Exelon Generation 10-Q 1 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2018shares
Entity Registrant Name	EXELON CORP
Entity Central Index Key	1,109,357
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding	967,009,746
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	127,021,324
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				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Operating revenues
Operating Revenue	$ 4,971		$ 4,455		$ 14,387		$ 12,955
Regulated Operating Revenue	4,457		4,259		12,824		12,034
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(25)		54		(41)		191
Operating revenues from affiliates	0	[1]	0	[1]	0	[2]	0
Total operating revenues	9,403		8,768		27,170		25,180
Operating expenses
Competitive businesses purchased power and fuel	2,977		2,316		8,542		7,268
Cost of Purchased Power	1,355		1,226		3,832		3,259
Operating and maintenance	2,346		2,275		7,036		7,658
Depreciation and amortization	1,105		1,002		3,284		2,814
Taxes other than income	469		456		1,342		1,313
Total operating expenses	8,252		7,275		24,036		22,312
Income (Loss) from Equity Method Investments					(22)		(26)
Gain (Loss) on sales of assets and businesses	(5)		(1)		55		4
Bargain purchase gain	0		7		0		233
Operating income (loss)	1,146		1,499		3,189		3,105
Other income and (deductions)
Interest expense, net	(387)		(377)		(1,119)		(1,165)
Interest expense to affiliates	(6)		(9)		(19)		(29)
Other, net	194		210		212		643
Total other income and (deductions)	(199)		(176)		(926)		(551)
Income (loss) before income taxes	947		1,323		2,263		2,554
Income taxes	137		451		262		601
Equity in earnings (losses) of unconsolidated affiliates	(10)		(7)		(22)		(25)
Net income (loss)	800		865		1,979		1,928
Net Income (Loss) Attributable to Noncontrolling Interest	67		42		121		21
Net income (loss) attributable to common shareholders	733		823		1,858		1,907
Other comprehensive income (loss), net of income taxes
Prior service benefit reclassified to periodic benefit cost	(17)		(14)		(50)		(42)
Actuarial loss reclassified to periodic benefit cost	62		49		186		147
Pension and non-pension postretirement benefit plan valuation adjustment	5		3		22		(55)
Unrealized gain (loss) on cash flow hedges	0		0		12		5
Unrealized gain on investments in unconsolidated affiliates	0		1		3		5
Unrealized gain (loss) on foreign currency translation	2		4		(4)		7
Unrealized gain on marketable securities	0		1		0		2
Other comprehensive income	52		44		169		69
Comprehensive income (loss)	852		909		2,148		1,997
Comprehensive income attributable to noncontrolling interests	$ 67		$ 42		$ 123		$ 19
Average shares of common stock outstanding:
Weighted Average Number of Shares Outstanding, Basic	968		962		967		941
Weighted Average Number of Shares Outstanding, Diluted	970		965		969		943
Earnings per average common share:
Earnings Per Share, Basic	$ 0.76		$ 0.86		$ 1.92		$ 2.03
Earnings Per Share, Diluted	0.76		0.85		1.92		2.02
Dividends declared per common share	$ 0.35		$ 0.33		$ 1.04		$ 0.98
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 785		$ 867		$ 2,025		$ 1,978
Exelon Generation Co L L C [Member]
Operating revenues
Operating Revenue	4,970		4,454		14,389		12,949
Regulated Operating Revenue			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates	308		296		979		894
Total operating revenues	5,278		4,750		15,368		13,843
Operating expenses
Competitive businesses purchased power and fuel	2,977		2,315		8,542		7,267
Purchased power from affiliate	3		16		10		19
Operating and maintenance	1,218		1,205		3,643		4,343
Operating and maintenance from affiliates	152		171		483		536
Depreciation and amortization	468		410		1,383		1,046
Taxes other than income	143		141		414		425
Total operating expenses	4,961		4,258		14,475		13,636
Income (Loss) from Equity Method Investments					(23)		(26)
Gain (Loss) on sales of assets and businesses	(6)		(2)		48		3
Bargain purchase gain	0		7		0		233
Operating income (loss)	311		497		941		443
Other income and (deductions)
Interest expense, net	(93)		(103)		(278)		(313)
Interest expense to affiliates	(8)		(10)		(27)		(29)
Other, net	179		209		164		648
Total other income and (deductions)	78		96		(141)		306
Income (loss) before income taxes	389		593		800		749
Income taxes	78		239		110		215
Equity in earnings (losses) of unconsolidated affiliates	(11)		(8)		(23)		(26)
Net income (loss)	300		346		667		508
Net Income (Loss) Attributable to Noncontrolling Interest	66		42		120		21
Net income (loss) attributable to membership interest	234		304		547		487
Other comprehensive income (loss), net of income taxes
Unrealized gain (loss) on cash flow hedges	0		0		12		5
Unrealized gain on investments in unconsolidated affiliates	0		0		3		4
Unrealized gain (loss) on foreign currency translation	2		4		(4)		7
Other comprehensive income	2		4		11		16
Comprehensive income (loss)	302		350		678		524
Comprehensive income attributable to noncontrolling interests	66		42		122		19
Earnings per average common share:
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	236		308		556		505
Commonwealth Edison Co [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	1,609		1,552		4,512		4,167
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(15)		16		(27)		48
Operating revenues from affiliates	4		3		23		12
Total operating revenues	1,598		1,571		4,508		4,227
Operating expenses
Purchased power	496		489		1,281		1,178
Purchased power from affiliate	123		40		421		63
Operating and maintenance	276		277		785		897
Operating and maintenance from affiliates	61		69		189		199
Depreciation and amortization	237		212		696		631
Taxes other than income	82		80		238		223
Total operating expenses	1,275		1,167		3,610		3,191
Income (Loss) from Equity Method Investments					0		0
Gain (Loss) on sales of assets and businesses	0		0		5		0
Operating income (loss)	323		404		903		1,036
Other income and (deductions)
Interest expense, net	(82)		(86)		(251)		(265)
Interest expense to affiliates	(3)		(3)		(10)		(10)
Other, net	7		5		21		14
Total other income and (deductions)	(78)		(84)		(240)		(261)
Income (loss) before income taxes	245		320		663		775
Income taxes	52		131		140		328
Net income (loss)	193		189		523		447
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	193		189		523		447
PECO Energy Co [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	697		660		1,886		1,798
Natural gas operating revenues	57		53		382		338
Revenues from alternative revenue programs	1		0		2		0
Operating revenues from affiliates	2		2		5		5
Total operating revenues	757		715		2,275		2,141
Operating expenses
Purchased power	215		190		576		483
Purchased fuel	14		14		148		126
Purchased power from affiliate	34		31		94		110
Operating and maintenance	184		161		572		488
Operating and maintenance from affiliates	35		36		114		107
Depreciation and amortization	75		72		224		213
Taxes other than income	46		42		125		116
Total operating expenses	603		546		1,853		1,643
Income (Loss) from Equity Method Investments					0		0
Gain (Loss) on sales of assets and businesses	0		0		1		0
Operating income (loss)	154		169		423		498
Other income and (deductions)
Interest expense, net	(28)		(28)		(85)		(84)
Interest expense to affiliates	(4)		(3)		(11)		(9)
Other, net	2		2		4		6
Total other income and (deductions)	(30)		(29)		(92)		(87)
Income (loss) before income taxes	124		140		331		411
Income taxes	(2)		28		(5)		84
Net income (loss)	126		112		336		327
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	126		112		336		327
Baltimore Gas and Electric Company [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	652		626		1,847		1,811
Natural gas operating revenues	79		73		527		438
Revenues from alternative revenue programs	(6)		36		(23)		102
Operating revenues from affiliates	6		3		18		12
Total operating revenues	731		738		2,369		2,363
Operating expenses
Purchased power	183		159		510		407
Purchased fuel	21		13		176		118
Purchased power from affiliate	68		97		195		328
Operating and maintenance	144		138		462		421
Operating and maintenance from affiliates	38		37		116		111
Depreciation and amortization	110		109		358		348
Taxes other than income	64		61		188		180
Total operating expenses	628		614		2,005		1,913
Income (Loss) from Equity Method Investments					0		0
Gain (Loss) on sales of assets and businesses	0		0		1		0
Operating income (loss)	103		124		365		450
Other income and (deductions)
Interest expense, net	(27)		(24)		(78)		(69)
Interest expense to affiliates	0		(2)		0		(11)
Other, net	5		4		14		12
Total other income and (deductions)	(22)		(22)		(64)		(68)
Income (loss) before income taxes	81		102		301		382
Income taxes	18		40		59		151
Net income (loss)	63		62		242		231
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	63		62		242		231
Pepco Holdings LLC [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	1,340		1,278		3,541		3,376
Natural gas operating revenues	23		18		129		105
Revenues from alternative revenue programs	(5)		2		7		41
Operating revenues from affiliates	3		12		11		35
Total operating revenues	1,361		1,310		3,688		3,557
Operating expenses
Purchased power	415		354		1,077		901
Purchased fuel	12		7		65		46
Purchased power from affiliate	82		112		268		371
Operating and maintenance	261		214		751		666
Operating and maintenance from affiliates	31		37		106		108
Depreciation and amortization	192		179		555		511
Taxes other than income	123		122		343		344
Total operating expenses	1,116		1,025		3,165		2,947
Income (Loss) from Equity Method Investments					1		0
Gain (Loss) on sales of assets and businesses	0		0		0		1
Operating income (loss)	245		285		523		611
Other income and (deductions)
Interest expense, net	(65)		(62)		(193)		(183)
Other, net	11		13		33		40
Total other income and (deductions)	(54)		(49)		(160)		(143)
Income (loss) before income taxes	191		236		363		468
Income taxes	4		83		28		109
Equity in earnings (losses) of unconsolidated affiliates	0		0		1		0
Net income (loss)	187		153		336		359
Earnings per average common share:
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	187		153		336		359
Potomac Electric Power Company [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	630		600		1,697		1,622
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(4)		3		6		23
Operating revenues from affiliates	2		1		5		4
Total operating revenues	628		604		1,708		1,649
Operating expenses
Purchased power	131		111		354		268
Purchased power from affiliate	46		57		143		210
Operating and maintenance	84		89		216		296
Operating and maintenance from affiliates	52		14		167		40
Depreciation and amortization	99		82		286		242
Taxes other than income	104		102		288		282
Total operating expenses	516		455		1,454		1,338
Income (Loss) from Equity Method Investments					0		0
Gain (Loss) on sales of assets and businesses	0		0		0		1
Operating income (loss)	112		149		254		312
Other income and (deductions)
Interest expense, net	(32)		(31)		(96)		(89)
Other, net	7		7		23		22
Total other income and (deductions)	(25)		(24)		(73)		(67)
Income (loss) before income taxes	87		125		181		245
Income taxes	(2)		38		7		57
Net income (loss)	89		87		174		188
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	89		87		174		188
Delmarva Power and Light Company [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	302		308		861		851
Natural gas operating revenues	24		18		129		105
Revenues from alternative revenue programs	0		(1)		5		9
Operating revenues from affiliates	2		2		6		6
Total operating revenues	328		327		1,001		971
Operating expenses
Purchased power	96		75		258		215
Purchased fuel	11		7		64		46
Purchased power from affiliate	26		47		103		138
Operating and maintenance	44		71		137		204
Operating and maintenance from affiliates	38		8		119		23
Depreciation and amortization	47		45		135		124
Taxes other than income	15		15		43		43
Total operating expenses	277		268		859		793
Income (Loss) from Equity Method Investments					0		0
Operating income (loss)	51		59		142		178
Other income and (deductions)
Interest expense, net	(15)		(13)		(42)		(38)
Other, net	2		4		7		10
Total other income and (deductions)	(13)		(9)		(35)		(28)
Income (loss) before income taxes	38		50		107		150
Income taxes	5		19		17		43
Net income (loss)	33		31		90		107
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	33		31		90		107
Atlantic City Electric Company [Member]
Operating revenues
Operating Revenue			0				0
Regulated Operating Revenue			0				0
Electric operating revenues	406		370		983		904
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(1)		0		(4)		9
Operating revenues from affiliates	1		0		2		2
Total operating revenues	406		370		981		915
Operating expenses
Purchased power	188		169		465		418
Purchased power from affiliate	10		7		21		24
Operating and maintenance	52		66		146		205
Operating and maintenance from affiliates	33		6		104		20
Depreciation and amortization	38		41		107		113
Taxes other than income	1		2		4		6
Total operating expenses	322		291		847		786
Income (Loss) from Equity Method Investments					0		0
Operating income (loss)	84		79		134		129
Other income and (deductions)
Interest expense, net	(16)		(15)		(48)		(46)
Other, net	1		1		2		6
Total other income and (deductions)	(15)		(14)		(46)		(40)
Income (loss) before income taxes	69		65		88		89
Income taxes	8		24		12		12
Net income (loss)	61		41		76		77
Other comprehensive income (loss), net of income taxes
Comprehensive income (loss)	$ 61		$ 41		$ 76		$ 77
[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]	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	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 1,979	$ 1,928
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	4,511	3,999
Impairment of long-lived assets and losses on regulatory assets	49	488
Gain on sales of assets and businesses	(55)	(5)
Bargain purchase gain	0	(233)
Deferred income taxes and amortization of investment tax credits	97	444
Net fair value changes related to derivatives	67	149
Net realized and unrealized gains on nuclear decommissioning trust fund investments	(21)	(429)
Other non-cash operating activities	804	603
Changes in assets and liabilities:
Accounts receivable	(167)	184
Inventories	(24)	(87)
Accounts payable and accrued expenses	84	(591)
Option premiums (paid) received, net	(36)	35
Collateral received (posted), net	222	(100)
Income taxes	166	167
Pension and non-pension postretirement benefit contributions	(362)	(344)
Other assets and liabilities	(639)	(535)
Net cash flows provided by (used in) operating activities	6,675	5,673
Cash flows from investing activities
Capital expenditures	(5,497)	(5,556)
Proceeds from nuclear decommissioning trust fund sales	6,379	6,848
Investment in nuclear decommissioning trust funds	(6,553)	(7,044)
Acquisition of assets and businesses, net	(57)	(208)
Proceeds from sales of assets and businesses	90	219
Other investing activities	29	(2)
Net cash flows provided by (used in) investing activities	(5,609)	(5,743)
Cash flows from financing activities
Changes in short-term borrowings	(218)	(570)
Proceeds from short-term borrowings with maturities greater than 90 days	126	621
Repayments on short-term borrowings with maturities greater than 90 days	(1)	(610)
Issuance of long-term debt	2,664	2,616
Retirement of long-term debt	(1,480)	(1,728)
Retirement of long-term debt to financing trust	0	(250)
Sale of noncontrolling interest	0	396
Dividends paid on common stock	(999)	(921)
Common stock issued from treasury stock	0	1,150
Proceeds from employee stock plans	67	61
Other financing activities	(94)	(64)
Net cash flows provided by (used in) financing activities	65	701
Increase (Decrease) in cash and cash equivalents	1,131	631
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	1,190	914
Cash, Cash Equivalents and Restricted Cash at End of Period	2,321	1,545
Exelon Generation Co L L C [Member]
Cash flows from operating activities
Net income	667	508
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	2,608	2,231
Impairment of long-lived assets and losses on regulatory assets	49	485
Gain on sales of assets and businesses	(48)	(3)
Bargain purchase gain	0	(233)
Deferred income taxes and amortization of investment tax credits	(278)	(179)
Net fair value changes related to derivatives	73	160
Net realized and unrealized gains on nuclear decommissioning trust fund investments	(21)	(429)
Other non-cash operating activities	187	132
Changes in assets and liabilities:
Accounts receivable	126	66
Receivables from and payables to affiliates, net	(7)	27
Inventories	(10)	(43)
Accounts payable and accrued expenses	(59)	(255)
Option premiums (paid) received, net	(36)	35
Collateral received (posted), net	228	(77)
Income taxes	220	154
Pension and non-pension postretirement benefit contributions	(134)	(122)
Other assets and liabilities	(154)	(187)
Net cash flows provided by (used in) operating activities	3,411	2,270
Cash flows from investing activities
Capital expenditures	(1,660)	(1,654)
Proceeds from nuclear decommissioning trust fund sales	6,379	6,848
Investment in nuclear decommissioning trust funds	(6,553)	(7,044)
Acquisition of assets and businesses, net	(57)	(208)
Proceeds from sales of assets and businesses	90	218
Other investing activities	(5)	(35)
Net cash flows provided by (used in) investing activities	(1,806)	(1,875)
Cash flows from financing activities
Changes in short-term borrowings	0	(620)
Proceeds from short-term borrowings with maturities greater than 90 days	1	121
Repayments on short-term borrowings with maturities greater than 90 days	(1)	(110)
Issuance of long-term debt	14	789
Retirement of long-term debt	(100)	(541)
Sale of noncontrolling interest	0	396
Changes in Exelon intercompany money pool	(54)	91
Distributions to member	(688)	(494)
Contributions from member	54	102
Other financing activities	(46)	(31)
Net cash flows provided by (used in) financing activities	(820)	(297)
Increase (Decrease) in cash and cash equivalents	785	98
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	554	448
Cash, Cash Equivalents and Restricted Cash at End of Period	1,339	546
Commonwealth Edison Co [Member]
Cash flows from operating activities
Net income	523	447
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	696	631
Deferred income taxes and amortization of investment tax credits	214	455
Other non-cash operating activities	187	112
Changes in assets and liabilities:
Accounts receivable	(190)	31
Receivables from and payables to affiliates, net	8	346
Inventories	4	6
Accounts payable and accrued expenses	(38)	(706)
Collateral received (posted), net	(10)	(22)
Income taxes	(65)	(205)
Pension and non-pension postretirement benefit contributions	(41)	(38)
Other assets and liabilities	(170)	63
Net cash flows provided by (used in) operating activities	1,118	1,120
Cash flows from investing activities
Capital expenditures	(1,540)	(1,698)
Other investing activities	22	17
Net cash flows provided by (used in) investing activities	(1,518)	(1,681)
Cash flows from financing activities
Issuance of long-term debt	1,350	1,000
Retirement of long-term debt	(840)	(425)
Dividends paid on common stock	(345)	(316)
Contributions from parent	387	567
Other financing activities	(16)	(14)
Net cash flows provided by (used in) financing activities	536	812
Increase (Decrease) in cash and cash equivalents	136	251
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	144	58
Cash, Cash Equivalents and Restricted Cash at End of Period	280	309
PECO Energy Co [Member]
Cash flows from operating activities
Net income	336	327
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	224	213
Gain on sales of assets and businesses	(1)	0
Deferred income taxes and amortization of investment tax credits	5	37
Other non-cash operating activities	41	38
Changes in assets and liabilities:
Accounts receivable	(85)	45
Receivables from and payables to affiliates, net	1	(10)
Inventories	(13)	(5)
Accounts payable and accrued expenses	(1)	(41)
Income taxes	(16)	51
Pension and non-pension postretirement benefit contributions	(25)	(23)
Other assets and liabilities	26	(29)
Net cash flows provided by (used in) operating activities	492	603
Cash flows from investing activities
Capital expenditures	(615)	(537)
Changes in Exelon intercompany money pool	0	74
Other investing activities	6	6
Net cash flows provided by (used in) investing activities	(609)	(457)
Cash flows from financing activities
Issuance of long-term debt	700	325
Retirement of long-term debt	(500)	0
Dividends paid on common stock	(300)	(216)
Contributions from parent	71	16
Other financing activities	(22)	(4)
Net cash flows provided by (used in) financing activities	(51)	121
Increase (Decrease) in cash and cash equivalents	(168)	267
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	275	67
Cash, Cash Equivalents and Restricted Cash at End of Period	107	334
Baltimore Gas and Electric Company [Member]
Cash flows from operating activities
Net income	242	231
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	358	348
Deferred income taxes and amortization of investment tax credits	82	141
Other non-cash operating activities	42	52
Changes in assets and liabilities:
Accounts receivable	72	95
Receivables from and payables to affiliates, net	(4)	(13)
Inventories	(8)	(18)
Accounts payable and accrued expenses	(3)	(25)
Collateral received (posted), net	1	0
Income taxes	(48)	12
Pension and non-pension postretirement benefit contributions	(50)	(50)
Other assets and liabilities	(9)	(72)
Net cash flows provided by (used in) operating activities	675	701
Cash flows from investing activities
Capital expenditures	(667)	(615)
Other investing activities	8	6
Net cash flows provided by (used in) investing activities	(659)	(609)
Cash flows from financing activities
Changes in short-term borrowings	(77)	(45)
Issuance of long-term debt	300	300
Retirement of long-term debt	0	(41)
Retirement of long-term debt to financing trust	0	(250)
Dividends paid on common stock	(157)	(148)
Contributions from parent	18	77
Other financing activities	(2)	(5)
Net cash flows provided by (used in) financing activities	82	(112)
Increase (Decrease) in cash and cash equivalents	98	(20)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	18	50
Cash, Cash Equivalents and Restricted Cash at End of Period	116	30
Pepco Holdings LLC [Member]
Cash flows from operating activities
Net income	336	359
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	555	511
Deferred income taxes and amortization of investment tax credits	50	190
Other non-cash operating activities	109	66
Changes in assets and liabilities:
Accounts receivable	(89)	(42)
Receivables from and payables to affiliates, net	10	(13)
Inventories	0	(29)
Accounts payable and accrued expenses	115	(49)
Income taxes	(31)	82
Pension and non-pension postretirement benefit contributions	(66)	(74)
Other assets and liabilities	(144)	(206)
Net cash flows provided by (used in) operating activities	845	795
Cash flows from investing activities
Capital expenditures	(988)	(995)
Proceeds from sales of assets and businesses	0	1
Other investing activities	2	4
Net cash flows provided by (used in) investing activities	(986)	(990)
Cash flows from financing activities
Changes in short-term borrowings	(141)	96
Proceeds from short-term borrowings with maturities greater than 90 days	125	0
Repayments on short-term borrowings with maturities greater than 90 days	0	(500)
Issuance of long-term debt	300	202
Retirement of long-term debt	(33)	(127)
Changes in Exelon intercompany money pool	10	1
Distributions to member	(232)	(267)
Contributions from parent	237	758
Other financing activities	(6)	(2)
Net cash flows provided by (used in) financing activities	260	161
Increase (Decrease) in cash and cash equivalents	119	(34)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	95	236
Cash, Cash Equivalents and Restricted Cash at End of Period	214	202
Potomac Electric Power Company [Member]
Cash flows from operating activities
Net income	174	188
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	286	242
Deferred income taxes and amortization of investment tax credits	(5)	90
Other non-cash operating activities	42	8
Changes in assets and liabilities:
Accounts receivable	(36)	(43)
Receivables from and payables to affiliates, net	(9)	(10)
Inventories	6	(15)
Accounts payable and accrued expenses	104	(24)
Income taxes	(18)	80
Pension and non-pension postretirement benefit contributions	(11)	(69)
Other assets and liabilities	(137)	(99)
Net cash flows provided by (used in) operating activities	396	348
Cash flows from investing activities
Capital expenditures	(475)	(439)
Proceeds from sales of assets and businesses	0	1
Other investing activities	3	0
Net cash flows provided by (used in) investing activities	(472)	(438)
Cash flows from financing activities
Changes in short-term borrowings	38	(23)
Issuance of long-term debt	100	202
Retirement of long-term debt	(8)	(7)
Dividends paid on common stock	(128)	(133)
Contributions from parent	85	161
Other financing activities	(4)	(1)
Net cash flows provided by (used in) financing activities	83	199
Increase (Decrease) in cash and cash equivalents	7	109
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	40	42
Cash, Cash Equivalents and Restricted Cash at End of Period	47	151
Delmarva Power and Light Company [Member]
Cash flows from operating activities
Net income	90	107
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	135	124
Deferred income taxes and amortization of investment tax credits	24	61
Other non-cash operating activities	16	6
Changes in assets and liabilities:
Accounts receivable	13	7
Receivables from and payables to affiliates, net	(14)	0
Inventories	(3)	(6)
Accounts payable and accrued expenses	18	0
Income taxes	0	33
Other assets and liabilities	13	(40)
Net cash flows provided by (used in) operating activities	292	292
Cash flows from investing activities
Capital expenditures	(254)	(294)
Other investing activities	1	1
Net cash flows provided by (used in) investing activities	(253)	(293)
Cash flows from financing activities
Changes in short-term borrowings	(216)	54
Issuance of long-term debt	200	0
Retirement of long-term debt	(4)	(14)
Dividends paid on common stock	(58)	(82)
Contributions from parent	150	0
Other financing activities	(3)	0
Net cash flows provided by (used in) financing activities	69	(42)
Increase (Decrease) in cash and cash equivalents	108	(43)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	2	46
Cash, Cash Equivalents and Restricted Cash at End of Period	110	3
Atlantic City Electric Company [Member]
Cash flows from operating activities
Net income	76	77
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation, amortization and accretion, including nuclear fuel and energy contract amortization	107	113
Deferred income taxes and amortization of investment tax credits	24	28
Other non-cash operating activities	24	21
Changes in assets and liabilities:
Accounts receivable	(66)	(7)
Receivables from and payables to affiliates, net	(3)	(5)
Inventories	(2)	(7)
Accounts payable and accrued expenses	21	9
Income taxes	(3)	(9)
Pension and non-pension postretirement benefit contributions	(6)	0
Other assets and liabilities	(12)	(62)
Net cash flows provided by (used in) operating activities	160	158
Cash flows from investing activities
Capital expenditures	(247)	(242)
Other investing activities	(1)	0
Net cash flows provided by (used in) investing activities	(248)	(242)
Cash flows from financing activities
Changes in short-term borrowings	37	65
Proceeds from short-term borrowings with maturities greater than 90 days	125	0
Retirement of long-term debt	(22)	(25)
Dividends paid on common stock	(46)	(53)
Net cash flows provided by (used in) financing activities	94	(13)
Increase (Decrease) in cash and cash equivalents	6	(97)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	31	133
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 37	$ 36

