at December 31, 2017 Valuation Technique Unobservable Input Range Mark-to-market derivatives — Economic Hedges (Exelon and Generation) (a)(b) $ 445 Discounted Forward power price $3 - $124 Forward gas price $1.27 - $12.80 Option Model Volatility percentage 11% - 139% Mark-to-market derivatives — Proprietary trading (Exelon and Generation) (a)(b) $ 26 Discounted Forward power price $14 - $94 Mark-to-market derivatives (Exelon and ComEd) $ (256 ) Discounted Cash Flow Forward heat (c) 9x - 10x Marketability reserve 4% - 8% Renewable factor 88% - 120% _________ (a) The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions. (b) The fair values do not include cash collateral posted on level three positions of $186 million and $81 million as of March 31, 2018 and December 31, 2017 , respectively. (c) Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.
Exelon Generation Co L L C [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	Generation March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 166 $ — $ 166 $ — $ 166 Long-term debt (including amounts due within one year) (b)(c) 8,965 — 7,585 1,610 9,195 SNF obligation 1,151 — 922 — 922 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 2 $ — $ 2 $ — $ 2 Long-term debt (including amounts due within one year) (b)(c) 8,990 — 7,839 1,673 9,512 SNF obligation 1,147 — 936 — 936
Commonwealth Edison Co [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	ComEd March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 317 $ — $ 317 $ — $ 317 Long-term debt (including amounts due within one year) (b)(c) 7,694 — 8,061 — 8,061 Long-term debt to financing trusts (d) 205 — — 222 222 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 7,601 $ — $ 8,418 $ — $ 8,418 Long-term debt to financing trusts (d) 205 — — 227 227
PECO Energy Co [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	PECO March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 220 $ — $ 220 $ — $ 220 Long-term debt (including amounts due within one year) (b)(c) 2,723 — 2,870 — 2,870 Long-term debt to financing trusts (d) 184 — — 199 199 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 2,903 $ — $ 3,194 $ — $ 3,194 Long-term debt to financing trusts (d) 184 — — 204 204
Baltimore Gas and Electric Company [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	BGE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 45 $ — $ 45 $ — $ 45 Long-term debt (including amounts due within one year) (b)(c) $ 2,578 $ — $ 2,689 $ — $ 2,689 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 77 $ — $ 77 $ — $ 77 Long-term debt (including amounts due within one year) (b)(c) 2,577 — 2,825 — 2,825
PEPCO Holdings Inc [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	PHI March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 407 $ — $ 407 $ — $ 407 Long-term debt (including amounts due within one year) (b)(c) 5,849 — 5,423 283 5,706 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 350 $ — $ 350 $ — $ 350 Long-term debt (including amounts due within one year) (b)(c) 5,874 — 5,722 297 6,019
Potomac Electric Power Company [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	Pepco March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 60 $ — $ 60 $ — $ 60 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 2,933 9 2,942 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 26 $ — $ 26 $ — $ 26 Long-term debt (including amounts due within one year) (b)(c) 2,540 — 3,114 9 3,123
Delmarva Power and Light Company [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	DPL March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 211 $ — $ 211 $ — $ 211 Long-term debt (including amounts due within one year) (b)(c) 1,296 — 1,320 — 1,320 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 216 $ — $ 216 $ — $ 216 Long-term debt (including amounts due within one year) (b)(c) 1,300 — 1,393 — 1,393
Atlantic City Electric Company [Member]
Fair Value Tables [Line Items]
Fair value of financial liabilities recorded at the carrying amount	ACE March 31, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 136 $ — $ 136 $ — $ 136 Long-term debt (including amounts due within one year) (b)(c) 1,114 — 916 274 1,190 December 31, 2017 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 108 $ — $ 108 $ — $ 108 Long-term debt (including amounts due within one year) (b)(c) 1,121 — 949 288 1,237

Derivative Financial Instrume36

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of the derivative fair value	The following table provides a summary of the derivative fair value balances recorded by the Registrants as of March 31, 2018 : Generation ComEd DPL Exelon Derivatives Economic Hedges Proprietary Trading Collateral and Netting (a)(e) Subtotal (b) Economic Hedges (c) Economic Hedges (d) Collateral and Netting (a) Subtotal Total Derivatives Mark-to-market derivative assets (current assets) $ 3,343 $ 166 $ (2,533 ) $ 976 $ — $ — $ — $ — $ 976 Mark-to-market derivative assets (noncurrent assets) 1,758 43 (1,286 ) 515 — — — — 515 Total mark-to-market derivative assets 5,101 209 (3,819 ) 1,491 — — — — 1,491 Mark-to-market derivative liabilities (current liabilities) (3,185 ) (151 ) 2,945 (391 ) (24 ) — — — (415 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,750 ) (28 ) 1,558 (220 ) (243 ) — — — (463 ) Total mark-to-market derivative liabilities (4,935 ) (179 ) 4,503 (611 ) (267 ) — — — (878 ) Total mark-to-market derivative net assets (liabilities) $ 166 $ 30 $ 684 $ 880 $ (267 ) $ — $ — $ — $ 613 _________ (a) Exelon, Generation and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $192 million and $103 million , respectively, and current and noncurrent liabilities are shown net of collateral of $220 million and $169 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $684 million at March 31, 2018 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $156 million represents variation margin on the exchanges. The following table provides a summary of the derivative fair value balances recorded by the Registrants as of December 31, 2017 : Generation ComEd DPL Exelon Description Economic Proprietary Collateral (a)(e) Subtotal (b) Economic (c) Economic (d) Collateral and (a) Subtotal Total Mark-to-market derivative assets (current assets) $ 3,061 $ 56 $ (2,144 ) $ 973 $ — $ — $ — $ — $ 973 Mark-to-market derivative assets (noncurrent assets) 1,164 12 (845 ) 331 — — — — 331 Total mark-to-market derivative assets 4,225 68 (2,989 ) 1,304 — — — — 1,304 Mark-to-market derivative liabilities (current liabilities) (2,646 ) (43 ) 2,480 (209 ) (21 ) (1 ) 1 — (230 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,137 ) (10 ) 975 (172 ) (235 ) — — — (407 ) Total mark-to-market derivative liabilities (3,783 ) (53 ) 3,455 (381 ) (256 ) (1 ) 1 — (637 ) Total mark-to-market derivative net assets (liabilities) $ 442 $ 15 $ 466 $ 923 $ (256 ) $ (1 ) $ 1 $ — $ 667 _________ (a) Exelon, Generation and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, and letters of credit and other forms of non-cash collateral. These are not reflected in the table above. (b) Current and noncurrent assets are shown net of collateral of $169 million and $53 million , respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017 . (c) Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers. (d) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC. (e) Of the collateral posted/(received), $(117) million represents variation margin on the exchanges. 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: Three Months Ended March 31, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (7 ) $ (4 ) $ 13 $ 8 Below is a summary of the interest rate and foreign exchange hedge balances as of March 31, 2018 : Generation Exelon Corporate Exelon Description Derivatives Designated as Hedging Instruments Economic Hedges Collateral and Netting (a) Subtotal Derivatives Designated as Hedging Instruments Total Mark-to-market derivative assets (current assets) $ — $ 5 $ (3 ) $ 2 $ — $ 2 Mark-to-market derivative assets (noncurrent assets) 12 1 (1 ) 12 — 12 Total mark-to-market derivative assets 12 6 (4 ) 14 — 14 Mark-to-market derivative liabilities (current liabilities) — (3 ) 3 — — — Mark-to-market derivative liabilities (noncurrent liabilities) — (2 ) 1 (1 ) (4 ) (5 ) Total mark-to-market derivative liabilities — (5 ) 4 (1 ) (4 ) (5 ) Total mark-to-market derivative net assets (liabilities) $ 12 $ 1 $ — $ 13 $ (4 ) $ 9 __________ (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 Designated as Hedging Instruments 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.
Derivative Instruments, Gain (Loss) [Table Text Block]	For the three months ended March 31, 2018 and 2017 , Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also located in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ (100 ) $ 46 Purchased power and fuel (167 ) (93 ) Total Exelon and Generation $ (267 ) $ (47 ) For the three months ended March 31, 2018 and 2017 , 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. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Generation Operating Revenues $ 2 $ (2 ) Generation Purchased Power and Fuel (1 ) — Total Generation $ 1 $ (2 ) Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Exelon Operating Revenues $ 2 $ (2 ) Exelon Purchased Power and Fuel (1 ) — Total Exelon $ 1 $ (2 )
Schedule of Derivative Instruments Included in Trading Activities [Table Text Block]	For the three months ended March 31, 2018 and 2017 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses) which are also included in the "Net fair value changes related to derivatives" on the Consolidated Statements of Cash Flows. The Utility Registrants do not execute derivatives for proprietary trading purposes. Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ 2 $ (1 ) For the three months ended March 31, 2018 and 2017 Exelon and Generation recognized the following net pre-tax commodity mark-to-market gains (losses). Three Months Ended 2018 2017 Income Statement Location Gain (Loss) Operating Revenues $ — $ (1 )
Information on Generation's credit exposure for all derivative instruments, normal purchase normal sales, and applicable payables and receivables, net of collateral and instruments that are subject to master netting agreements	The following tables provide information on Generation’s credit exposure for all derivative instruments, NPNS and applicable payables and receivables, net of collateral and instruments that are subject to master netting agreements, as of March 31, 2018 . The tables further delineate that exposure by credit rating of the counterparties and provide guidance on the concentration of credit risk to individual counterparties. 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 $31 million , $21 million , $25 million , $34 million , $9 million , and $5 million as of March 31, 2018 , respectively. Rating as of March 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 $ 986 $ 1 $ 985 2 $ 412 Non-investment grade 112 46 66 No external ratings Internally rated — investment grade 223 — 223 Internally rated — non-investment grade 100 17 83 Total $ 1,421 $ 64 $ 1,357 2 $ 412 Net Credit Exposure by Type of Counterparty As of Financial institutions $ 189 Investor-owned utilities, marketers, power producers 656 Energy cooperatives and municipalities 438 Other 74 Total $ 1,357 _________ (a) As of March 31, 2018 , credit collateral held from counterparties where Generation had credit exposure included $41 million of cash and $23 million of letters of credit. The credit collateral does not include non-liquid collateral. The aggregate fair value of all derivative instruments with credit-risk related contingent features in a liability position that are not fully collateralized (excluding transactions on the exchanges that are fully collateralized) is detailed in the table below: Credit-Risk Related Contingent Feature March 31, 2018 December 31, 2017 Gross fair value of derivative contracts containing this feature (a) $ (2,141 ) $ (926 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 1,562 577 Net fair value of derivative contracts containing this feature (c) $ (579 ) $ (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.
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	The table below provides the notional amounts of fixed-to-floating hedges outstanding held by Exelon at March 31, 2018 and December 31, 2017 : As of March 31, 2018 December 31, 2017 Fixed-to-floating hedges $ 800 $ 800 The following table provides notional amounts outstanding held by Exelon and Generation at March 31, 2018 and December 31, 2017 related to foreign currency exchange rate swaps that are marked-to-market to manage the exposure associated with international purchases of commodities in currencies other than U.S. dollars. As of March 31, 2018 December 31, 2017 Foreign currency exchange rate swaps $ 87 $ 94 The table below provides the notional amounts of floating-to-fixed hedges outstanding held by Exelon and Generation as of March 31, 2018 . As of March 31, 2018 December 31, 2017 Floating-to-fixed hedges $ 636 $ 636

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Commercial Paper Borrowings	The Registrants had the following amounts of commercial paper borrowings outstanding as of March 31, 2018 and December 31, 2017 : Commercial Paper Borrowings March 31, 2018 December 31, 2017 Exelon $ 1,154 $ 427 Generation 165 — ComEd 317 — PECO 220 — BGE 45 77 PHI (a) 407 350 Pepco 60 26 DPL 211 216 ACE 136 108
Schedule of Long-term Debt Instruments [Table Text Block]	During the three months ended March 31, 2018 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.72 % April 30, 2018 $ 1 Funding to install energy conservation measures for the Smithsonian Zoo project. Generation Energy Efficiency Project Financing 3.17 % April 30, 2018 $ 1 Funding to install energy conservation measures in Brooklyn, NY. Generation Energy Efficiency Project Financing 2.61 % September 30, 2018 $ 2 Funding to install energy conservation measures for the Pensacola project. ComEd First Mortgage Bonds, Series 124 4.00 % March 1, 2048 $ 800 Refinance one series of maturing first mortgage bonds, to repay a portion of ComEd’s outstanding commercial paper obligations and to fund general corporate purposes. PECO First and Refunding Mortgage Bonds 3.90 % March 1, 2048 $ 325 Refinance a portion of maturing mortgage bonds.

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
ScheduleOfRemeasurementsOfDeferredIncomeTaxesDueToTaxReform [Table Text Block]	The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below: 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 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 Exelon (b) Generation ComEd PECO BGE PHI Pepco DPL ACE Net Deferred Income Tax Benefit/(Expense) Recorded $ 1,309 $ 1,895 $ 1 $ 13 $ (4 ) $ (35 ) $ (8 ) $ (5 ) $ (2 ) __________ (a) Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers. (b) Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans. (c) Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information.
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The effective income tax rate from continuing operations varies from the U.S. Federal statutory rate principally due to the following: Three Months Ended March 31, 2018 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 4.1 2.4 8.2 (3.9) 6.3 4.6 1.7 6.3 6.6 Qualified nuclear decommissioning trust fund income (0.4) (1.3) — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.3) (4.3) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.3) Plant basis differences (2.7) — 0.1 (14.2) (0.7) (2.6) (3.4) (1.3) (2.6) Production tax credits and other credits (2.8) (9.5) (0.1) — — — — — — Noncontrolling interests (0.7) (2.5) — — — — — — — Excess deferred tax amortization (6.0) — (7.5) (4.8) (8.6) (10.6) (12.8) (7.9) (8.7) Other (2.8) (1.3) 0.3 0.2 — — (0.3) 0.5 (3.5) Effective income tax rate 8.4% 4.5% 21.8% (1.8)% 17.9% 12.2% 6.1% 18.4% 12.5% Three Months Ended March 31, 2017 (a) 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 0.9 1.0 4.9 0.1 5.2 4.9 4.6 5.3 5.6 Qualified nuclear decommissioning trust fund income 3.5 7.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.4) (0.7) (0.2) (0.1) (0.1) (0.2) (0.1) (0.3) (0.4) Plant basis differences (2.4) — (0.2) (13.2) (0.9) (3.8) (5.8) (1.9) (3.4) Production tax credits and other credits (0.7) (1.5) — — — — — — — Noncontrolling interest — 0.1 — — — — — — — Merger expenses (b) (11.5) (3.4) — — — (42.4) (34.2) (21.9) (167.1) Fitzpatrick bargain purchase gain (6.6) (14.8) — — — — — — — Other (0.1) (0.4) — 0.3 (0.2) (0.4) 0.5 — (3.0) Effective income tax rate 17.7% 23.1% 39.5% 22.1% 39.0% (6.9)% 0.0% 16.2% (133.3)% _________ (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 a remeasurement of uncertain state income tax positions for Pepco and DPL.
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The Registrants have the following unrecognized tax benefits as of March 31, 2018 and December 31, 2017 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE March 31, 2018 $ 733 $ 464 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14

Nuclear Decommissioning (Tables

Nuclear Decommissioning (Tables)	3 Months Ended
	Mar. 31, 2018
Schedule Of Nuclear Decommissioning [Line Items]
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]	The following table provides the pledged assets and payables to ZionSolutions, and withdrawals by ZionSolutions at March 31, 2018 and December 31, 2017 : Exelon and Generation March 31, 2018 December 31, 2017 Carrying value of Zion Station pledged assets (a) $ 30 $ 39 Payable to Zion Solutions (b)(c) 28 37 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 949 942 _________ (a) Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets. (b) Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized. (c) Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets. (d) Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings	[1],[2],[3],[4]
Schedule of Change in Asset Retirement Obligation [Table Text Block]	The following table provides a rollforward of the nuclear decommissioning ARO reflected on Exelon’s and Generation’s Consolidated Balance Sheets from December 31, 2017 to March 31, 2018 : Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 Accretion expense 117 Net increase due to changes in, and timing of, estimated future cash flows 32 Costs incurred related to decommissioning plants (4 ) Nuclear decommissioning ARO at March 31, 2018 (a) $ 9,807 _________ (a) Includes $64 million and $13 million for the current portion of the ARO at March 31, 2018 and December 31, 2017 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.	[5]
Unrealized Gain (Loss) on Investments [Table Text Block]	The following table provides net unrealized gains (losses) on NDT funds for the three months ended March 31, 2018 and 2017 : Exelon and Generation Three Months Ended 2018 2017 Net unrealized gains (losses) on decommissioning trust funds — Regulatory Agreement Units (a) $ (75 ) $ 222 Net unrealized gains (losses) on decommissioning trust funds — Non-Regulatory Agreement Units (b)(c) (96 ) 166 _________ (a) Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets. (b) Excludes $(2) million and $(1) million of net unrealized losses related to the Zion Station pledged assets for the three months ended March 31, 2018 and 2017 , respectively. Net unrealized losses related to Zion Station pledged assets are included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets in 2018 and 2017 , respectively. (c) Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.	[6],[7],[8]
[1]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.
[2]	Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets.
[3]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.
[4]	Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings
[5]	Includes $64 million and $13 million for the current portion of the ARO at March 31, 2018 and December 31, 2017, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.
[6]	Excludes $(2) million and $(1) million of net unrealized losses related to the Zion Station pledged assets for the three months ended March 31, 2018 and 2017, respectively. Net unrealized losses related to Zion Station pledged assets are included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets in 2018 and 2017, respectively.
[7]	Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets.
[8]	Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs [Table Text Block]	The following table presents the components of Exelon's net periodic benefit costs, prior to capitalization, for the three months ended March 31, 2018 and 2017 . Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 101 $ 95 $ 28 $ 26 Interest cost 201 210 43 45 Expected return on assets (312 ) (299 ) (43 ) (41 ) Amortization of: Prior service benefit — — (46 ) (47 ) Actuarial loss 157 152 16 16 Net periodic benefit cost $ 147 $ 158 $ (2 ) $ (1 ) _________ (a) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017.
Schedule Of Pension And Other Postretirement Benefit Costs	The amounts below represent Exelon's, Generation's, ComEd's, PECO's, BGE's, BSC's, PHI's, Pepco's, DPL's, ACE's, and PHISCO's allocated portion of the pension and postretirement benefit plan 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 three months ended March 31, 2017. The amounts below represent the Registrants’ as well as BSC's and PHISCO's pension and postretirement benefit plan net periodic benefit costs. For Exelon, the service cost component is included in Operating and maintenance expense and Property, plant and equipment for the three months ended March 31, 2018 and 2017, while the non-service cost components are included in Other, net and Regulatory assets for the three months ended March 31, 2018 and in Other, net and Property, plant and equipment for the three months ended March 31, 2017. For the Registrants other than Exelon, the service cost and non-service cost components are included in Operating and maintenance expense and Property, plant and equipment on their consolidated financial statements for the three months ended March 31, 2018 and 2017. Three Months Ended March 31, Pension and Other Postretirement Benefit Costs 2018 2017 Exelon (a)(b) $ 145 $ 157 Generation (b) 51 54 ComEd 45 44 PECO 5 7 BGE 15 16 BSC (c) 14 12 PHI (a)(d) 15 24 Pepco 4 7 DPL — 3 ACE 3 3 PHISCO (d) 8 11 _________ (a) Exelon reflects the consolidated pension and other postretirement benefit costs of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated pension and other postretirement benefit costs of Pepco, DPL, ACE, and PHISCO. (b) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017. (c) 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. (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.
Schedule Of Defined Contributions	The following table presents the matching contributions to the savings plans during the three months ended March 31, 2018 and 2017 , respectively. Three Months Ended March 31, Savings Plan Matching Contributions 2018 2017 Exelon (a)(b) $ 32 $ 30 Generation (b) 15 14 ComEd 7 7 PECO 2 2 BGE 2 2 BSC (c) 3 2 PHI (a)(d) 3 3 Pepco 1 1 DPL 1 1 PHISCO (d) 1 1 _________ (a) Exelon reflects the consolidated savings plan matching contributions of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated savings plan matching contributions of Pepco, DPL, and PHISCO. (b) FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017. (c) 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 or DPL amounts above. (d) These amounts represent amounts billed to Pepco and DPL through intercompany allocations. These amounts are not included in Pepco or DPL amounts above.

Severance (Tables)

Severance (Tables)	3 Months Ended
	Mar. 31, 2018
Restructuring and Related Activities [Abstract]
Severance	For the three months ended March 31, 2018 and 2017 , these costs were immaterial. For the three months ended March 31, 2018 and 2017 , the Registrants recorded the following severance costs associated with these ongoing severance benefits within Operating and maintenance expense in their Consolidated Statements of Operations and Comprehensive Income: Exelon Generation (a) ComEd (a) PECO (a) BGE (a) PHI (a) Pepco (a) DPL (a) ACE (a) Three Months Ended March 31, 2018 $ 8 $ 2 $ 1 $ — $ 1 $ 4 $ 2 $ 1 $ 1 March 31, 2017 4 3 1 — — — — — — _________ (a) The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017 . Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017 .
Severance Liability	Amounts included in the table below represent the severance liability recorded for employees of each Registrant and exclude amounts included at Exelon and billed through intercompany allocations: Severance Liability Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Balance at December 31, 2017 $ 94 $ 58 $ 3 $ — $ — $ 20 $ — $ — $ — Severance charges (a) 9 3 1 — 1 2 1 — — Payments (16 ) (5 ) (1 ) — — (6 ) (1 ) — — Balance at March 31, 2018 $ 87 $ 56 $ 3 $ — $ 1 $ 16 $ — $ — $ — __________ (a) Includes salary continuance and health and welfare severance benefits.

Changes in Accumulated Other 42

Changes in Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 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 three months ended March 31, 2018 and 2017 : Three Months Ended March 31, 2018 Gains Unrealized Gains and (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (14 ) $ 10 $ (2,998 ) (d) $ (23 ) $ (1 ) $ (3,026 ) OCI before reclassifications 8 — 18 1 — 27 Amounts reclassified from AOCI (b) — — 44 — — 44 Net current-period OCI 8 — 62 1 — 71 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (10 ) (c) — — — (10 ) Ending balance $ (6 ) $ — $ (2,936 ) $ (22 ) $ (1 ) $ (2,965 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 7 — — (1 ) — 6 Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI 7 — — (1 ) — 6 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (3 ) (c) — — — (3 ) Ending balance $ (9 ) $ — $ — $ (24 ) $ (1 ) $ (34 ) 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 Liabilities standard — (1 ) (c) — — — (1 ) Ending balance $ — $ — $ — $ — $ — $ — Three Months Ended March 31, 2017 Gains Unrealized Gains and (losses) on Marketable Securities Pension and Non-Pension Postretirement Benefit Plan Items Foreign Currency Items AOCI of Investments in Unconsolidated Affiliates Total Exelon (a) Beginning balance $ (17 ) $ 4 $ (2,610 ) $ (30 ) $ (7 ) $ (2,660 ) OCI before reclassifications 2 1 (59 ) 1 5 (50 ) Amounts reclassified from AOCI (b) 4 — 36 — — 40 Net current-period OCI 6 1 (23 ) 1 5 (10 ) Ending balance $ (11 ) $ 5 $ (2,633 ) $ (29 ) $ (2 ) $ (2,670 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications 2 — — 1 6 9 Amounts reclassified from AOCI (b) 4 — — — — 4 Net current-period OCI 6 — — 1 6 13 Ending balance $ (13 ) $ 2 $ — $ (29 ) $ (1 ) $ (41 ) 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 interest. 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 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 2 — New Accounting Standards 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 2 — New Accounting Standards 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 three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 Actuarial losses (b) (83 ) Total before tax (60 ) Tax benefit 16 Net of tax $ (44 ) Total Reclassifications $ (44 ) Comprehensive income Three Months Ended March 31, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains and (losses) on cash flow hedges Other cash flow hedges $ (7 ) $ (7 ) Interest expense Total before tax (7 ) (7 ) Tax benefit 3 3 Net of tax $ (4 ) $ (4 ) Comprehensive income Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (81 ) — Total before tax (58 ) — Tax benefit 22 — Net of tax $ (36 ) $ — Total Reclassifications $ (40 ) $ (4 ) Comprehensive income _________ (a) Amounts in parenthesis represent a decrease in net income. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional details).
Schedule Of Other Comprehensive Income Loss Tax	The following table presents income tax expense (benefit) allocated to each component of other comprehensive income (loss) during the three months ended March 31, 2018 and 2017 : Three Months Ended 2018 2017 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 10 Actuarial loss reclassified to periodic benefit cost (22 ) (32 ) Pension and non-pension postretirement benefit plans valuation adjustment (7 ) — Change in unrealized (loss) on cash flow hedges (3 ) (1 ) Change in unrealized (loss) on investments in unconsolidated affiliates (1 ) (4 ) Change in unrealized (loss) on marketable securities — (1 ) Total $ (27 ) $ (28 ) Generation Change in unrealized (loss) on cash flow hedges $ (3 ) $ (1 ) Change in unrealized (loss) on investments in unconsolidated affiliates (1 ) (3 ) Total $ (4 ) $ (4 )

Earnings Per Share and Equity43

Earnings Per Share and Equity (Tables)	3 Months Ended
	Mar. 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: Three Months Ended March 31, 2018 2017 Exelon Net income attributable to common shareholders $ 585 $ 990 Weighted average common shares outstanding — basic 966 928 Assumed exercise and/or distributions of stock-based awards 2 2 Weighted average common shares outstanding — diluted 968 930

Commitments and Contingencies44

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments And Contingencies Tables Disclosure [Line Items]
Other Commitments	The following amounts represent total commitment costs for Exelon, PHI, Pepco, DPL and ACE that have been recorded since the acquisition date and the remaining obligations as of March 31, 2018 : Description Expected Payment Period Pepco DPL ACE PHI Exelon Rate credits 2016 - 2017 $ 91 $ 67 $ 101 $ 259 $ 259 Energy efficiency 2016 - 2021 — — — — 122 Charitable contributions 2016 - 2026 28 12 10 50 50 Delivery system modernization Q2 2017 — — — — 22 Green sustainability fund Q2 2017 — — — — 14 Workforce development 2016 - 2020 — — — — 17 Other 1 5 — 6 29 Total commitments $ 120 $ 84 $ 111 $ 315 $ 513 Remaining commitments $ 75 $ 12 $ 8 $ 95 $ 165 Commercial Commitments (All Registrants) The Registrants’ commercial commitments as of March 31, 2018 , representing commitments potentially triggered by future events were as follows: Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Letters of credit (non-debt) (a) $ 1,586 $ 1,533 $ 2 $ 1 $ 5 $ 1 $ 1 $ — $ — Surety bonds (b) 1,651 1,463 9 9 10 66 32 4 5 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (c) 22 — — — — 22 7 9 6 Total commercial commitments $ 3,637 $ 2,996 $ 211 $ 188 $ 15 $ 89 $ 40 $ 13 $ 11 _________ (a) Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties. Includes letters of credits issued under credit facility agreements arranged at minority and community banks and nonrecourse debt letters of credits. (b) Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds. (c) Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $58 million , $17 million of which is a guarantee by Pepco, $24 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.
Accrued environmental liabilities	of March 31, 2018 and December 31, 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: March 31, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 462 $ 313 Generation 117 — ComEd 283 281 PECO 29 28 BGE 5 4 PHI 28 — Pepco 26 — 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 —

Supplemental Financial Inform45

Supplemental Financial Information (Tables)	3 Months Ended
	Mar. 31, 2018
Supplemental Financial Information [Abstract]
Components of non-operating income and expenses	The following tables provide additional information about the Registrants’ Consolidated Statements of Operations and Comprehensive Income for the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 46 $ 46 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 56 56 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (75 ) (75 ) — — — — — — — Non-regulatory agreement units (96 ) (96 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (2 ) (2 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) 24 24 — — — — — — — Total decommissioning-related activities (47 ) (47 ) — — — — — — — Investment income 4 2 — — — — — — — Interest income related to uncertain income tax positions 2 1 — — — — — — — AFUDC — Equity 18 — 6 2 4 6 5 1 — Non-service net periodic benefit cost (10 ) — — — — — — — — Other 5 — 2 — — 5 3 1 1 Other, net $ (28 ) $ (44 ) $ 8 $ 2 $ 4 $ 11 $ 8 $ 2 $ 1 Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other, Net Decommissioning-related activities: Net realized income on decommissioning trust funds (a) Regulatory agreement units $ 68 $ 68 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 32 32 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 222 222 — — — — — — — Non-regulatory agreement units 166 166 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (1 ) (1 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (234 ) (234 ) — — — — — — — Total decommissioning-related activities 253 253 — — — — — — — Investment income 2 2 — — — — — — — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 17 — 2 2 4 9 5 2 2 Non-service net periodic benefit cost (26 ) — — — — — — — — Other 10 4 2 — — 4 3 1 — Other, net $ 257 $ 259 $ 4 $ 2 $ 4 $ 13 $ 8 $ 3 $ 2 _________ (a) Includes investment income and realized gains and losses on sales of investments of the trust funds. (b) Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2017 Form 10-K for additional information regarding the accounting for nuclear decommissioning.
Schedule Of Taxes Excluding Income And Excise Taxes [Text Block]	The following utility taxes are included in revenues and expenses for the three months ended March 31, 2018 and 2017 . Generation’s utility tax expense represents gross receipts tax related to its retail operations, and the Utility Registrants' utility tax expense represents municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 235 $ 32 $ 61 $ 33 $ 26 $ 83 $ 77 $ 6 $ — Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 224 $ 32 $ 59 $ 31 $ 26 $ 76 $ 71 $ 5 $ —
Components of depreciation, amortization and accretion, and other, net	The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the three months ended March 31, 2018 and 2017 . Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 926 $ 436 $ 201 $ 68 $ 82 $ 117 $ 53 $ 32 $ 23 Amortization of regulatory assets (a) 152 — 27 7 52 66 43 13 10 Amortization of intangible assets, net (a) 13 12 — — — — — — — Amortization of energy contract assets and liabilities (b) 3 3 — — — — — — — Nuclear fuel (c) 287 287 — — — — — — — ARO accretion (d) 120 120 — — — — — — — Total depreciation, amortization and accretion $ 1,501 $ 858 $ 228 $ 75 $ 134 $ 183 $ 96 $ 45 $ 33 Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 754 $ 289 $ 190 $ 64 $ 80 $ 112 $ 50 $ 30 $ 21 Amortization of regulatory assets (a) 128 — 18 7 48 55 32 9 14 Amortization of intangible assets, net (a) 14 13 — — — — — — — Amortization of energy contract assets and liabilities (b) 2 2 — — — — — — — Nuclear fuel (c) 264 264 — — — — — — — ARO accretion (d) 112 110 — — — — — — — Total depreciation, amortization and accretion $ 1,274 $ 678 $ 208 $ 71 $ 128 $ 167 $ 82 $ 39 $ 35 _________ (a) Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income. (b) Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (c) Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. (d) Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income
Cash Flow Supplemental Disclosures	Three Months Ended March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 145 $ 51 $ 45 $ 5 $ 14 $ 15 $ 4 $ — $ 3 Loss from equity method investments 7 7 — — — — — — — Provision for uncollectible accounts 64 11 8 17 8 20 6 8 5 Stock-based compensation costs 29 — — — — — — — — Other decommissioning-related activity (a) (31 ) (31 ) — — — — — — — Energy-related options (b) (7 ) (7 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral 7 — — — — 7 1 6 — Amortization of debt fair value adjustment (3 ) (3 ) — — — — — — — Discrete impacts from EIMA and FEJA (c) (4 ) — (4 ) — — — — — — Amortization of debt costs 9 3 1 — — 1 — — — Provision for excess and obsolete inventory 13 12 1 — — — — — — Other 9 2 (6 ) (1 ) (2 ) 9 (1 ) 5 1 Total other non-cash operating activities $ 240 $ 45 $ 46 $ 21 $ 20 $ 53 $ 10 $ 19 $ 9 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (177 ) $ (131 ) $ (48 ) $ (25 ) $ (11 ) $ 61 $ 19 $ 14 $ 27 Increase in PPE related to ARO update 32 32 — — — — — — — Dividends on stock compensation 1 — — — — — — — — Three Months Ended March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 157 $ 54 $ 44 $ 7 $ 16 $ 24 $ 7 $ 3 $ 3 Loss from equity method investments 10 10 — — — — — — — Provision for uncollectible accounts 34 9 7 17 5 (4 ) (5 ) (1 ) 1 Stock-based compensation costs 31 — — — — — — — — Other decommissioning-related activity (a) (84 ) (84 ) — — — — — — — Energy-related options (b) (4 ) (4 ) — — — — — — — Amortization of regulatory asset related to debt costs 2 — 1 — — 1 — — — Amortization of rate stabilization deferral (14 ) — — — 7 (21 ) (15 ) (6 ) — Amortization of debt fair value adjustment (5 ) (3 ) — — — (2 ) — — — Discrete impacts from EIMA and FEJA (c) (24 ) — (24 ) — — — — — — Amortization of debt costs 9 4 1 — — — — — — Provision for excess and obsolete inventory 2 1 1 — — — — — — Other 4 3 1 (1 ) (4 ) (6 ) (2 ) (3 ) (2 ) Total other non-cash operating activities $ 118 $ (10 ) $ 31 $ 23 $ 24 $ (8 ) $ (15 ) $ (7 ) $ 2 Non-cash investing and financing activities: Increase (decrease) in capital expenditures not paid $ (193 ) $ (56 ) $ (66 ) $ (42 ) $ 1 $ (5 ) $ (6 ) $ 9 $ — Non-cash financing of capital projects 10 10 — — — — — — — Dividends on stock compensation 2 — — — — — — — — _________ (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 of the Exelon 2017 Form 10-K 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 in Operating revenues. (c) Reflects the change in distribution rates pursuant to EIMA and FEJA, which allows for the recovery of distribution costs by a utility through a pre-established performance-based formula rate tariff. Beginning June 1, 2017, also reflects the change in energy efficiency rates pursuant to FEJA, which allows for the recovery of energy efficiency costs by a utility through a pre-established performance-based formula rate tariff. See Note 6 — Regulatory Matters for more information.
Supplemental Balance Sheet Disclosures	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. March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 787 $ 610 $ 70 $ 21 $ 22 $ 43 $ 15 $ 7 $ 10 Restricted cash 209 127 9 5 2 40 33 — 7 Restricted cash included in other long-term assets 103 — 83 — — 20 — — 20 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 1,099 $ 737 $ 162 $ 26 $ 24 $ 103 $ 48 $ 7 $ 37 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 shown in the statement of cash flows $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 March 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 609 $ 400 $ 31 $ 28 $ 11 $ 109 $ 8 $ 44 $ 54 Restricted cash 254 140 3 4 43 41 33 — 7 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 889 $ 540 $ 34 $ 32 $ 57 $ 173 $ 41 $ 44 $ 84 December 31, 2016 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 635 $ 290 $ 56 $ 63 $ 23 $ 170 $ 9 $ 46 $ 101 Restricted cash 253 158 2 4 24 43 33 — 9 Restricted cash included in other long-term assets 26 — — — 3 23 — — 23 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 914 $ 448 $ 58 $ 67 $ 50 $ 236 $ 42 $ 46 $ 133 For additional information on restricted cash see Note 1 — Significant Accounting Policies of the Exelon 2017 Form 10-K. Supplemental Balance Sheet Information The following tables provide additional information about assets and liabilities of the Registrants as of March 31, 2018 and December 31, 2017 . March 31, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 21,905 (a) $ 11,936 (a) $ 4,391 $ 3,445 $ 3,471 $ 575 $ 3,224 $ 1,273 $ 1,086 Accounts receivable: Allowance for uncollectible accounts $ 369 $ 115 $ 89 $ 68 $ 31 $ 66 $ 24 $ 22 $ 20 December 31, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 21,064 (b) $ 11,428 (b) $ 4,269 $ 3,411 $ 3,405 $ 487 $ 3,177 $ 1,247 $ 1,066 Accounts receivable: Allowance for uncollectible accounts $ 322 $ 114 $ 73 $ 56 $ 24 $ 55 $ 21 $ 16 $ 18 _________ (a) Includes accumulated amortization of nuclear fuel in the reactor core of $3,263 million . (b) Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 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 three months ended March 31, 2018 and 2017 is as follows: Three Months Ended March 31, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 4,509 $ — $ — $ — $ — $ — $ (391 ) $ 4,118 Competitive businesses natural gas revenues 955 — — — — — (8 ) 947 Competitive businesses other revenues 48 — — — — — — 48 Rate-regulated electric revenues — 1,512 634 658 1,169 — (18 ) 3,955 Rate-regulated natural gas revenues — — 232 319 78 — (4 ) 625 Shared service and other revenues — — — — 4 451 (455 ) — Total operating revenues 5,512 1,512 866 977 1,251 451 (876 ) 9,693 2017 Competitive businesses electric revenues $ 3,710 $ — $ — $ — $ — $ — $ (328 ) $ 3,382 Competitive businesses natural gas revenues 918 — — — — — — 918 Competitive businesses other revenues 250 — — — — — — 250 Rate-regulated electric revenues — 1,298 590 667 1,097 — (8 ) 3,644 Rate-regulated natural gas revenues — — 206 284 66 — (3 ) 553 Shared service and other revenues — — — — 12 419 (431 ) — Total operating revenues 4,878 1,298 796 951 1,175 419 (770 ) 8,747 Shared service and other revenues Intersegment revenues (d) : 2018 $ 400 $ 14 $ 2 $ 6 $ 4 $ 450 $ (876 ) $ — 2017 328 5 1 5 12 419 (770 ) — Net income (loss): 2018 $ 186 $ 165 $ 113 $ 128 $ 65 $ (21 ) $ — $ 636 2017 399 141 127 125 140 39 — 971 Total assets: March 31, 2018 $ 48,375 $ 30,002 $ 10,218 $ 9,195 $ 21,375 $ 8,833 $ (10,980 ) $ 117,018 December 31, 2017 48,457 29,726 10,170 9,104 21,247 8,618 (10,552 ) 116,770 __________ (a) Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the three months ended March 31, 2018 include revenue from sales to PECO of $37 million , sales to BGE of $65 million , sales to Pepco of $52 million , sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation. For the three months ended March 31, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $45 million , sales to BGE of $134 million , sales to Pepco of $83 million , sales to DPL of $51 million and sales to ACE of $9 million in the Mid-Atlantic region, and sales to ComEd of $5 million in the Midwest region, which eliminate upon consolidation. (b) Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities. (c) Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017 . (d) Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income. PHI: Pepco DPL ACE Other (b) Intersegment PHI Operating revenues (a) : Three Months Ended March 31, 2018 Rate-regulated electric revenues $ 557 $ 306 $ 310 $ — $ (4 ) $ 1,169 Rate-regulated natural gas revenues — 78 — — — 78 Shared service and other revenues — — — 113 (109 ) 4 Total operating revenues 557 384 310 113 (113 ) 1,251 Three Months Ended March 31, 2017 Rate-regulated electric revenues $ 530 $ 296 $ 275 $ — $ (4 ) $ 1,097 Rate-regulated natural gas revenues — 66 — — — 66 Shared service and other revenues — — — 12 — 12 Total operating revenues 530 362 275 12 (4 ) 1,175 Intersegment revenues: Three Months Ended March 31, 2018 $ 2 $ 2 $ 1 $ 112 $ (113 ) $ 4 Three Months Ended March 31, 2017 1 2 1 13 (5 ) 12 Net income (loss): Three Months Ended March 31, 2018 $ 31 $ 31 $ 7 $ (8 ) $ 4 $ 65 Three Months Ended March 31, 2017 58 57 28 (15 ) 12 140 Total assets: March 31, 2018 $ 7,896 $ 4,383 $ 3,530 $ 10,514 $ (4,948 ) $ 21,375 December 31, 2017 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 on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017 . (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities
Analysis and reconciliation of reportable segment revenues for Generation	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 three months ended March 31, 2018 and 2017 . 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): Three Months Ended March 31, 2018 Revenues from external parties (a) Intersegment Revenues Total Revenues Contracts with customers Other (b) Total Mid-Atlantic $ 1,355 $ 80 $ 1,435 $ 5 $ 1,440 Midwest 1,273 71 1,344 2 1,346 New England 725 68 793 (1 ) 792 New York 439 (29 ) 410 (1 ) 409 ERCOT 149 59 208 1 209 Other Power Regions 210 109 319 (31 ) 288 Total Competitive Businesses Electric Revenues 4,151 358 4,509 (25 ) 4,484 Competitive Businesses Natural Gas Revenues 522 433 955 25 980 Competitive Businesses Other Revenues (c) 134 (86 ) 48 — 48 Total Generation Consolidated Operating Revenues $ 4,807 $ 705 $ 5,512 $ — $ 5,512 Three Months Ended March 31, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,494 $ (65 ) $ 1,429 $ (4 ) $ 1,425 Midwest 980 71 1,051 2 1,053 New England 589 (40 ) 549 (2 ) 547 New York 303 (3 ) 300 (3 ) 297 ERCOT 168 24 192 (1 ) 191 Other Power Regions 128 61 189 (5 ) 184 Total Competitive Businesses Electric Revenues 3,662 48 3,710 (13 ) 3,697 Competitive Businesses Natural Gas Revenues 768 150 918 12 930 Competitive Businesses Other Revenues (c) 206 44 250 1 251 Total Generation Consolidated Operating Revenues $ 4,636 $ 242 $ 4,878 $ — $ 4,878 __________ (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 $3 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the three months ended March 31, 2017 , unrealized mark-to-market losses of $98 million and gains of $44 million for the three months ended March 31, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 RNF from external customers (a) Intersegment RNF Total RNF RNF from external customers (a) Intersegment RNF Total RNF Mid-Atlantic $ 836 $ 14 $ 850 $ 755 $ 18 $ 773 Midwest 847 13 860 704 11 715 New England 122 (3 ) 119 115 (4 ) 111 New York 282 1 283 143 — 143 ERCOT 106 (70 ) 36 94 (25 ) 69 Other Power Regions 157 (40 ) 117 108 (44 ) 64 Total Revenues net of purchased power and fuel expense for Reportable Segments 2,350 (85 ) 2,265 1,919 (44 ) 1,875 Other (b) (131 ) 85 (46 ) 161 44 205 Total Generation Revenues net of purchased power and fuel expense $ 2,219 $ — $ 2,219 $ 2,080 $ — $ 2,080 __________ (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 $3 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended March 31, 2017 , unrealized mark-to-market losses of $266 million and $49 million for the three months ended March 31, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 7 - Early Nuclear Plant Retirements of the Combined Notes to Consolidated Financial Statements of $15 million decrease to revenue net of purchased power and fuel expense for the three months ended March 31, 2018 , and the elimination of intersegment revenue net of purchased power and fuel expense.
Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]	Electric and Gas Revenue by Customer Class (ComEd, PECO, BGE, PHI, PECO, DPL, ACE): Three Months Ended March 31, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 717 $ 403 $ 393 $ 610 $ 259 $ 191 $ 160 Small commercial & industrial 385 101 68 115 32 46 37 Large commercial & industrial 152 58 106 259 190 23 46 Public authorities & electric railroads 14 8 7 14 7 4 3 Other (a) 230 62 78 156 49 41 66 Total rate-regulated electric revenues (b) $ 1,498 $ 632 $ 652 $ 1,154 $ 537 $ 305 $ 312 Rate-regulated natural gas revenues Residential $ — $ 161 $ 224 $ 47 $ — $ 47 $ — Small commercial & industrial — 62 34 18 — 18 — Large commercial & industrial — 1 47 4 — 4 — Transportation — 6 — 5 — 5 — Other (c) — 2 27 4 — 4 — Total rate-regulated natural gas revenues (d) $ — $ 232 $ 332 $ 78 $ — $ 78 $ — Total rate-regulated revenues from contracts with customers $ 1,498 $ 864 $ 984 $ 1,232 $ 537 $ 383 $ 312 Other revenues Revenues from alternative revenue programs 5 (1 ) (13 ) 18 19 1 (2 ) Other rate-regulated electric revenues (e) 9 3 4 1 1 — — Other rate-regulated natural gas revenues (e) — — 2 — — — — Total other revenues 14 2 (7 ) 19 20 1 (2 ) Total rate-regulated revenues for reportable segments $ 1,512 $ 866 $ 977 $ 1,251 $ 557 $ 384 $ 310 Three Months Ended March 31, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 611 $ 382 $ 386 $ 554 $ 236 $ 176 $ 142 Small commercial & industrial 328 97 69 114 34 44 36 Large commercial & industrial 107 52 108 257 188 24 45 Public authorities & electric railroads 12 8 7 15 8 4 3 Other (a) 218 48 68 126 48 38 43 Total rate-regulated electric revenues (b) $ 1,276 $ 587 $ 638 $ 1,066 $ 514 $ 286 $ 269 Rate-regulated natural gas revenues Residential $ — $ 142 $ 185 $ 40 $ — $ 40 $ — Small commercial & industrial — 55 30 17 — 17 — Large commercial & industrial — — 44 2 — 2 — Transportation — 6 — 5 — 5 — Other (c) — 3 14 2 — 2 — Total rate-regulated natural gas revenues (d) $ — $ 206 $ 273 $ 66 $ — $ 66 $ — Total rate-regulated revenues from contracts with customers $ 1,276 $ 793 $ 911 $ 1,132 $ 514 $ 352 $ 269 Other revenues Revenues from alternative revenue programs 14 — 35 30 15 9 6 Other rate-regulated electric revenues (e) 8 3 4 2 1 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Other revenues (f) — — — 11 — — — Total other revenues 22 3 40 43 16 10 6 Total rate-regulated revenues for reportable segments $ 1,298 $ 796 $ 951 $ 1,175 $ 530 $ 362 $ 275 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $14 million , $2 million , $2 million , $4 million , $2 million , $2 million , and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2018 and $5 million , $1 million , $2 million , $1 million , $1 million , $2 million , and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2017. (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, for the three months ended March 31, 2018 and less than $1 million and $3 million at PECO and BGE, respectively, for the three months ended March 31, 2017 . (e) Includes late payment charge revenues.