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents		$ 1,918	$ 898
Restricted cash and cash equivalents		240	207
Accounts receivable, net
Customer		4,239	4,445
Other		1,246	1,132
Mark-to-market derivative assets, current		696	976
Unamortized energy contract assets, current		42	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		349	340
Materials and Supplies		1,316	1,311
Regulatory Assets, Current		1,340	1,267
Assets Held for Sale		910	0
Other		1,177	1,260
Total current assets		13,473	11,896
Property, plant and equipment, net		75,840	74,202
Deferred debits and other assets
Regulatory Assets, Noncurrent		8,002	8,021
Nuclear decommissioning trust funds		12,464	13,272
Investments		649	640
Goodwill		6,677	6,677
Mark-to-market derivative assets, noncurrent		449	337
Unamortized energy contract assets, noncurrent		371	395
Other		1,560	1,330
Total deferred debits and other assets		30,172	30,672
Total assets	[1]	119,485	116,770
Current Liabilities
Short-term borrowings		834	929
Long-term debt due within one year		771	2,088
Accounts payable		3,348	3,532
Accrued expenses		1,964	1,837
Payable to affiliates, current		5	5
Regulatory Liability, Current		689	523
Mark-to-market derivative liabilities, current		329	232
Unamortized energy contract liabilities, current		158	231
Renewable energy credit obligation		256	352
PHI merger related obligation		63	87
Liabilities Held for Sale		788	0
Other		935	982
Total current liabilities		10,140	10,798
Long-term debt		34,519	32,176
Long-term debt to financing trust		390	389
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		11,702	11,235
Asset Retirement Obligations, Noncurrent		9,747	10,029
Pension obligations		3,385	3,736
Non-pension postretirement benefit obligations		2,155	2,093
Spent nuclear fuel obligation		1,164	1,147
Regulatory Liability, Noncurrent		9,756	9,865
Mark-to-market derivative liabilities, noncurrent		482	409
Unamortized energy contract liabilities, noncurrent		497	609
Other		2,160	2,097
Total deferred credits and other liabilities		41,048	41,220
Total liabilities	[1]	86,097	84,583
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		19,063	18,964
Treasury stock, at cost (2 shares at September 30, 2018 and December 31, 2017)		(123)	(123)
Retained Earnings		14,949	14,081
Accumulated other comprehensive loss, net		(2,869)	(3,026)
Total shareholders’ equity		31,020	29,896
Member’s equity
Noncontrolling Interests		2,368	2,291
Total equity		33,388	32,187
Total liabilities and shareholders’ equity		119,485	116,770
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,804	9,597
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,606	3,618
Exelon Generation Co L L C [Member]
Current Assets
Cash and cash equivalents		1,187	416
Restricted cash and cash equivalents		152	138
Accounts receivable, net
Customer		2,545	2,697
Other		278	321
Mark-to-market derivative assets, current		696	976
Receivable from affiliates, current		182	140
Unamortized energy contract assets, current		42	60
Inventories, net
Energy Related Inventory, Other Fossil Fuel		255	264
Materials and Supplies		948	937
Assets Held for Sale		910	0
Other		854	933
Total current assets		8,049	6,882
Property, plant and equipment, net		24,168	24,906
Deferred debits and other assets
Nuclear decommissioning trust funds		12,464	13,272
Investments		433	433
Goodwill		47	47
Mark-to-market derivative assets, noncurrent		449	334
Prepaid pension asset		1,472	1,502
Unamortized energy contract assets, noncurrent		370	395
Deferred income taxes		25	16
Other		730	670
Total deferred debits and other assets		15,990	16,669
Total assets	[2]	48,207	48,457
Current Liabilities
Short-term borrowings		0	2
Long-term debt due within one year		336	346
Accounts payable		1,450	1,773
Accrued expenses		1,200	1,022
Payable to affiliates, current		144	123
Borrowings from Exelon intercompany money pool		0	54
Mark-to-market derivative liabilities, current		305	211
Unamortized energy contract liabilities, current		33	43
Renewable energy credit obligation		256	352
Liabilities Held for Sale		788	0
Other		255	265
Total current liabilities		4,767	4,191
Long-term debt		7,605	7,734
Long-term debt to affiliate		901	910
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,532	3,811
Asset Retirement Obligations, Noncurrent		9,521	9,844
Non-pension postretirement benefit obligations		903	916
Spent nuclear fuel obligation		1,164	1,147
Payables to affiliates, noncurrent		2,959	3,065
Mark-to-market derivative liabilities, noncurrent		237	174
Unamortized energy contract liabilities, noncurrent		23	48
Other		635	658
Total deferred credits and other liabilities		18,974	19,663
Total liabilities	[2]	32,247	32,498
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Retained Earnings		4,214	4,349
Accumulated other comprehensive loss, net		(31)	(37)
Member’s equity
Membership Interest		9,411	9,357
Total members' equity		13,594	13,669
Noncontrolling Interests		2,366	2,290
Total equity		15,960	15,959
Total liabilities and shareholders’ equity		48,207	48,457
Variable Interest Entity, Consolidated, Assets, Not Pledged		9,768	9,556
Variable Interest Entity, Consolidated, Liabilities, No Recourse		3,528	3,516
Commonwealth Edison Co [Member]
Current Assets
Cash and cash equivalents		124	76
Restricted cash and cash equivalents		12	5
Accounts receivable, net
Customer		590	559
Other		450	266
Receivable from affiliates, current		13	13
Inventories, net
Inventories, net		146	152
Regulatory Assets, Current		256	225
Other		94	68
Total current assets		1,685	1,364
Property, plant and equipment, net		21,642	20,723
Deferred debits and other assets
Regulatory Assets, Noncurrent		1,229	1,054
Investments		6	6
Goodwill		2,625	2,625
Receivable from affiliate, noncurrent		2,469	2,528
Prepaid pension asset		1,083	1,188
Other		380	238
Total deferred debits and other assets		7,792	7,639
Total assets		31,119	29,726
Current Liabilities
Long-term debt due within one year		300	840
Accounts payable		576	568
Accrued expenses		253	327
Payable to affiliates, current		82	74
Regulatory Liability, Current		320	249
Mark-to-market derivative liabilities, current		24	21
Customer deposits		111	112
Other		90	103
Total current liabilities		1,756	2,294
Long-term debt		7,800	6,761
Long-term debt to financing trust		205	205
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		3,744	3,469
Asset Retirement Obligations, Noncurrent		115	111
Non-pension postretirement benefit obligations		206	219
Regulatory Liability, Noncurrent		6,318	6,328
Mark-to-market derivative liabilities, noncurrent		235	235
Other		633	562
Total deferred credits and other liabilities		11,251	10,924
Total liabilities		21,012	20,184
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		1,588	1,588
Other paid-in capital		7,209	6,822
Retained Earnings, Unappropriated		(1,639)	(1,639)
Retained Earnings, Appropriated		2,949	2,771
Total shareholders’ equity		10,107	9,542
Member’s equity
Total liabilities and shareholders’ equity		31,119	29,726
PECO Energy Co [Member]
Current Assets
Cash and cash equivalents		102	271
Restricted cash and cash equivalents		5	4
Accounts receivable, net
Customer		307	327
Other		190	105
Inventories, net
Energy Related Inventory, Other Fossil Fuel		39	31
Materials and Supplies		35	30
Regulatory Assets, Current		84	29
Prepaid Taxes		32	8
Other		19	17
Total current assets		813	822
Property, plant and equipment, net		8,461	8,053
Deferred debits and other assets
Regulatory Assets, Noncurrent		448	381
Investments		26	25
Receivable from affiliate, noncurrent		489	537
Prepaid pension asset		350	340
Other		34	12
Total deferred debits and other assets		1,347	1,295
Total assets		10,621	10,170
Current Liabilities
Long-term debt due within one year		0	500
Accounts payable		387	370
Accrued expenses		89	114
Payable to affiliates, current		53	53
Regulatory Liability, Current		159	141
Customer deposits		67	66
Other		31	23
Total current liabilities		786	1,267
Long-term debt		3,083	2,403
Long-term debt to financing trust		184	184
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,909	1,789
Asset Retirement Obligations, Noncurrent		27	27
Non-pension postretirement benefit obligations		288	288
Regulatory Liability, Noncurrent		581	549
Other		79	86
Total deferred credits and other liabilities		2,884	2,739
Total liabilities		6,937	6,593
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		2,560	2,489
Retained Earnings		1,124	1,087
Accumulated other comprehensive loss, net		0	1
Total shareholders’ equity		3,684	3,577
Member’s equity
Total liabilities and shareholders’ equity		10,621	10,170
Baltimore Gas and Electric Company [Member]
Current Assets
Cash and cash equivalents		113	17
Restricted cash and cash equivalents		3	1
Accounts receivable, net
Customer		296	375
Other		96	94
Receivable from affiliates, current		0	1
Inventories, net
Materials and Supplies		39	40
Gas Held in Storage		46	37
Regulatory Assets, Current		195	174
Prepaid Taxes		0	69
Other		10	3
Total current assets		798	811
Property, plant and equipment, net		8,039	7,602
Deferred debits and other assets
Regulatory Assets, Noncurrent		402	397
Investments		5	5
Prepaid pension asset		290	285
Other		7	4
Total deferred debits and other assets		704	691
Total assets		9,541	9,104
Current Liabilities
Short-term borrowings		0	77
Accounts payable		277	265
Accrued expenses		146	164
Payable to affiliates, current		47	52
Regulatory Liability, Current		95	62
Customer deposits		119	116
Other		23	24
Total current liabilities		707	760
Long-term debt		2,876	2,577
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,345	1,244
Asset Retirement Obligations, Noncurrent		24	23
Non-pension postretirement benefit obligations		200	202
Regulatory Liability, Noncurrent		1,070	1,101
Other		75	56
Total deferred credits and other liabilities		2,714	2,626
Total liabilities		6,297	5,963
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		1,623	1,605
Retained Earnings		1,621	1,536
Total shareholders’ equity		3,244	3,141
Member’s equity
Total liabilities and shareholders’ equity		9,541	9,104
Pepco Holdings LLC [Member]
Current Assets
Cash and cash equivalents		153	30
Restricted cash and cash equivalents		42	42
Accounts receivable, net
Customer		500	486
Other		266	206
Receivable from affiliates, current		0	0
Inventories, net
Materials and Supplies		149	151
Gas Held in Storage		9	7
Regulatory Assets, Current		521	554
Other		60	75
Total current assets		1,700	1,551
Property, plant and equipment, net		13,167	12,498
Deferred debits and other assets
Regulatory Assets, Noncurrent		2,374	2,493
Investments		133	132
Long-term note receivable		0	4
Goodwill		4,005	4,005
Prepaid pension asset		499	490
Deferred income taxes		12	4
Other		67	70
Total deferred debits and other assets		7,090	7,198
Total assets	[3]	21,957	21,247
Current Liabilities
Short-term borrowings		334	350
Long-term debt due within one year		117	396
Accounts payable		505	348
Accrued expenses		269	261
Payable to affiliates, current		102	90
Borrowings from Exelon intercompany money pool		10	0
Regulatory Liability, Current		99	56
Unamortized energy contract liabilities, current		125	188
Customer deposits		113	119
Merger related obligation		38	42
Other		57	81
Total current liabilities		1,769	1,931
Long-term debt		5,972	5,478
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		2,243	2,070
Asset Retirement Obligations, Noncurrent		53	16
Non-pension postretirement benefit obligations		102	105
Regulatory Liability, Noncurrent		1,783	1,872
Unamortized energy contract liabilities, noncurrent		474	561
Other		395	389
Total deferred credits and other liabilities		5,050	5,013
Total liabilities	[3]	12,791	12,422
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Retained Earnings		94	(10)
Member’s equity
Membership Interest		9,072	8,835
Total members' equity		9,166	8,825
Total equity		9,166	8,825
Total liabilities and shareholders’ equity		21,957	21,247
Variable Interest Entity, Consolidated, Assets, Not Pledged		36	41
Variable Interest Entity, Consolidated, Liabilities, No Recourse		78	102
Potomac Electric Power Company [Member]
Current Assets
Cash and cash equivalents		12	5
Restricted cash and cash equivalents		35	35
Accounts receivable, net
Customer		235	250
Other		102	87
Inventories, net
Inventories, net		81	87
Regulatory Assets, Current		284	213
Other		9	33
Total current assets		758	710
Property, plant and equipment, net		6,337	6,001
Deferred debits and other assets
Regulatory Assets, Noncurrent		662	678
Investments		105	102
Prepaid pension asset		318	322
Other		19	19
Total deferred debits and other assets		1,104	1,121
Total assets		8,199	7,832
Current Liabilities
Short-term borrowings		64	26
Long-term debt due within one year		14	19
Accounts payable		234	139
Accrued expenses		141	137
Payable to affiliates, current		70	74
Regulatory Liability, Current		5	3
Customer deposits		53	54
Merger related obligation		38	42
Current portion of DC PLUG obligation		30	28
Other		9	28
Total current liabilities		658	550
Long-term debt		2,611	2,521
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		1,139	1,063
Non-pension postretirement benefit obligations		31	36
Regulatory Liability, Noncurrent		759	829
Other		337	300
Total deferred credits and other liabilities		2,266	2,228
Total liabilities		5,535	5,299
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		1,555	1,470
Retained Earnings		1,109	1,063
Total shareholders’ equity		2,664	2,533
Member’s equity
Total liabilities and shareholders’ equity		8,199	7,832
Delmarva Power and Light Company [Member]
Current Assets
Cash and cash equivalents		110	2
Restricted cash and cash equivalents		0	0
Accounts receivable, net
Customer		121	146
Other		53	38
Inventories, net
Materials and Supplies		37	36
Gas Held in Storage		9	7
Regulatory Assets, Current		66	69
Other		18	27
Total current assets		414	325
Property, plant and equipment, net		3,748	3,579
Deferred debits and other assets
Regulatory Assets, Noncurrent		235	245
Goodwill		8	8
Prepaid pension asset		188	193
Other		8	7
Total deferred debits and other assets		439	453
Total assets		4,601	4,357
Current Liabilities
Short-term borrowings		0	216
Long-term debt due within one year		79	83
Accounts payable		104	82
Accrued expenses		52	35
Payable to affiliates, current		30	46
Regulatory Liability, Current		67	42
Customer deposits		35	35
Other		6	8
Total current liabilities		373	547
Long-term debt		1,415	1,217
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		645	603
Non-pension postretirement benefit obligations		15	14
Regulatory Liability, Noncurrent		587	593
Other		49	48
Total deferred credits and other liabilities		1,296	1,258
Total liabilities		3,084	3,022
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		914	764
Retained Earnings		603	571
Total shareholders’ equity		1,517	1,335
Member’s equity
Total liabilities and shareholders’ equity		4,601	4,357
Atlantic City Electric Company [Member]
Current Assets
Cash and cash equivalents		11	2
Restricted cash and cash equivalents		7	6
Accounts receivable, net
Customer		144	92
Other		59	56
Receivable from affiliates, current		0	0
Inventories, net
Inventories, net		31	29
Regulatory Assets, Current		44	71
Prepaid Taxes		0	0
Other		21	2
Total current assets		317	258
Property, plant and equipment, net		2,883	2,706
Deferred debits and other assets
Regulatory Assets, Noncurrent		383	359
Long-term note receivable		0	4
Prepaid pension asset		70	73
Other		41	45
Total deferred debits and other assets		494	481
Total assets	[4]	3,694	3,445
Current Liabilities
Short-term borrowings		270	108
Long-term debt due within one year		22	281
Accounts payable		149	118
Accrued expenses		38	33
Payable to affiliates, current		25	29
Regulatory Liability, Current		27	11
Customer deposits		26	31
Other		9	8
Total current liabilities		566	619
Long-term debt		1,078	840
Deferred credits and other liabilities
Deferred income taxes and unamortized investment tax credits		534	493
Non-pension postretirement benefit obligations		16	14
Regulatory Liability, Noncurrent		401	411
Other		26	25
Total deferred credits and other liabilities		977	943
Total liabilities	[4]	2,621	2,402
Commitments and contingencies
Stockholders' Equity Attributable to Parent
Common stock		912	912
Retained Earnings		161	131
Total shareholders’ equity		1,073	1,043
Member’s equity
Total liabilities and shareholders’ equity		3,694	3,445
Variable Interest Entity, Consolidated, Assets, Not Pledged		26	29
Variable Interest Entity, Consolidated, Liabilities, No Recourse		$ 68	$ 90
[1]	Exelon’s consolidated assets include $9,804 million and $9,597 million at September 30, 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 $3,606 million and $3,618 million at September 30, 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 for additional information.
[2]	Generation’s consolidated assets include $9,768 million and $9,556 million at September 30, 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 $3,528 million and $3,516 million at September 30, 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 for additional information.
[3]	PHI’s consolidated total assets include $36 million and $41 million at September 30, 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 $78 million and $102 million at September 30, 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 for additional information.
[4]	ACE’s consolidated total assets include $26 million and $29 million at September 30, 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 $68 million and $90 million at September 30, 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 for additional information.