Significant Accounting Polici47

Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		$ 5,113	$ 4,550
Regulated Operating Revenue		4,570	4,118
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs		10	79
Revenue from Related Parties	[1]	0	0
Revenues		9,693	8,747
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			4,560
Regulated Operating Revenue			4,197
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			8,757
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			(10)
Regulated Operating Revenue			(79)
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs			79
Revenue from Related Parties			0
Revenues			(10)
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		5,114	4,548
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs			0
Revenue from Related Parties		398	330
Revenues		5,512	4,878
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			4,558
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			330
Revenues			4,888
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			(10)
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs			0
Revenue from Related Parties			0
Revenues			(10)
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		1,493	1,279
Natural gas operating revenues			0
Revenues from alternative revenue programs		5	14
Revenue from Related Parties		14	5
Revenues		1,512	1,298
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
Regulated Operating Revenue			0
Electric operating revenues			1,293
Natural gas operating revenues			0
Revenue from Related Parties			5
Revenues			1,298
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
Regulated Operating Revenue			0
Electric operating revenues			(14)
Natural gas operating revenues			0
Revenues from alternative revenue programs			14
Revenue from Related Parties			0
Revenues			0
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		633	589
Natural gas operating revenues		232	206
Revenues from alternative revenue programs		(1)	0
Revenue from Related Parties		2	1
Revenues		866	796
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
Regulated Operating Revenue			0
Electric operating revenues			589
Natural gas operating revenues			206
Revenue from Related Parties			1
Revenues			796
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
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenues from alternative revenue programs			0
Revenue from Related Parties			0
Revenues			0
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		654	640
Natural gas operating revenues		330	271
Revenues from alternative revenue programs		(13)	35
Revenue from Related Parties		6	5
Revenues		977	951
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
Regulated Operating Revenue			0
Electric operating revenues			665
Natural gas operating revenues			281
Revenue from Related Parties			5
Revenues			951
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
Regulated Operating Revenue			0
Electric operating revenues			(25)
Natural gas operating revenues			(10)
Revenues from alternative revenue programs			35
Revenue from Related Parties			0
Revenues			0
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		1,151	1,067
Natural gas operating revenues		78	66
Revenues from alternative revenue programs		18	30
Revenue from Related Parties		4	12
Revenues		1,251	1,175
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 operating revenues			1,097
Natural gas operating revenues			66
Revenue from Related Parties			12
Revenues			1,175
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 operating revenues			(30)
Natural gas operating revenues			0
Revenues from alternative revenue programs			30
Revenue from Related Parties			0
Revenues			0
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		536	514
Natural gas operating revenues			0
Revenues from alternative revenue programs		19	15
Revenue from Related Parties		2	1
Revenues		557	530
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
Regulated Operating Revenue			0
Electric operating revenues			529
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			530
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
Regulated Operating Revenue			0
Electric operating revenues			(15)
Natural gas operating revenues			0
Revenues from alternative revenue programs			15
Revenue from Related Parties			0
Revenues			0
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		303	285
Natural gas operating revenues		78	66
Revenues from alternative revenue programs		1	9
Revenue from Related Parties		2	2
Revenues		384	362
Delmarva Power and 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
Regulated Operating Revenue			0
Electric operating revenues			294
Natural gas operating revenues			66
Revenue from Related Parties			2
Revenues			362
Delmarva Power and 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
Regulated Operating Revenue			0
Electric operating revenues			(9)
Natural gas operating revenues			0
Revenues from alternative revenue programs			9
Revenue from Related Parties			0
Revenues			0
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Electric operating revenues		311	268
Natural gas operating revenues			0
Revenues from alternative revenue programs		(2)	6
Revenue from Related Parties		1	1
Revenues		$ 310	275
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
Regulated Operating Revenue			0
Electric operating revenues			274
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			275
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
Regulated Operating Revenue			0
Electric operating revenues			(6)
Natural gas operating revenues			0
Revenues from alternative revenue programs			6
Revenue from Related Parties			0
Revenues			$ 0
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

Significant Accounting Polici48

Significant Accounting Policies Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	$ 1,502	$ 1,074
Quantifying Misstatement in Current Year Financial Statements, Amount		(127)
Net Cash Provided by (Used in) Investing Activities	(1,857)	(2,283)
Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		1,074
Net Cash Provided by (Used in) Investing Activities		2,283
Exelon Generation Co L L C [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	855	420
Quantifying Misstatement in Current Year Financial Statements, Amount		(320)
Net Cash Provided by (Used in) Investing Activities	(615)	(910)
Exelon Generation Co L L C [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		420
Net Cash Provided by (Used in) Investing Activities		910
Commonwealth Edison Co [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	134	236
Quantifying Misstatement in Current Year Financial Statements, Amount		91
Net Cash Provided by (Used in) Investing Activities	(523)	(619)
Commonwealth Edison Co [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		236
Net Cash Provided by (Used in) Investing Activities		619
PECO Energy Co [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	19	106
Quantifying Misstatement in Current Year Financial Statements, Amount		42
Net Cash Provided by (Used in) Investing Activities	(215)	(69)
PECO Energy Co [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		106
Net Cash Provided by (Used in) Investing Activities		69
Baltimore Gas and Electric Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities	313	208
Quantifying Misstatement in Current Year Financial Statements, Amount		40
Net Cash Provided by (Used in) Investing Activities	$ (223)	(202)
Baltimore Gas and Electric Company [Member] | Scenario, Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by (Used in) Operating Activities		208
Net Cash Provided by (Used in) Investing Activities		$ 202

New Accounting Standards Revenu

New Accounting Standards Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		$ 5,113	$ 4,550
Regulated Operating Revenue		4,570	4,118
Revenues from alternative revenue programs		10	79
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties	[1]	0	0
Revenues		9,693	8,747
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			(10)
Regulated Operating Revenue			(79)
Revenues from alternative revenue programs			79
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			(10)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			4,560
Regulated Operating Revenue			4,197
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			8,757
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue		5,114	4,548
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties		398	330
Revenues		5,512	4,878
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			(10)
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			(10)
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			4,558
Regulated Operating Revenue			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			330
Revenues			4,888
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		5	14
Electric operating revenues		1,493	1,279
Natural gas operating revenues			0
Revenue from Related Parties		14	5
Revenues		1,512	1,298
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			14
Electric operating revenues			(14)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			1,293
Natural gas operating revenues			0
Revenue from Related Parties			5
Revenues			1,298
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(1)	0
Electric operating revenues		633	589
Natural gas operating revenues		232	206
Revenue from Related Parties		2	1
Revenues		866	796
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			0
Electric operating revenues			0
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			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
Regulated Operating Revenue			0
Electric operating revenues			589
Natural gas operating revenues			206
Revenue from Related Parties			1
Revenues			796
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(13)	35
Electric operating revenues		654	640
Natural gas operating revenues		330	271
Revenue from Related Parties		6	5
Revenues		977	951
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			35
Electric operating revenues			(25)
Natural gas operating revenues			(10)
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			665
Natural gas operating revenues			281
Revenue from Related Parties			5
Revenues			951
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		18	30
Electric operating revenues		1,151	1,067
Natural gas operating revenues		78	66
Revenue from Related Parties		4	12
Revenues		1,251	1,175
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
Revenues from alternative revenue programs			30
Electric operating revenues			(30)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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 operating revenues			1,097
Natural gas operating revenues			66
Revenue from Related Parties			12
Revenues			1,175
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		19	15
Electric operating revenues		536	514
Natural gas operating revenues			0
Revenue from Related Parties		2	1
Revenues		557	530
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			15
Electric operating revenues			(15)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			529
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			530
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		1	9
Electric operating revenues		303	285
Natural gas operating revenues		78	66
Revenue from Related Parties		2	2
Revenues		384	362
Delmarva Power and 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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			9
Electric operating revenues			(9)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
Delmarva Power and 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
Regulated Operating Revenue			0
Electric operating revenues			294
Natural gas operating revenues			66
Revenue from Related Parties			2
Revenues			362
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Electrical Generation Revenue			0
Regulated Operating Revenue			0
Revenues from alternative revenue programs		(2)	6
Electric operating revenues		311	268
Natural gas operating revenues			0
Revenue from Related Parties		1	1
Revenues		$ 310	275
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
Regulated Operating Revenue			0
Revenues from alternative revenue programs			6
Electric operating revenues			(6)
Natural gas operating revenues			0
Revenue from Related Parties			0
Revenues			0
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
Regulated Operating Revenue			0
Electric operating revenues			274
Natural gas operating revenues			0
Revenue from Related Parties			1
Revenues			$ 275
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details) $ in Millions		3 Months Ended
		Mar. 31, 2018USD ($)VIE	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)VIE	Apr. 01, 2014USD ($)
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
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 58
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]	618		$ 618
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		9
Payment Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted					$ 245
Financial Guarantee [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted					165
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		$ 30
Related Party Purchase Of Nuclear Output By Third Party Percentage		50.01%
Other Nonconsolidated Variable Interest Entity Ownership Interests		$ 9
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Receivables from affiliates		337			$ 400
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Equity Method Investment Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Current Carrying Value		637
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		16
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		$ 8	$ 19
[1]	These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.

Variable Interest Entities - Ca

Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 823	$ 662
Noncurrent assets	[1]	9,279	9,317
Total assets	[1]	10,102	9,979
Current liabilities	[1]	269	308
Noncurrent liabilities	[1]	3,292	3,316
Total liabilities	[1]	3,561	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		812	652
Noncurrent assets		9,251	9,286
Total assets		10,063	9,938
Current liabilities		236	272
Noncurrent liabilities		3,230	3,250
Total liabilities		3,466	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	11	10
Noncurrent assets	[1]	28	31
Total assets	[1]	39	41
Current liabilities	[1]	33	36
Noncurrent liabilities	[1]	62	66
Total liabilities	[1]	95	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		7	6
Noncurrent assets		20	23
Total assets		27	29
Current liabilities		29	32
Noncurrent liabilities		54	58
Total liabilities		$ 83	$ 90
[1]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.

Variable Interest Entities - As

Variable Interest Entities - Assets and Liabilities of VIES which Creditors or Beneficiaries have no Recourse (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 787	$ 898	$ 609	$ 635
Restricted cash		209	207	254	253
Accounts receivable, net
Customer		4,190	4,445
Other		1,103	1,132
Mark-to-market derivatives assets		978	976
Inventory
Materials and supplies		1,291	1,311
Other current assets		1,495	1,260
Total current assets		11,533	11,896
Property, plant and equipment, net		74,711	74,202
Nuclear decommissioning trust funds		13,149	13,272
Goodwill		6,677	6,677
Mark-to-market derivative assets		527	337
Other noncurrent assets		1,333	1,330
Total assets	[1]	117,018	116,770
Long-term debt due within one year		1,203	2,088
Accounts payable		3,207	3,532
Accrued expenses		1,569	1,837
Mark-to-market derivative liabilities		415	232
Unamortized energy contract liabilities		202	231
Other		956	982
Total current liabilities		10,153	10,798
Long-term debt		32,905	32,176
Asset retirement obligations		10,126	10,029
Pension obligation		3,433	3,736
Unamortized energy contract liabilities		579	609
Other noncurrent liabilities		2,067	2,097
Total liabilities	[1]	84,453	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	280	126
Restricted cash	[2]	73	64
Accounts receivable, net
Customer	[2]	154	170
Other	[2]	29	25
Inventory
Materials and supplies	[2]	202	205
Other current assets	[2]	55	45
Total current assets	[2]	793	635
Property, plant and equipment, net	[2]	6,181	6,186
Nuclear decommissioning trust funds	[2]	2,483	2,502
Other noncurrent assets	[2]	270	274
Total noncurrent assets	[2]	8,934	8,962
Total assets	[2]	9,727	9,597
Long-term debt due within one year	[2]	102	102
Accounts payable	[2]	93	114
Accrued expenses	[2]	52	67
Unamortized energy contract liabilities	[2]	17	18
Other	[2]	5	7
Total current liabilities	[2]	269	308
Long-term debt	[2]	1,125	1,154
Asset retirement obligations	[2]	2,062	2,035
Unamortized energy contract liabilities	[2]	1	5
Other noncurrent liabilities	[2]	99	116
Total noncurrent liabilities	[2]	3,287	3,310
Total liabilities	[2]	3,556	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		610	416	400	290
Restricted cash		127	138	140	158
Accounts receivable, net
Customer		2,478	2,697
Other		294	321
Mark-to-market derivatives assets		978	976
Inventory
Materials and supplies		916	937
Other current assets		1,122	933
Total current assets		6,884	6,882
Property, plant and equipment, net		24,714	24,906
Nuclear decommissioning trust funds		13,149	13,272
Goodwill		47	47
Mark-to-market derivative assets		527	334
Other noncurrent assets		657	670
Total assets	[3]	48,375	48,457
Long-term debt due within one year		373	346
Accounts payable		1,447	1,773
Accrued expenses		951	1,022
Mark-to-market derivative liabilities		391	211
Unamortized energy contract liabilities		39	43
Other		288	265
Total current liabilities		4,156	4,191
Long-term debt		7,685	7,734
Asset retirement obligations		9,941	9,844
Unamortized energy contract liabilities		40	48
Other noncurrent liabilities		686	658
Total liabilities	[3]	32,417	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		280	126
Restricted cash		66	58
Accounts receivable, net
Customer		154	170
Other		29	25
Inventory
Materials and supplies		202	205
Other current assets		51	41
Total current assets		782	625
Property, plant and equipment, net		6,181	6,186
Nuclear decommissioning trust funds		2,483	2,502
Other noncurrent assets		242	243
Total noncurrent assets		8,906	8,931
Total assets		9,688	9,556
Long-term debt due within one year		70	67
Accounts payable		93	114
Accrued expenses		51	66
Unamortized energy contract liabilities		17	18
Other		5	7
Total current liabilities		236	272
Long-term debt		1,063	1,088
Asset retirement obligations		2,062	2,035
Unamortized energy contract liabilities		1	5
Other noncurrent liabilities		99	116
Total noncurrent liabilities		3,225	3,244
Total liabilities		3,461	3,516
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		22	17	11	23
Restricted cash		2	1	43	24
Accounts receivable, net
Customer		394	375
Other		91	94
Inventory
Materials and supplies		45	40
Other current assets		5	3
Total current assets		755	811
Property, plant and equipment, net		7,725	7,602
Other noncurrent assets		6	4
Total assets		9,195	9,104
Accounts payable		253	265
Accrued expenses		162	164
Other		26	24
Total current liabilities		757	760
Long-term debt		2,578	2,577
Asset retirement obligations		22	23
Other noncurrent liabilities		53	56
Total liabilities		5,978	5,963
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		43	30	109	170
Restricted cash		40	42	41	43
Accounts receivable, net
Customer		484	486
Other		210	206
Inventory
Materials and supplies		152	151
Other current assets		55	75
Total current assets		1,493	1,551
Property, plant and equipment, net		12,688	12,498
Goodwill		4,005	4,005
Other noncurrent assets		69	70
Total assets	[4]	21,375	21,247
Long-term debt due within one year		385	396
Accounts payable		469	348
Accrued expenses		246	261
Unamortized energy contract liabilities		162	188
Other		52	81
Total current liabilities		2,067	1,931
Long-term debt		5,464	5,478
Asset retirement obligations		16	16
Unamortized energy contract liabilities		539	561
Other noncurrent liabilities		377	389
Total liabilities	[4]	12,556	12,422
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]	7	6
Accounts receivable, net
Customer	[2]	0	0
Other	[2]	0	0
Inventory
Materials and supplies	[2]	0	0
Other current assets	[2]	4	4
Total current assets	[2]	11	10
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Other noncurrent assets	[2]	28	31
Total noncurrent assets	[2]	28	31
Total assets	[2]	39	41
Long-term debt due within one year	[2]	32	35
Accounts payable	[2]	0	0
Accrued expenses	[2]	1	1
Unamortized energy contract liabilities	[2]	0	0
Other	[2]	0	0
Total current liabilities	[2]	33	36
Long-term debt	[2]	62	66
Asset retirement obligations	[2]	0	0
Unamortized energy contract liabilities	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	62	66
Total liabilities	[2]	95	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		10	2	54	101
Restricted cash		7	6	$ 7	$ 9
Accounts receivable, net
Customer		97	92
Other		51	56
Inventory
Other current assets		4	2
Total current assets		263	258
Property, plant and equipment, net		2,767	2,706
Other noncurrent assets		43	45
Total assets	[5]	3,530	3,445
Long-term debt due within one year		278	281
Accounts payable		166	118
Accrued expenses		41	33
Other		7	8
Total current liabilities		703	619
Long-term debt		836	840
Other noncurrent liabilities		24	25
Total liabilities	[5]	2,489	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		7	6
Accounts receivable, net
Customer		0	0
Other		0	0
Inventory
Materials and supplies		0	0
Other current assets		0	0
Total current assets		7	6
Property, plant and equipment, net		0	0
Nuclear decommissioning trust funds		0	0
Other noncurrent assets		20	23
Total noncurrent assets		20	23
Total assets		27	29
Long-term debt due within one year		28	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		29	32
Long-term debt		54	58
Asset retirement obligations		0	0
Unamortized energy contract liabilities		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		54	58
Total liabilities		$ 83	$ 90
[1]	Exelon’s consolidated assets include $9,727 million and $9,597 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,556 million and $3,618 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[3]	Generation’s consolidated assets include $9,688 million and $9,556 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,461 million and $3,516 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities.
[4]	PHI’s consolidated total assets include $39 million and $41 million at March 31, 2018 and December 31, 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 $95 million and $102 million at March 31, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 — Variable Interest Entities.
[5]	ACE’s consolidated total assets include $27 million and $29 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE that can only be used to settle the liabilities of the VIE. ACE’s consolidated total liabilities include $83 million and $90 million at March 31, 2018 and December 31, 2017, respectively, of ACE's consolidated VIE for which the VIE creditors do not have recourse to ACE. See Note 3 — Variable Interest Entities.

Variable Interest Entities - Su

Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,127	$ 1,134
Total liabilities	[1]	262	265
Exelon's ownership interest in VIE	[1]	246	251
Other ownership interests in VIE	[1]	618	618
Registrants' maximum exposure to loss		9
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		246	251
Contract intangible asset
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		8	8
Net assets pledged for Zion Station decommissioning(b)
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss	[2]	2	2
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	626	625
Total liabilities	[1]	37	37
Exelon's ownership interest in VIE	[1]	0	0
Other ownership interests in VIE	[1]	588	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		8	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	[2]	2	2
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	501	509
Total liabilities	[1]	225	228
Exelon's ownership interest in VIE	[1]	246	251
Other ownership interests in VIE	[1]	30	30
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		246	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	[2]	0	0
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Other ownership interests in VIE		9
Held-to-maturity Securities Pledged as Collateral	[3]	30	39
Accounts Payable, Interest-bearing, Noncurrent	[4],[5]	$ 28	$ 37
[1]	These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon’s or Generation’s Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.
[2]	These items represent amounts on Exelon’s and Generation’s Consolidated Balance Sheets related to the asset sale agreement with ZionSolutions, LLC. The net assets pledged for Zion Station decommissioning includes gross pledged assets of $30 million and $39 million as of March 31, 2018 and December 31, 2017, respectively; offset by payables to ZionSolutions, LLC of $28 million and $37 million as of March 31, 2018 and December 31, 2017, respectively. These items are included to provide information regarding the relative size of the ZionSolutions, LLC unconsolidated VIE. See Note 13 — Nuclear Decommissioning for additional details.
[3]	Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets.
[4]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.
[5]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.

Mergers, Acquisitions, and Di54

Mergers, Acquisitions, and Dispositions - Narrative (Details) - USD ($) $ in Millions	Apr. 04, 2018	Feb. 28, 2018	Mar. 31, 2017	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross				$ 0		$ 212
Bargain Purchase Gain				0		226
Fitzpatrick [Member]
Business Acquisition [Line Items]
Bargain Purchase Gain					$ 7	226	$ 233
Business Combination, Integration Related Costs						32
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 87		0		212
Bargain Purchase Gain				$ 0		226
Exelon Generation Co L L C [Member] | Subsequent Event [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
Business Combination, Consideration Transferred, Other			179
Bargain Purchase Gain					$ 7	226	233
Business Combination, Integration Related Costs						$ 32
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred			$ 110				110
Business Combination, Consideration Transferred, Other							$ 125

Mergers, Acquisitions, and Di55

Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions		Mar. 31, 2017	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Bargain Purchase Gain			$ 0		$ 226
Fitzpatrick [Member]
Business Acquisition [Line Items]
Bargain Purchase Gain				$ 7	226	$ 233
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Bargain Purchase Gain			$ 0		226
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 289				289
Business Combination, Consideration Transferred, Other		179
Current assets						60
Property, plant and equipment						298
Nuclear decommissioning trust funds						807
Other assets	[1]					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				$ 7	$ 226	233
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets						110
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 110				110
Business Combination, Consideration Transferred, Other						125
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Nuclear Fuel [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred, Other						$ 54
[1]	Includes a $110 million asset associated with a contractual right to reimbursement from the New York Power Authority (NYPA), a prior owner of FitzPatrick, associated with the DOE one-time fee obligation. See Note 23-Commitments and Contingencies of the Exelon 2017 Form 10-K for additional background regarding SNF obligations to the DOE.

Revenue from Contracts with C56

Revenue from Contracts with Customers Contract Assets and Liabilites (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net, Current	$ 302		$ 283
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	28
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	(216)
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	227
Contract with Customer, Liability, Current	46		35
Contract with Customer, Asset, Reclassified to Receivable	(9)
Capitalized Contract Cost, Net [Abstract]
Capitalized Contract Cost, Gross	25		$ 26
Capitalized Contract Cost, Amortization	$ 5	$ 9

Revenue from Contracts with C57

Revenue from Contracts with Customers Revenue Remaining Performance Obligation (Details) $ in Millions	Mar. 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	$ 544
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	264
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	104
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	46
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	128
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	1,086
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	544
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	264
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	104
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	46
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	128
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	$ 1,086

Regulatory Matters - Narrative

Regulatory Matters - Narrative (Details) - USD ($) $ in Millions	Apr. 20, 2018	Apr. 17, 2018	Mar. 29, 2018	Mar. 26, 2018	Mar. 17, 2018	Mar. 08, 2018	Mar. 02, 2018	Feb. 09, 2018	Feb. 06, 2018	Feb. 05, 2018	Jan. 31, 2018	Jan. 18, 2018	Jan. 02, 2018	Dec. 19, 2017	Dec. 18, 2017	Nov. 16, 2017	Nov. 07, 2017	Oct. 18, 2017	Aug. 17, 2017	Jul. 14, 2017	May 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2022	Dec. 31, 2017	Apr. 21, 2016
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						$ 9,308				$ 9,288
Regulatory Liabilities																						10,246				10,388
Revenues																						9,693	$ 8,747
Payments to Acquire Property, Plant, and Equipment																						1,880	2,009
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						82
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																						5,512	4,878
Payments to Acquire Property, Plant, and Equipment																						628	625
License Costs																						32
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											$ 3
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation																											$ 7
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						1,351				1,279
Regulatory Liabilities																						6,424				6,577
Tax Savings From Tax Cuts and Jobs Act												$ 201
Revenues																						1,512	1,298
Payments to Acquire Property, Plant, and Equipment																						531	626
Commonwealth Edison Co [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						41
Commonwealth Edison Co [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																								$ 23
Public Utilities, Requested Increase (Decrease), Amount																								58
Public Utilities, Approved Rate Increase (Decrease), Amount																								$ 35
Public Utilities, Requested Equity Capital Structure, Percentage																								6.52%
Public Utilities, Requested Rate Increase (Decrease), Percentage																								8.69%
Public Utilities, Approved Equity Capital Structure, Percentage																								6.52%
Public Utilities, Approved Rate Increase (Decrease), Percentage																								8.69%
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						486				410
Regulatory Liabilities																						646				690
Tax Savings From Tax Cuts and Jobs Act			$ 71
Revenues																						866	796
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																					$ 22
Public Utilities, Requested Equity Capital Structure, Percentage																					11.00%
Payments to Acquire Property, Plant, and Equipment																						217	201
PECO Energy Co [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											$ 4
PECO Energy Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											68
Public Utilities, Requested Increase (Decrease), Amount			$ 82
Public Utilities, Requested Equity Capital Structure, Percentage			10.95%
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						540				571
Regulatory Liabilities																						1,185				1,163
Tax Savings From Tax Cuts and Jobs Act											103
Revenues																						977	951
Payments to Acquire Property, Plant, and Equipment																						224	206
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act											31
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
Baltimore Gas and Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						22
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						2,960				3,047
Regulatory Liabilities																						1,965				1,928
Revenues																						1,251	1,175
Payments to Acquire Property, Plant, and Equipment																						258	320
Pepco Holdings LLC [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						19
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						863				891
Regulatory Liabilities																						845				832
Revenues																						557	530
Payments to Acquire Property, Plant, and Equipment																						127	139
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 39
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 3
Public Utilities, Requested Increase (Decrease), Amount										$ 11			$ 41	$ 66
Public Utilities, Requested Return on Equity, Percentage														10.10%
Public Utilities, Requested Rate Increase (Decrease), Percentage													10.10%
Potomac Electric Power Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						9
Potomac Electric Power Company [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act Through Effective Date		$ 19
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 15	$ 24
Public Utilities, Requested Return on Equity, Percentage		9.50%
Public Utilities, Requested Rate Increase (Decrease), Percentage	9.50%
Public Utilities, Rate Credit	$ 10
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						305				314
Regulatory Liabilities																						646				635
Tax Savings From Tax Cuts and Jobs Act								$ 26
Revenues																						384	362
Public Utilities, Requested Return on Equity, Percentage																			10.10%
Public Utilities, Interim Rate Increase (Decrease), Amount																		$ 2.5
Payments to Acquire Property, Plant, and Equipment																						65	82
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								7
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																	$ 11
Public Utilities, Requested Increase (Decrease), Amount																			$ 13
Public Utilities, Interim Rate Increase (Decrease), Amount					$ 1
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								19
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																$ 19		$ 31
Public Utilities, Requested Increase (Decrease), Amount																			$ 24	$ 27
Public Utilities, Approved Rate Increase (Decrease), Amount															$ 13
Public Utilities, Requested Return on Equity, Percentage																				10.10%
Public Utilities, Approved Return on Equity, Percentage															9.50%
Public Utilities, Interim Rate Increase (Decrease), Amount					$ 3
Delmarva Power and Light Company [Member] | Electric Distribution [Member] | Maryland Service Territory [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act								$ 13		31												14
Public Utilities, Rate Credit																						2
Delmarva Power and Light Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						7
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																						441				430
Regulatory Liabilities																						437				422
Tax Savings From Tax Cuts and Jobs Act							$ 23
Revenues																						310	275
Payments to Acquire Property, Plant, and Equipment																						63	$ 88
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount				$ 13						$ 19
Atlantic City Electric Company [Member] | Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																						3
Atlantic City Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Payments to Acquire Property, Plant, and Equipment																									$ 338
Zero Emission Standard [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						8				112
Zero Emission Standard [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																						202
Other Revenue, Net																						150
Zero Emission Standard [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						8				112
Zero Emission Standard [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0				0
Zero Emission Standard [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0				0
Zero Emission Standard [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0				0
Zero Emission Standard [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0				0
Zero Emission Standard [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						0				0
Zero Emission Standard [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																						$ 0				$ 0