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - shares	Sep. 30, 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	967,009,746	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		$ 1,928							$ 508						$ 447					$ 327					$ 231			$ 359			$ 188			$ 107			$ 77
Other Comprehensive Income (Loss), Net of Tax		$ 69				71	[1]		16			18	[1]										0	[1]
Ending balance at Sep. 30, 2017	[1]					(2,589)
Ending Balance at Sep. 30, 2017	[1]											(36)
Ending Balance at Sep. 30, 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		$ 1,979			1,858			121	667		547	0		120	523			523		336	0	336	0		242	0	242	336		336	174		174	90		90	76		76
Stock Issued During Period, Shares, Share-based Compensation, Gross		2,677
Stock Issued During Period, Value, Share-based Compensation, Gross		$ 32	32	0	0	0		0
Stock Issued During Period, Shares, Employee Stock Purchase Plans		997
Stock Issued During Period, Value, Employee Stock Purchase Plan		$ 67	67	0	0	0		0
Noncontrolling Interest, Period Increase (Decrease)		(46)						(46)	(46)					(46)
Common stock dividends		(1,004)			(1,004)										(345)				(345)	(300)	0	(300)	0		(157)	0	(157)				(128)		(128)	(58)		(58)	(46)		(46)
Equity Contribution																				71	71
Other Comprehensive Income (Loss), Net of Tax		169				167	[1]	2	11		0	9	[1]	2									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									(688)		(688)																	(232)		(232)
Adjustments to Additional Paid in Capital, Other									54	54					387		387								18	18	0	237	237		85	85		150	150
Ending Balance (in shares) at Sep. 30, 2018		968,842
Ending balance at Sep. 30, 2018		$ 33,388	$ 19,063	$ (123)	$ 14,949	$ (2,869)	[1]	$ 2,368
Ending Balance at Sep. 30, 2018									$ 15,960	$ 9,411	$ 4,214	$ (31)	[1]	$ 2,366														$ 9,166	$ 9,072	$ 94
Ending Balance at Sep. 30, 2018		$ 31,020													10,107	$ 1,588	$ 7,209	(1,639)	2,949	$ 3,684	$ 2,560	$ 1,124	$ 0	[1]	$ 3,244	$ 1,623	$ 1,621				$ 2,664	$ 1,555	$ 1,109	$ 1,517	$ 914	$ 603	$ 1,073	$ 912	$ 161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Retained Earnings, Appropriated															$ (2,949)			$ (523)	$ (523)
[1]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 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 R egistrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. The accompanying consolidated financial statements as of September 30, 2018 and 2017 and for the three and nine 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 f or 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) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Incom e, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. 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 additional 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 additional 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 additional 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 additional information. Three Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 4,456 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,313 — — — — — — — — Operating revenues — 4,455 — — — — — — — Electric operating revenues — — 1,568 660 657 1,280 603 307 370 Natural gas operating revenues — — — 53 78 18 — 18 — Operating revenues from affiliates — 296 3 2 3 12 1 2 — Total operating revenues $ 8,769 $ 4,751 $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 Operating Revenues - Adjustments Competitive business revenues $ (1 ) $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (54 ) — — — — — — — — Operating revenues — (1 ) — — — — — — — Electric operating revenues — — (16 ) — (31 ) (2 ) (3 ) 1 — Natural gas operating revenues — — — — (5 ) — — — — Revenues from alternative revenue programs 54 — 16 — 36 2 3 (1 ) — Operating revenues from affiliates — — — — — — — — — Total operating revenues $ (1 ) $ (1 ) $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 4,455 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,259 — — — — — — — — Operating revenues — 4,454 — — — — — — — Electric operating revenues — — 1,552 660 626 1,278 600 308 370 Natural gas operating revenues — — — 53 73 18 — 18 — Revenues from alternative revenue programs 54 — 16 — 36 2 3 (1 ) — Operating revenues from affiliates — 296 3 2 3 12 1 2 — Total operating revenues $ 8,768 $ 4,750 $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 12,924 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 12,225 — — — — — — — — Operating revenues — 12,918 — — — — — — — Electric operating revenues — — 4,215 1,798 1,890 3,417 1,645 860 913 Natural gas operating revenues — — — 338 461 105 — 105 — Operating revenues from affiliates — 894 12 5 12 35 4 6 2 Total operating revenues $ 25,149 $ 13,812 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915 Operating Revenues - Adjustments Competitive business revenues $ 31 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (191 ) — — — — — — — — Operating revenues — 31 — — — — — — — Electric operating revenues — — (48 ) — (79 ) (41 ) (23 ) (9 ) (9 ) Natural gas operating revenues — — — — (23 ) — — — — Revenues from alternative revenue programs 191 — 48 — 102 41 23 9 9 Operating revenues from affiliates — — — — — — — — — Total operating revenues $ 31 $ 31 $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 12,955 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 12,034 — — — — — — — — Operating revenues — 12,949 — — — — — — — Electric operating revenues — — 4,167 1,798 1,811 3,376 1,622 851 904 Natural gas operating revenues — — — 338 438 105 — 105 — Revenues from alternative revenue programs 191 — 48 — 102 41 23 9 9 Operating revenues from affiliates — 894 12 5 12 35 4 6 2 Total operating revenues $ 25,180 $ 13,843 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915 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 additional 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. See Note 6 — Regulatory Matters and Note 10 — Derivative Financial Instruments for additional information. Taxes Directly Imposed on Revenue-Producing Transactions. The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees that are levied by state or local governments on the sale or distribution of 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)	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
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 or the Utility Registrants. 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.
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	New Accounting Standards Issued and Not Yet Adopted as of September 30, 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 September 30, 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 July 2018, the FASB issued an amendment to the standard giving entities the option to apply the requirements of the standard in the period of adoption (January 1, 2019) with no restatement of prior periods. Exelon will elect this expedient. 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 will 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 will elect this practical expedient. 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. • 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. The Registrants are currently assessing the impacts of this standard. 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 September 30, 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 standard is effective January 1, 2019, with early adoption permitted, and must be applied using a modified retrospective transition approach. Given the de-designation of hedge accounting relationships as of July 1, 2018, this standard is not expected to impact the Registrants' financial reporting as discussed in Note 10 - Derivative Financial Instruments . Cloud Computing Arrangements (Issued August 2018) : Aligns the requirements for capitalizing costs incurred to implement a cloud computing arrangement with the internal-use software guidance. As a result, certain implementation costs incurred in a cloud computing arrangement that are currently expensed as incurred will be deferred and amortized over the non-cancellable term of the arrangement plus any reasonably certain renewal periods. The standard is effective January 1, 2020, with early adoption permitted, and can be applied using either a prospective or retrospective transition approach. A retrospective approach requires a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Registrants are currently assessing the impacts of this standard. Defined Benefit Plan Disclosures (Issued August 2018): Eliminates existing disclosure requirements related to amounts in accumulated other comprehensive income expected to be recognized in net periodic benefit cost over the next year and the effects of a one-percentage-point change in the assumed health care cost trend rates. In addition, new disclosures were added such as the weighted-average interest crediting rates for cash balance plans and an explanation for the reasons for significant gains and losses related to changes in the benefit obligation. The standard is effective January 1, 2021, with early adoption permitted, and must be applied retrospectively. Exelon will early adopt this standard in the fourth quarter 2018. Fair Value Measurement Disclosures (Issued August 2018) : Removes, modifies and adds disclosure requirements for fair value measurements and aims to reduce costs for preparers and improve the usefulness of information for financial statement users. The standard is effective January 1, 2020, with early adoption permitted, and most amendments must be applied retrospectively with the exception of three amendments which must be applied prospectively. In addition, entities are permitted to delay adoption of the additional disclosure requirements until the effective date and early adopt the removal or modified disclosure requirements. The Registrants are currently assessing the impacts of this standard as well as the potential to early adopt.