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory Assets		$ 9,308	$ 9,288
Current		1,245	1,267
Regulatory Assets, Noncurrent		8,063	8,021
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	3,844	3,848
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		336	306
Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	621	640
Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	256	244
Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		220	166
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		108	116
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		745	758
Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		701	750
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		111	109
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		284	295
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		69	61
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		268	258
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8],[9]	117	82
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		46	27
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		559	596
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[10],[11],[12]	46	45
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[13]	44	55
COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33	35
Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		27	19
Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71	79
CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12	8
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		535	529
DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		187	190
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		63	67
Under funded Benefit Post Retirement Obligation [Member] | Constellation Energy Group LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		427	440
Under funded Benefit Post Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		934	953
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,351	1,279
Current		226	225
Regulatory Assets, Noncurrent		1,125	1,054
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		151	155
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	256	244
Commonwealth Edison Co [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		220	166
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36	37
Commonwealth Edison Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		75	73
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		263	273
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		69	61
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		267	256
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[6]	8	6
Commonwealth Edison Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Commonwealth Edison Co [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6	8
Commonwealth Edison Co [Member] | Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		195	186
Commonwealth Edison Co [Member] | Recoverable Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		61	58
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		486	410
Current		78	29
Regulatory Assets, Noncurrent		408	381
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		327	297
PECO Energy Co [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33	36
PECO Energy Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	1
PECO Energy Co [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		22	22
PECO Energy Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		21	22
PECO Energy Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[8]	43	1
PECO Energy Co [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	1
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14	6
PECO Energy Co [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12	8
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
PECO Energy Co [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12	16
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		540	571
Current		149	174
Regulatory Assets, Noncurrent		391	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] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	208	214
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11	11
Baltimore Gas and Electric Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14	14
Baltimore Gas and Electric Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[5]	21	23
Baltimore Gas and Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		269	285
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	6
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[13]	6	14
Baltimore Gas and Electric Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Baltimore Gas and Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6	4
Baltimore Gas and Electric Company [Member] | Unamortized AMI Expenses [Member]
Regulatory Assets [Line Items]
Regulatory Assets		125	129
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]
Regulatory Assets [Line Items]
Regulatory Assets		51	53
Baltimore Gas and Electric Company [Member] | Recoverable Smart Meter Related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		32	32
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		13	7
Baltimore Gas and Electric Company [Member] | Abandonment costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3	3
Baltimore Gas and Electric Company [Member] | Under-Recovered Natural Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets			8
Baltimore Gas and Electric Company [Member] | Under-Recovered Electric Revenue Decoupling [Member]
Regulatory Assets [Line Items]
Regulatory Assets		6	10
Baltimore Gas and Electric Company [Member] | UnderRecoveredNaturalGasDecouplingRevenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11	4
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,960	3,047
Current		507	554
Regulatory Assets, Noncurrent		2,453	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] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	9
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		229	235
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71	73
Pepco Holdings LLC [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		607	619
Pepco Holdings LLC [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		701	750
Pepco Holdings LLC [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	2
Pepco Holdings LLC [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[7],[9]	45	52
Pepco Holdings LLC [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		46	27
Pepco Holdings LLC [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		289	310
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[10],[11],[12]	41	39
Pepco Holdings LLC [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		38	41
Pepco Holdings LLC [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Pepco Holdings LLC [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33	35
Pepco Holdings LLC [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		13	13
Pepco Holdings LLC [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71	79
Pepco Holdings LLC [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Pepco Holdings LLC [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		535	529
Pepco Holdings LLC [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		187	190
Pepco Holdings LLC [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		39	39
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		863	891
Current		207	213
Regulatory Assets, Noncurrent		656	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] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	9
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		154	158
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		15	15
Potomac Electric Power Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
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] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9]	7	11
Potomac Electric Power Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12	7
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		212	229
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[11]	20	20
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		38	38
Potomac Electric Power Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33	35
Potomac Electric Power Company [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Potomac Electric Power Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		150	150
Potomac Electric Power Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		187	190
Potomac Electric Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		26	29
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3	8
Potomac Electric Power Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4	3
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11	11
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInDCServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	9
Delmarva Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		305	314
Current		63	69
Regulatory Assets, Noncurrent		242	245
Delmarva Power and Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		75	77
Delmarva Power and Light Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7	8
Delmarva Power and Light Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	1
Delmarva Power and Light Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[7]	14	15
Delmarva Power and Light Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Delmarva Power and Light Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		77	81
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	11	10
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	3
Delmarva Power and Light Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Delmarva Power and Light Company [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		8	8
Delmarva Power and Light Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		94	93
Delmarva Power and Light Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Delmarva Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9	8
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3	7
Delmarva Power and Light Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11	8
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4	4
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets			5
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritoryElectric [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritoryGas [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2
Delmarva Power and Light Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandAndDelawareServiceTerritories [Member]
Regulatory Assets [Line Items]
Regulatory Assets			1
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		441	430
Current		64	71
Regulatory Assets, Noncurrent		377	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] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Atlantic City Electric Company [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1	1
Atlantic City Electric Company [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4]	24	26
Atlantic City Electric Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		29	15
Atlantic City Electric Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[10]	10	9
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		5	5
Atlantic City Electric Company [Member] | Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71	79
Atlantic City Electric Company [Member] | CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		292	286
Atlantic City Electric Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		0	0
Atlantic City Electric Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		4	4
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		15	15
Atlantic City Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 9	$ 11
[1]	Includes regulatory regulatory assets established at the Constellation and PHI merger dates of $427 million and $934 million, respectively, as of March 31, 2018 and $440 million and $953 million, respectively, as of December 31, 2017 related to the rate regulated portions of the deferred costs associated with legacy Constellation’s and PHI’s pension and other postretirement benefit plans that are being amortized and recovered over approximately 12 years and 3 to 15 years, respectively (as established at the respective acquisition dates). The Utility Registrants are not earning or paying a return on these amounts.
[2]	As of March 31, 2018, BGE's regulatory asset of $208 million includes $125 million of unamortized incremental deployment costs under the program, $51 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016. As of December 31, 2017, BGE's regulatory asset of $214 million includes $129 million of unamortized incremental deployment costs under the program, $53 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $32 million related to post-test year incremental program deployment costs incurred prior to approval became effective June 2016.
[3]	As of March 31, 2018, ComEd’s regulatory asset of $256 million was comprised of $195 million for the 2016, 2017 and 2018 annual reconciliations and $61 million related to significant one-time events. As of December 31, 2017, ComEd’s regulatory asset of $244 million was comprised of $186 million for the 2016 and 2017 annual reconciliations and $58 million related to significant one-time events.
[4]	As of March 31, 2018, ACE's regulatory asset of $24 million included $9 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of March 31, 2018, ACE's regulatory liability of $12 million related to over-recovered electric energy costs. As of December 31, 2017, ACE's regulatory asset of $26 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of December 31, 2017, ACE's regulatory liability of $3 million related to over-recovered electric energy costs.
[5]	As of March 31, 2018, BGE's regulatory asset of $21 million included $13 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of March 31, 2018, BGE's regulatory liability of $22 million related to over-recovered natural gas costs. As of December 31, 2017, BGE’s regulatory asset of $23 million included $7 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval and $8 million of under-recovered natural gas costs.
[6]	As of March 31, 2018, ComEd’s regulatory asset of $8 million represents transmission costs recoverable through its FERC approved formula rate. As of March 31, 2018, ComEd’s regulatory liability of $53 million included $21 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2017, ComEd’s regulatory asset of $6 million represents transmission costs recoverable through its FERC approved formula rate. As of December 31, 2017, ComEd’s regulatory liability of $47 million included $14 million related to over-recovered energy costs and $33 million associated with revenues received for renewable energy requirements.
[7]	As of March 31, 2018, DPL's regulatory asset of $14 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018, DPL's regulatory liability of $6 million related to over-recovered electric energy and gas fuel costs. As of December 31, 2017, DPL's regulatory asset of $15 million included $8 million of transmission costs recoverable through its FERC approved formula rate and $7 million related to under-recovered electric energy costs. As of December 31, 2017, DPL's regulatory liability of $1 million related to over-recovered electric energy costs.
[8]	As of March 31, 2018, PECO's regulatory liability of $56 million included $44 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $9 million related to over-recovered non-bypassable transmission service charges. As of December 31, 2017, PECO's regulatory liability of $60 million included $36 million related to over-recovered costs under the DSP program, $12 million related to over-recovered non-bypassable transmission service charges and $12 million related to the over-recovered natural gas costs under the PGC.
[9]	As of March 31, 2018, Pepco's regulatory asset of $7 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018, Pepco's regulatory liability of $4 million related to over-recovered electric energy costs. As of December 31, 2017, Pepco's regulatory asset of $11 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $8 million of under-recovered electric energy costs.
[10]	As of March 31, 2018 and December 31, 2017, ACE’s regulatory asset of $10 million and $9 million, respectively, represents previously incurred PHI integration costs expected to be recovered in the New Jersey service territory.
[11]	As of March 31, 2018 and December 31, 2017, Pepco’s regulatory asset of $20 million represents previously incurred PHI integration costs, including $11 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory.
[12]	As of March 31, 2018, DPL’s regulatory asset of $11 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates and $2 million authorized for recovery in Delaware gas rates.
[13]	Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of March 31, 2018, BGE had a regulatory asset of $6 million related to under-recovered electric revenue decoupling and a regulatory liability of $11 million related to over-recovered natural gas revenue decoupling. As of December 31, 2017, BGE had a regulatory asset of $10 million related to under-recovered electric revenue decoupling and $4 million related to under-recovered natural gas revenue decoupling.

Regulatory Matters Regulatory60

Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 10,246		$ 10,388
Regulatory Liability, Current		522		523
Regulatory Liability, Noncurrent		9,724		9,865
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		26		30
Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	5,189		5,241
Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2,969		3,064
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,570		1,573
Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		35		36
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		16		23
Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		7		7
Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		27		35
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		8		9
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2],[4],[5],[6]	153	[3],[7]	111
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	14
Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		81		63
Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		8		112
Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4		2
Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[9]	1
TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	54
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		84		82
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		6,424		6,577
Regulatory Liability, Current		212		249
Regulatory Liability, Noncurrent		6,212		6,328
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	2,458		2,479
Commonwealth Edison Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2,464		2,528
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,348		1,338
Commonwealth Edison Co [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4		4
Commonwealth Edison Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[4]	53		47
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Commonwealth Edison Co [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		81		63
Commonwealth Edison Co [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		8		112
Commonwealth Edison Co [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Commonwealth Edison Co [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Commonwealth Edison Co [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	0
Commonwealth Edison Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		8		6
Commonwealth Edison Co [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		479		484
Commonwealth Edison Co [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		21		14
Commonwealth Edison Co [Member] | Renewable energy Requirements [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		32		33
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		646		690
Regulatory Liability, Current		117		141
Regulatory Liability, Noncurrent		529		549
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		505		536
PECO Energy Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		11		19
PECO Energy Co [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		7		7
PECO Energy Co [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		27		35
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		8		9
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[6]	56		60
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PECO Energy Co [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
PECO Energy Co [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	10
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		22		24
PECO Energy Co [Member] | Default Service Provider Program [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		44		36
PECO Energy Co [Member] | Over-Recovered Natural Gas Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3		12
PECO Energy Co [Member] | Over Recovered NonBypassable Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		9		12
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,185		1,163
Regulatory Liability, Current		102		62
Regulatory Liability, Noncurrent		1,083		1,101
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	1,011		1,032
Baltimore Gas and Electric Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		92		105
Baltimore Gas and Electric Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		22	[3]	0
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	11
Baltimore Gas and Electric Company [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Baltimore Gas and Electric Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	17
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		32		26
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		135		137
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,965		1,928
Regulatory Liability, Current		77		56
Regulatory Liability, Noncurrent		1,888		1,872
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	1,720		1,730
Pepco Holdings LLC [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		130		130
Pepco Holdings LLC [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		35		36
Pepco Holdings LLC [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1		0
Pepco Holdings LLC [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2],[5]	22	[7]	4
Pepco Holdings LLC [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3
Pepco Holdings LLC [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Pepco Holdings LLC [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4		2
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[9]	1
Pepco Holdings LLC [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	27
Pepco Holdings LLC [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		22		26
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		845		832
Regulatory Liability, Current		7		3
Regulatory Liability, Noncurrent		838		829
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	804		809
Potomac Electric Power Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		20		20
Potomac Electric Power Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4	[7]	0
Potomac Electric Power Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Potomac Electric Power Company [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Potomac Electric Power Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	14
Potomac Electric Power Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3		3
Potomac Electric Power Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		146		147
Potomac Electric Power Company [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		646		635
Regulatory Liability, Current		48		42
Regulatory Liability, Noncurrent		598		593
Delmarva Power and Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	506		510
Delmarva Power and Light Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		110		110
Delmarva Power and Light Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[5]	6		1
Delmarva Power and Light Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3
Delmarva Power and Light Company [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1
Delmarva Power and Light Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	7
Delmarva Power and Light Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		13		14
Delmarva Power and Light Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		147		148
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		437		422
Regulatory Liability, Current		21		11
Regulatory Liability, Noncurrent		416		411
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	410		411
Atlantic City Electric Company [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1		0
Atlantic City Electric Company [Member] | Dlc Program Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Electric Transmission And Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2]	12		3
Atlantic City Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0
Atlantic City Electric Company [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		0		0
Atlantic City Electric Company [Member] | Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4		2
Atlantic City Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[9]	0
Atlantic City Electric Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	6
Atlantic City Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4		6
Atlantic City Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		147		$ 147
Atlantic City Electric Company [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 12
[1]	As of March 31, 2018, includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $479 million, $135 million, $146 million, $147 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively. As of December 31, 2017, includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $484 million, $137 million, $147 million, $148 million and $147 million for ComEd, BGE, Pepco, DPL and ACE, respectively.
[2]	As of March 31, 2018, ACE's regulatory asset of $24 million included $9 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of March 31, 2018, ACE's regulatory liability of $12 million related to over-recovered electric energy costs. As of December 31, 2017, ACE's regulatory asset of $26 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $15 million of under-recovered electric energy costs. As of December 31, 2017, ACE's regulatory liability of $3 million related to over-recovered electric energy costs.
[3]	As of March 31, 2018, BGE's regulatory asset of $21 million included $13 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of March 31, 2018, BGE's regulatory liability of $22 million related to over-recovered natural gas costs. As of December 31, 2017, BGE’s regulatory asset of $23 million included $7 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $5 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval and $8 million of under-recovered natural gas costs.
[4]	As of March 31, 2018, ComEd’s regulatory asset of $8 million represents transmission costs recoverable through its FERC approved formula rate. As of March 31, 2018, ComEd’s regulatory liability of $53 million included $21 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2017, ComEd’s regulatory asset of $6 million represents transmission costs recoverable through its FERC approved formula rate. As of December 31, 2017, ComEd’s regulatory liability of $47 million included $14 million related to over-recovered energy costs and $33 million associated with revenues received for renewable energy requirements.
[5]	As of March 31, 2018, DPL's regulatory asset of $14 million included $11 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018, DPL's regulatory liability of $6 million related to over-recovered electric energy and gas fuel costs. As of December 31, 2017, DPL's regulatory asset of $15 million included $8 million of transmission costs recoverable through its FERC approved formula rate and $7 million related to under-recovered electric energy costs. As of December 31, 2017, DPL's regulatory liability of $1 million related to over-recovered electric energy costs.
[6]	As of March 31, 2018, PECO's regulatory liability of $56 million included $44 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $9 million related to over-recovered non-bypassable transmission service charges. As of December 31, 2017, PECO's regulatory liability of $60 million included $36 million related to over-recovered costs under the DSP program, $12 million related to over-recovered non-bypassable transmission service charges and $12 million related to the over-recovered natural gas costs under the PGC.
[7]	As of March 31, 2018, Pepco's regulatory asset of $7 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $3 million related to under-recovered electric energy costs. As of March 31, 2018, Pepco's regulatory liability of $4 million related to over-recovered electric energy costs. As of December 31, 2017, Pepco's regulatory asset of $11 million included $3 million of transmission costs recoverable through its FERC approved formula rate and $8 million of under-recovered electric energy costs.
[8]	Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of March 31, 2018, BGE had a regulatory asset of $6 million related to under-recovered electric revenue decoupling and a regulatory liability of $11 million related to over-recovered natural gas revenue decoupling. As of December 31, 2017, BGE had a regulatory asset of $10 million related to under-recovered electric revenue decoupling and $4 million related to under-recovered natural gas revenue decoupling.
[9]	As of March 31, 2018, DPL’s regulatory asset of $11 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates and $2 million authorized for recovery in Delaware gas rates.
[10]	Represents over-recoveries related to the change in the federal income tax rate with the enactment of the TCJA. These regulatory liabilities will be amortized as the TCJA income tax benefits are passed back to customers. See Tax Cuts and Jobs Act disclosures above for further details on the regulatory proceedings.

Regulatory Matters Regulatory61

Regulatory Matters Regulatory Matters - Capitalized Ratemaking Amount Not Recognized (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		$ 69	$ 69
Commonwealth Edison Co [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[1]	7	6
PECO Energy Co [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		0	0
Baltimore Gas and Electric Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[2]	52	53
Pepco Holdings LLC [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes		10	10
Potomac Electric Power Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	6	6
Delmarva Power and Light Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Amount of Allowance for Earnings on Equity Capitalized for Rate Making Purposes	[3]	4	4
Atlantic City Electric Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
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 Regulatory62

Regulatory Matters Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		$ 317	$ 298
Allowance for Doubtful Accounts Receivable	[1]	(35)	(31)
Payments to Acquire Other Receivables, Net		282	267
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		88	87
Allowance for Doubtful Accounts Receivable	[1]	(16)	(14)
Payments to Acquire Other Receivables, Net		72	73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		73	70
Allowance for Doubtful Accounts Receivable	[1]	(6)	(5)
Payments to Acquire Other Receivables, Net		67	65
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		64	58
Allowance for Doubtful Accounts Receivable	[1]	(4)	(3)
Payments to Acquire Other Receivables, Net		60	55
Pepco Holdings LLC [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		92	83
Allowance for Doubtful Accounts Receivable	[1]	(9)	(9)
Payments to Acquire Other Receivables, Net		83	74
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		55	56
Allowance for Doubtful Accounts Receivable	[1]	(5)	(5)
Payments to Acquire Other Receivables, Net		50	51
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		17	9
Allowance for Doubtful Accounts Receivable	[1]	(1)	(1)
Payments to Acquire Other Receivables, Net		16	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		20	18
Allowance for Doubtful Accounts Receivable	[1]	(3)	(3)
Payments to Acquire Other Receivables, Net		$ 17	$ 15
[1]	For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through its Purchase of Receivables with Consolidated Billing tariff.

Impairment of Long-Lived Asse63

Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Property, plant and equipment, net	$ 74,711		$ 74,202
Impairment of long-lived assets and losses on regulatory assets	$ 0	$ 10

Early Nuclear Plant Retiremen64

Early Nuclear Plant Retirements Early Nuclear Plant Retirements - Narrative (Details) - USD ($) $ in Millions		3 Months Ended				12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 74,711	$ 74,202			$ 74,202
Facility Closing [Member] | Mystic Generating Station [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials, Gross		26
Nuclear Fuel, Net of Amortization		18
Property, plant and equipment, net		896
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress		4
Prepaid Expense	[1]	9
Asset Retirement Obligation		(5)
Accrued Liabilities	[1]	(2)
Facility Closing [Member] | Salem [Member]
Property, Plant and Equipment [Line Items]
Inventory, Raw Materials, Gross		45
Nuclear Fuel, Net of Amortization		102
Property, plant and equipment, net		618
Asset Retirement Obligation		(446)
Facility Closing [Member] | Three Mile Island [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Incurred Cost			114	$ 117	$ 108	339
Facility Closing [Member] | TMI,OysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Incurred Cost		178
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 24,714	$ 24,906			$ 24,906
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share		42.59%
[1]	(a)Reflects ending balances only as they relate to Mystic's Long-term Service Agreement.

Early Nuclear Plant Retiremen65

Early Nuclear Plant Retirements Early Nuclear Plant Retirement - Pretax Expense (Details) - USD ($) $ in Millions		3 Months Ended					12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017
Property, plant and equipment, net		$ 74,711	$ 74,202				$ 74,202
Other, net		(28)				$ 257
Facility Closing [Member] | Salem [Member]
Inventory, Raw Materials, Gross		45
Nuclear Fuel, Net of Amortization		102
Property, plant and equipment, net		618
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress		27
Asset Retirement Obligation		(446)
Facility Closing [Member] | Three Mile Island [Member]
Restructuring and Related Cost, Accelerated Depreciation	[1],[2]		109	$ 106	$ 35		250
Nuclear Fuel Amortization	[2]		4	6	2		12
Other Cost and Expense, Operating	[3]		1	5	71		77
Restructuring and Related Cost, Incurred Cost			$ 114	$ 117	$ 108		$ 339
Facility Closing [Member] | TMI,OysterCreek [Member]
Restructuring and Related Cost, Accelerated Depreciation	[4],[5]	137
Nuclear Fuel Amortization	[4]	15
Other Cost and Expense, Operating	[6]	26
Restructuring and Related Cost, Incurred Cost		$ 178
[1]	Reflects incremental accelerated depreciation of plant assets, including any ARC.
[2]	Reflects incremental charges for TMI including incremental accelerated depreciation and amortization from May 30, 2017 through December 31, 2017.
[3]	Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.
[4]	Reflects incremental accelerated depreciation and amortization for TMI for the quarter ended March 31, 2018, and for Oyster Creek from February 2, 2018 through March 31, 2018.
[5]	Reflects incremental accelerated depreciation of plant assets, including any ARC.
[6]	Primarily includes materials and supplies inventory reserve adjustments, employee related costs and CWIP impairments.