Variable Interest Entities (All

Variable Interest Entities (All Registrants)	9 Months Ended
	Sep. 30, 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 September 30, 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 September 30, 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 September 30, 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 September 30, 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 September 30, 2018 and December 31, 2017 , ComEd, PECO, BGE, Pepco and DPL did not have any material consolidated VIEs. As of September 30, 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 $34 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: • under power purchase agreements with CENG, Generation purchased or will purchase 50.01% of the available output generated by the CENG nuclear plants not subject to other contractual agreements from January 2015 through the end of the operating life of each respective plant. However, pursuant to amendments dated March 31, 2015, the energy obligations under the Ginna Nuclear Power Plant (Ginna) PPAs were suspended during the term of the RSSA, through the end of March 31, 2017. With the expiration of the RSSA, the PPA was reinstated beginning April 1, 2017, • Generation provided a $400 million loan to CENG. As of September 30, 2018 , the remaining obligation is $194 million , • 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 additional information), • 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 September 30, 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 and nine months ended September 30, 2018 , ACE transferred $9 million and $23 million to ATF, respectively. During the three and nine months ended September 30, 2017 , ACE transferred $11 million and $39 million to ATF, respectively. 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 September 30, 2018 and December 31, 2017 are as follows: September 30, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 891 $ 881 $ 10 $ 7 $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,259 9,233 26 19 9,317 9,286 31 23 Total assets $ 10,150 $ 10,114 $ 36 $ 26 $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 329 $ 303 $ 26 $ 23 $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,284 3,232 52 45 3,316 3,250 66 58 Total liabilities $ 3,613 $ 3,535 $ 78 $ 68 $ 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 September 30, 2018 and December 31, 2017 , these assets and liabilities primarily consisted of the following: September 30, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 316 $ 316 $ — $ — $ 126 $ 126 $ — $ — Restricted cash 77 70 7 7 64 58 6 6 Accounts receivable, net Customer 165 165 — — 170 170 — — Other 30 30 — — 25 25 — — Inventory, net Materials and supplies 214 214 — — 205 205 — — Other current assets 65 62 3 — 45 41 4 — Total current assets 867 857 10 7 635 625 10 6 Property, plant and equipment, net 6,158 6,158 — — 6,186 6,186 — — Nuclear decommissioning trust funds 2,523 2,523 — — 2,502 2,502 — — Other noncurrent assets 256 230 26 19 274 243 31 23 Total noncurrent assets 8,937 8,911 26 19 8,962 8,931 31 23 Total assets $ 9,804 $ 9,768 $ 36 $ 26 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 97 $ 72 $ 25 $ 22 $ 102 $ 67 $ 35 $ 31 Accounts payable 128 128 — — 114 114 — — Accrued expenses 73 72 1 1 67 66 1 1 Unamortized energy contract liabilities 16 16 — — 18 18 — — Other current liabilities 14 14 — — 7 7 — — Total current liabilities 328 302 26 23 308 272 36 32 Long-term debt 1,087 1,035 52 45 1,154 1,088 66 58 Asset retirement obligations 2,116 2,116 — — 2,035 2,035 — — Other noncurrent liabilities 75 75 — — 121 121 — — Total noncurrent liabilities 3,278 3,226 52 45 3,310 3,244 66 58 Total liabilities $ 3,606 $ 3,528 $ 78 $ 68 $ 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 September 30, 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 September 30, 2018 and December 31, 2017 , the Utility Registrants did not have any material unconsolidated VIEs. As of September 30, 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 $15 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 $15 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: September 30, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 606 $ 481 $ 1,087 Total liabilities (a) 36 221 257 Exelon's ownership interest in VIE (a) — 232 232 Other ownership interests in VIE (a) 570 28 598 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 232 232 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) — — — December 31, 2017 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 625 $ 509 $ 1,134 Total liabilities (a) 37 228 265 Exelon's ownership interest in VIE (a) — 251 251 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 251 251 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) 2 — 2 _________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not 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 $9 million and $39 million as of September 30, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions, LLC of $9 million and $37 million as of September 30, 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 — Asset Retirement Obligations for additional information. 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	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions	Mergers, Acquisitions and Dispositions (Exelon and Generation) Acquisition of FirstEnergy Solutions Load Business On July 9, 2018, Generation entered into an Asset Purchase Agreement (the Purchase Agreement) with FirstEnergy Solutions Corporation (FirstEnergy). Pursuant to the Purchase Agreement, FirstEnergy will assign all of its retail electricity and wholesale load serving contracts and certain other related commodity contracts to Generation for an all cash purchase price of $140 million . Pursuant to the Purchase Agreement, Generation has agreed to use its commercially reasonable efforts to replace the guarantees and other credit support currently being provided by FirstEnergy in support of the ongoing competitive retail businesses and to reimburse FirstEnergy for any payments arising pursuant to such arrangements continuing for any post-closing period. The transaction is expected to close in the fourth quarter of 2018. The closing of the transaction is subject to certain conditions including the approval of the Purchase Agreement by the United States Bankruptcy Court for the Northern District of Ohio following the auction and expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. Either party may terminate the Purchase Agreement if the transaction has not been consummated by December 31, 2018. The Purchase Agreement also includes various representations, warranties, covenants, indemnification and other provisions customary for a transaction of this nature. Acquisition of Handley Generating Station 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 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 — Asset Retirement Obligations 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 information regarding SNF obligations to the DOE. Exelon and Generation incurred $16 million and $47 million of merger and integration costs related to FitzPatrick for the three and nine months ended September 30, 2017 , respectively, 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 and nine months ended September 30, 2018 . Disposition of Oyster Creek On July 31, 2018, Generation entered into an agreement with Holtec International (Holtec) and its indirect wholly owned subsidiary, Oyster Creek Environmental Protection, LLC (OCEP), for the sale and decommissioning of the Oyster Creek Generating Station (Oyster Creek) located in Forked River, New Jersey. On September 17, 2018, Oyster Creek permanently ceased generation operations. Under the terms of the transaction, Generation will transfer to OCEP substantially all the assets associated with Oyster Creek, including assets held in NDT funds, along with the assumption of liability for all responsibility for the site, including full decommissioning and ongoing management of spent fuel until the spent fuel is moved offsite. In addition to the assumption of liability for the full decommissioning and ongoing management of spent fuel, other consideration to be received in the transaction is contingent on several factors, including a requirement that Generation deliver a minimum NDT fund balance at closing, subject to adjustment for specific terms that include income taxes that would be imposed on any net unrealized built-in gains and certain decommissioning activities to be performed during the pre-close period after the unit shuts down in the fall of 2018 and prior to the anticipated close of the transaction. The terms of the transaction also include various forms of performance assurance for the obligations of OCEP to timely complete the required decommissioning, including a parental guaranty from Holtec for all performance and payment obligations of OCEP, and a requirement for Holtec to deliver a letter of credit to Generation upon the occurrence of specified events. As a result of the transaction, in the third quarter of 2018, Exelon and Generation reclassified certain Oyster Creek assets and liabilities on Exelon’s and Generation’s Consolidated Balance Sheets as held for sale at their respective fair values. Upon remeasurement of the Oyster Creek ARO in the third quarter of 2018, Exelon and Generation recognized an $84 million pre-tax charge to Operating and maintenance expense. Completion of the transaction contemplated by the sale agreement is subject to the satisfaction of several closing conditions, including approval of the license transfer from the NRC and other regulatory approvals, and the receipt of a private letter ruling from the IRS. Generation currently anticipates satisfaction of the closing conditions to occur in the second half of 2019. Other Asset Disposition 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 Generation's Consolidated Balance Sheet. On February 28, 2018, Generation completed the sale of its interest for $87 million , resulting in a pre-tax gain which is included within Gain on sales of assets and businesses on Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. In June 2018, additional proceeds were received, and a pre-tax gain was recorded within Gain on sales of assets and businesses on Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income.

Revenue from Contracts with Cus

Revenue from Contracts with Customers Revenue from Contracts with Customers (All Registrants)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue from Contracts with Customers (All Registrants) The Registrants recognize revenue from contracts with customers to depict the transfer of goods or services to customers at an amount that the entities expect to be entitled to in exchange for those goods or services. Generation’s primary sources of revenue include competitive sales of power, natural gas, and other energy-related products and services. The Utility Registrants’ primary sources of revenue include regulated electric and gas tariff sales, distribution and transmission services. The performance obligations associated with these sources of revenue are further discussed below. Unless otherwise noted, for each of the significant revenue categories and related performance obligations described below, the Registrants have the right to consideration from the customer in an amount that corresponds directly with the value transferred to the customer for the performance completed to date. Therefore, the Registrant's have elected to use the right to invoice practical expedient for the contracts within these revenue categories and generally recognize revenue in the amount for which they have the right to invoice the customer. As a result, there are generally no significant judgments used in determining or allocating the transaction price. Competitive Power Sales (Exelon and Generation) Generation sells power and other energy-related commodities to both wholesale and retail customers across multiple geographic regions through its customer-facing business, Constellation. Power sale contracts generally contain various performance obligations including the delivery of power and other energy-related commodities such as capacity, ZECs, RECs or other ancillary services. Certain performance obligations such as power and capacity are generally delivered over time whereas other performance obligations such as RECs and ZECs are generally delivered at a point in time. In either case, revenues related to all of the performance obligations in such bundled power sale contracts are generally recognized concurrently as the power is generated. Except as noted in the paragraph below, there are no significant judgments in allocating the transaction price since all performance obligations are satisfied simultaneously upon the generation of power. Payment terms generally require that the customers pay for the power or the energy-related commodity within the month following delivery to the customer and there are generally no significant financing components. Certain contracts may contain limits on the total amount of revenue we are able to collect over the entire term of the contract. In such cases, the Registrants estimate the total consideration expected to be received over the term of the contract net of the constraint and allocate the expected consideration to the performance obligations in the contract such that revenue is recognized ratably over the term of the entire contract as the performance obligations are satisfied. Competitive Natural Gas Sales (Exelon and Generation) Generation sells natural gas on a full requirements basis or for an agreed upon volume to both commercial and residential customers. The primary performance obligation associated with natural gas sale contracts is the delivery of the natural gas to the customer. Revenues related to the sale of natural gas are recognized over time as the natural gas is delivered to and consumed by the customer. Payment from customers is typically due within the month following delivery of the natural gas to the customer and there are generally no significant financing components. Other Competitive Products and Services (Exelon and Generation) Generation also sells other energy-related products and services such as long-term construction and installation of energy efficiency assets and new power generating facilities, primarily to commercial and industrial customers. These contracts generally contain a single performance obligation, which is the construction and/or installation of the asset for the customer. The average contract term for these projects is approximately 18 months. Revenues, and associated costs, are recognized throughout the contract term using an input method to measure progress towards completion. The method recognizes revenue based on the various inputs used to satisfy the performance obligation, such as costs incurred and total labor hours expended. The total amount of revenue that will be recognized is based on the agreed upon contractually-stated amount. Payments from customers are typically due within 30 or 45 days from the date the invoice is generated and sent to the customer. Regulated Electric and Gas Tariff Sales (Exelon and the Utility Registrants) The Utility Registrants sell electricity and electricity distribution services to residential, commercial, industrial and governmental customers through regulated tariff rates approved by their state regulatory commissions. PECO, BGE and DPL also sell natural gas and gas distribution services to residential, commercial, and industrial customers through regulated tariff rates approved by their state regulatory commissions. The performance obligation associated with these tariff sale contracts is the delivery of electricity and/or natural gas. Tariff sales are generally considered daily contracts given that customers can discontinue service at any time. Revenues are generally recognized over time (each day) as the electricity and/or natural gas is delivered to customers. Payment terms generally require that customers pay for the services within the month following delivery of the electricity or natural gas to the customer and there are generally no significant financing components or variable consideration. Electric and natural gas utility customers have the choice to purchase electricity or natural gas from competitive electric generation and natural gas suppliers. While the Utility Registrants are required under state legislation to bill their customers for the supply and distribution of electricity and/or natural gas, they recognize revenue related only to the distribution services when customers purchase their electricity or natural gas from competitive suppliers. Regulated Transmission Services (Exelon and the Utility Registrants) Under FERC’s open access transmission policy, the Utility Registrants, as owners of transmission facilities, are required to provide open access to their transmission facilities under filed tariffs at cost-based rates approved by FERC. The Utility Registrants are members of PJM, the regional transmission organization designated by FERC to coordinate the movement of wholesale electricity in PJM’s region, which includes portions of the mid-Atlantic and Midwest. In accordance with FERC-approved rules, the Utility Registrants and other transmission owners in the PJM region make their transmission facilities available to PJM, which directs and controls the operation of these transmission facilities and accordingly compensates the Utility Registrants and other transmission owners. The performance obligations associated with the Utility Registrants’ contract with PJM include (i) Network Integration Transmission Services (NITS), (ii) scheduling, system control and dispatch services, and (iii) access to the wholesale grid. These performance obligations are satisfied over time, and Utility Registrants utilize output methods to measure the progress towards their completion. Passage of time is used for NITS and access to the wholesale grid and MWhs of energy transported over the wholesale grid is used for scheduling, system control and dispatch services. PJM pays the Utility Registrants for these services on a weekly basis and there are no financing components or variable consideration. Costs to Obtain or Fulfill a Contract with a Customer (Exelon and Generation) Generation incurs incremental costs in order to execute certain retail power and gas sales contracts. These costs primarily relate to retail broker fees and sales commissions. Generation has capitalized such contract acquisition costs in the amount of $30 million and $26 million as of September 30, 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 $6 million and $16 million for the three and nine months ended September 30, 2018 , respectively, and $7 million and $24 million for the three and nine months ended September 30, 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 September 30, 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 34 Amounts reclassified to receivables (120 ) Balance at September 30, 2018 $ 197 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 September 30, 2018 : Contract Liabilities Exelon and Generation Balance as of January 1, 2018 $ 35 Increases as a result of additional cash received or due 389 Amounts recognized into revenues (387 ) Balance at September 30, 2018 $ 37 The Utility Registrants also record contract liabilities when consideration is received prior to the satisfaction of the performance obligations. As of September 30, 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 September 30, 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 $ 647 $ 302 $ 119 $ 47 $ 137 $ 1,252 Generation 647 302 119 47 137 1,252 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)	9 Months Ended
	Sep. 30, 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. See Note 12 — Income Taxes for additional information 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 and the annual reconciliation for 2017 provides for a weighted average debt and equity return on distribution rate base of 6.52% inclusive of an allowed ROE of 8.69% , reflecting the average rate on 30 -year treasury notes plus 580 basis points. See table below for ComEd's regulatory assets associated with its electric distribution formula rate. See Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K for additional information on ComEd's distribution formula rate filings. 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 formula rate regulatory asset in the first quarter 2017. Energy Efficiency Formula Rate (Exelon and ComEd). On June 1, 2018, ComEd filed its annual energy efficiency formula rate update with the ICC. The filing establishes the 2019 application year 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 and 2019 expenditures 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 increase to the revenue requirement of $39 million , reflecting an increase of $38 million for the initial revenue requirement for 2018 and an increase of $1 million related to the annual reconciliation for 2017. The revenue requirement for the 2019 application year provides for a weighted average debt and equity return on 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. 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. During the three months ended September 30, 2018 , Generation recognized revenue of $61 million . During the nine months ended September 30, 2018 , Generation recognized revenue of $315 million , 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 argued that the Illinois ZEC program would distort PJM's FERC-approved energy and capacity market auction system of setting wholesale prices and sought a permanent injunction preventing the implementation of the program. Exelon intervened and filed motions to dismiss in both lawsuits. On July 14, 2017, the district court granted the motions to dismiss. On July 17, 2017, the plaintiffs appealed the decision to the U.S. Court of Appeals for the Seventh Circuit. On February 21, 2018, the U.S. Court of Appeals for the Seventh Circuit issued an order inviting the Solicitor General to express the views of the United States on the matter. On May 29, 2018, the Solicitor General and FERC filed its brief in the U.S. Court of Appeals for the Seventh Circuit stating that the Illinois ZEC program does not violate federal law or interfere with FERC’s authority to regulate wholesale power markets. On September 13, 2018, the U.S. Circuit Court of Appeals for the Seventh Circuit affirmed the lower court's dismissal of both lawsuits. On September 27, 2018, the plaintiffs filed a request for a panel rehearing with the U.S. Circuit Court of Appeals for the Seventh Circuit. On October 9, 2018, the U.S. Circuit Court of Appeals for the Seventh Circuit panel denied the request for rehearing. 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 was 10.95% . On August 28, 2018, PECO and interested parties filed with the PAPUC a petition for partial settlement for an increase of $25 million in annual electric distribution service revenues, which 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. No overall ROE was specified in the partial settlement. On October 18, 2018, the Administrative Law Judges issued a Recommended Decision to the PAPUC that the partial settlement be approved without modification. A final ruling from the PAPUC is expected before December 31, 2018, and if approved, the new electric distribution base rates will become effective on January 1, 2019. Tax Cuts and Jobs Act (Exelon and PECO). On May 17, 2018, the PAPUC issued an order to all Pennsylvania utility companies, including PECO, requiring that the annual tax savings beginning on January 1, 2018 associated with TCJA be passed back to customers. The order directs Pennsylvania utility companies without an existing base rate case, including PECO’s gas distribution business, to start passing back the savings from January 1, 2018 onward through a negative surcharge mechanism to be effective on July 1, 2018. Pursuant to the May 17, 2018 order, PECO filed a negative surcharge mechanism and began on July 1, 2018, to return an estimated $4 million in annual 2018 tax savings to its natural gas distribution customers. For Pennsylvania utility companies with existing base rate cases, including PECO’s electric distribution base rate case, the timing of when and how to pass the annual TCJA savings to customers will be resolved through the base rate case proceeding. 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 of which the majority will be passed back in January 2019 with the remainder refunded over the balance of the year. The TCJA tax savings would be an additional offset to the proposed increase to its electric distribution rates. The amounts being proposed to be passed back to customers reflect the respective annual benefits of lower income tax rates established upon enactment of the TCJA. See Note 12 — Income Taxes for additional information 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. BGE's natural gas distribution rate case filing in June 2018 included a request to provide to customers the natural gas portion of the January 2018 TCJA savings over a 5-year period. 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. On May 31, 2018, the MDPSC issued an order approving the settlement agreement with an effective date of June 1, 2018. See discussion below for additional information. 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 additional information 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. The Maryland Strategic Infrastructure Development and Enhancement Program (Exelon and BGE). On December 1, 2017 (and as amended on January 22, 2018), BGE filed an application with the MDPSC seeking approval for a new gas infrastructure replacement plan and associated surcharge, effective for the five-year period from 2019 through 2023. On May 30, 2018, the MDPSC approved with modifications a new infrastructure plan and associated surcharge, subject to BGE's acceptance of the Order. On June 1, 2018, BGE accepted the MDPSC Order and the associated surcharge will be effective in rates beginning in January 2019. The new five-year plan calls for capital expenditures over the 2019-2023 timeframe of $732 million , with an associated revenue requirement of $200 million . 2018 Maryland Natural Gas Distribution Base Rates (Exelon and BGE). On June 8, 2018, and as amended on August 24, 2018 and October 12, 2018, BGE filed an application with the MDPSC to increase natural gas revenues by $61 million , reflecting a requested ROE of 10.5% . BGE expects a decision in the first quarter of 2019 but cannot predict how much of the requested increase the MDPSC will approve. 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% . 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. On May 31, 2018, the MDPSC issued an order approving the settlement agreement with an effective date of June 1, 2018. Pepco issued the $10 million to customers in July 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. In the second quarter of 2018, DPL discovered a rate design issue in Maryland such that the current rates were not sufficient to collect the full amount of the $13 million revenue increase agreed to by the parties in the recent settlement. On September 5, 2018, the MDPSC approved DPL’s proposed revisions to resolve the rate design issue on a prospective basis, effective September 5, 2018. 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 further information on the proposed treatment of the TCJA tax savings in DPL’s pending electric and natural gas distribution base rate cases. 2017 Delaware Electric and Natural Gas Distribution Base Rates (Exelon, PHI and DPL). On August 17, 2017 (as updated on February 9, 2018 to reflect $19 million and $7 million of ongoing annual TCJA tax savings for electric and natural gas, respectively), DPL filed applications with the DPSC to increase its annual electric and natural gas distribution base rates by $12 million and $4 million , respectively, reflecting a requested ROE of 10.1% . The ongoing annual TCJA tax savings 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. Of the proposed electric and natural gas rate increases, $2.5 million of each were put into effect in the fourth quarter 2017 and an additional $3 million and $1 million , respectively, were put into effect in the first quarter 2018, all of which are subject to refund based on the final DPSC order. On June 27, 2018, DPL entered into a settlement agreement with all active parties in the proceeding related to its pending electric distribution base rate case. The settlement agreement provides for a net decrease to annual electric distribution base rates of $7 million , which includes annual ongoing TCJA tax savings, and reflects a ROE of 9.7% . In addition, the settlement agreement separately provides a one-time bill credit to customers of approximately $3 million representing the TCJA tax savings from February 1, 2018 through March 17, 2018, when full interim rates were put into effect. On August 21, 2018, the DPSC approved the settlement agreement as filed. DPL expects to issue the $3 million to customers in the fourth quarter of 2018. On September 7, 2018 (as amended and restated on October 2, 2018), DPL entered into a partial settlement agreement with several parties in its pending gas distribution base rate case proceeding that provides for a net decrease to annual gas distribution base rates of $4 million , which includes annual ongoing TCJA tax savings, and reflects a ROE of 9.7% . In addition, the settlement agreement separately provides a one-time bill credit to customers of approximately $1 million , which includes the TCJA tax savings from February 1, 2018 through March 17, 2018, when full interim rates were put into effect. DPL expects a decision on the settlement agreement in the fourth quarter of 2018 but cannot predict if the DPSC will approve the settlement agreement as filed. See Note 12 — Income Taxes for additional information 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. On August 9, 2018, the DCPSC approved the settlement agreement with an effective date of August 13, 2018. See discussion below for additional information. 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 reflects a ROE of 9.525% . On August 9, 2018, the DCPSC approved the settlement agreement with an effective date of August 13, 2018. In addition, the settlement agreement separately provides for 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. As rates did not go into effect until August 13, 2018, on September 7, 2018, Pepco submitted an updated filing for a one-time bill credit to customers of approximately $20 million , and an increase of $4 million to the customer base rate credit established in connection with the merger between Exelon and PHI for residential customers, representing the TCJA benefits for the period January 1, 2018 through August 12, 2018. Following the expiration of the comment period with no objections filed, Pepco issued the $20 million to customers in September 2018. See Note 12 — Income Taxes for additional information 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. 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 related to the lower income tax rates. 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. On August 29, 2018, the NJBPU issued an order approving final rates with an effective date of September 8, 2018, which reflects the full amount of ACE’s proposed $23 million reduction, including a one-time bill credit to customers of approximately $6 million representing the TCJA tax savings from January 1, 2018 through June 30, 2018. ACE expects to issue the $6 million to customers in the fourth quarter of 2018. ACE's treatment of the TCJA tax savings for the period July 1, 2018 through the effective date of the final rates is the subject of ongoing discussions, and ACE anticipates that the NJBPU will issue a clarifying order in the fourth quarter of 2018. See Note 12 — Income Taxes for additional information 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 of a series of investments through a new rider mechanism, totaling $338 million , between 2019-2022 to provide safe and reliable service for its customers. The IIP will allow for more timely recovery of investments made to modernize and enhance ACE’s electric system. ACE currently expects a decision in this matter in the first quarter of 2019 but cannot predict if the NJBPU will approve the application as filed. Update and Reconciliation of Certain Over and 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. As filed, the net impact of adjusting the charges as proposed would have been an overall annual rate decrease of $19 million , including New Jersey sales and use tax. On May 22, 2018, the NJBPU approved a stipulation of settlement among certain interested parties providing for an overall annual rate decrease of $33 million , effective June 1, 2018. The rate decrease was placed into effect provisionally, subject to a review by the NJBPU and the Division of Rate Counsel of the final underlying costs for reasonableness and prudence. This rate decrease will have no effect on ACE’s operating income, since these revenues provide for recovery of deferred costs under an approved deferral mechanism. The matter is pending at the NJBPU. New Jersey Clean Energy Legislation (Exelon, Generation and ACE). On May 23, 2018, the Governor of New Jersey signed new legislation, which became effective immediately, that establishes and modifies New Jersey’s clean energy and energy efficiency programs and solar and renewable energy portfolio standards. The new legislation expands the state's renewable portfolio standard to require that 50% of electric generation sold be from renewable energy sources by 2030; modifies the New Jersey solar renewable energy portfolio standard to require that 5.1% of electric generation sold in New Jersey be from solar electric power by 2021, lowers the solar alternative compliance payment amount starting in 2019 and requires the NJBPU to adopt rules to replace the current solar renewable energy credit program; and requires the NJBPU to increase its offshore wind energy credit program to 3,500 MW. The new legislation further imposes an energy efficiency standard that each electric public utility will be required to reduce annual usage by 2% and provides for utilities to annually file for recovery of the costs of the programs, including the revenue impact of sales losses resulting from the programs. The NJBPU is required to initiate a study to determine the savings targets for each public utility, to adopt other rules regarding the programs, and to approve energy efficiency and peak demand reduction programs for each utility. The new legislation also requires the NJBPU to conduct an energy storage analysis including the potential costs and benefits and to initiate a proceeding to establish a goal of achieving 2,000 MW of energy storage by 2030; requires the utilities to conduct a study on voltage optimization on their distribution system; and requires the NJBPU to establish a community solar program to permit customers to participate in a solar project that is not located on the customer’s property. On the same day, the Governor of New Jersey also signed new legislation, which became effective immediately, that will establish a ZEC program providing compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. PSEG’s Salem nuclear plant is expected to apply for approval to participate in the ZEC program. Under the new legislation, the NJBPU will issue ZECs to qualifying nuclear power plants and the electric distribution utilities in New Jersey, including ACE, will be required to purchase those ZECs. The NJBPU 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. The quantity of ZECs issued will be determined based on the greater of 40% of the total number of MWh of electricity distributed by the public electric distribution utilities in New Jersey in the prior year, or the total number of MWh of electricity generated in the prior year by the selected nuclear power plants. The ZEC price is approximately $10 per MWh during the first 3-year eligibility period. For eligibility periods following the first 3-year eligibility period, the NJBPU has discretion to reduce the ZEC price. Electric distribution utilities in New Jersey, including ACE, will be authorized to collect from retail distribution customers through a non-bypassable charge all costs associated with the utility’s procurement of the ZECs. On August 29, 2018, the NJBPU issued an order opening a proceeding in which stakeholders can provide input on implementation of the ZEC program. See Note 8 - Early Plant Retirements for additional information on New Jersey’s ZEC program potential impacts to PSEG’s Salem nuclear plant. 2018 New Jersey Electric Distribution Base Rates (Exelon, PHI and ACE). On June 15, 2018, ACE submitted an application with the NJBPU to increase its annual electric distribution base rates by $99.7 million (before New Jersey sales and use tax), based upon a requested ROE of 10.1% . Included in the $99.7 million request is $40 million of higher depreciation expense related to ACE's updated depreciation study. On July 25, 2018, the NJBPU dismissed ACE’s base rate case due to the number of forecasted months included in the twelve month test period. Historically, ACE and other New Jersey utilities have filed distribution base rate cases with a similar number of forecasted months in the test period. On August 21, 2018, ACE refiled its application with the NJBPU, requesting an increase to its electric distribution rates of $109 million (before New Jersey sales and use tax), reflecting a requested ROE of 10.1% . Included in the $109 million request is $40 million of higher depreciation expense related to ACE's updated depreciation study. ACE currently expects a decision in this matter in the third quarter of 2019 but cannot predict if the NJBPU will approve the application as filed. New York Regulatory Matters New York Clean Energy Standard (Exelon and Generation). On August 1, 2016, the 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

Impairment of Long-lived Assets

Impairment of Long-lived Assets (Exelon and Generation)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Asset Impairment Charges [Text Block]	Impairment of Long-Lived Assets (Exelon and Generation) Registrants evaluate long-lived assets for recoverability whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. In the second quarter of 2018, updates to Exelon's long-term view of energy and capacity prices suggested that the carrying value of a group of merchant wind assets, located in West Texas, may be impaired. Upon review, the estimated undiscounted future cash flows and fair value of the group were less than its carrying value. The fair value analysis was based on the income approach using significant unobservable inputs (Level 3) including revenue and generation forecasts, projected capital and maintenance expenditures and discount rates. As a result, long-lived merchant wind assets held and used with a net carrying amount of $41 million were fully impaired and a pre-tax impairment charge of $41 million was recorded during the second quarter of 2018 within Operating and maintenance expense in Exelon's and Generation's Consolidated Statements of Operations and Comprehensive Income. During the first quarter of 2018, Mystic Unit 9 did not clear in the ISO-NE capacity auction for the 2021 - 2022 planning year. On March 29, 2018, Generation 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. On May 2, 2017, EGTP entered into a consent agreement with its lenders to initiate an orderly sales process to sell the assets of its wholly owned subsidiaries. As a result, Exelon and Generation classified certain of EGTP's assets and liabilities as held for sale at their respective fair values less costs to sell and recorded a pre-tax impairment charge of $460 million within Operating and maintenance expense on their Consolidated Statements of Operations and Comprehensive Income of which $418 million was recorded in the second quarter of 2017. On November 7, 2017, EGTP and its wholly owned subsidiaries filed voluntary petitions for relief under Chapter 11 of Title 11 of the United States Code in the United States Bankruptcy Court for the District of Delaware and, as a result, Exelon and Generation deconsolidated EGTP's assets and liabilities from their consolidated financial statements. See Note 4 — Mergers, Acquisitions and Dispositions for additional information.