Intangibles Intangibles - Narra

Intangibles Intangibles - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2015
Finite-Lived Intangible Assets, Gross [Abstract]
Finite-Lived Intangible Assets, Gross	$ 25	$ 25

Fair Value of Financial Asset67

Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		$ 389	$ 389
Spent Nuclear Fuel Obligation, Noncurrent		1,151	1,147
Deferred Finance Costs, Net		213	201
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		1
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,108	34,264
Due to Related Parties, Noncurrent	[4]	389	389
Spent Nuclear Fuel Obligation, Noncurrent		1,151	1,147
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	34,984	36,705
Due to Related Parties, Noncurrent	[4]	421	431
Spent Nuclear Fuel Obligation, Noncurrent		922	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	1,654	929
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	33,091	34,735
Due to Related Parties, Noncurrent	[4]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		922	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,893	1,970
Due to Related Parties, Noncurrent	[4]	421	431
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Spent Nuclear Fuel Obligation, Noncurrent		1,151	1,147
Deferred Finance Costs, Net		57	60
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,965	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,151	1,147
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	9,195	9,512
Spent Nuclear Fuel Obligation, Noncurrent		922	936
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	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]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	166	2
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,585	7,839
Spent Nuclear Fuel Obligation, Noncurrent		922	936
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,610	1,673
Spent Nuclear Fuel Obligation, Noncurrent		0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		205	205
Deferred Finance Costs, Net		60	52
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	7,694	7,601
Due to Related Parties, Noncurrent	[4]	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,061	8,418
Due to Related Parties, Noncurrent	[4]	222	227
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	317
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	8,061	8,418
Due to Related Parties, Noncurrent	[4]	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Due to Related Parties, Noncurrent	[4]	222	227
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		184	184
Deferred Finance Costs, Net		20	17
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,723	2,903
Long-term debt to financing trust	[4]	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,870	3,194
Long-term debt to financing trust	[4]	199	204
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Long-term debt to financing trust	[4]	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	220
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,870	3,194
Long-term debt to financing trust	[4]	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value		0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Long-term debt to financing trust	[4]	199	204
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		16	17
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	45	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,578
Long-term debt to financing trust	[2],[3]		2,577
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	45	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,689
Long-term debt to financing trust	[2],[3]		2,825
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0
Long-term debt to financing trust	[2],[3]		0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	45	77
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,689
Long-term debt to financing trust	[2],[3]		2,825
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0
Long-term debt to financing trust	[2],[3]		0
Pepco Holdings LLC [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		6	6
Pepco Holdings LLC [Member] | Reported Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,849	5,874
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,706	6,019
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	407	350
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	5,423	5,722
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Successor [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	283	297
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		32	32
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,540	2,540
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,942	3,123
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	60	26
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	2,933	3,114
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	9	9
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		11	11
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,296	1,300
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,320	1,393
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	211	216
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,320	1,393
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deferred Finance Costs, Net		5	5
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,114	1,121
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	1,190	1,237
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	0	0
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	136	108
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	916	949
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt, Fair Value	[1]	0	0
Long-term debt (including amounts due within one year)(b)(c)	[2],[3]	$ 274	$ 288
[1]	Level 1 securities consist of dividends payable (included in other current liabilities). Level 2 securities consist of short term borrowings.
[2]	Includes unamortized debt issuance costs which are not fair valued of $213 million, $57 million, $60 million, $20 million, $16 million, $6 million, $32 million, $11 million and $5 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of March 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.
[3]	Level 2 securities consist of fixed-rate taxable debt securities, fixed-rate tax-exempt debt, variable rate tax-exempt debt and variable rate non-recourse debt. Level 3 securities consist of fixed-rate private placement taxable debt securities, fixed rate nonrecourse debt and government-backed fixed rate non-recourse debt.
[4]	Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of March 31, 2018 and December 31, 2017.

Fair Value of Financial Asset68

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		$ 415		$ 232
Derivative Liability, Noncurrent		468		409
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Collateral, Right to Reclaim Cash		53		77
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		2		1
Derivative Asset, Notional Amount		949		811
Margin Deposit Assets		156		(117)
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		531		389
Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		51		145
Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		103		85
Nuclear Decommissioning Trust Fund Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments		84		82
Pledged Assets For Zion Station Decommissioning [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments		1		0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	517		656
FinancialAssetsFairValueDisclosure1		15,686		15,716
Deferred Compensation Liability, Current and Noncurrent		(138)		(145)
Financial Liabilities Fair Value Disclosure		(1,021)		(786)
FinancialAssetLiabilitiesNetFairValueDisclosure1		14,665		14,930
Alternative Investment, Fair Value Disclosure		3,519		3,534
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		878		637
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		5,202		4,040
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		179		53
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(4,503)		(3,456)
Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		5		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]
Total mark-to-market derivative liabilities		4		2
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		5		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]
Total mark-to-market derivative liabilities		(4)		(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]	(13,359)		(13,431)
Alternative Investment, Fair Value Disclosure	[4]	3,519		3,510
Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[5]	(327)		(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		(7,104)		(7,254)
Alternative Investment, Fair Value Disclosure		2,119		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		(4,691)		(4,736)
Alternative Investment, Fair Value Disclosure		532		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		(1,957)		(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		(86)		(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		(254)		(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]	(571)		(557)
Alternative Investment, Fair Value Disclosure	[6]	532		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		(496)		(528)
Alternative Investment, Fair Value Disclosure		127		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		(253)		(222)
Alternative Investment, Fair Value Disclosure		253		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		(488)		(471)
Alternative Investment, Fair Value Disclosure		488		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		(29)		(39)	[7]
Alternative Investment, Fair Value Disclosure		0		24	[7]
Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(13)		(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				(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		(16)		(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	[8]	(240)		(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		(77)		(77)
Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(59)		(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		(10)		(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		(94)		(93)
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		5,101		4,225
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		209		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]	(3,819)		(2,989)
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,491		1,304
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		14		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		12		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		6		10
Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(4)		(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		(36)		(37)
Fair Value, Inputs, Level 1 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties		80		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 equivalents	[1]	517		656
FinancialAssetsFairValueDisclosure1		6,709		6,980
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		(63)
FinancialAssetLiabilitiesNetFairValueDisclosure1		6,709		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]
Total mark-to-market derivative liabilities		0		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]
Total mark-to-market derivative liabilities		415		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]
Total mark-to-market derivative liabilities		0		2
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(415)		(651)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		1		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]
Total mark-to-market derivative liabilities		(1)		(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]	(6,093)		(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]
Investments, Fair Value Disclosure	[5]	(222)		(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		(4,002)		(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		(1,869)		(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		(1,869)		(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		(13)		(2)	[7]
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]
Investments, Fair Value Disclosure		(13)		(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
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	[8]	(136)		(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		(77)		(77)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(59)		(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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		286		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]	(335)		(585)
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		(49)		(26)
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		(1)		(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		(1)		(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]
Collateral received from counterparties, net of collateral paid to counterparties		418		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 equivalents	[1]	0		0
FinancialAssetsFairValueDisclosure1		3,719		3,793
Deferred Compensation Liability, Current and Noncurrent		(138)		(145)
Financial Liabilities Fair Value Disclosure		(617)		(329)
FinancialAssetLiabilitiesNetFairValueDisclosure1		3,102		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]
Total mark-to-market derivative liabilities		474		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]
Total mark-to-market derivative liabilities		3,317		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]
Total mark-to-market derivative liabilities		164		42
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(3,007)		(2,089)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		5		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		4		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]
Total mark-to-market derivative liabilities		(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]	(3,138)		(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]
Investments, Fair Value Disclosure	[5]	(105)		(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		(983)		(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		(2,050)		(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		(1,583)		(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		(88)		(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		(86)		(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		(254)		(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]	(39)		(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)	[7]
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]
Investments, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure				(1)
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	[8]	(81)		(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 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] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(10)		(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		(71)		(71)
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		2,923		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		151		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]	(2,589)		(1,769)
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		485		640
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		15		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		12		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		6		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]
Collateral received from counterparties, net of collateral paid to counterparties		186		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 equivalents	[1]	0		0
FinancialAssetsFairValueDisclosure1		1,739		1,409
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		(404)		(394)
FinancialAssetLiabilitiesNetFairValueDisclosure1		1,335		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]
Total mark-to-market derivative liabilities		404		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]
Total mark-to-market derivative liabilities		1,470		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]
Total mark-to-market derivative liabilities		15		9
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(1,081)		(716)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]	(609)		(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]
Investments, 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		(240)		(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		(240)		(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		(369)		(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		(16)		(12)	[7]
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]
Investments, 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
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		(16)		(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	[8]	(23)		(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 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] | 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		(23)		(22)
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		1,892		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		58		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]	(895)		(635)
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		1,055		690
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		(36)		(37)
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		391		211
Derivative Liability, Noncurrent		221		174
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 equivalents		371		259
Exelon Generation Co L L C [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		23		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 equivalents	[1]	343		168
FinancialAssetsFairValueDisclosure1		15,323		15,035
Deferred Compensation Liability, Current and Noncurrent		(35)		(38)
Financial Liabilities Fair Value Disclosure		(647)		(423)
FinancialAssetLiabilitiesNetFairValueDisclosure1		14,676		14,612
Alternative Investment, Fair Value Disclosure		3,519		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]
Total mark-to-market derivative liabilities		611		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]
Total mark-to-market derivative liabilities		4,935		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]
Total mark-to-market derivative liabilities		179		53
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(4,503)		(3,455)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		1		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		5		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]
Total mark-to-market derivative liabilities		(4)		(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]	(13,359)		(13,431)
Alternative Investment, Fair Value Disclosure	[4]	3,519		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]
Investments, Fair Value Disclosure	[5]	(327)		(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		(7,104)		(7,254)
Alternative Investment, Fair Value Disclosure		2,119		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		(4,691)		(4,736)
Alternative Investment, Fair Value Disclosure		532		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		(1,957)		(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		(86)		(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		(254)		(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]	(571)		(557)
Alternative Investment, Fair Value Disclosure	[6]	532		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		(496)		(528)
Alternative Investment, Fair Value Disclosure		127		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		(253)		(222)
Alternative Investment, Fair Value Disclosure		253		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		(488)		(471)
Alternative Investment, Fair Value Disclosure		488		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		(29)		(39)	[7]
Alternative Investment, Fair Value Disclosure		0		24	[7]
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]
Investments, Fair Value Disclosure		(13)		(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				(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		(16)		(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	[8]	(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 Funds [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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		5,101		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		209		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]	(3,819)		(2,989)
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		1,491		1,304
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		14		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		12		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		6		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		(4)		(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		(36)		(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 equivalents	[1]	343		168
FinancialAssetsFairValueDisclosure1		6,428		6,385
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		(63)
FinancialAssetLiabilitiesNetFairValueDisclosure1		6,428		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]
Total mark-to-market derivative liabilities		0		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]
Total mark-to-market derivative liabilities		415		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]
Total mark-to-market derivative liabilities		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 Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(415)		(650)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		1		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]
Total mark-to-market derivative liabilities		(1)		(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]	(6,093)		(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]
Investments, Fair Value Disclosure	[5]	(222)		(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		(4,002)		(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		(1,869)		(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		(1,869)		(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		(13)		(2)	[7]
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]
Investments, Fair Value Disclosure		(13)		(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
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	[8]	(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 Funds [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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		286		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]	(335)		(585)
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		(49)		(26)
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		(1)		(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		(1)		(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 equivalents	[1]	0		0
FinancialAssetsFairValueDisclosure1		3,660		3,729
Deferred Compensation Liability, Current and Noncurrent		(35)		(38)
Financial Liabilities Fair Value Disclosure		(510)		(222)
FinancialAssetLiabilitiesNetFairValueDisclosure1		3,150		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]
Total mark-to-market derivative liabilities		474		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]
Total mark-to-market derivative liabilities		3,317		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]
Total mark-to-market derivative liabilities		164		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 Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(3,007)		(2,089)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		1		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		4		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]
Total mark-to-market derivative liabilities		(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]	(3,138)		(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]
Investments, Fair Value Disclosure	[5]	(105)		(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		(983)		(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		(2,050)		(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		(1,583)		(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		(88)		(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		(86)		(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		(254)		(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]	(39)		(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)	[7]
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]
Investments, Fair Value Disclosure		0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure				(1)
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	[8]	(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 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] | 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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		2,923		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		151		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]	(2,589)		(1,769)
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		485		640
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		15		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		12		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		6		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 equivalents	[1]	0		0
FinancialAssetsFairValueDisclosure1		1,716		1,387
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		(137)		(138)
FinancialAssetLiabilitiesNetFairValueDisclosure1		1,579		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]
Total mark-to-market derivative liabilities		137		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]
Total mark-to-market derivative liabilities		1,203		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]
Total mark-to-market derivative liabilities		15		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 Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities	[2],[3]	(1,081)		(716)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interestrateandforeigncurrencyderivativeliabilities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]
Total mark-to-market derivative liabilities		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]	(609)		(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]
Investments, 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		(240)		(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		(240)		(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		(369)		(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		(16)		(12)	[7]
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]
Investments, 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
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		(16)		(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	[8]	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 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] | 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] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		1,892		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		58		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]	(895)		(635)
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		1,055		690
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		(36)		(37)
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		24		21
Derivative Liability, Noncurrent		243		235
Commonwealth Edison Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		69		45
Commonwealth Edison Co [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		83		62
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[9]	93		98
FinancialAssetsFairValueDisclosure1		93		98
Total mark-to-market derivative liabilities	[10]	(267)		(256)
Deferred Compensation Liability, Current and Noncurrent		(8)		(8)
Financial Liabilities Fair Value Disclosure		(275)		(264)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(182)		(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	[11]	0		0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	93		98
FinancialAssetsFairValueDisclosure1		93		98
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		93		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	[11]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		(8)		(8)
Financial Liabilities Fair Value Disclosure		(8)		(8)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(8)		(8)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[11]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities	[10]	(267)		(256)
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		(267)		(256)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(267)		(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	[11]	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents		20		47
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[9]	6		228
FinancialAssetsFairValueDisclosure1		23		245
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		(11)		(11)
Financial Liabilities Fair Value Disclosure		(11)		(11)
FinancialAssetLiabilitiesNetFairValueDisclosure1		12		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	[11]	17		17
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	6		228
FinancialAssetsFairValueDisclosure1		13		235
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		13		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	[11]	7		7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		10		10
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		(11)		(11)
Financial Liabilities Fair Value Disclosure		(11)		(11)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)		(1)
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[11]	10		10
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[11]	0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents		22		17
Baltimore Gas and Electric Company [Member] | Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		6		6
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		(4)		(5)
Financial Liabilities Fair Value Disclosure		(4)		(5)
FinancialAssetLiabilitiesNetFairValueDisclosure1		2		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	[11]	6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		6		6
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		6		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	[11]	6		6
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		(4)		(5)
Financial Liabilities Fair Value Disclosure		(4)		(5)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(4)		(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	[11]	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [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 equivalents	[9]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities	[10]	0		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[11]	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Funds [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Successor [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		36		12
Pepco Holdings LLC [Member] | Successor [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		20		23
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	67		83
FinancialAssetsFairValueDisclosure1		195		212
Total mark-to-market derivative liabilities		0
Deferred Compensation Liability, Current and Noncurrent		(23)		(25)
Financial Liabilities Fair Value Disclosure		(23)		(25)
FinancialAssetLiabilitiesNetFairValueDisclosure1		172		187
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]	0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(128)		(129)
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(72)		(72)
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(10)		(12)
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(46)		(45)
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities				0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			(1)
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				(1)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	67		83
FinancialAssetsFairValueDisclosure1		139		155
Total mark-to-market derivative liabilities		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		139		155
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(72)		(72)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(72)		(72)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			(1)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				(1)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
FinancialAssetsFairValueDisclosure1		33		35
Total mark-to-market derivative liabilities		0
Deferred Compensation Liability, Current and Noncurrent		(23)		(25)
Financial Liabilities Fair Value Disclosure		(23)		(25)
FinancialAssetLiabilitiesNetFairValueDisclosure1		10		10
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(33)		(35)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(10)		(12)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(23)		(23)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
FinancialAssetsFairValueDisclosure1		23		22
Total mark-to-market derivative liabilities		0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		23		22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]	0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(23)		(22)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		(23)		(22)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Predecessor [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				0
Potomac Electric Power Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		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 equivalents	[12]	33		36
FinancialAssetsFairValueDisclosure1		133		137
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		(4)		(4)
Financial Liabilities Fair Value Disclosure		(4)		(4)
FinancialAssetLiabilitiesNetFairValueDisclosure1		129		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(100)		(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		(44)		(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		(10)		(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		(46)		(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 equivalents	[12]	33		36
Investments, Fair Value Disclosure		0
FinancialAssetsFairValueDisclosure1		77		80
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		77		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(44)		(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		(44)		(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 equivalents	[12]	0		0
Investments, Fair Value Disclosure				0
FinancialAssetsFairValueDisclosure1		33		35
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		(4)		(4)
Financial Liabilities Fair Value Disclosure		(4)		(4)
FinancialAssetLiabilitiesNetFairValueDisclosure1		29		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(33)		(35)
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		(10)		(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		(23)		(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 equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		23		22
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		23		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	(23)		(22)
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		(23)		(22)
Delmarva Power and Light Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		7		2
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		(1)		(1)
Financial Liabilities Fair Value Disclosure		(1)		(1)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)		(1)
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			(1)
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				(1)
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			(1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				(1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		(1)		(1)
Financial Liabilities Fair Value Disclosure		(1)		(1)
FinancialAssetLiabilitiesNetFairValueDisclosure1		(1)		(1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Noncurrent				0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0		0
Atlantic City Electric Company [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		10		2
Atlantic City Electric Company [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		20		23
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	27		29
FinancialAssetsFairValueDisclosure1		27		29
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		27		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	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 equivalents	[12]	27		29
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		27		29
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		27		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]
Financial Liabilities Fair Value Disclosure	[13]			0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	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 equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	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 equivalents	[12]	0		0
Investments, Fair Value Disclosure		0		0
FinancialAssetsFairValueDisclosure1		0		0
Total mark-to-market derivative liabilities				0
Deferred Compensation Liability, Current and Noncurrent		0		0
Financial Liabilities Fair Value Disclosure		0		0
FinancialAssetLiabilitiesNetFairValueDisclosure1		0		0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Financial Liabilities Fair Value Disclosure	[13]			0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral 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] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	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
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)	[15],[16]	(10)
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Exelon Generation Co L L C [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)	[15],[16]	(3)
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		1	$ 1
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | PECO Energy Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)	[15],[16]	$ (1)
[1]	Generation excludes cash of $371 million and $259 million at March 31, 2018 and December 31, 2017 and restricted cash of $23 million and $127 million at March 31, 2018 and December 31, 2017. Exelon excludes cash of $531 million and $389 million at March 31, 2018 and December 31, 2017 and restricted cash of $51 million and $145 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $103 million and $85 million at March 31, 2018 and December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[2]	Collateral posted/(received) from counterparties totaled $80 million, $418 million and $186 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2018. Collateral posted/(received) from counterparties, net of collateral paid to 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.
[3]	Of the collateral posted/(received), $156 million represents variation margin on the exchanges as of March 31, 2018. Of the collateral posted/(received), $(117) million represents variation margin on the exchanges as of December 31, 2017.
[4]	Excludes net liabilities of $84 million and $82 million at March 31, 2018 and December 31, 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 $53 million and $77 million of cash received from outstanding repurchase agreements at March 31, 2018 and December 31, 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 $2 million and less than $1 million, which have a total notional amount of $949 million and $811 million at March 31, 2018 and December 31, 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]	Excludes net assets of $1 million at March 31, 2018. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.
[8]	The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the three months ended March 31, 2018 and March 31, 2017, respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million and $2 million for the three months ended March 31, 2018 and March 31, 2017, respectively.
[9]	ComEd excludes cash of $69 million and $45 million at March 31, 2018 and December 31, 2017 and includes long-term restricted cash of $83 million and $62 million at March 31, 2018 and December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $20 million and $47 million at March 31, 2018 and December 31, 2017. BGE excludes cash of $22 million and $17 million at March 31, 2018 and December 31, 2017 and restricted cash of $2 million and $1 million at March 31, 2018 and December 31, 2017.
[10]	The Level 3 balance consists of the current and noncurrent liability of $24 million and $243 million, respectively, at March 31, 2018, and $21 million and $235 million, respectively, at December 31, 2017, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[11]	The amount of unrealized gains/(losses) at ComEd, PECO and BGE totaled less than $1 million for the three months ended March 31, 2018 and March 31, 2017, respectively.
[12]	PHI excludes cash of $36 million and $12 million at March 31, 2018 and December 31, 2017, respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017, respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $15 million and $4 million at March 31, 2018 and December 31, 2017, respectively. DPL excludes cash of $7 million and $2 million at March 31, 2018 and December 31, 2017, respectively. ACE excludes cash of $10 million and $2 million at March 31, 2018 and December 31, 2017, respectively, and includes long-term restricted cash of $20 million and $23 million at March 31, 2018 and December 31, 2017, respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[13]	Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.
[14]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjhhYjQ5Njk1ZGY1YjQ3MzJiODQ1NjM5OWU2ZGRmZDBlfFRleHRTZWxlY3Rpb246MzBFMzY0RjI0NzM0ODJFMjMxNDc2M0I4NzhEODg1REEM}
[15]	All amounts are net of tax and noncontrolling interest. Amounts in parenthesis represent a decrease in AOCI.
[16]	Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and 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 2 — New Accounting Standards for additional information.

Fair Value of Financial Asset69

Fair Value of Financial Assets and Liabilities - Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ (1,335)	$ (1,046)	$ (1,015)	$ (993)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		186	(38)
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		(4)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets		(4)	(15)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral		105	38
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		(90)	(89)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		3	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances			1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(48)	(23)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		8	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(2)	6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(258)	(62)
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		7	9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets		7	9
Exelon Generation Co L L C [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings		(72)	(102)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(1,579)	(1,308)	(1,249)	(1,231)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		185	(39)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		(7)	(9)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		(4)
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		105	38
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		(90)	(89)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		3	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(48)	(23)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		8	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(2)	6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(257)	(61)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(609)	(683)	(648)	(677)
Total realized / unrealized gains (losses)
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		(7)	(9)
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
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		(2)	(17)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(48)	(23)
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
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	(2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(16)	(20)	(12)	(19)
Total realized / unrealized gains (losses)
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		(4)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			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		0	(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		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
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 And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(918)	(565)	(552)	(493)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	184	(43)
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
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral		105	38
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		(88)	69
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		3	2
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		8	1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0	11
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(256)	(59)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		(36)	(40)	(37)	(42)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		1	1
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets			0
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	(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		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)	5
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(1)	0
Commonwealth Edison Co [Member] | Derivative [Member] | Interest Rate Swap [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Realized Investment Gains (Losses)		6	6
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		267	(282)	256	(258)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates		0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets	[2]	(11)	(24)
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, 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
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	0
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)		(17)	(30)
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	[3]	(23)	(20)	$ (22)	$ (20)
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[3]	(1)	(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	[3]	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable	[3]	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets	[3]	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral	[3]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	[3]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	[3]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances	[3]		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	[3]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[3]	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	[3]	0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[3]	$ (1)	$ (1)
[1]	Includes a reduction for the reclassification of $72 million and $102 million of realized gains due to the settlement of derivative contracts for the three months ended March 31, 2018 and March 31, 2017, respectively.
[2]	Includes $17 million of decreases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2018. Includes $30 million of decreases in fair value and an increase for realized losses due to settlements of $6 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended March 31, 2017.
[3]	The amounts represented are life insurance contracts at Pepco.