Early Plant Retirements Early P

Early Plant Retirements Early Plant Retirements (Exelon, Generation)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Implications Of Potential Early Retirement Disclosure [Text Block]	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 nuclear 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. See Note 6 — Regulatory Matters for additional information on the Illinois ZES and New York CES. 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 nuclear plant at the end of its current operating cycle in 2018. On September 17, 2018, Oyster Creek permanently ceased generation operations. 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 early nuclear plant retirement decisions, Exelon and Generation recognized one-time charges in Operating and maintenance expense related to materials and supplies inventory reserve adjustments, employee-related costs and CWIP impairments, among other items. In addition to these one-time charges, annual incremental non-cash charges to earnings stemming from shortening the expected economic useful lives primarily related to accelerated depreciation of plant assets (including any ARC), accelerated amortization of nuclear fuel, and additional ARO accretion expense associated with the changes in decommissioning timing and cost assumptions were also recorded. See Note 13 — Asset Retirement Obligations for additional information on changes to the nuclear decommissioning ARO balance. During the three and nine months ended September 30, 2018 , both Exelon's and Generation's results include a net incremental $174 million and $525 million , respectively, 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) Q3 2018 YTD 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 152 $ 441 Accelerated nuclear fuel amortization 18 52 Operating and maintenance (c) 4 32 Total $ 174 $ 525 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI and Oyster Creek for the three and nine months ended September 30, 2018 . The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 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. It does not include remeasurement of the Oyster Creek ARO. Refer to Note 13 - Asset Retirement Obligations for additional detail. 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 May 23, 2018, the Governor of New Jersey signed new legislation, which became effective immediately, that will establish a ZEC program providing compensation for nuclear plants that demonstrate to the NJBPU that they meet certain requirements, including that they make a significant contribution to air quality in the state and that their revenues are insufficient to cover their costs and risks. Under the new legislation, the NJBPU will issue ZECs to qualifying nuclear power plants and the electric distribution utilities in New Jersey, including ACE, will be required to purchase those ZECs. The NJBPU 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. Assuming the successful implementation of the New Jersey ZEC program and the selection of Salem as one of the qualifying facilities, the New Jersey ZEC program has the potential to mitigate the heightened risk of earlier retirement for Salem. See Note 6 — Regulatory Matters for additional information on the New Jersey ZEC program. The following table provides the balance sheet amounts as of September 30, 2018 for Generation’s ownership share of the significant assets and liabilities associated with Salem that would potentially be impacted by a decision to permanently cease generation operations. September 30, 2018 Asset Balances Materials and supplies inventory $ 45 Nuclear fuel inventory, net 114 Completed plant, net 605 Construction work in progress 34 Liability Balances Asset retirement obligation (455 ) 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 and 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 capacity commitment period. The ISO-NE announced that it would take a three-step approach to fuel security. First, on May 1, 2018, ISO-NE made a filing with FERC requesting waiver of certain tariff provisions to allow it to retain Mystic Units 8 and 9 for fuel security for the 2022 - 2024 capacity commitment periods. Second, ISO-NE planned to 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 stated its intention to work with stakeholders to develop long-term market rule changes to address system resiliency considering significant reliability risks identified in ISO-NE’s January 2018 fuel security report. Changes to market rules are necessary because critical units to the region, such as Mystic Units 8 and 9, cannot recover future operating costs, including the cost of procuring fuel. On May 16, 2018, Generation made a filing with FERC to establish cost-of-service compensation and terms and conditions of service for Mystic Units 8 and 9 for the period between June 1, 2022 - May 31, 2024. Among the costs included in the filing are costs associated with the Distrigas facility. Generation asked that FERC establish an expedited settlement process that would allow Generation to know the outcome of the cost-of-service proceeding prior to making a final decision as to whether to unconditionally retire the plants beginning June 1, 2022. A number of parties filed protests in response to the May 16, 2018 filing. On July 2, 2018, FERC issued an order denying ISO-NE’s May 1, 2018 waiver request on procedural grounds but accepting ISO-NE’s conclusions that retirement of Mystic Units 8 and 9 could cause a violation of mandatory reliability standards as soon as 2022. Accordingly, FERC ordered ISO-NE to (i) make a filing within 60 days providing for the filing of a short-term cost-of-service agreement to address demonstrated fuel security concerns and (ii) make a filing by July 1, 2019 proposing permanent tariff revisions that would improve its market design to better address regional fuel security concerns. FERC also extended the deadline by which Generation must make a retirement decision for Mystic Units 8 and 9 to January 4, 2019. In addition, notwithstanding its denial of the waiver request, FERC stated that it will continue to evaluate Mystic’s May 16, 2018 cost-of-service agreement filing. On August 31, 2018, ISO-NE filed a compliance filing in response to FERC's July 2, 2018 order proposing short-term tariff changes to permit it to retain a resource for fuel security reliability reasons. A number of parties, including Generation, have submitted comments on the proposal, which is pending before FERC. On July 13, 2018, FERC issued an order accepting Generation’s cost-of-service agreement for filing and making findings on certain issues, including that recovery of fuel supply costs for the Distrigas facility are not prohibited if they are just and reasonable. Additionally, the order established hearing procedures on an expedited schedule. Any settlement discussions are to be undertaken on a parallel track with the hearing. Generation has requested that FERC issue an order by December 21, 2018, but FERC is not obligated to meet this date. Exelon and Generation cannot predict the final outcome of these proceedings or the potential financial impact, if any, on Exelon or Generation. The following table provides the balance sheet amounts as of September 30, 2018 for Generation’s significant assets and liabilities associated with the Mystic Generating Station assets that would potentially be impacted by a decision to permanently cease generation operations. September 30, 2018 Asset Balances Materials and supplies inventory $ 21 Fuel inventory 18 Completed plant, net 877 Construction work in progress 5 Prepaid expenses (a) 15 Liability Balances Asset retirement obligation (5 ) Accrued expenses (a) (2 ) _________ (a) Reflects ending balances only as they relate to Mystic's Long-term Service Agreement. On October 1, 2018, Generation acquired the Distrigas liquefied natural gas import terminal to ensure the continued reliable supply of fuel to Mystic Units 8 and 9 while they remain operating.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities (All Registrants)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities (All Registrants)	Fair Value of Financial Assets and Liabilities (All Registrants) Fair Value of Financial Liabilities Recorded at 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 September 30, 2018 and December 31, 2017 : Exelon September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 834 $ — $ 834 $ — $ 834 Long-term debt (including amounts due within one year) (b)(c) 35,290 — 33,608 2,079 35,687 Long-term debt to financing trusts (d) 390 — — 411 411 SNF obligation 1,164 — 993 — 993 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 8,842 $ — $ 7,563 $ 1,461 $ 9,024 SNF obligation 1,164 — 993 — 993 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 8,100 — 8,317 — 8,317 Long-term debt to financing trusts (d) 205 — — 214 214 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 3,083 — 3,130 50 3,180 Long-term debt to financing trusts 184 — — 196 196 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 184 — — 204 204 BGE September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 2,876 — 2,933 — 2,933 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 334 $ — $ 334 $ — $ 334 Long-term debt (including amounts due within one year) (b)(c) 6,089 — 5,323 568 5,891 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 64 $ — $ 64 $ — $ 64 Long-term debt (including amounts due within one year) (b)(c) $ 2,625 $ — $ 2,890 $ 101 $ 2,991 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 1,494 $ — $ 1,299 $ 196 $ 1,495 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 270 $ — $ 270 $ — $ 270 Long-term debt (including amounts due within one year) (b)(c) 1,100 — 887 271 1,158 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 $219 million , $53 million , $64 million , $23 million , $19 million , $11 million , $34 million , $12 million and $4 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of September 30, 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, government-backed fixed rate non-recourse debt and loan agreements. (d) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of September 30, 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 nine months ended September 30, 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 September 30, 2018 and December 31, 2017 : Generation Exelon As of September 30, 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) $ 1,099 $ — $ — $ — $ 1,099 $ 1,906 $ — $ — $ — $ 1,906 NDT fund investments Cash equivalents (b) 278 92 — — 370 278 92 — — 370 Equities 3,206 1,608 1 1,942 6,757 3,206 1,608 1 1,942 6,757 Fixed income Corporate debt — 1,629 231 — 1,860 — 1,629 231 — 1,860 U.S. Treasury and agencies 2,031 99 — — 2,130 2,031 99 — — 2,130 Foreign governments — 49 — — 49 — 49 — — 49 State and municipal debt — 165 — — 165 — 165 — — 165 Other (c) — 29 — 854 883 — 29 — 854 883 Fixed income subtotal 2,031 1,971 231 854 5,087 2,031 1,971 231 854 5,087 Middle market lending — — 334 235 569 — — 334 235 569 Private equity — — — 303 303 — — — 303 303 Real estate — — — 490 490 — — — 490 490 NDT fund investments subtotal (d) 5,515 3,671 566 3,824 13,576 5,515 3,671 566 3,824 13,576 Pledged assets for Zion Station decommissioning Cash equivalents 9 — — — 9 9 — — — 9 Pledged assets for Zion Station (e) 9 — — — 9 9 — — — 9 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 25 — — — 25 76 — — — 76 Fixed income — — — — — — 16 — — 16 Life insurance contracts — 23 — — 23 — 73 37 — 110 Rabbi trust investments subtotal (f) 30 23 — — 53 124 89 37 — 250 Generation Exelon As of September 30, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Commodity derivative assets Economic hedges 234 2,117 2,019 — 4,370 234 2,117 2,019 — 4,370 Proprietary trading — 84 90 — 174 — 84 90 — 174 Effect of netting and allocation of collateral (g) (h) (230 ) (1,887 ) (1,302 ) — (3,419 ) (230 ) (1,887 ) (1,302 ) — (3,419 ) Commodity derivative assets subtotal 4 314 807 — 1,125 4 314 807 — 1,125 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — — — — — Economic hedges — 21 — — 21 — 21 — — 21 Effect of netting and allocation of collateral — (1 ) — — (1 ) — (1 ) — — (1 ) Interest rate and foreign currency derivative assets subtotal — 20 — — 20 — 20 — — 20 Other investments — — 52 — 52 — — 52 — 52 Total assets 6,657 4,028 1,425 3,824 15,934 7,558 4,094 1,462 3,824 16,938 Liabilities Commodity derivative liabilities Economic hedges (329 ) (2,056 ) (1,660 ) — (4,045 ) (329 ) (2,056 ) (1,919 ) — (4,304 ) Proprietary trading — (95 ) (32 ) — (127 ) — (95 ) (32 ) — (127 ) Effect of netting and allocation of collateral (g) (h) 247 1,987 1,397 — 3,631 247 1,987 1,397 — 3,631 Commodity derivative liabilities subtotal (82 ) (164 ) (295 ) — (541 ) (82 ) (164 ) (554 ) — (800 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (10 ) — — (10 ) Economic hedges — (2 ) — — (2 ) — (2 ) — — (2 ) Effect of netting and allocation of collateral — 1 — — 1 — 1 — — 1 Interest rate and foreign currency derivative liabilities subtotal — (1 ) — — (1 ) — (11 ) — — (11 ) Deferred compensation obligation — (36 ) — — (36 ) — (142 ) — — (142 ) Total liabilities (82 ) (201 ) (295 ) — (578 ) (82 ) (317 ) (554 ) — (953 ) Total net assets $ 6,575 $ 3,827 $ 1,130 $ 3,824 $ 15,356 $ 7,476 $ 3,777 $ 908 $ 3,824 $ 15,985 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 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 3 — — 3 — 6 — — 6 Economic hedges — 10 — — 10 — 10 — — 10 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of 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 $183 million and $259 million at September 30, 2018 and December 31, 2017 and restricted cash of $57 million and $127 million at September 30, 2018 and December 31, 2017 . Exelon excludes cash of $330 million and $389 million at September 30, 2018 and December 31, 2017 and restricted cash of $85 million and $145 million at September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $163 million and $85 million at September 30, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $37 million and $77 million of cash received from outstanding repurchase agreements at September 30, 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 $ (4) million and less than $1 million, which have a total notional amount of $915 million and $811 million at September 30, 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 Exelon and Generation's exposure to credit or market loss. (d) Excludes net liabilities of $89 million and $82 million at September 30, 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 less than $1 million at September 30, 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 for the three months ended September 30, 2018 and September 30, 2017 . The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the nine months ended September 30, 2018 and September 30, 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended September 30, 2018 and September 30, 2017 . The amount of unrealized gains/(losses) at Exelon totaled $2 million and $3 million for the nine months ended September 30, 2018 and September 30, 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $18 million , $100 million and $94 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of September 30, 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), $(166) million represents variation margin on the exchanges as of September 30, 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 $71 million as of September 30, 2018 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three and nine months ended September 30, 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 September 30, 2018 and December 31, 2017 : ComEd PECO BGE As of September 30, 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) $ 211 $ — $ — $ 211 $ 84 $ — $ — $ 84 $ 100 $ — $ — $ 100 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 11 — 11 — — — — Rabbi trust investments subtotal (b) — — — — 7 11 — 18 6 — — 6 Total assets 211 — — 211 91 11 — 102 106 — — 106 Liabilities Deferred compensation obligation — (7 ) — (7 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (259 ) (259 ) — — — — — — — — Total liabilities — (7 ) (259 ) (266 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 211 $ (7 ) $ (259 ) $ (55 ) $ 91 $ 1 $ — $ 92 $ 106 $ (5 ) $ — $ 101 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 September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $144 million and $62 million at September 30, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $23 million and $47 million at September 30, 2018 and December 31, 2017 . BGE excludes cash of $13 million and $17 million at September 30, 2018 and December 31, 2017 and restricted cash of $3 million and $1 million at September 30, 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 and nine months ended September 30, 2018 and September 30, 2017 , respectively. (c) The Level 3 balance consists of the current and noncurrent liability of $24 million and $235 million , respectively, at September 30, 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 September 30, 2018 and December 31, 2017 : As of September 30, 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) $ 182 $ — $ — $ 182 $ 83 $ — $ — $ 83 Rabbi trust investments Cash equivalents 42 — — 42 72 — — 72 Mutual funds 15 — — 15 — — — — Fixed income — 16 — 16 — 12 — 12 Life insurance contracts — 22 37 59 — 23 22 45 Rabbi trust investments subtotal (b) 57 38 37 132 72 35 22 129 Total assets 239 38 37 314 155 35 22 212 Liabilities Deferred compensation obligation — (22 ) — (22 ) — (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 — (22 ) — (22 ) — (25 ) — (25 ) Total net assets $ 239 $ 16 $ 37 $ 292 $ 155 $ 10 $ 22 $ 187 Pepco DPL ACE As of September 30, 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) $ 35 $ — $ — $ 35 $ 102 $ — $ — $ 102 $ 26 $ — $ — $ 26 Rabbi trust investments Cash equivalents 41 — — 41 — — — — — — — — Fixed income — 6 — 6 — — — — — — — — Life insurance contracts — 22 36 58 — — — — — — — — Rabbi trust investments subtotal (b) 41 28 36 105 — — — — — — — — Total assets 76 28 36 140 102 — — 102 26 — — 26 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 76 $ 25 $ 36 $ 137 $ 102 $ (1 ) $ — $ 101 $ 26 $ — $ — $ 26 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 $33 million and $12 million at September 30, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $12 million and $4 million at September 30, 2018 and December 31, 2017 , respectively. DPL excludes cash of $8 million and $2 million at September 30, 2018 and December 31, 2017 , respectively. ACE excludes cash of $11 million and $2 million at September 30, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 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 totaled less than $1 million for the three months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Pepco totaled $1 million and less than $1 million for the three months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at PHI totaled $1 million and less than $1 million for the nine months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for the nine months ended September 30, 2018 and 2017 , respectively. (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 and nine months ended September 30, 2018 and 2017 : Generation ComEd PHI Exelon Three Months Ended September 30, 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 June 30, 2018 $ 585 $ 18 $ 737 $ 36 $ 1,376 $ (252 ) $ 36 $ — $ 1,160 Total realized / unrealized gains (losses) Included in net income (1 ) — (259 ) (a) 13 (247 ) — 1 — (246 ) Included in noncurrent payables to affiliates (4 ) — — — (4 ) — — 4 — Included in payable for Zion Station decommissioning — 2 — — 2 — — — 2 Included in regulatory assets/liabilities — — — — — (7 ) (b) — (4 ) (11 ) Change in collateral — — (44 ) — (44 ) — — — (44 ) Purchases, sales, issuances and settlements Purchases 15 — 81 3 99 — — — 99 Sales — (20 ) — — (20 ) — — — (20 ) Settlements (29 ) — — — (29 ) — — — (29 ) Transfers into Level 3 — — 3 — 3 — — — 3 Transfers out of Level 3 — — (6 ) — (6 ) — — — (6 ) Balance at September 30, 2018 $ 566 $ — $ 512 $ 52 $ 1,130 $ (259 ) $ 37 $ — $ 908 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2018 $ (1 ) $ — $ (104 ) $ 13 $ (92 ) $ — $ — $ — $ (92 ) Generation ComEd PHI Exelon Nine Months Ended September 30, 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 (1 ) — (188 ) (a) 14 (175 ) — 3 — (172 ) Included in noncurrent payables to affiliates — — — — — — — — — Included in payable for Zion Station decommissioning — 7 — — 7 — — — 7 Included in regulatory assets — — — — — (3 ) (b) — — (3 ) Change in collateral — — 14 — 14 — — — 14 Purchases, sales, issuances and settlements Purchases 34 1 181 3 219 — — — 219 Sales — (20 ) (3 ) — (23 ) — — — (23 ) Settlements (115 ) — — — (115 ) — 12 — (103 ) Transfers into Level 3 — — (21 ) — (21 ) — — — (21 ) Transfers out of Level 3 — — (23 ) (2 ) (25 ) — — — (25 ) Balance as of September 30, 2018 $ 566 $ — $ 512 $ 52 $ 1,130 $ (259 ) $ 37 $ — $ 908 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2018 $ (5 ) $ — $ 159 $ 14 $ 168 $ — $ — $ — $ 168 __________ (a) Includes a reduction for the reclassification of $155 million and $347 million of realized losses due to the settlement of derivative contracts for the three and nine months ended September 30, 2018 , respectively. (b) Includes $4 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2018 . Includes $9 million of decreases in fair value and an increase for realized losses due to settlements of $12 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 2018 . (c) The amounts represented are life insurance contracts at Pepco. Generation ComEd PHI Exelon Three Months Ended September 30, 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) Total Balance as of June 30, 2017 $ 683 $ 21 $ 589 $ 41 $ 1,334 $ (256 ) $ 20 $ 1,098 Total realized / unrealized gains (losses) Included in net income — — (82 ) (a) 1 (81 ) — 1 (80 ) Included in noncurrent payables to affiliates — — — — — — — — Included in payable for Zion Station decommissioning — (4 ) — — (4 ) — — (4 ) Included in regulatory assets — — — — — (21 ) (b) — (21 ) Change in collateral — — 11 — 11 — — 11 Purchases, sales, issuances and settlements Purchases 19 — 57 1 77 — — 77 Sales — — — — — — — — Settlements (31 ) — 10 — (21 ) — — (21 ) Transfers into Level 3 — — — — — — — — Transfers out of Level 3 — — 10 — 10 — — 10 Balance as of September 30, 2017 $ 671 $ 17 $ 595 $ 43 $ 1,326 $ (277 ) $ 21 $ 1,070 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2017 $ — $ — $ 24 $ 1 $ 25 $ — $ 1 $ 26 Generation ComEd PHI Exelon Nine Months Ended September 30, 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 4 — (110 ) (a) 2 (104 ) — 2 — (102 ) Included in noncurrent payables to affiliates 13 — — — 13 — — (13 ) — Included in payable for Zion Station decommissioning — (3 ) — — (3 ) — — — (3 ) Included in regulatory assets — — — — — (19 ) (b) — 13 (6 ) Change in collateral — — 81 — 81 — — — 81 Purchases, sales, issuances and settlements Purchases 54 1 146 4 205 — — — 205 Sales — — (15 ) — (15 ) — — — (15 ) Issuances — — — — — — (1 ) — (1 ) Settlements (77 ) (8 ) (85 ) — — — (85 ) Transfers into Level 3 — — (9 ) — (9 ) — — — (9 ) Transfers out of Level 3 — — 17 (5 ) 12 — — — 12 Balance as of September 30, 2017 $ 671 $ 17 $ 595 $ 43 $ 1,326 $ (277 ) $ 21 $ — $ 1,070 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2017 $ 2 $ — $ 161 $ 2 $ 165 $ — $ 2 $ — $ 167 __________ (a) Includes a reduction for the reclassification of $96 million and $279 million of realized gains due to the settlement of derivative contracts for the three and nine months ended September 30, 2017 , respectively. (b) Includes $24 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2017 . Includes $32 million of decreases in fair value and an increase for realized losses due to settlements of $13 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 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 and nine mon

Derivative Financial Instrument

Derivative Financial Instruments (All Registrants)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments (All Registrants)	Derivative Financial Instruments (All Registrants) The Registrants use derivative instruments to manage commodity price risk, interest rate risk and foreign exchange risk related to ongoing business operations. Commodity Price Risk (All Registrants) To the extent the amount of energy Generation produces differs from the amount of energy it has contracted to sell, Exelon and Generation are exposed to market fluctuations in the prices of electricity, fossil fuels and other commodities. Each of the Registrants employ established policies and procedures to manage their risks associated with market fluctuations in commodity prices by entering into physical and financial derivative contracts, including swaps, futures, forwards, options and short-term and long-term commitments to purchase and sell energy and commodity products. The Registrants believe these instruments, which are either determined to be non-derivative or classified as economic hedges, mitigate exposure to fluctuations in commodity prices. Derivative authoritative guidance requires that derivative instruments be recognized as either assets or liabilities at fair value, with changes in fair value of the derivative recognized in earnings immediately. Other accounting treatments are available through special election and designation, provided they meet specific, restrictive criteria both at the time of designation and on an ongoing basis. These alternative permissible accounting treatments include normal purchase normal sale (NPNS), cash flow hedges and fair value hedges. For Generation, all derivative economic hedges related to commodities are recorded at fair value through earnings for the consolidated company, referred to as economic hedges in the following tables. Additionally, Generation is exposed to certain market risks through its proprietary trading activities. The proprietary trading activities are a complement to Generation’s energy marketing portfolio but represent a small portion of Generation’s overall energy marketing activities. Fair value authoritative guidance and disclosures about offsetting assets and liabilities requires the fair value of derivative instruments to be shown in the Combined Notes to Consolidated Financial Statements on a gross basis, even when the derivative instruments are subject to legally enforceable master netting agreements and qualify for net presentation in the Consolidated Balance Sheet. A master netting agreement is an agreement between two counterparties that may have derivative and non-derivative contracts with each other providing for the net settlement of all referencing contracts via one payment stream, which takes place as the contracts deliver, when collateral is requested or in the event of default. Generation’s use of cash collateral is generally unrestricted, unless Generation is downgraded below investment grade (i.e., to BB+ or Ba1). In the table below, Generation’s energy-related economic hedges and proprietary trading derivatives are shown gross. The impact of the netting of fair value balances with the same counterparty that are subject to legally enforceable master netting agreements, as well as netting of cash collateral, including margin on exchange positions, is aggregated in the collateral and netting column. As of September 30, 2018, $23 million of cash collateral posted, and as of December 31, 2017 , $4 million of cash collateral held, was not offset against derivative positions because such collateral was not associated with any energy-related derivatives, were associated with accrual positions, or had no positions to offset as of the balance sheet date. Excluded from the tables below are economic hedges that qualify for the NPNS scope exception and other non-derivative contracts that are accounted for under the accrual method of accounting. ComEd’s use of cash collateral is generally unrestricted unless ComEd is downgraded below investment grade (i.e., to BB+ or Ba1). Cash collateral held by PECO and BGE must be deposited in an unaffiliated major U.S. commercial bank or foreign bank with a U.S. branch office that meet certain qualifications. In the table below, DPL's economic hedges are shown gross. The impact of the netting of fair value balances with the same counterparty that are subject to legally enforceable master netting agreements, as well as netting of cash collateral, in cluding 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 September 30, 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) $ 2,987 $ 113 $ (2,406 ) $ 694 $ — $ — $ — $ — $ 694 Mark-to-market derivative assets (noncurrent assets) 1,383 61 (1,013 ) 431 — — — — 431 Total mark-to-market derivative assets 4,370 174 (3,419 ) 1,125 — — — — 1,125 Mark-to-market derivative liabilities (current liabilities) (2,761 ) (86 ) 2,543 (304 ) (24 ) — — — (328 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,284 ) (41 ) 1,088 (237 ) (235 ) — — — (472 ) Total mark-to-market derivative liabilities (4,045 ) (127 ) 3,631 (541 ) (259 ) — — — (800 ) Total mark-to-market derivative net assets (liabilities) $ 325 $ 47 $ 212 $ 584 $ (259 ) $ — $ — $ — $ 325 _________ (a) Exelon, G eneration 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 $71 million and $28 million , respectively, and current and noncurrent liabilities are shown net of collateral of $66 million and $47 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $212 million at September 30, 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 p osted/(received), $(166) 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 al l 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/(rece ived), $(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 and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ 8 $ 55 $ (99 ) $ (41 ) Purchased power and fuel 66 21 (4 ) (114 ) Total Exelon and Generation $ 74 $ 76 $ (103 ) $ (155 ) In general, increases and decreases in forward market prices have a positive and negative impact, respectively, on G eneration’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 September 30, 2018 , the percentage of expected generation hedged is 98% - 101% , 82% - 85% and 48% - 51% 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 2018 PAPUC PGC settlement and to reduce the exposure of PECO and its customers to natural gas price volatility, PECO has continued its program to purchase natural gas for both winter and summer supplies using a layered approach of locking-in prices ahead of each season with long-term gas purchase agreements (those with primary terms of at least twelve months). Under the terms of the 2018 and previous PGC settlements, PECO is required to lock in (i.e., economically hedge) the price of a minimum volume of its long-term gas commodity purchases. PECO’s gas-hedging program is designed to cover about 20% of planned natural gas purchases in support of projected firm sales. The hedging program for natural gas procurement has no direct impact on PECO’s results of operations and financial position as natural gas costs are fully recovered from customers under the PGC. BGE has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC. The SOS rates charged recover BGE's wholesale power supply costs and include an administrative fee. BGE’s commodity price risk related to electric supply procurement is limited. BGE locks in fixed prices for all of its SOS requirements through full requirements contracts. Certain of BGE’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other BGE full requirements contracts are not derivatives. BGE provides natural gas to its customers under a MBR mechanism approved by the MDPSC. Under this mechanism, BGE’s actual cost of gas is compared to a market index (a measure of the market price of gas in a given period). The difference between BGE’s actual cost and the market index is shared equally between shareholders and customers. BGE must also secure fixed price contracts for at least 10% , but not more than 20% , of forecasted system supply requirements for flowing (i.e., non-storage) gas for the November through March period. These fixed-price contracts are not subject to sharing under the MBR mechanism. BGE also ensures it has sufficient pipeline transportation capacity to meet customer requirements. BGE’s natural gas supply and asset management agreements qualify for the NPNS scope exception and result in physical delivery. Pepco has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and DCPSC. The SOS rates charged recover Pepco's wholesale power supply costs and include an administrative fee. The administrative fee includes an incremental cost component and a shareholder return component for residential and commercial rate classes. Pepco’s commodity price risk related to electric supply procurement is limited. Pepco locks in fixed prices for its SOS requirements through full requirements contracts. Certain of Pepco’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other Pepco full requirements contracts are not derivatives. DPL has contracts to procure SOS electric supply that are executed through a competitive procurement process approved by the MDPSC and the DPSC. The SOS rates charged recover DPL's wholesale power supply costs. In Delaware, DPL is also entitled to recover a Reasonable Allowance for Retail Margin (RARM). The RARM includes a fixed annual margin of approximately $2.75 million , plus an incremental cost component and a cash working capital allowance. In Maryland, DPL charges an administrative fee intended to allow it to recover its administrative costs. DPL locks in fixed prices for its SOS requirements through full requirements contracts. DPL’s commodity price risk related to electric supply procurement is limited. Certain of DPL’s full requirements contracts, which are considered derivatives, qualify for the NPNS scope exception under current derivative authoritative guidance. Other DPL full requirements contracts are not derivatives. DPL provides natural gas to its customers under an Annual GCR mechanism approved by the DPSC. Under this mechanism, DPL’s Annual GCR Filing establishes a future GCR for firm bundled sales customers by using a forecast of demand and commodity costs. The actual costs are trued up against 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 s upply 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 and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ (3 ) $ 5 $ 14 $ 4 Interest Rate and Foreign Exchange Risk (All Registrants) The Registrants use a combination of fixed-rate and variable-rate debt to manage interest rate exposure. The Registrants also utilize interest rate swaps, which are treated as economic hedges, to manage their interest rate exposure. To manage foreign exchange rate exposure associated with international commodity purchases in currencies other than U.S. dollars, Generation utilizes foreign currency derivatives, which are treated as economic hedges. Below is a summary of the interest rate and foreign exchange hedge balances as of September 30, 2018 : Generation Exelon Corporate Exelon Description Economic Hedges Collateral and Netting (a) Subtotal Economic Hedges Total Mark-to-market derivative assets (current assets) $ 3 $ (1 ) $ 2 $ — $ 2 Mark-to-market derivative assets (noncurrent assets) 18 — 18 — 18 Total mark-to-market derivative assets 21 (1 ) 20 — 20 Mark-to-market derivative liabilities (current liabilities) (2 ) 1 (1 ) — (1 ) Mark-to-market derivative liabilities (noncurrent liabilities) — — — (10 ) (10 ) Total mark-to-market derivative liabilities (2 ) 1 (1 ) (10 ) (11 ) Total mark-to-market derivative net assets (liabilities) $ 19 $ — $ 19 $ (10 ) $ 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 $ 1 $ 1 $ — $ 2 $ 3 $ 5 __________ (a) Exelon and Generation net all available amounts allowed under the derivative authoritative guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral. In some cases, Exelon and Generation may have other offsetting counterparty exposures subject to a master netting or similar agreement, such as accrued interest, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral, which are not reflected in the table above. Economic Hedges (Interest Rate and Foreign Exchange Risk) Exelon and Generation execute these instruments to mitigate exposure to fluctuations in interest rates or foreign exchange but for which the fair value or cash flow hedge elections were not made. On July 1, 2018, Exelon de-designated its fair value hedges related to interest rate risk and Generation de-designated its cash flow hedges related to interest rate risk. The amount deferred in AOCI associated with the previously designated cash flow hedges will be reclassified into earnings as the underlying forecasted transaction occurs. The result of this de-designation is that all economic hedges for interest rate swaps will be recorded at fair value through earnings going forward, referred to as economic hedges in the following tables. The following table provides notional amounts outstanding held by Exelon and Generation at September 30, 2018 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 88 $ — $ 88 Interest rate swaps 625 800 1,425 Total $ 713 $ 800 $ 1,513 The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 94 $ — $ 94 Interest rate swaps (a) 1 — 1 Total $ 95 $ — $ 95 __________ (a) On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017. For the three and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Generation Operating Revenues $ (2 ) $ (3 ) $ 3 $ (6 ) Generation Purchased Power and Fuel (1 ) — (4 ) — Generation Interest Expense 4 — 4 — Total Generation $ 1 $ (3 ) $ 3 $ (6 ) Three Months Ended Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Exelon Operating Revenues $ (2 ) $ (3 ) $ 3 $ (6 ) Exelon Purchased Power and Fuel (1 ) — (4 ) — Exelon Interest Expense 2 — 2 — Total Exelon $ (1 ) $ (3 ) $ 1 $ (6 ) Fair Value Hedges (Interest Rate Risk) For derivative instruments that qualify and are designated as fair value hedges, the gain or loss on the derivative as well as the offsetting loss or gain on the hedged item attributable to the hedged risk are recognized in earnings immediately. Exelon had no fixed-to-floating swaps designated as fair value hedges as of September 30, 2018 and had $800 million notional amounts designated as fair value hedges as of December 31, 2017 . Exelon and Generation include the gain or loss on the hedged items and the offsetting loss or gain on the related interest rate swaps as follows: Three Months Ended September 30, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ — $ (2 ) $ — $ 6 Nine Months Ended September 30, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (11 ) $ (6 ) $ 20 $ 17 During the three months ended September 30, 2018 , due to the de-designation of fair value hedges, there was no impact on the results of operations as a result of ineffectiveness from fair value hedges. During the three months ended September 30, 2017 , the impact on the results of operations as a result of ineffectiveness from fair value hedges was a $4 million gain. During the nine months ended September 30, 2018 and 2017 , the impact on the results of operations as a result of ineffectiveness from fair value hedges was a $9 million gain and a $11 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. Exelon and Generation have no floating-to-fixed swaps designated as cash flow hedges as of September 30, 2018, and had $636 million notional amounts designated as cash flow hedges as of December 31, 2017. The tables below provide the activity of OCI related to cash flow hedges for the three and nine months ended September 30, 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 September 30, 2018 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at June 30, 2018 $ (4 ) $ (2 ) Reclassifications from AOCI to net income Interest Expense — — AOCI derivative loss at September 30, 2018 $ (4 ) $ (2 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Nine Months Ended September 30, 2018 Income Statement Location Total Cash Total Cash AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Effective portion of changes in fair value 11 11 Reclassifications from AOCI to net income Interest Expense 1 1 AOCI derivative loss at September 30, 2018 $ (4 ) $ (2 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Three Months Ended September 30, 2017 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at June 30, 2017 $ (14 ) $ (12 ) Effective portion of changes in fair value 1 1 Reclassifications from AOCI to net income Interest Expense (1 ) (a) (1 ) (a) AOCI derivative loss at September 30, 2017 $ (14 ) $ (12 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Nine Months Ended September 30, 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 3 (b) 3 (b) AOCI derivative loss at September 30, 2017 $ (14 ) $ (12 ) _________ (a) Amount is net of related income tax benefit of $1 million for the three months ended September 30, 2017 . (b) Amount is net of related income tax expense of $2 million for the nine months ended September 30, 2017 . During the three months ended September 30, 2018 , due to the de-designation of cash flow hedges, there was no impact on the results of operations as a result of ineffectiveness. During the nine months ended September 30, 2018 and the three and nine months ended September 30, 2017 , the impact on the results of operations as a result of ineffectiveness from cash flow hedges was immaterial. The estimated amount of existing gains and losses that are reported in AOCI at the reporting date that are expected to be reclassified into earnings within the next twelve months is immaterial. Proprietary Trading (Interest Rate and Foreign Exchange Risk) Generation also executes derivative contracts for proprietary trading purposes to hedge risk associated with the interest rate and foreign exchange component