Fair Value of Financial Asset70

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Narrative (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	$ 68,000,000
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	(2,000,000)	$ (1,000,000)
Spent Nuclear Fuel Obligation, Noncurrent	1,151,000,000	1,147,000,000
Forward Power Basis	2.99
Forward Gas Basis	0.46
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	1,151,000,000	$ 1,147,000,000
Equity Funds [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	208,000,000
Fixed Income Securities [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	65,000,000
Middle Market Lending [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	386,000,000
Private Equity Funds [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	194,000,000
Real Estate Funds [Member] | Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 107,000,000

Fair Value of Financial Asset71

Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		$ (186)	$ 38
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		258	62
Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		335	88
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		309	140
Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(151)	(131)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(53)	(81)
Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	1	4
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	1	3
Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(185)	39
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		257	61
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		335	88
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		309	140
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		(151)	(131)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(53)	(81)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	1	3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	1	2
Pepco Holdings LLC [Member] | Other, net [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[1]	1	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[1]	1	1
6311 Life Insurance [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	[2]	1	1
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	[2]	$ 1	$ 1
[1]	Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation, accrued interest on a convertible promissory note at Generation and the life insurance contracts held by PHI and Pepco.
[2]	The amounts represented are life insurance contracts at Pepco.

Fair Value of Financial Asset72

Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - USD ($)		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2016		Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Cash Collateral Posted		$ 41,000,000
Exelon Generation Co L L C [Member]
Derivatives, Fair Value [Line Items]
Cash Collateral Posted		742,000,000			$ 497,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Cash Collateral Posted		186,000,000			81,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[1],[2]	689,000,000			445,000,000
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		1			3
Forward gas price assets		1.12			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		202			124
Forward gas price assets		$ 12.80			12.80
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		9.67%	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		226.91%	139.00%
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	[1],[2]	$ 43,000,000			(26,000,000)
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		4			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		202			94
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ (267,000,000)			$ (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]
Forward heat rate		900.00%	800.00%	[3]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs, Discount for Lack of Marketability		4.00%	4.00%
Fair Value Inputs Renewable Factor		87.00%	88.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward heat rate		1000.00%	900.00%	[3]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs, Discount for Lack of Marketability		8.00%	8.00%
Fair Value Inputs Renewable Factor		122.00%	120.00%
[1]	The fair values do not include cash collateral posted on level three positions of $186 million and $81 million as of March 31, 2018 and December 31, 2017, respectively.
[2]	The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.
[3]	Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.

Derivative Financial Instrume73

Derivative Financial Instruments Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Derivative [Line Items]
Mark-to-market derivatives assets		$ 978		$ 976
Derivative Asset, Noncurrent		527		337
Derivative Liability, Current		(415)		(232)
Derivative Liability, Noncurrent		(468)		(409)
Derivative, Collateral, Right to Reclaim Cash		53		77
Margin Deposit Assets		(156)		117
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		976		973
Derivative Asset, Noncurrent		515		331
Total mark-to-market derivative assets		1,491		1,304
Derivative Liability, Current		(415)		(230)
Derivative Liability, Noncurrent		(463)		(407)
Total mark-to-market derivative liabilities		(878)		(637)
Total mark-to-market derivative net assets (liabilities)		613		667
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		978		976
Derivative Asset, Noncurrent		527		334
Derivative Liability, Current		(391)		(211)
Derivative Liability, Noncurrent		(221)		(174)
Derivative Liability, Fair Value, Amount Offset Against Collateral	[1]	(1,562)		(577)
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		976	[2]	973	[3]
Derivative Asset, Noncurrent		515	[2]	331	[3]
Total mark-to-market derivative assets		1,491	[2]	1,304	[3]
Derivative Liability, Current		(391)	[2]	(209)	[3]
Derivative Liability, Noncurrent		(220)	[2]	(172)	[3]
Total mark-to-market derivative liabilities		(611)	[2]	(381)	[3]
Total mark-to-market derivative net assets (liabilities)		880	[2]	923	[3]
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current		(24)		(21)
Derivative Liability, Noncurrent		(243)		(235)
Delmarva Power and Light Company [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0		0
Derivative Asset, Noncurrent		0		0
Total mark-to-market derivative assets		0		0
Derivative Liability, Current		0		0
Derivative Liability, Noncurrent		0		0
Total mark-to-market derivative liabilities		0		0
Total mark-to-market derivative net assets (liabilities)		0		0
Collateral And Netting [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[4]	(2,533)	[5]	(2,144)	[6]
Derivative Asset, Noncurrent	[4]	(1,286)	[5]	(845)	[6]
Total mark-to-market derivative assets	[4]	(3,819)	[5]	(2,989)	[6]
Derivative Liability, Current	[4]	2,945	[5]	2,480	[6]
Derivative Liability, Noncurrent	[4]	1,558	[5]	975	[6]
Total mark-to-market derivative liabilities	[4]	4,503	[5]	3,455	[6]
Total mark-to-market derivative net assets (liabilities)	[4]	684	[5]	466	[6]
Collateral And Netting [Member] | Delmarva Power and Light Company [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[4]	0		0
Derivative Asset, Noncurrent	[4]	0		0
Total mark-to-market derivative assets	[4]	0		0
Derivative Liability, Current	[4]	0		1
Derivative Liability, Noncurrent	[4]	0		0
Total mark-to-market derivative liabilities	[4]	0		1
Total mark-to-market derivative net assets (liabilities)	[4]	0		1
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		3,343		3,061
Derivative Asset, Noncurrent		1,758		1,164
Total mark-to-market derivative assets		5,101		4,225
Derivative Liability, Current		(3,185)		(2,646)
Derivative Liability, Noncurrent		(1,750)		(1,137)
Total mark-to-market derivative liabilities		(4,935)		(3,783)
Total mark-to-market derivative net assets (liabilities)		166		442
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commonwealth Edison Co [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[7]	0		0
Derivative Asset, Noncurrent	[7]	0		0
Total mark-to-market derivative assets	[7]	0		0
Derivative Liability, Current	[7]	(24)		(21)
Derivative Liability, Noncurrent	[7]	(243)		(235)
Total mark-to-market derivative liabilities	[7]	(267)		(256)
Total mark-to-market derivative net assets (liabilities)	[7]	(267)		(256)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Delmarva Power and Light Company [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[8]	0		0
Derivative Asset, Noncurrent	[8]	0		0
Total mark-to-market derivative assets	[8]	0		0
Derivative Liability, Current	[8]	0		(1)
Derivative Liability, Noncurrent	[8]	0		0
Total mark-to-market derivative liabilities	[8]	0		(1)
Total mark-to-market derivative net assets (liabilities)	[8]	0		(1)
Not Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		166		56
Derivative Asset, Noncurrent		43		12
Total mark-to-market derivative assets		209		68
Derivative Liability, Current		(151)		(43)
Derivative Liability, Noncurrent		(28)		(10)
Total mark-to-market derivative liabilities		(179)		(53)
Total mark-to-market derivative net assets (liabilities)		30		15
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(684)		(466)
Current liabilities collateral offset		220		167
Noncurrent liabilities collateral offset		169		77
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Other Current Assets [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		192		169
Margin Deposit Assets		156
Derivative Liability, Fair Value, Amount Offset Against Collateral				(117)
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member] | Other Noncurrent Assets [Member]
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash		$ 103		$ 53
[1]	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.
[2]	Current and noncurrent assets are shown net of collateral of $192 million and $103 million, respectively, and current and noncurrent liabilities are shown net of collateral of $220 million and $169 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $684 million at March 31, 2018.
[3]	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.
[4]	Exelon, Generation and DPL net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.
[5]	Of the collateral posted/(received), $156 million represents variation margin on the exchanges.
[6]	Of the collateral posted/(received), $(117) million represents variation margin on the exchanges.
[7]	Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[8]	Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.

Derivative Financial Instrume74

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (259)	$ (47)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(264)	(51)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	1	(2)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	1	(2)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	2	(2)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(1)	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(267)	(47)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(100)	46
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (167)	$ (93)

Derivative Financial Instrume75

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (259)	$ (47)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(264)	(51)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	2	(1)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 0	$ (1)

Derivative Financial Instrume76

Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Mark-to-market derivatives assets		$ 978	$ 976
Derivative Asset, Noncurrent		527	337
Derivative Liability, Current		(415)	(232)
Derivative Liability, Noncurrent		(468)	(409)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		978	976
Derivative Asset, Noncurrent		527	334
Derivative Liability, Current		(391)	(211)
Derivative Liability, Noncurrent		(221)	(174)
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		2	3
Derivative Asset, Noncurrent		12	6
Total mark-to-market derivative assets		14	9
Derivative Liability, Current		0	(2)
Derivative Liability, Noncurrent		(5)	(2)
Total mark-to-market derivative liabilities		(5)	(4)
Total mark-to-market derivative net assets (liabilities)		9	5
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		2	3
Derivative Asset, Noncurrent		12	3
Total mark-to-market derivative assets		14	6
Derivative Liability, Current		0	(2)
Derivative Liability, Noncurrent		(1)	(2)
Total mark-to-market derivative liabilities		(1)	(4)
Total mark-to-market derivative net assets (liabilities)		13	2
Collateral And Netting [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[1]	(3)	(7)
Derivative Asset, Noncurrent	[1]	(1)	0
Total mark-to-market derivative assets	[1]	(4)	(7)
Derivative Liability, Current	[1]	3	7
Derivative Liability, Noncurrent	[1]	1	0
Total mark-to-market derivative liabilities	[1]	4	7
Total mark-to-market derivative net assets (liabilities)	[1]	0	0
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0	0
Derivative Asset, Noncurrent		12	3
Total mark-to-market derivative assets		12	3
Derivative Liability, Current		0	(2)
Derivative Liability, Noncurrent		0	0
Total mark-to-market derivative liabilities		0	(2)
Total mark-to-market derivative net assets (liabilities)		12	1
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0	0
Derivative Asset, Noncurrent		0	3
Total mark-to-market derivative assets		0	3
Derivative Liability, Current		0	0
Derivative Liability, Noncurrent		(4)	0
Total mark-to-market derivative liabilities		(4)	0
Total mark-to-market derivative net assets (liabilities)		(4)	3
Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		5	10
Derivative Asset, Noncurrent		1	0
Total mark-to-market derivative assets		6	10
Derivative Liability, Current		(3)	(7)
Derivative Liability, Noncurrent		(2)	(2)
Total mark-to-market derivative liabilities		(5)	(9)
Total mark-to-market derivative net assets (liabilities)		$ 1	$ 1
[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 Instrume77

Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Beginning Balance		$ (3,026)
Ending Balance		(2,965)
Income taxes		59	$ 211
Amounts reclassified from AOCI		(44)	(40)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Amounts reclassified from AOCI	[1],[2]	0	(4)
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(14)	(17)
Ending Balance		(6)	(11)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		8	2
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance		(37)
Ending Balance		(34)
Income taxes		9	123
Amounts reclassified from AOCI			(4)
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Amounts reclassified from AOCI	[1],[2]	0	(4)
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(16)	(19)
Ending Balance		(9)	(13)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		$ 7	2
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Amounts reclassified from AOCI	[3]		4
Interest Expense [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Amounts reclassified from AOCI	[3]		4
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes			3
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Income taxes	[4]		3
Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Income taxes	[4]		$ 3
[1]	All amounts are net of tax and noncontrolling interest. Amounts in parenthesis represent a decrease in AOCI.
[2]	See next tables for details about these reclassifications.
[3]	Amount is net of related income tax expense of $3 million for the three months ended March 31, 2017.
[4]	Amounts in parenthesis represent a decrease in net income.

Derivative Financial Instrume78

Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest Rate Swap [Member]
Derivative [Line Items]
Gain (loss) on Swaps	$ (7)	$ (4)
Price Risk Derivative [Member]
Derivative [Line Items]
Gain (loss) on Borrowings	$ 13	$ 8

Derivative Financial Instrume79

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Cash Collateral Posted		$ 41
Letters Of Credit Posted		23
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Financial institutions		189
Investor-owned utilities, marketers and power producers		656
Energy Cooperatives And Municipalities		438
Other		74
Cash Collateral Posted		742	$ 497
Letters Of Credit Posted		493	$ 293
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade		986
Non-investment grade		112
No external ratings - internally rated - investment grade		223
No external ratings - internally rated - non-investment grade		100
Total		1,421
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade		1
Non-investment grade		46
No external ratings - internally rated - investment grade		0
No external ratings - internally rated - non-investment grade		17
Total	[1]	64
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade		985
Non-investment grade		66
No external ratings - internally rated - investment grade		223
No external ratings - internally rated - non-investment grade		83
Total		1,357
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		2
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		2
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		412
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		$ 412
[1]	As of March 31, 2018, credit collateral held from counterparties where Generation had credit exposure included $41 million of cash and $23 million of letters of credit. The credit collateral does not include non-liquid collateral.

Derivative Financial Instrume80

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features	[1]	$ (2,141)	$ (926)
Contractual right of offset related to derivative assets	[2]	1,562	577
Net liability position after contractual right of offset	[3]	$ (579)	$ (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 Instrume81

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Ineffective portion recognized in income	$ 6,000	$ 4,000
Cash collateral posted	41,000
Letters of credit posted	23,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	(8,000)		$ 4,000
Cash collateral posted	742,000		497,000
Letters of credit held	46,000		33,000
Letters of credit posted	493,000		293,000
Cash collateral held	66,000		35,000
Incremental collateral for loss of investment grade credit rating	1,900,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	13,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	10,000
Credit Exposure Under Off System Sales	$ 1,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 33,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	49,000
Credit Exposure Under Off System Sales	12,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	$ 14,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	91.00%
Expected Generation Hedged In Year Two	63.00%
Expected generation hedged in year three	33.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	94.00%
Expected Generation Hedged In Year Two	66.00%
Expected generation hedged in year three	36.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Other Contract [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 87,000		94,000
Energy Related Derivative [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	9
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue	$ 2,750
Renewable Energy Program [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	14
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	$ 9,000		5,000
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	13,000		2,000
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800,000		800,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	31,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	21,000
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	25,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	34,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	9,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	5,000
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	12,000		1,000
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 636,000		$ 636,000

Derivative Financial Instrume82

Derivative Financial Instruments Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 636	$ 636
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800	800
Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 87	$ 94

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Commercial paper borrowings		$ 1,154	$ 427
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		165	0
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		317	0
PECO Energy Co [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		220	0
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		45	77
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial paper borrowings	[1]	407	350
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		60	26
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		211	216
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		$ 136	$ 108
[1]	PHI reflects the commercial paper borrowings outstanding of Pepco, DPL and ACE.

Debt and Credit Agreements - Is

Debt and Credit Agreements - Issuance of Long-Term Debt (Details)	Mar. 31, 2018USD ($)
Exelon Generation Co L L C [Member] | EEPF372Apr2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.72%
Debt Instrument, Face Amount	$ 1,000,000
Exelon Generation Co L L C [Member] | EEPF317Apr2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.17%
Debt Instrument, Face Amount	$ 1,000,000
Exelon Generation Co L L C [Member] | EEPF261Sep2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	2.61%
Debt Instrument, Face Amount	$ 2,000,000
Commonwealth Edison Co [Member] | FMB400Mar2048Member | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.00%
Debt Instrument, Face Amount	$ 800,000,000
PECO Energy Co [Member] | FRMB390Mar2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 325,000,000

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 15, 2018	Mar. 23, 2017	Jan. 13, 2016
Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable			$ 500
Debt Instrument, Interest Rate Terms	LIBOR plus 1%
Exelon Generation Co L L C [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 30
Line of Credit Facility, Maximum Borrowing Capacity		$ 95
Pepco Holdings LLC [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable				$ 500
Debt Instrument, Interest Rate Terms	LIBOR plus 1%

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		4.10%	0.90%
Qualified nuclear decommissioning trust fund income		(0.40%)	3.50%
Amortization of investment tax credit, including deferred taxes on basis difference		(1.30%)	(0.40%)
Plant basis differences		(2.70%)	(2.40%)
Production tax credits and other credits		(2.80%)	(0.70%)
Noncontrolling interests		(0.70%)	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(6.00%)
Statute of limitations expiration	[1]		(11.50%)
EffectiveIncomeTaxRateReconciliationPenalties			(6.60%)
Other		(2.80%)	(0.10%)
Effective income tax rate		8.40%	17.70%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		2.40%	1.00%
Qualified nuclear decommissioning trust fund income		(1.30%)	7.80%
Amortization of investment tax credit, including deferred taxes on basis difference		(4.30%)	(0.70%)
Plant basis differences		0.00%	0.00%
Production tax credits and other credits		(9.50%)	(1.50%)
Noncontrolling interests		(2.50%)	0.10%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		0.00%
Statute of limitations expiration	[1]		(3.40%)
EffectiveIncomeTaxRateReconciliationPenalties			(14.80%)
Other		(1.30%)	(0.40%)
Effective income tax rate		4.50%	23.10%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		8.20%	4.90%
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		0.10%	(0.20%)
Production tax credits and other credits		(0.10%)	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(7.50%)
Statute of limitations expiration	[1]		0.00%
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		0.30%	(0.00%)
Effective income tax rate		21.80%	39.50%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(3.90%)	0.10%
Qualified nuclear decommissioning trust fund income		(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)
Plant basis differences		(14.20%)	(13.20%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(4.80%)
Statute of limitations expiration	[1]		0.00%
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		0.20%	0.30%
Effective income tax rate		(1.80%)	22.10%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		6.30%	5.20%
Qualified nuclear decommissioning trust fund income		(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)
Plant basis differences		(0.70%)	(0.90%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(8.60%)
Statute of limitations expiration	[1]		0.00%
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		(0.00%)	(0.20%)
Effective income tax rate		17.90%	39.00%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		1.70%	4.60%
Qualified nuclear decommissioning trust fund income		(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)
Plant basis differences		(3.40%)	(5.80%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(12.80%)
Statute of limitations expiration	[1]		(34.20%)
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		(0.30%)	0.50%
Effective income tax rate		6.10%	0.00%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		6.30%	5.30%
Qualified nuclear decommissioning trust fund income		(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.20%)	(0.30%)
Plant basis differences		(1.30%)	(1.90%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(7.90%)
Statute of limitations expiration	[1]		(21.90%)
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		0.50%	(0.00%)
Effective income tax rate		18.40%	16.20%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		6.60%	5.60%
Qualified nuclear decommissioning trust fund income		(0.00%)	(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.30%)	(0.40%)
Plant basis differences		(2.60%)	(3.40%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(8.70%)
Statute of limitations expiration	[1]		(167.10%)
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		(3.50%)	(3.00%)
Effective income tax rate		12.50%	(133.30%)
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		4.60%	4.90%
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		(2.60%)	(3.80%)
Production tax credits and other credits		0.00%	0.00%
Noncontrolling interests		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		(10.60%)
Statute of limitations expiration	[1]		(42.40%)
EffectiveIncomeTaxRateReconciliationPenalties			0.00%
Other		(0.00%)	(0.40%)
Effective income tax rate		12.20%	(6.90%)
[1]	Includes a remeasurement of uncertain state income tax positions for Pepco and DPL.

Income Taxes Income Tax Unrecog

Income Taxes Income Tax Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 733	$ 743
Exelon Generation Co L L C [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	464	468
Commonwealth Edison Co [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	2	2
PECO Energy Co [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	0	0
Baltimore Gas and Electric Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	120	120
Pepco Holdings LLC [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	125	125
Potomac Electric Power Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	59	59
Delmarva Power and Light Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	21	21
Atlantic City Electric Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 14	$ 14

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended				12 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%	21.00%	35.00%
BonusDepreciationPercentage							50.00%
AllowableExpensingForCostOfQualifiedProperty						30.00%
LimitationonDeductibleInterestExpense				100.00%
Regulatory Liabilities			$ 10,246	$ 10,388			$ 10,388
Unrecognized Tax Benefits			733	743			743
Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Gain on Sale of Property								$ 1,200
Decrease in Unrecognized Tax Benefits is Reasonably Possible			33
IRS asserted penalties for understatement of tax			$ 90
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Unrecognized Tax Benefits			$ 464	468			468
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 6,424	6,577			6,577
Unrecognized Tax Benefits			2	2			2
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			$ 2
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 646	690			690
Unrecognized Tax Benefits			$ 0	0			0
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 1,185	1,163			1,163
Unrecognized Tax Benefits			$ 120	120			120
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 1,965	1,928			1,928
Unrecognized Tax Benefits			$ 125	125			125
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 845	832			832
Unrecognized Tax Benefits			$ 59	59			59
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 646	635			635
Unrecognized Tax Benefits			$ 21	21			21
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%		35.00%
Regulatory Liabilities			$ 437	422			422
Unrecognized Tax Benefits			14	14			14
State and Local Jurisdiction [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate			0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			679
Increase (Decrease) in Other Deferred Liability		$ 17
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate			458
Decrease in Unrecognized Tax Benefits is Reasonably Possible			465
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Other Deferred Liability		5
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes			272
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			120
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Other Deferred Liability		18
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes					$ 8
Decrease in Unrecognized Tax Benefits is Reasonably Possible			94
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Deferred Tax Assets, State Taxes					$ 8
Decrease in Unrecognized Tax Benefits is Reasonably Possible			59
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member] | Subsequent Event [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Other Deferred Liability		17
State and Local Jurisdiction [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			21
Increase (Decrease) in Other Deferred Liability		$ 1
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			14
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		7,315
Increase (Decrease) in Other Deferred Liability	[2]		8,624
Deferred Income Tax Expense (Benefit)	[2]		1,309
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Other Deferred Liability			1,895
Deferred Income Tax Expense (Benefit)			1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		2,818
Increase (Decrease) in Other Deferred Liability			2,819
Deferred Income Tax Expense (Benefit)			1
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1],[3]		1,394
Increase (Decrease) in Other Deferred Liability			1,407
Deferred Income Tax Expense (Benefit)			13
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		1,124
Increase (Decrease) in Other Deferred Liability			1,120
Deferred Income Tax Expense (Benefit)			(4)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		1,979
Increase (Decrease) in Other Deferred Liability			1,944
Deferred Income Tax Expense (Benefit)			(35)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		976
Increase (Decrease) in Other Deferred Liability			968
Deferred Income Tax Expense (Benefit)			(8)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		545
Increase (Decrease) in Other Deferred Liability			540
Deferred Income Tax Expense (Benefit)			(5)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[1]		458
Increase (Decrease) in Other Deferred Liability			456
Deferred Income Tax Expense (Benefit)			$ (2)
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				3,040			3,040
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				1,400			1,400
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[4]			533			533
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				459			459
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				648			648
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				299			299
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				195			195
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				153			153
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				1,694			1,694
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[4]			573			573
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[4]			43			43
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				324			324
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				754			754
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				391			391
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				194			194
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				170			170
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				4,734			4,734
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				1,973			1,973
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities	[4]			576			576
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				783			783
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				1,402			1,402
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				690			690
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				389			389
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Liabilities				$ 323			$ 323
[1]	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.
[2]	Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans.
[3]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information.
[4]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information.