Debt and Credit Agreements (All

Debt and Credit Agreements (All Registrants)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt and Credit Agreements (All Registrants)	Debt and Credit Agreements (All Registrants) Short-Term Borrowings Exelon Corporate, ComEd, BGE, Pepco, DPL and ACE meet their short-term liquidity requirements primarily through the issuance of commercial paper. Generation and PECO meet their short-term liquidity requirements primarily through the issuance of commercial paper and borrowings from the Exelon intercompany money pool. PHI Corporate meets its short-term liquidity requirements primarily through the issuance of short-term notes and the Exelon intercompany money pool. The Registrants may use their respective credit facilities for general corporate purposes, including meeting short-term funding requirements and the issuance of letters of credit. Commercial Paper The Registrants had the following amounts of commercial paper borrowings outstanding as of September 30, 2018 and December 31, 2017 : Commercial Paper Borrowings September 30, 2018 December 31, 2017 Exelon $ 209 $ 427 BGE — 77 PHI (a) 209 350 Pepco 64 26 DPL — 216 ACE 145 108 _________ (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. On May 23, 2018, ACE entered into two term loan agreements in the aggregate amount of $125 million , which expire on May 22, 2019. Pursuant to the term loan agreements, loans made thereunder bear interest at a variable rate equal to LIBOR plus 0.55% and all indebtedness thereunder is unsecured. Credit Agreements As of March 15, 2018, the credit agreement for a Generation bilateral credit facility of $30 million was amended to increase the overall facility size to $95 million . This facility will solely be used by Generation to issue letters of credit. On May 26, 2018, each of the Registrants' respective syndicated revolving credit facilities had their maturity dates extended to May 26, 2023. Long-Term Debt Issuance of Long-Term Debt During the nine months ended September 30, 2018 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.72 % November 30, 2018 $ 4 Funding to install energy conservation measures for the Smithsonian Zoo project. Generation Energy Efficiency Project Financing 3.17 % October 31, 2018 $ 1 Funding to install energy conservation measures in Brooklyn, NY. Generation Energy Efficiency Project Financing 2.61 % September 30, 2018 $ 5 Funding to install energy conservation measures for the Pensacola project. Generation Energy Efficiency Project Financing 4.17 % January 1, 2019 $ 1 Funding to install energy conservation measures for the General Services Administration Philadelphia project. Generation Energy Efficiency Project Financing 4.26 % May 1, 2019 $ 3 Funding to install energy conservation measures for the National Institutes of Health Multi-Buildings Phase II 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. ComEd First Mortgage Bonds, Series 125 3.70 % August 15, 2028 $ 550 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. PECO Loan Agreement 2.00 % June 20, 2023 $ 50 Funding to implement Electric Long-term Infrastructure Improvement Plan. PECO First and Refunding Mortgage Bonds 3.90 % March 1, 2048 $ 325 Satisfy short-term borrowings from the Exelon intercompany money pool and for general corporate purposes. BGE Senior Notes 4.25 % September 15, 2048 $ 300 Repay commercial paper obligations and for general corporate purposes. Pepco First Mortgage Bonds 4.27 % June 15, 2048 $ 100 Repay existing indebtedness and for general corporate purposes. DPL First Mortgage Bonds 4.27 % June 15, 2048 $ 200 Repay existing indebtedness and for general corporate purposes. On October 16, 2018, ACE issued $ 350 million of 4.00% First Mortgage Bonds due October 15, 2028. The proceeds will be used to refinance ACE’s 7.75% First Mortgage Bonds due November 15, 2018, reduce short-term borrowings and for general corporate purposes. On November 1, 2018, Pepco issued $ 100 million of 4.31% First Mortgage Bonds due November 1, 2048. The proceeds will be used to repay existing indebtedness and for general corporate purposes.

Income Taxes (All Registrants)

Income Taxes (All Registrants)	9 Months Ended
	Sep. 30, 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 additional information. The Registrants assessed 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. On August 3, 2018, the U.S. Department of Treasury in conjunction with the IRS released proposed regulations clarifying the immediate expensing depreciation provisions enacted by the TCJA, specifically that regulated utility property acquired after September 27, 2017 and placed in service by December 31, 2017 qualifies for 100% expensing. Until the proposed regulations are finalized, taxpayers may rely on the proposed regulations for tax years ending after September 28, 2017. While the Registrants have recorded the impacts of the TCJA based on their interpretation of the provisions as enacted, it is expected that Treasury and the IRS will issue additional interpretative guidance in the future which could result in changes to previously finalized provisions. At this time, many of the states in which Exelon does business have issued guidance regarding TCJA and the impact is not material. The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below. The impact of the August 3, 2018 proposed regulations to these balances is not material. 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 was in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. See Note 6 - 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. See Note 6 - 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, the pass back period is subject to determinations by the rate regulators. See Note 6 - Regulatory Matters for the status of and information regarding the Registrants' TCJA-related regulatory filings. 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 September 30, 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 (1.2) (9.0) 8.3 (3.6) 7.3 0.2 1.0 6.6 7.3 Qualified nuclear decommissioning trust fund income 2.4 5.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.6) (1.1) (0.2) (0.1) — (0.2) (0.1) (0.3) (0.3) Plant basis differences (2.5) — (0.3) (15.2) (0.8) (2.0) (3.4) (0.7) (1.3) Production tax credits and other credits (1.2) (2.9) (0.1) — — — — — — Noncontrolling interests (1.1) (2.8) — — — — — — — Excess deferred tax amortization (6.8) — (7.8) (4.6) (7.9) (17.7) (21.2) (14.0) (15.4) Tax Cuts and Jobs Act of 2017 1.3 3.5 — — — 0.2 0.1 — — Other 3.2 5.6 0.3 0.9 2.6 0.6 0.3 0.6 0.3 Effective income tax rate 14.5% 20.1% 21.2% (1.6)% 22.2% 2.1% (2.3)% 13.2% 11.6% Three Months Ended September 30, 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 2.2 5.6 6.6 (0.1) 5.3 5.1 2.2 5.3 5.6 Qualified nuclear decommissioning trust fund income 2.6 5.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.1) (2.2) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.4) Plant basis differences (2.6) — (0.3) (14.6) (0.8) (4.9) (6.7) (1.9) (3.4) Production tax credits and other credits (2.2) (4.9) — — — — — — — Noncontrolling interests 0.5 1.1 — — — — — — — Fitzpatrick bargain purchase gain (0.2) (0.4) — — — — — — — Other (0.1) 0.3 (0.2) (0.2) (0.2) 0.2 — (0.2) 0.1 Effective income tax rate 34.1% 40.3% 40.9% 20.0% 39.2% 35.2% 30.4% 38.0% 36.9% Nine Months Ended September 30, 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 1.7 (2.6) 8.2 (3.6) 6.6 2.7 2.4 6.5 7.3 Qualified nuclear decommissioning trust fund income 0.9 2.6 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9) (2.2) (0.2) (0.1) (0.1) (0.2) (0.1) (0.3) (0.3) Plant basis differences (2.7) — (0.1) (15.4) (0.7) (1.9) (2.9) (0.7) (1.3) Production tax credits and other credits (1.8) (5.1) (0.1) — — — — — — Noncontrolling interests (1.1) (3.2) — — — — — — — Excess deferred tax amortization (6.1) — (7.6) (3.4) (8.1) (14.5) (16.5) (11.0) (14.0) Tax Cuts and Jobs Act of 2017 0.2 1.3 (0.2) — — 0.3 — — — Other 0.4 2.0 0.1 — 0.9 0.3 — 0.4 0.9 Effective income tax rate 11.6% 13.8% 21.1% (1.5)% 19.6% 7.7% 3.9% 15.9% 13.6% Nine Months Ended September 30, 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 0.7 2.2 5.9 (0.1) 5.2 4.9 3.0 5.1 5.6 Qualified nuclear decommissioning trust fund income 4.0 13.6 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9) (2.7) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.4) Plant basis differences (3.4) — (0.3) (14.4) (0.8) (4.6) (6.3) (1.8) (3.4) Production tax credits and other credits (1.8) (6.0) — — — — — — — Noncontrolling interests 0.1 0.3 — — — — — — — Merger expenses (c) (5.4) (2.4) — — — (11.8) (8.0) (10.0) (23.0) FitzPatrick bargain purchase gain (3.2) (10.9) — — — — — — — Like-Kind Exchange (b) (1.7) — 1.7 — — — — — — Other 0.1 (0.4) 0.2 — 0.2 — (0.3) 0.6 (0.3) Effective income tax rate 23.5% 28.7% 42.3% 20.4% 39.5% 23.3% 23.3% 28.7% 13.5% _________ (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) Exelon and ComEd recorded the impact of the IRS's finalization of the LKE computation in the second quarter of 2017. (c) Includes a remeasurement of uncertain federal and state income tax positions. Accounting for Uncertainty in Income Taxes The Registrants have the following unrecognized tax benefits as of September 30, 2018 and December 31, 2017 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE September 30, 2018 $ 804 $ 527 $ 2 $ — $ 120 $ 134 $ 67 $ 21 $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14 As a result of a court decision issued in July 2018 to an unrelated taxpayer, Exelon's and Generation’s unrecognized federal and state tax benefits increased in the third quarter of 2018 by approximately $71 million . Approximately $20 million of this increase impacted Exelon's and Generation’s effective tax rate and resulted in a charge to earnings in the third quarter of 2018. 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 September 30, 2018 , Exelon and ComEd have approximately $33 million and $2 million , respectively, of unrecognized federal and state tax benefits related to the like-kind exchange litigation described further below. If Exelon decides not to appeal the October 2018 U.S. Court of Appeals for the Seventh Circuit's decision, Exelon's and ComEd's unrecognized tax benefits will decrease in the fourth quarter. See below for further details. Settlement of Income Tax Audits, Refund Claims, and Litigation As of September 30, 2018 , Exelon, Generation, PHI and ACE have approximately $515 million , $501 million , $14 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 $473 million that, if recognized, would decrease the effective tax rate. The unrecognized tax benefits related to PHI and ACE, if recognized, may be included in future regulated base rates and that portion would have no impact to the effective tax rate. As of September 30, 2018 , Exelon, Generation, BGE, PHI, Pepco and DPL have approximately $241 million , $33 million , $120 million , $88 million , $67 million , and $21 million , respectively, of unrecognized state tax benefits that will decrease in the fourth quarter of 2018 due to the receipt of favorable guidance with respect to the deductibility of certain depreciable fixed assets. The recognition of these tax benefits will decrease the effective tax rate at Exelon and Generation in the fourth quarter of 2018, which will result in an income tax benefit of approximately $26 million . The recognition of the tax benefits related to BGE, PHI, Pepco and DPL will be offset by corresponding regulatory liabilities and that portion will have no immediate impact to their 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. In October 2018, the U.S. Court of Appeals for the Seventh Circuit affirmed the Tax Court’s decision. Exelon is evaluating whether to pursue any further appeals of the decision. State Income Tax Law Changes On April 24, 2018, Maryland enacted companion bills, House Bill 1794 and Senate Bill 1090, providing for a phase in of a single sales factor apportionment formula from the current three factor formula for determining an entity's Maryland state income taxes. The single sales factor will be fully phased in by 2022. In the second quarter of 2018, Exelon, Generation, PHI, Pepco and DPL recorded a one-time increase to deferred income taxes of approximately $16 million , $5 million , $17 million , $16 million and $1 million , respectively. At PHI, Pepco and DPL, the increase to the Maryland deferred income tax liability was offset by regulatory assets. Further, the change in tax law is not expected to have a material ongoing impact to Exelon's, Generation's, PHI's, Pepco's or DPL's future results of operations. Long-Term Marginal State Income Tax Rate (Exelon, Generation, PHI and Pepco) In the third quarter of 2018, Exelon reviewed and updated its marginal state income tax rates based on 2017 state apportionment rates. As a result of the rate changes, in the third quarter of 2018, Exelon, Generation, PHI and DPL recorded a one-time decrease to deferred income taxes of approximately $50 million , $53 million , $4 million and $2 million , respectively. Pepco recorded a one-time increase to deferred incomes taxes of approximately $1 million . Exelon, PHI and DPL recorded a corresponding regulatory liability of approximately $1 million , $1 million and $2 million , respectively. Pepco recorded a corresponding regulatory asset of approximately $1 million . In the third quarter of 2018 , Exelon, Generation and PHI recorded a decrease to income tax expense (net of federal taxes) of approximately $50 million , $53 million and $3 million , respectively.