Income Taxes Deferred Tax Revis

Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Regulatory Liabilities		$ 10,246	$ 10,388
Commonwealth Edison Co [Member]
Regulatory Liabilities		6,424	6,577
PECO Energy Co [Member]
Regulatory Liabilities		646	690
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities		1,185	1,163
Pepco Holdings LLC [Member]
Regulatory Liabilities		1,965	1,928
Potomac Electric Power Company [Member]
Regulatory Liabilities		845	832
Delmarva Power and Light Company [Member]
Regulatory Liabilities		646	635
Atlantic City Electric Company [Member]
Regulatory Liabilities		437	422
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Increase (Decrease) in Other Deferred Liability	[1]	8,624
Deferred Income Tax Expense (Benefit)	[1]	1,309
Regulatory Liabilities	[2]	7,315
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Increase (Decrease) in Other Deferred Liability		1,895
Deferred Income Tax Expense (Benefit)		1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Increase (Decrease) in Other Deferred Liability		2,819
Deferred Income Tax Expense (Benefit)		1
Regulatory Liabilities	[2]	2,818
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Increase (Decrease) in Other Deferred Liability		1,407
Deferred Income Tax Expense (Benefit)		13
Regulatory Liabilities	[2],[3]	1,394
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Increase (Decrease) in Other Deferred Liability		1,120
Deferred Income Tax Expense (Benefit)		(4)
Regulatory Liabilities	[2]	1,124
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Increase (Decrease) in Other Deferred Liability		1,944
Deferred Income Tax Expense (Benefit)		(35)
Regulatory Liabilities	[2]	1,979
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Increase (Decrease) in Other Deferred Liability		968
Deferred Income Tax Expense (Benefit)		(8)
Regulatory Liabilities	[2]	976
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power and Light Company [Member]
Increase (Decrease) in Other Deferred Liability		540
Deferred Income Tax Expense (Benefit)		(5)
Regulatory Liabilities	[2]	545
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Increase (Decrease) in Other Deferred Liability		456
Deferred Income Tax Expense (Benefit)		(2)
Regulatory Liabilities	[2]	$ 458
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member]
Regulatory Liabilities			3,040
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities			1,400
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		533
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			459
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			648
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			299
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			195
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToIRSNormalizationRules [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			153
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member]
Regulatory Liabilities			1,694
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities	[4]		573
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		43
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			324
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			754
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			391
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			194
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomersSubjectToRateRegulatorDeterminations [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			170
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member]
Regulatory Liabilities			4,734
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Commonwealth Edison Co [Member]
Regulatory Liabilities			1,973
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | PECO Energy Co [Member]
Regulatory Liabilities	[4]		576
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Liabilities			783
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Pepco Holdings LLC [Member]
Regulatory Liabilities			1,402
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Potomac Electric Power Company [Member]
Regulatory Liabilities			690
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Delmarva Power and Light Company [Member]
Regulatory Liabilities			389
NetRegulatoryLiabilitiesAssociatedWithUltimateSettlementToCustomers [Member] | Atlantic City Electric Company [Member]
Regulatory Liabilities			$ 323
[1]	Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans.
[2]	Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers.
[3]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. Refer to Note 3 - Regulatory Matters for additional information.
[4]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO remains in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. As a result, the amount of customer benefits resulting from the TCJA subject to the discretion of PECO's rate regulators are lower relative to the other Utility Registrants. Refer to Note 3 - Regulatory Matters for additional information.

Nuclear Decommissioning - Rollf

Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended
		Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Asset Retirement Obligation, Accretion Expense	[1]		$ 120	$ 112
Exelon Generation Co L L C [Member]
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Asset Retirement Obligation, Accretion Expense	[1]		120	$ 110
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)			145
Recovery Stranded Costs		$ 4
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Asset Retirement Obligation, Accretion Expense			117
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)			32
Asset Retirement Obligation, Liabilities Settled			9,807
Asset Retirement Obligation, Revision of Estimate			(4)
Current portion of ARO			$ 64		$ 13
[1]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

Nuclear Decommissioning (Detail

Nuclear Decommissioning (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended
		Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments			$ 13,149	$ 13,272
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Recovery Stranded Costs		$ 4
Asset Retirement Obligation, Period Increase (Decrease)			145
Decommissioning Fund Investments			13,149	13,272
Nuclear Decommissioning [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Period Increase (Decrease)			32
Proceeds from Customers	[1]			9,662
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Liability, Noncurrent			115
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments			$ 13,275	$ 13,349
[1]	Includes $64 million and $13 million for the current portion of the ARO at March 31, 2018 and December 31, 2017, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.

Nuclear Decommissioning - Unrea

Nuclear Decommissioning - Unrealized Gains on NDT Funds (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments		$ (2)	$ (1)
Collateral Pledged [Member] | Regulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[1]	(75)	222
Collateral Pledged [Member] | Unregulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[2],[3]	$ (96)	$ 166
[1]	Net unrealized gains (losses) related to Generation’s NDT funds associated with Regulatory Agreement Units are included in Regulatory liabilities on Exelon’s Consolidated Balance Sheets and Noncurrent payables to affiliates on Generation’s Consolidated Balance Sheets.
[2]	Excludes $(2) million and $(1) million of net unrealized losses related to the Zion Station pledged assets for the three months ended March 31, 2018 and 2017, respectively. Net unrealized losses related to Zion Station pledged assets are included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets in 2018 and 2017, respectively.
[3]	Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included in Other, net on Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

Nuclear Decommissioning - Asset

Nuclear Decommissioning - Assets, Payables and Withdrawals by ZionSolutions (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Nuclear Decommissioning Additional Narrative Information [Line Items]
Held-to-maturity Securities Pledged as Collateral	[1]	$ 30	$ 39
Accounts Payable, Interest-bearing, Noncurrent	[2],[3]	28	37
Accounts Payable, Interest-bearing, Current	[4]	$ 949	$ 942
[1]	Included in Other current assets within Exelon's and Generation's Consolidated Balance sheets.
[2]	Excludes a liability recorded within Exelon’s and Generation’s Consolidated Balance Sheets related to the tax obligation on the unrealized activity associated with the Zion Station NDT funds. The NDT funds will be utilized to satisfy the tax obligations as gains and losses are realized.
[3]	Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.
[4]	Includes project expenses to decommission Zion Station and estimated tax payments on Zion Station NDT fund earnings

Retirement Benefits - Narrative

Retirement Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Obligation, Pension Benefits		$ 23
Increase (Decrease) in Obligation, Other Postretirement Benefits		14
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		(18)
Defined Benefit Plan Amounts Recognized In Regulatory Assets Before Tax		61
Defined Benefit Plan Amounts Recognized In Regulatory Liabilities Before Tax		1
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets	7.00%
Discount rate	3.62%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets	6.60%
Discount rate	3.61%
Fitzpatrick [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Obligation, Pension Benefits	$ 16	38
Increase (Decrease) in Obligation, Other Postretirement Benefits	$ 17	$ 11

Retirement Benefits - Calculati

Retirement Benefits - Calculation of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amortization of:
Net periodic benefit cost	$ (10)	$ (26)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	101	95
Interest cost	201	210
Expected return on assets	(312)	(299)
Amortization of:
Prior service benefit	0	0
Actuarial loss	157	152
Net periodic benefit cost	147	158
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	28	26
Interest cost	43	45
Expected return on assets	(43)	(41)
Amortization of:
Prior service benefit	(46)	(47)
Actuarial loss	16	16
Net periodic benefit cost	(2)	(1)
Pepco Holdings LLC [Member]
Amortization of:
Net periodic benefit cost	$ 0	$ 0

Retirement Benefits - Allocated

Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		$ 145		$ 157
Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[1],[2]	145		157
Corporate, Non-Segment [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[3]	14		12
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		51		54
Exelon Generation Co L L C [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[2]	51		54
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		45		44
Commonwealth Edison Co [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		45		44
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		5		7
PECO Energy Co [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		5		7
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		14		16
Baltimore Gas and Electric Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		15		16
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		4		7
Potomac Electric Power Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		4		7
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		0		3
Delmarva Power and Light Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		0		3
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3		3
Atlantic City Electric Company [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		3		3
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		15		24
Pepco Holdings LLC [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[1]	15	[4]	24
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member] | Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[4]	$ 8		$ 11
[1]	Exelon reflects the consolidated pension and other postretirement benefit costs of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated pension and other postretirement benefit costs of Pepco, DPL, ACE, and PHISCO.
[2]	FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017.
[3]	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.
[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 - Defined C

Retirement Benefits - Defined Contribution Savings Plans (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[1],[2]	$ 32	$ 30
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[3]	3	2
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[2]	15	14
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		7	7
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		2	2
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		2	2
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	1
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	1
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[1],[4]	3	3
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[4]	$ 1	$ 1
[1]	Exelon reflects the consolidated savings plan matching contributions of Generation, ComEd, PECO, BGE, BSC, and PHI. PHI reflects the consolidated savings plan matching contributions of Pepco, DPL, and PHISCO.
[2]	FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017.
[3]	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 or DPL amounts above.
[4]	These amounts represent amounts billed to Pepco and DPL through intercompany allocations. These amounts are not included in Pepco or DPL amounts above.

Severance - Ongoing Severance P

Severance - Ongoing Severance Plans (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 8	$ 4
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	3
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	1
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Pepco Holdings LLC [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		4	0
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	0
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 1	$ 0
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.

Severance Severance - Cost Mana

Severance Severance - Cost Management Program-Related (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 8	$ 4
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	3
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	1
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 1	$ 0
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.

Severance - PHI Merger (Details

Severance - PHI Merger (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 8	$ 4
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	3
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	1
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Pepco Holdings LLC [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		4	0
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	0
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 1	$ 0
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.

Severance - Severance Liabiliti

Severance - Severance Liabilities (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Severance Costs		$ 8	$ 4
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		94
Severance Costs	[1]	9
Payments for Restructuring		(16)
Ending Balance		87
Exelon Generation Co L L C [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	2	3
Exelon Generation Co L L C [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		58
Severance Costs	[1]	3
Payments for Restructuring		(5)
Ending Balance		56
Commonwealth Edison Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	1
Commonwealth Edison Co [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		3
Severance Costs	[1]	1
Payments for Restructuring		(1)
Ending Balance		3
PECO Energy Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	0	0
PECO Energy Co [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	0
Payments for Restructuring		0
Ending Balance		0
Baltimore Gas and Electric Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	1
Payments for Restructuring		0
Ending Balance		1
Pepco Holdings LLC [Member]
Restructuring Reserve [Roll Forward]
Severance Costs		4	0
Pepco Holdings LLC [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		20
Severance Costs	[1]	2
Payments for Restructuring		(6)
Ending Balance		16
Potomac Electric Power Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	2	0
Potomac Electric Power Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	(1)
Payments for Restructuring		(1)
Ending Balance		0
Delmarva Power and Light Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0
Delmarva Power and Light Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	0
Payments for Restructuring		0
Ending Balance		0
Atlantic City Electric Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	$ 0
Atlantic City Electric Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	0
Payments for Restructuring		0
Ending Balance		$ 0
[1]	Includes salary continuance and health and welfare severance benefits.
[2]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.

Severance Severance - Narrative

Severance Severance - Narrative (Details) - USD ($) $ in Millions		1 Months Ended			3 Months Ended
		Nov. 30, 2017	Jun. 30, 2017	Aug. 31, 2015	Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs					$ 8	$ 4
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Effect on Future Earnings, Amount		$ 250		$ 400
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]				$ 2	$ 3
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			$ 17
[1]	The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.

Mezzanine Equity Mezzanine Equi

Mezzanine Equity Mezzanine Equity (Details) - USD ($) $ in Millions	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross		$ 0	$ 212
Exelon Generation Co L L C [Member]
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross	$ 87	$ 0	$ 212

Changes in Accumulated Other104

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		$ 32,187
Beginning Balance		29,896
Amounts reclassified from AOCI(b)		44		$ 40
Other comprehensive income (loss)		72		(12)
Ending balance		32,565
Ending Balance		30,231
Gains and (losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(14)		(17)
OCI before reclassifications	[1]	8		2
Amounts reclassified from AOCI(b)	[1],[2]	0		4
Other comprehensive income (loss)	[1]	8		6
Ending balance	[1]	(6)		(11)
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	[1]	0
Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	10		4
OCI before reclassifications	[1]	0		1
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		1
Ending balance	[1]	0		5
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	[1],[3]	(10)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(2,998)	[4]	(2,610)
OCI before reclassifications	[1]	18		(59)
Amounts reclassified from AOCI(b)	[1],[2],[5]	44		36
Other comprehensive income (loss)	[1]	62		(23)
Ending balance	[1]	(2,936)		(2,633)
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	[1]	0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(23)		(30)
OCI before reclassifications	[1]	1		1
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	1		1
Ending balance	[1]	(22)		(29)
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	[1]	0
AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(1)		(7)
OCI before reclassifications	[1]	0		5
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		5
Ending balance	[1]	(1)		(2)
AOCI of Investments in 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	[1]	0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]	(3,026)		(2,660)
OCI before reclassifications	[1]	27		(50)
Amounts reclassified from AOCI(b)	[1],[2]	44		40
Other comprehensive income (loss)	[1]	71		(10)
Ending balance	[1]	(2,965)		(2,670)
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	[1]	(10)
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		15,959
Amounts reclassified from AOCI(b)				4
Other comprehensive income (loss)		7		11
Ending Balance		15,958
Exelon Generation Co L L C [Member] | Gains and (losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	(16)		(19)
OCI before reclassifications	[1]	7		2
Amounts reclassified from AOCI(b)	[1],[2]	0		4
Other comprehensive income (loss)	[1]	7		6
Ending Balance	[1]	(9)		(13)
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	[1]	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	[1]	3		2
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	0		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	[1],[3]	(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	[1]	0		0
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0	[5]
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	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	[1]	0
Exelon Generation Co L L C [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	(23)		(30)
OCI before reclassifications	[1]	(1)		1
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	(1)		1
Ending Balance	[1]	(24)		(29)
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	[1]	0
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	(1)		(7)
OCI before reclassifications	[1]	0		6
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		6
Ending Balance	[1]	(1)		(1)
Exelon Generation Co L L C [Member] | AOCI of Investments in 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	[1]	0
Exelon Generation Co L L C [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	(37)		(54)
OCI before reclassifications	[1]	6		9
Amounts reclassified from AOCI(b)	[1],[2]	0		4
Other comprehensive income (loss)	[1]	6		13
Ending Balance	[1]	(34)		(41)
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	[1]	(3)
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance		3,577
Ending Balance		3,403
PECO Energy Co [Member] | Gains and (losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	0		0
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	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	[1]	0
PECO Energy Co [Member] | Unrealized Gains and (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	1		1
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	0		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	[1],[3]	(1)
PECO Energy Co [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	0		0
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	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	[1]	0
PECO Energy Co [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	0		0
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	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	[1]	0
PECO Energy Co [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	0		0
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	0		0
PECO Energy Co [Member] | AOCI of Investments in 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	[1]	0
PECO Energy Co [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[1]	1		1
OCI before reclassifications	[1]	0		0
Amounts reclassified from AOCI(b)	[1],[2]	0		0
Other comprehensive income (loss)	[1]	0		0
Ending Balance	[1]	0		$ 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	[1]	$ (1)
[1]	All amounts are net of tax and noncontrolling interest. Amounts in parenthesis represent a decrease in AOCI.
[2]	See next tables for details about these reclassifications.
[3]	Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and 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 2 — New Accounting Standards for additional information.
[4]	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 2 — New Accounting Standards for additional information.
[5]	Amounts in parenthesis represent a decrease in net income.

Changes in Accumulated Other105

Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		$ 59	$ 211
Amortization of pension and other postretirement benefit plan items		4
Amounts reclassified from AOCI		(44)	(40)
Gains and (losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[1],[2]	0	(4)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[3],[4]	23	23
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[3],[4]	(83)	(81)
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	[3]	(60)	(58)
Tax benefit	[3]	16	22
Amounts reclassified from AOCI	[1],[2],[3]	(44)	(36)
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)			3
Cash Flow Hedging [Member] | Gains and (losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other cash flow hedges	[3]		(7)
Total before tax	[3]		(7)
Income Tax Expense (Benefit)	[3]		3
Net of tax	[3]		(4)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		9	123
Amortization of pension and other postretirement benefit plan items		3
Amounts reclassified from AOCI			(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	[1],[2]	0	(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	[3],[4]		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	[3],[4]		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	[3]		0
Tax benefit	[3]		0
Amounts reclassified from AOCI	[1],[2]	$ 0	0	[3]
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Gains and (losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other cash flow hedges	[3]		(7)
Total before tax	[3]		(7)
Income Tax Expense (Benefit)	[3]		3
Net of tax	[3]		$ (4)
[1]	All amounts are net of tax and noncontrolling interest. Amounts in parenthesis represent a decrease in AOCI.
[2]	See next tables for details about these reclassifications.
[3]	Amounts in parenthesis represent a decrease in net income.
[4]	This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional details).

Changes in Accumulated Other106

Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ (27)	$ (28)
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	6	10
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(22)	(32)
Pension and Non-Pension Postretirement Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(7)	0
Gains and (losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(3)	(1)
Unrealized Gains and (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized (loss) on investments in unconsolidated affiliates	(1)	(4)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0	(1)
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(4)	(4)
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	(3)	(1)
Exelon Generation Co L L C [Member] | Unrealized Gains and (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized (loss) on investments in unconsolidated affiliates	$ (1)	$ (3)

Earnings Per Share and Equity -

Earnings Per Share and Equity - Schedule of Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 585	$ 990
Weighted average common shares outstanding — basic	966	928
Assumed exercise and/or distributions of stock-based awards	2	2
Weighted average common shares outstanding — diluted	968	930

Earnings Per Share and Equit108

Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Statement Of Equity Line Item [Line Items]
Treasury Stock, Shares	1,832,457		1,832,457
Treasury Stock, Value	$ 123		$ 123
Employee Stock Option [Member]
Statement Of Equity Line Item [Line Items]
Stock options not included in the calculation of diluted common shares outstanding	5,000,000	9,000,000
Pepco Holdings [Member]
Statement Of Equity Line Item [Line Items]
Stock options not included in the calculation of diluted common shares outstanding	0	0

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Mar. 31, 2018USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,637
Guarantor Obligations, Maximum Exposure, Undiscounted	58
Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,586	[1]
Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	378
Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,651	[2]
Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,996
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,533	[1]
Exelon Generation Co L L C [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,463	[2]
Commonwealth Edison Co [Member]
Other Commitments [Line Items]
Other Commitment	211
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	2	[1]
Commonwealth Edison Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	188
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	15
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	5	[1]
Baltimore Gas and Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	10	[2]
PEPCO Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	89
PEPCO Holdings Inc [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
PEPCO Holdings Inc [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
PEPCO Holdings Inc [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	66	[2]
PEPCO Holdings Inc [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	40
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1	[1]
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Potomac Electric Power Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	32	[2]
Potomac Electric Power Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	7	[3]
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	13
Guarantor Obligations, Maximum Exposure, Undiscounted	24
Delmarva Power and Light Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Delmarva Power and Light Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Delmarva Power and Light Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	4	[2]
Delmarva Power and Light Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	9	[3]
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	11
Guarantor Obligations, Maximum Exposure, Undiscounted	16
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	5	[2]
Atlantic City Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	$ 6	[3]
[1]	(a)Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[2]	(b)Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[3]	(c)Represents the maximum potential obligation in the event that the fair value of certain leased equipment and fleet vehicles is zero at the end of the maximum lease term. The maximum lease term associated with these assets ranges from 3 to 8 years. The maximum potential obligation at the end of the minimum lease term would be $58 million, $17 million of which is a guarantee by Pepco, $24 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.

Commitments and Contingencie110

Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 462	$ 466
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	117	117
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	283	285
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	29	30
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	5	5
PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	28	29
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	26	27
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	313	315
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	281	283
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	28	28
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	4	4
Accrual For MGP Investigation And Remediation [Member] | PEPCO Holdings Inc [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0

Commitments and Contingencie111

Commitments and Contingencies - Narrative (Details) shares in Millions, number in Millions, $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2018USD ($)Open_claimMWshares	Mar. 31, 2017shares	Dec. 31, 2016MW	Dec. 31, 2017USD ($)Open_claim	Mar. 31, 2018	Mar. 31, 2018MGPSite	Mar. 31, 2018gal	Sep. 30, 2017USD ($)MGPSite
Commitments And Contingencies Additional Narrative Information [Line Items]
Commitments and Contingencies
BusinessAcquisitionResidualcommitment | MW	55
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 58
Loss Contingency, Loss in Period	$ 50
Power Volume | MW	220		10
Open Asbestos Related Personal Injury Claims | Open_claim				232
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Commitments and Contingencies
Estimated Insurance Recoveries	3,200
Accrued Insurance, Current	13,200
Prepaid Reinsurance Premiums	360
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	450
Maximum liability per nuclear incident	13,000
Costs Incurred, Development Costs	458
Accrual for Environmental Loss Contingencies, Component Amount								$ 90
Liability for Asbestos and Environmental Claims, Gross	76			78
Liability for Asbestos and Environmental Claims, Net	21
Liability for Asbestos and Environmental Claims, Net, Payment for Claims	55
Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Environmental Remediation Expense	10
Number of Real Estate Properties | MGPSite								9
Commonwealth Edison Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Mgp Site Contingency Approved Cleanup Count | MGPSite						42
Mgp Site Contingency Count | MGPSite						20
Mgp Site Contingency Monitoring Count | MGPSite						22
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Accrued Liabilities and Other Liabilities	30			$ 28
PECO Energy Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Mgp Site Contingency Approved Cleanup Count | MGPSite						26
Mgp Site Contingency Count | MGPSite						17
Mgp Site Contingency Monitoring Count | MGPSite						9
Baltimore Gas and Electric Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Mgp Site Contingency Approved Cleanup Count | MGPSite						13
Mgp Site Contingency Monitoring Count					13	4
Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	24
Mgp Site Contingency Approved Cleanup Count | gal							3
Mgp Site Contingency Count | MGPSite						2
Maximum [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Loss Contingency, New Claims Filed, Number | Open_claim				20,000,000
Maximum [Member] | Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Loss Contingency, Estimate of Possible Loss								$ 18
Maximum [Member] | Calpine Corporation [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Loss Contingency, Estimate of Possible Loss								10
Minimum [Member] | Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Loss Contingency, Estimate of Possible Loss								$ 7
Nuclear Insurance Premiums [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	2,800
Nuclear Insurance Premiums [Member] | Maximum [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	$ 420
Pepco Holdings [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares	0	0
West Lake [Member] | Minimum [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Loss Contingency, New Claims Filed, Number | Open_claim	340,000,000

Commitments and Contingencies M

Commitments and Contingencies Merger Commitment (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)MGPSiteMW	Dec. 31, 2017USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,637
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,996
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	$ 40
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Mgp Site Contingency Count | MGPSite	2
Other Commitment	$ 13
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	11
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	513	$ 0
Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	122
Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	165
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings LLC [Member] | Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	75
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	84
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	67
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings LLC [Member] | Delmarva Power and Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	8
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	315
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings LLC [Member] | Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 95
Wind Assets [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
OtherNonFinancialCommitment1 | MW	100
Purchase Commitment | MW	120
Other Solar Projects [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
OtherNonFinancialCommitment1 | MW	27
Business Acquisition, Expected New Generation Mwh | MW	37
Minimum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	285
Maximum [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Business Acquisition, Expected New Generation Mwh | MW	300
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member] | Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Mutual Property Insurance Distribution To Members	$ 31

Supplemental Financial Infor113

Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 235	$ 224
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		46	68	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		56	32	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(75)	222
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(96)	166
Net unrealized income (losses) on pledged assets		(2)	(1)
Regulatory offset to decommissioning trust fund-related activities		24	(234)	[2]
Total decommissioning-related activities		47	(253)
Investment income		4	2
Unrecognized Tax Benefits Interest Income		2	1
AFUDC - equity		18	17
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		10	26
Other Income		5	10
Other, net		(28)	257
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		32	32
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	46	68
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	56	32
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(75)	222
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		(96)	166
Net unrealized income (losses) on pledged assets		(2)	(1)
Regulatory offset to decommissioning trust fund-related activities	[2]	24	(234)
Total decommissioning-related activities		47	(253)
Investment income		2	2
Unrecognized Tax Benefits Interest Income		1	0
AFUDC - equity		0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		0	4
Other, net		(44)	259
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		61	59
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		6	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		2	2
Other, net		8	4
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		33	31
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		2	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		0	0
Other, net		2	2
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		26	26
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		4	4
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		0	0
Other, net		4	4
Pepco Holdings LLC [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		83	76
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		6	9
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		5	4
Other, net		11	13
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		77	71
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		5	5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		3	3
Other, net		8	8
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		6	5
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		1	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		1	1
Other, net		2	3
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		0	0
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units		0	0	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units		0	0	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0
Net unrealized income (losses) on pledged assets		0	0
Regulatory offset to decommissioning trust fund-related activities		0	0	[2]
Total decommissioning-related activities		0	0
Investment income		0	0
Unrecognized Tax Benefits Interest Income		0	0
AFUDC - equity		0	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0
Other Income		1	0
Other, net		$ 1	$ 2
[1]	Includes investment income and realized gains and losses on sales of investments of the trust funds.
[2]	Includes the elimination of NDT fund activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 15 — Asset Retirement Obligations of the Exelon 2017 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

Supplemental Financial Infor114

Supplemental Financial Information Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 235	$ 224
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	32	32
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	61	59
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	33	31
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	26	26
Pepco Holdings LLC [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	83	76
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	77	71
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	6	5
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 0	$ 0

Supplemental Financial Infor115

Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		$ 926	$ 754
Regulatory assets	[1]		152	128
Amortization of intangible assets, net	[1]		13	14
Amortization of Power Contracts Emission Credits	[2]		3	2
Amortization of Nuclear Fuel Lease	[3]		287	264
Asset Retirement Obligation, Accretion Expense	[4]		120	112
Total depreciation, amortization and accretion			1,501	1,274
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			145	157
Gain (loss) on equity method investments			7	10
Provision for uncollectible accounts			64	34
Stock-based compensation costs			29	31
Other Decommissioning Related Activity	[5]		(31)	(84)
Energy-related options	[6]		(7)	(4)
Amortization of regulatory asset related to debt costs			2	2
Amortization of rate stabilization deferral			7	(14)
Amortization of debt fair value adjustment			(3)	(5)
Discrete impacts from EIMA	[7]		(4)	(24)
Amortization of debt costs			9	9
Inventory Write-down			13	2
Other			9	4
Total other noncash operating activities			240	118
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(177)	(193)
Payments to Acquire Businesses, Gross			0	212
Capitalized Costs, Asset Retirement Costs			32
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				10
Stock Issued			1	2
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		436	289
Regulatory assets	[1]		0	0
Amortization of intangible assets, net	[1]		12	13
Amortization of Power Contracts Emission Credits	[2]		3	2
Amortization of Nuclear Fuel Lease	[3]		287	264
Asset Retirement Obligation, Accretion Expense	[4]		120	110
Total depreciation, amortization and accretion			858	678
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			51	54
Gain (loss) on equity method investments			7	10
Provision for uncollectible accounts			11	9
Stock-based compensation costs			0	0
Other Decommissioning Related Activity	[5]		(31)	(84)
Energy-related options	[6]		(7)	(4)
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			(3)	(3)
Discrete impacts from EIMA			0	0
Amortization of debt costs			3	4
Inventory Write-down			12	1
Other			2	3
Total other noncash operating activities			45	(10)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(131)	(56)
Payments to Acquire Businesses, Gross		$ 87	0	212
Capitalized Costs, Asset Retirement Costs			32
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				10
Stock Issued			0	0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		201	190
Regulatory assets	[1]		27	18
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			228	208
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			45	44
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			8	7
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			1	1
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA	[7]		(4)	(24)
Amortization of debt costs			1	1
Inventory Write-down			1	1
Other			(6)	1
Total other noncash operating activities			46	31
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(48)	(66)
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		68	64
Regulatory assets	[1]		7	7
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			75	71
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			5	7
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			17	17
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Other			(1)	(1)
Total other noncash operating activities			21	23
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(25)	(42)
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		82	80
Regulatory assets	[1]		52	48
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense			0	0	[4]
Total depreciation, amortization and accretion			134	128
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			14	16
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			8	5
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	7
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Other			(2)	(4)
Total other noncash operating activities			20	24
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(11)	1
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		53	50
Regulatory assets	[1]		43	32
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			96	82
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			4	7
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			6	(5)
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			1	(15)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Other			(1)	(2)
Total other noncash operating activities			10	(15)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			(19)	(6)
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		32	30
Regulatory assets	[1]		13	9
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			45	39
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			0	3
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			8	(1)
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			6	(6)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Other			5	(3)
Total other noncash operating activities			19	(7)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			14	9
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		23	21
Regulatory assets	[1]		10	14
Amortization of intangible assets, net	[1]		0	0
Amortization of Power Contracts Emission Credits	[2]		0	0
Amortization of Nuclear Fuel Lease	[3]		0	0
Asset Retirement Obligation, Accretion Expense	[4]		0	0
Total depreciation, amortization and accretion			33	35
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			3	3
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			5	1
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Other			1	(2)
Total other noncash operating activities			9	2
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			27	0
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation			117	112
Regulatory assets			66	55
Amortization of intangible assets, net			0	0
Amortization of Power Contracts Emission Credits			0	0
Amortization of Nuclear Fuel Lease			0	0
Asset Retirement Obligation, Accretion Expense			0	0
Total depreciation, amortization and accretion			183	167
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			15	24
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			20	(4)
Stock-based compensation costs			0	0
Other Decommissioning Related Activity			0	0
Energy-related options			0	0
Amortization of regulatory asset related to debt costs			1	1
Amortization of rate stabilization deferral			7	(21)
Amortization of debt fair value adjustment			0	(2)
Discrete impacts from EIMA			0	0
Amortization of debt costs			1	0
Inventory Write-down			0	0
Other			9	(6)
Total other noncash operating activities			53	(8)
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Capital Expenditures Incurred but Not yet Paid			61	(5)
Capitalized Costs, Asset Retirement Costs			0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			$ 0	$ 0
[1]	Included in Depreciation and amortization on the Registrants' Consolidated Statements of Operations and Comprehensive Income.
[2]	Included in Operating revenues or Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[3]	Included in Purchased power and fuel expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[4]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[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 of the Exelon 2017 Form 10-K 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 in Operating revenues.
[7]	Reflects the change in distribution rates pursuant to EIMA and FEJA, which allows for the recovery of distribution costs by a utility through a pre-established performance-based formula rate tariff. Beginning June 1, 2017, also reflects the change in energy efficiency rates pursuant to FEJA, which allows for the recovery of energy efficiency costs by a utility through a pre-established performance-based formula rate tariff. See Note 6 — Regulatory Matters for more information.

Supplemental Financial Infor116

Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2018		Dec. 31, 2017		Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 21,905	[1]	$ 21,064	[2]
Accounts receivable, net
Allowance for uncollectible accounts	369		322
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	1,099		1,190		$ 889	$ 914	$ 889	$ 914
Cash and Cash Equivalents, at Carrying Value	787		898		609	635
Restricted Cash, Noncurrent	103		85		26	26
Restricted cash	209		207		254	253
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	11,936	[1]	11,428	[2]
Accounts receivable, net
Allowance for uncollectible accounts	115		114
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	737		554		540	448
Cash and Cash Equivalents, at Carrying Value	610		416		400	290
Restricted Cash, Noncurrent	0		0		0	0
Restricted cash	127		138		140	158
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,263		3,159
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,391		4,269
Accounts receivable, net
Allowance for uncollectible accounts	89		73
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	162		144		34	58
Cash and Cash Equivalents, at Carrying Value	70		76		31	56
Restricted Cash, Noncurrent	83		63		0	0
Restricted cash	9		5		3	2
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,445		3,411
Accounts receivable, net
Allowance for uncollectible accounts	68		56
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	26		275		32	67
Cash and Cash Equivalents, at Carrying Value	21		271		28	63
Restricted Cash, Noncurrent	0		0		0	0
Restricted cash	5		4		4	4
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,471		3,405
Accounts receivable, net
Allowance for uncollectible accounts	31		24
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	24		18		57	50
Cash and Cash Equivalents, at Carrying Value	22		17		11	23
Restricted Cash, Noncurrent	0		0		3	3
Restricted cash	2		1		43	24
Pepco Holdings LLC [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	575		487
Accounts receivable, net
Allowance for uncollectible accounts	66		55
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	103		95		173	236
Cash and Cash Equivalents, at Carrying Value	43		30		109	170
Restricted Cash, Noncurrent	20		23		23	23
Restricted cash	40		42		41	43
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,224		3,177
Accounts receivable, net
Allowance for uncollectible accounts	24		21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	48		40		41	42
Cash and Cash Equivalents, at Carrying Value	15		5		8	9
Restricted Cash, Noncurrent	0		0		0	0
Restricted cash	33		35		33	33
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,273		1,247
Accounts receivable, net
Allowance for uncollectible accounts	22		16
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	7		2		44	46
Cash and Cash Equivalents, at Carrying Value	7		2		44	46
Restricted Cash, Noncurrent	0		0		0	0
Restricted cash	0		0		0	0
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,086		1,066
Accounts receivable, net
Allowance for uncollectible accounts	20		18
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash at End of Period	37		31		84	133
Cash and Cash Equivalents, at Carrying Value	10		2		54	101
Restricted Cash, Noncurrent	20		23		23	23
Restricted cash	$ 7		$ 6		$ 7	$ 9
[1]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,263 million.
[2]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million.

Supplemental Financial Infor117

Supplemental Financial Information - Narrative (Details) - PECO Energy Co [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Net	$ 8	$ 11
Financing Receivable, Allowance for Credit Losses	10	11
Risk Level, Medium [Member]
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Allowance for Credit Losses	3	3
Risk Level, High [Member]
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Allowance for Credit Losses	$ 7	$ 8

Segment Information - Narrative

Segment Information - Narrative (Details)	3 Months Ended
	Mar. 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 - Reconcili

Segment Information - Reconciliation to Consolidated Financial Statements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Rate-regulated electric revenues			$ 0
Rate-regulated natural gas revenues			0
Revenues		$ 9,693	8,747
Operating revenues from affiliates	[1]	0	0
Net income (loss)		636	971
Assets	[2]	117,018		$ 116,770
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,151	1,067
Rate-regulated natural gas revenues		78	66
Revenues		1,251	1,175
Operating revenues from affiliates		4	12
Net income (loss)		65	140
Assets	[3]	21,375		21,247
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues			0
Rate-regulated natural gas revenues			0
Revenues		5,512	4,878
Operating revenues from affiliates		398	330
Net income (loss)		186	399
Assets	[4]	48,375		48,457
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	4,118	3,382
Competitive businesses natural gas revenues	[5]	947	918
Competitive businesses other revenues	[5]	48	250
Rate-regulated electric revenues	[5]	3,955	3,644
Rate-regulated natural gas revenues	[5]	625	553
Shared service and other revenues	[5]	0	0
Revenues	[5]	9,693	8,747
Net income (loss)		636	971
Assets		117,018		116,770
Operating Segments [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Revenues	[6]		11
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	(391)	(328)
Competitive businesses natural gas revenues	[5]	(8)	0
Competitive businesses other revenues	[5]	0	0
Rate-regulated electric revenues	[5]	(18)	(8)
Rate-regulated natural gas revenues	[5]	(4)	(3)
Shared service and other revenues	[5]	(455)	(431)
Revenues	[5]	(876)	(770)
Operating revenues from affiliates	[1]	(876)	(770)
Net income (loss)		0	0
Assets		(10,980)		(10,552)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]	(4)	(4)
Rate-regulated natural gas revenues	[7]	0	0
Shared service and other revenues	[7]	(109)	0
Revenues	[7]	(113)	(4)
Operating revenues from affiliates		(113)	(5)
Net income (loss)		4	12
Assets		(4,948)		(4,987)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[8]	4,509	3,710
Competitive businesses natural gas revenues	[5],[8]	955	918
Competitive businesses other revenues	[5],[8]	48	250
Rate-regulated electric revenues	[5],[8]	0	0
Rate-regulated natural gas revenues	[5],[8]	0	0
Shared service and other revenues	[5],[8]	0	0
Revenues	[5],[8]	5,512	4,878
Net income (loss)	[8]	186	399
Assets	[8]	48,375		48,457
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[8]	400	328
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0	0
Competitive businesses natural gas revenues	[5]	0	0
Competitive businesses other revenues	[5]	0	0
Rate-regulated electric revenues	[5]	1,512	1,298
Rate-regulated natural gas revenues	[5]	0	0
Shared service and other revenues	[5]	0	0
Revenues	[5]	1,512	1,298
Net income (loss)		165	141
Assets		30,002		29,726
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	14	5
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0	0
Competitive businesses natural gas revenues	[5]	0	0
Competitive businesses other revenues	[5]	0	0
Rate-regulated electric revenues	[5]	634	590
Rate-regulated natural gas revenues	[5]	232	206
Shared service and other revenues	[5]	0	0
Revenues	[5]	866	796
Net income (loss)		113	127
Assets		10,218		10,170
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	2	1
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0	0
Competitive businesses natural gas revenues	[5]	0	0
Competitive businesses other revenues	[5]	0	0
Rate-regulated electric revenues	[5]	658	667
Rate-regulated natural gas revenues	[5]	319	284
Shared service and other revenues	[5]	0	0
Revenues	[5]	977	951
Net income (loss)		128	125
Assets		9,195		9,104
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	6	5
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5]	0	0
Competitive businesses natural gas revenues	[5]	0	0
Competitive businesses other revenues	[5]	0	0
Rate-regulated electric revenues	[5],[7]	1,169	1,097
Rate-regulated natural gas revenues	[5],[7]	78	66
Shared service and other revenues	[5],[7]	4	12
Revenues	[5],[7]	1,251	1,175
Net income (loss)		65	140
Assets		21,375		21,247
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1]	4	12
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]	557	530
Rate-regulated natural gas revenues	[7]	0	0
Shared service and other revenues	[7]	0	0
Revenues	[7]	557	530
Net income (loss)		31	58
Assets		7,896		7,832
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	1
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]	306	296
Rate-regulated natural gas revenues	[7]	78	66
Shared service and other revenues	[7]	0	0
Revenues	[7]	384	362
Net income (loss)		31	57
Assets		4,383		4,357
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7]	310	275
Rate-regulated natural gas revenues	[7]	0	0
Shared service and other revenues	[7]	0	0
Revenues	[7]	310	275
Net income (loss)		7	28
Assets		3,530		3,445
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1	1
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues	[5],[9]	0	0
Competitive businesses natural gas revenues	[5],[9]	0	0
Competitive businesses other revenues	[5],[9]	0	0
Rate-regulated electric revenues	[5],[9]	0	0
Rate-regulated natural gas revenues	[5],[9]	0	0
Shared service and other revenues	[5],[9]	451	419
Revenues	[5],[9]	451	419
Net income (loss)	[9]	(21)	39
Assets	[9]	8,833		8,618
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues	[7],[10]	0	0
Rate-regulated natural gas revenues	[7],[10]	0	0
Shared service and other revenues	[7],[10]	113	12
Revenues	[7],[10]	113	12
Net income (loss)	[10]	(8)	(15)
Assets	[10]	10,514		$ 10,600
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[1],[9]	450	419
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[10]	112	13
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,440	1,425
Generation Mid Atlantic [Member] | PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		37	45
Generation Mid Atlantic [Member] | Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		65	134
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		52	83
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		46	51
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6	9
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[11]	1,435	1,429
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		5	(4)
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,346	1,053
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		194	5
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[11]	1,344	1,051
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ 2	$ 2
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[2]	Exelon’s consolidated assets include $9,727 million and $9,597 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Exelon’s consolidated liabilities include $3,556 million and $3,618 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Exelon. See Note 3 — Variable Interest Entities.
[3]	PHI’s consolidated total assets include $39 million and $41 million at March 31, 2018 and December 31, 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 $95 million and $102 million at March 31, 2018 and December 31, 2017, respectively, of PHI's consolidated VIE for which the VIE creditors do not have recourse to PHI. See Note 3 — Variable Interest Entities.
[4]	Generation’s consolidated assets include $9,688 million and $9,556 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs that can only be used to settle the liabilities of the VIE. Generation’s consolidated liabilities include $3,461 million and $3,516 million at March 31, 2018 and December 31, 2017, respectively, of certain VIEs for which the VIE creditors do not have recourse to Generation. See Note 3 — Variable Interest Entities.
[5]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017.
[6]	Includes late payment charge revenues.
[7]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017.
[8]	Generation includes the six reportable segments shown below: Mid-Atlantic, Midwest, New England, New York, ERCOT and Other Power Regions. Intersegment revenues for Generation for the three months ended March 31, 2018 include revenue from sales to PECO of $37 million, sales to BGE of $65 million, sales to Pepco of $52 million, sales to DPL of $46 million and sales to ACE of $6 million in the Mid-Atlantic region, and sales to ComEd of $194 million in the Midwest region, which eliminate upon consolidation. For the three months ended March 31, 2017, intersegment revenues for Generation include revenue from sales to PECO of $45 million, sales to BGE of $134 million, sales to Pepco of $83 million, sales to DPL of $51 million and sales to ACE of $9 million in the Mid-Atlantic region, and sales to ComEd of $5 million in the Midwest region, which eliminate upon consolidation.
[9]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[10]	Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities
[11]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.

Segment Information - Generatio

Segment Information - Generation Total Revenues (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenues		$ 9,693	$ 8,747
Operating revenues from affiliates	[1]	0	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,440	1,425
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,346	1,053
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		792	547
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		409	297
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		209	191
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		288	184
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,484	3,697
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		980	930
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2]	48	251
Unrealized Gain (Loss) on Securities		(98)	44
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,512	4,878
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	9,693	8,747
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,435	1,429
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,344	1,051
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	793	549
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	410	300
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	208	192
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	319	189
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,509	3,710
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	955	918
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts			(3)
Unrealized Gain (Loss) on Securities		(266)	(49)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	5,512	4,878
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[4]	48	250
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	(876)	(770)
Operating revenues from affiliates	[1]	(876)	(770)
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		5	(4)
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	2
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(1)	(2)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(1)	(3)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1	(1)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(31)	(5)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(25)	(13)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		25	12
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[2]	0	1
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0	0
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,355	1,494
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	1,273	980
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	725	589
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	439	303
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	149	168
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	210	128
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,151	3,662
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	522	768
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4]	4,807	4,636
Revenue from Contract with Customer [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[4]	134	206
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	80	(65)
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	71	71
Other [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	68	(40)
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	(29)	(3)
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	59	24
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	109	61
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	358	48
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	433	150
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues	[4],[5]	705	242
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[2],[4],[5]	$ (86)	$ 44
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[2]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $3 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the three months ended March 31, 2017, unrealized mark-to-market losses of $98 million and gains of $44 million for the three months ended March 31, 2018 and 2017, respectively, and elimination of intersegment revenues.
[3]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017.
[4]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.
[5]	Includes revenues from derivatives and leases.

Segment Information - Genera121

Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		$ 850	$ 773
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		860	715
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		119	111
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		283	143
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		36	69
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		117	64
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,265	1,875
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	[1]	(46)	205
Unrealized Gain (Loss) on Securities		(98)	44
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel		2,219	2,080
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	836	755
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	847	704
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	122	115
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	282	143
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	106	94
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	157	108
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	2,350	1,919
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[1],[2]	(131)	161
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			(3)
Unrealized Gain (Loss) on Securities		(266)	(49)
Nuclear Fuel Amortization		(15)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	[2]	2,219	2,080
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		14	18
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		13	11
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(3)	(4)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		1	0
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(70)	(25)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(40)	(44)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		(85)	(44)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	[1]	85	44
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel		$ 0	$ 0
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $3 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended March 31, 2017, unrealized mark-to-market losses of $266 million and $49 million for the three months ended March 31, 2018 and 2017, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 7 - Early Nuclear Plant Retirements of the Combined Notes to Consolidated Financial Statements of $15 million decrease to revenue net of purchased power and fuel expense for the three months ended March 31, 2018, and the elimination of intersegment revenue net of purchased power and fuel expense.
[2]	Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.

Segment Information Segment Inf

Segment Information Segment Information - Electric and Gas Revenue by Customer Class (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues			$ 0
Rate-regulated natural gas revenues			0
Revenues from alternative revenue programs		$ 10	79
Revenues		9,693	8,747
Revenue from Related Parties	[1]	0	0
Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[2]	3,955	3,644
Rate-regulated natural gas revenues	[2]	625	553
Revenues	[2]	9,693	8,747
Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		1,493	1,279
Rate-regulated natural gas revenues			0
Revenues from alternative revenue programs		5	14
Revenues		1,512	1,298
Revenue from Related Parties		14	5
Commonwealth Edison Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	5	14
Revenues	[3]		0
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	1,498	1,276
Revenue from Related Parties		14	5
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	9	8
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		717	611
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		385	328
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		152	107
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		14	12
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	230	218
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		1,498	1,276
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	14	22
PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		633	589
Rate-regulated natural gas revenues		232	206
Revenues from alternative revenue programs		(1)	0
Revenues		866	796
Revenue from Related Parties		2	1
PECO Energy Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	(1)	0
Revenues	[3]		0
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	632	587
Revenue from Related Parties		2	1
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	3	3
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		403	382
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		101	97
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		58	52
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		8	8
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	62	48
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	232	206
Revenue from Related Parties		0	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		161	142
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		62	55
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		1	0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		6	6
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	2	3
PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		864	793
PECO Energy Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	2	3
Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		654	640
Rate-regulated natural gas revenues		330	271
Revenues from alternative revenue programs		(13)	35
Revenues		977	951
Revenue from Related Parties		6	5
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	(13)	35
Revenues	[3]		0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	652	638
Revenue from Related Parties		2	2
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	4	4
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		393	386
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		68	69
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		106	108
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		7	7
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	78	68
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	332	273
Revenue from Related Parties		4	3
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	2	1
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		224	185
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		34	30
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		47	44
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	27	14
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		984	911
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	(7)	40
Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		1,151	1,067
Rate-regulated natural gas revenues		78	66
Revenues from alternative revenue programs		18	30
Revenues		1,251	1,175
Revenue from Related Parties		4	12
Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	18	30
Revenues	[3]		11
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	1,154	1,066
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	1	2
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		610	554
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		115	114
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		259	257
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		14	15
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	156	126
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	78	66
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		47	40
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		18	17
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		4	2
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		5	5
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	4	2
Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		1,232	1,132
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	19	43
Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		536	514
Rate-regulated natural gas revenues			0
Revenues from alternative revenue programs		19	15
Revenues		557	530
Revenue from Related Parties		2	1
Potomac Electric Power Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	19	15
Revenues	[3]		0
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	537	514
Revenue from Related Parties		2	1
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	1	1
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		259	236
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		32	34
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		190	188
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		7	8
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	49	48
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		537	514
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	20	16
Delmarva Power and Light Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		303	285
Rate-regulated natural gas revenues		78	66
Revenues from alternative revenue programs		1	9
Revenues		384	362
Revenue from Related Parties		2	2
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	1	9
Revenues	[3]		0
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	305	286
Revenue from Related Parties		2	2
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	0	1
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		191	176
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		46	44
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		23	24
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		4	4
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	41	38
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	78	66
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		47	40
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		18	17
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		4	2
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		5	5
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	4	2
Delmarva Power and Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		383	352
Delmarva Power and Light Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	1	10
Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		311	268
Rate-regulated natural gas revenues			0
Revenues from alternative revenue programs		(2)	6
Revenues		310	275
Revenue from Related Parties		1	1
Atlantic City Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	[3]	(2)	6
Revenues	[3]		0
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[4]	312	269
Revenue from Related Parties		1	1
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[3]	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		160	142
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		37	36
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		46	45
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues		3	3
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	[5]	66	43
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[6]	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[3]	0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues		0	0
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	[7]	0	0
Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues		312	269
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	[3]	$ (2)	$ 6
[1]	Intersegment revenues exclude sales to unconsolidated affiliates. The intersegment profit associated with Generation’s sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in Operating revenues in the Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended March 31, 2018 and 2017.
[3]	Includes late payment charge revenues.
[4]	Includes operating revenues from affiliates of $14 million, $2 million, $2 million, $4 million, $2 million, $2 million, and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2018 and $5 million, $1 million, $2 million, $1 million, $1 million, $2 million, and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended March 31, 2017.
[5]	Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue.
[6]	Includes operating revenues from affiliates of less than $1 million and $4 million at PECO and BGE, respectively, for the three months ended March 31, 2018 and less than $1 million and $3 million at PECO and BGE, respectively, for the three months ended March 31, 2017.
[7]	Includes revenues from off-system natural gas sales.

Subsequent Event (Details)

Subsequent Event (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)MW	Mar. 31, 2017USD ($)	Dec. 31, 2016MW
Subsequent Event [Line Items]
Power Volume | MW	220		10
Taxes, Miscellaneous | $	$ 446	$ 436