Asset Retirement Obligations (E

Asset Retirement Obligations (Exelon and Generation)	9 Months Ended
	Sep. 30, 2018
Environmental Remediation Obligations [Abstract]
Nuclear Decommissioning (Exelon and Generation)	Asset Retirement Obligations (Exelon, Generation and Pepco) Nuclear Decommissioning Asset Retirement Obligations (Exelon and Generation) 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 September 30, 2018 : Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 Oyster Creek transferred to Liabilities held for sale (783 ) Accretion expense 357 Net increase due to changes in, and timing of, estimated future cash flows 116 Costs incurred related to decommissioning plants (35 ) Nuclear decommissioning ARO at September 30, 2018 (a) $ 9,317 _________ (a) Includes $12 million and $13 million for the current portion of the ARO at September 30, 2018 and December 31, 2017 , respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets. During the nine months ended September 30, 2018 , Generation’s total nuclear ARO decreased by approximately $345 million , primarily reflecting the reclassification of Oyster Creek ARO as Liabilities held for sale on Exelon's and Generation's Consolidated Balance Sheets following the announced agreement to sell Oyster Creek, offset by the accretion of the ARO liability due to the passage of time, and the impacts of ARO updates completed during 2018. The $116 million increase in the ARO during 2018 due to changes in the amounts and timing of estimated decommissioning cash flows includes a $32 million increase in the first quarter for the impact of the early retirement of Oyster Creek and a $84 million increase in the third quarter for the remeasurement of the ARO to reflect the announced pending sale of Oyster Creek. See Note 4 — Mergers, Acquisitions and Dispositions and Note 8 - Early Plant Retirements for additional information. Nuclear Decommissioning Trust Fund Investments (Exelon and Generation) 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 $12,584 million and $13,349 million at September 30, 2018 and December 31, 2017 , respectively. The decrease is primarily driven by the reclassification of $903 million of Oyster Creek NDT as Assets held for sale on Exelon's and Generation's Consolidated Balance Sheets, partially offset by improved market performance. See Note 4 - Mergers, Acquisitions and Dispositions for additional information regarding the announced pending sale of Oyster Creek. The NDT fund investments include $120 million and $77 million for the current portion of the NDT at September 30, 2018 and December 31, 2017 , respectively, which are included in Other current assets on Exelon's and Generation's Consolidated Balance Sheets. The following table provides net unrealized gains (losses) on NDT funds for the three and nine months ended September 30, 2018 and 2017 : Exelon and Generation Exelon and Generation Three Months Ended Nine Months Ended 2018 2017 2018 2017 Net unrealized gains (losses) on decommissioning trust funds — Regulatory Agreement Units (a) $ (66 ) $ 44 $ (335 ) $ 253 Net unrealized gains (losses) on decommissioning trust funds — Non-Regulatory Agreement Units (b)(c) 72 111 (143 ) 347 _________ (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 $9 million and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2018 and 2017 , respectively. Excludes $7 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 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. (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. See 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 (Exelon and Generation) 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 $118 million which is included within the nuclear decommissioning ARO at September 30, 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 September 30, 2018 and December 31, 2017 : Exelon and Generation September 30, 2018 December 31, 2017 Carrying value of Zion Station pledged assets (a) $ 9 $ 39 Payable to Zion Solutions (b)(c) 9 37 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 965 942 _________ (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 (Exelon and Generation) 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. Generation will file its next decommissioning funding status report for all units with the NRC by March 31, 2019. This report will reflect the status of decommissioning funding assurance as of December 31, 2018. A shortfall at any unit could necessitate that Generation address the shortfall by, among other things, obtaining a parental guarantee for Generation's share of the funding assurance. However, the amount of any guarantee or other assurance will ultimately depend on the decommissioning approach, the associated level of costs, and the decommissioning trust fund investment performance going forward. Non-Nuclear Asset Retirement Obligations (Pepco) Pepco has AROs primarily associated with the abatement and disposal of equipment and buildings contaminated with asbestos and PCBs. In the third quarter of 2018, Pepco recorded an increase of $22 million in Operating and maintenance expense primarily related to asbestos identified at its Buzzard Point property as part of an annual ARO study. Buzzard Point is a waterfront property in the District of Columbia occupied by an active substation and former Pepco operated steam plant building, which Pepco retired and closed in 1981. Pepco’s AROs were $38 million and $3 million at September 30, 2018 and December 31, 2017 , respectively.

Retirement Benefits (All Regist

Retirement Benefits (All Registrants)	9 Months Ended
	Sep. 30, 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. See Note 4 — Mergers, Acquisitions and Dispositions for additional information 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 and nine months ended September 30, 2018 and 2017 . Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 100 $ 98 $ 28 $ 26 Interest cost 201 211 43 45 Expected return on assets (312 ) (300 ) (43 ) (39 ) Amortization of: Prior service cost (benefit) — (1 ) (47 ) (47 ) Actuarial loss 158 152 18 15 Settlement charges — 1 — — Net periodic benefit cost $ 147 $ 161 $ (1 ) $ — Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 303 $ 290 $ 84 $ 79 Interest cost 602 632 131 136 Expected return on assets (939 ) (898 ) (130 ) (121 ) Amortization of: Prior service cost (benefit) 1 — (140 ) (140 ) Actuarial loss 472 455 50 46 Settlement charges 1 3 — — Net periodic benefit cost $ 440 $ 482 $ (5 ) $ — _________ (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 and nine months ended September 30, 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, net, for the three and nine months ended September 30, 2018 and 2017, while the non-service cost components are included in Other, net and Regulatory assets for the three and nine months ended September 30, 2018 and in Other, net and Property, plant and equipment, net, for the three and nine months ended September 30, 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, net on their consolidated financial statements for the three and nine months ended September 30, 2018 and 2017. Three Months Ended September 30, Nine Months Ended September 30, Pension and Other Postretirement Benefit Costs 2018 2017 2018 2017 Exelon (a)(b) $ 145 $ 161 $ 435 $ 482 Generation (b) 50 57 151 170 ComEd 45 44 133 131 PECO 5 7 14 21 BGE 15 16 44 48 BSC (c) 13 13 42 40 PHI (a) 17 24 51 72 Pepco 3 6 10 19 DPL 2 3 5 10 ACE 3 3 10 10 PHISCO (d) 9 12 26 33 _________ (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, ACE or PHISCO 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 and nine months ended September 30, 2018 and 2017 , respectively. Three Months Ended September 30, Nine Months Ended Savings Plan Matching Contributions 2018 2017 2018 2017 Exelon (a)(b) $ 44 $ 34 $ 126 $ 97 Generation (b) 23 14 65 42 ComEd 8 9 23 24 PECO 2 3 7 7 BGE 2 3 5 7 BSC (c) 5 2 16 7 PHI (a) 4 3 10 10 Pepco 1 1 2 3 DPL 1 1 2 2 ACE 1 — 2 1 PHISCO (d) 1 1 4 4 _________ (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, 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, ACE or PHISCO 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.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Exelon, Generation, and PECO)	9 Months Ended
	Sep. 30, 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 nine months ended September 30, 2018 and 2017 : Nine Months Ended September 30, 2018 Gains (Losses) on Cash Flow Hedges Unrealized gains (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 11 — 22 (4 ) 1 30 Amounts reclassified from AOCI (b) 1 — 136 — — 137 Net current-period OCI 12 — 158 (4 ) 1 167 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (10 ) (c) — — — (10 ) Ending balance $ (2 ) $ — $ (2,840 ) $ (27 ) $ — $ (2,869 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 11 — — (4 ) 1 8 Amounts reclassified from AOCI (b) 1 — — — — 1 Net current-period OCI 12 — — (4 ) 1 9 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (3 ) (c) — — — (3 ) Ending balance $ (4 ) $ — $ — $ (27 ) $ — $ (31 ) 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 $ — $ — $ — $ — $ — $ — Nine Months Ended September 30, 2017 Gains (Losses) on Cash Flow Hedges Unrealized gains (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 2 (55 ) 7 7 (37 ) Amounts reclassified from AOCI (b) 3 — 105 — — 108 Net current-period OCI 5 2 50 7 7 71 Ending balance $ (12 ) $ 6 $ (2,560 ) $ (23 ) $ — $ (2,589 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications 2 — — 7 6 15 Amounts reclassified from AOCI (b) 3 — — — — 3 Net current-period OCI 5 — — 7 6 18 Ending balance $ (14 ) $ 2 $ — $ (23 ) $ (1 ) $ (36 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 _________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and 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 and nine months ended September 30, 2018 and 2017 . The following tables present amounts reclassified out of AOCI to Net income for Exelon and Generation during the three and nine months ended September 30, 2018 and 2017 . Three Months Ended September 30, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ — $ — Interest expense — — Total before tax — — Tax benefit $ — $ — Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (83 ) — (60 ) — Total before tax 15 — Tax benefit $ (45 ) $ — Net of tax Total Reclassifications $ (45 ) $ — Net of tax Nine Months Ended September 30, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (1 ) $ (1 ) Interest expense (1 ) (1 ) Total before tax — — Tax benefit $ (1 ) $ (1 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 68 $ — Actuarial losses (b) (251 ) — (183 ) — Total before tax 47 — Tax benefit $ (136 ) $ — Net of tax Total Reclassifications $ (137 ) $ (1 ) Net of tax Three Months Ended September 30, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ 2 $ 2 Interest expense 2 2 Total before tax (1 ) (1 ) Tax expense $ 1 $ 1 Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (81 ) — (58 ) — Total before tax 23 — Tax benefit $ (35 ) $ — Net of tax Total Reclassifications $ (34 ) $ 1 Net of tax Nine Months Ended September 30, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense (5 ) (5 ) Total before tax 2 2 Tax benefit $ (3 ) $ (3 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 69 $ — Actuarial losses (b) (243 ) — (174 ) — Total before tax 69 — Tax benefit $ (105 ) $ — Net of tax Total Reclassifications $ (108 ) $ (3 ) Net of tax _________ (a) Amounts in parenthesis represent a decrease in AOCI. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional information). The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the three and nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended 2018 2017 2018 2017 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 9 $ 18 $ 27 Actuarial loss reclassified to periodic benefit cost (21 ) (32 ) (65 ) (96 ) Pension and non-pension postretirement benefit plans valuation adjustment (2 ) — (8 ) 2 Change in unrealized gains on cash flow hedges — — (5 ) (3 ) Change in unrealized gains (losses) on investments in unconsolidated affiliates — 1 (1 ) (2 ) Change in unrealized gains on marketable securities — — — (2 ) Total $ (17 ) $ (22 ) $ (61 ) $ (74 ) Generation Change in unrealized gains on cash flow hedges $ — $ — $ (4 ) $ (3 ) Change in unrealized gains on investments in unconsolidated affiliates — — (1 ) (2 ) Change in unrealized gains on marketable securities — — — (1 ) Total $ — $ — $ (5 ) $ (6 )

Earnings Per Share and Equity (

Earnings Per Share and Equity (Exelon)	9 Months Ended
	Sep. 30, 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 shareholders 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Exelon Net income attributable to common shareholders $ 733 $ 823 $ 1,858 $ 1,907 Weighted average common shares outstanding — basic 968 962 967 941 Assumed exercise and/or distributions of stock-based awards 2 3 2 2 Weighted average common shares outstanding — diluted 970 965 969 943 The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 2 million and 3 million for the three and nine months ended September 30, 2018 , respectively, and 7 million and 9 million for the three and nine months ended September 30, 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 and nine months ended September 30, 2018 and 2017 . See Note 19 — Shareholders' Equity of the Exelon 2017 Form 10-K for additional 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 September 30, 2018 .

Commitments and Contingencies (

Commitments and Contingencies (All Registrants)	9 Months Ended
	Sep. 30, 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 additional information 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 September 30, 2018 : Description Expected Payment Period Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 259 $ 259 $ 91 $ 67 $ 101 Energy efficiency 2016 - 2021 122 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 513 $ 315 $ 120 $ 84 $ 111 Remaining commitments $ 138 $ 94 $ 75 $ 12 $ 7 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 in 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 September 30, 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 of Maryland. See Note 23 - Commitments and Contingencies of the Exelon 2017 Form 10-K for additional information regarding the Constellation Merger Commitments. Commercial Commitments (All Registrants) The Registrants’ commercial commitments as of September 30, 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) $ 1,584 $ 1,565 $ 2 $ — $ 3 $ 4 $ 4 $ — $ — Surety bonds (b) 1,402 1,201 9 9 25 65 32 4 3 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (c) 22 — — — — 22 7 9 6 Total commercial commitments $ 3,386 $ 2,766 $ 211 $ 187 $ 28 $ 91 $ 43 $ 13 $ 9 _________ (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 $60 million , $17 million of which is a guarantee by Pepco, $25 million by DPL and $17 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 September 30, 2018 , the current liability limit per incident is $13.1 billion and is subject to change to account for the effects of inflation and changes in the number of licensed reactors. Changes to account for the effects of inflation occur 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 $12.6 billion per incident in funds available for public liability claims. Participation in this secondary financial protection pool requires the operator of each reactor to fund its proportionate share of costs for any single incident that exceeds the primary layer of financial protection. Exelon’s share of this secondary layer would be approximately $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 $13.1 billion limit for a single incident. As part of the execution of the NOSA on April 1, 2014, Generation executed an Indemnity Agreement pursuant to which Generation agreed to indemnify EDF and its affiliates against third-party claims that may arise from any future nuclear incident (as defined in the Price-Anderson Act) in connection with the CENG nuclear plants or their operations. Exelon guarantees Generation’s obligations under this indemnity. See Note 2 — Variable Interest Entities 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 was $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 nine months ended September 30, 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 $345 million . NEIL requires its members to maintain an investment grade credit rating or to ensure collectability of their annual retrospective premium obligation by providing a financial guarantee, letter of credit, deposit premium, or some other means of assurance. NEIL provides “all risk” property damage, decontamination and premature decommissioning insurance for each station for losses resulting from damage to its nuclear plants, either due to accidents or acts of terrorism. If the decision is made to decommission the facility, a portion of the insurance proceeds will be allocated to a fund, which Generation is required by the NRC to maintain, to provide for decommissioning the facility. In the event of an insured loss, Generation is unable to predict the timing of the availability of insurance proceeds to Generation and the amount of such proceeds that would be available. In the event that one or more acts of terrorism cause accidental property damage within a twelve-month period from the first accidental property damage under one or more policies for all insured plants, the maximum recovery by Exelon will be an aggregate of $3.2 billion plus such additional amounts as the insurer may recover for all such losses from reinsurance, indemnity and any other source, applicable to such losses. For its insured losses, Generation is self-insured to the extent that losses are within the policy deductible or exceed the amount of insurance maintained. Uninsured losses and other expenses, to the extent not recoverable from insurers or the nuclear industry, could also be borne by Generation. Any such losses could have a material adverse effect on Exelon’s and Generation’s financial condition, results of operations and cash flows. Environmental Remediation Matters General (All Registrants) The Registrants’ operations have in the past, and may in the future, require substantial expenditures to comply with environmental laws. Additionally, under Federal and state environmental laws, the Registrants are generally liable for the costs of remediating environmental contamination of property now or formerly owned by them and of property contaminated by hazardous substances generated by them. The Registrants own or lease a number of real estate parcels, including parcels on which their operations or the operations of others may have resulted in contamination by substances that are considered hazardous under environmental laws. In addition, the Registrants are currently involved in a number of proceedings relating to sites where hazardous substances have been deposited and may be subject to additional proceedings in the future. Unless otherwise disclosed, the Registrants cannot reasonably estimate whether they will incur significant liabilities for additional investigation and remediation costs at these or additional sites identified by the Registrants, environmental agencies or others, or whether such costs will be recoverable from third parties, including customers. Additional costs could have a material, unfavorable impact on the Registrants' financial conditions, results of operations and cash flows. MGP Sites (Exelon, ComEd, PECO, BGE, PHI and DPL) ComEd, PECO, BGE and DPL have identified sites where former MGP or gas purification activities have or may have resulted in actual site contamination. For almost all of these sites, there are additional PRPs that may share responsibility for the ultimate remediation of each location. • ComEd has identified 42 sites, 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 2023. • PECO has identified 26 sites, 17 of which have been remediated in accordance with applicable PA DEP regulatory requirements and 9 that are currently under some degree of active study and/or remediation. PECO expects the majority of the remediation at these sites to continue through at least 2022. • BGE has identified 13 sites, 9 of which have been remediated and approved by the MDE and 4 that require some level of remediation and/or ongoing activity. BGE expects the majority of the remediation at these sites to continue through at least 2019. • DPL has identified 3 sites, for 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 and gas purification 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. During the third quarter of 2018, the Utility Registrants completed an annual study of their future estimated MGP remediation requirements. The study resulted in a $48 million increase to the environmental liability and related regulatory asset for ComEd. The increase was primarily due to a revised closure strategy at one site, which resulted in an increase in the excavation area and depth of impacted soils from the site. The study did not result in a material change to the environmental liability for PECO, BGE, Pepco, DPL and ACE. As of September 30, 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: September 30, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 486 $ 352 Generation 102 — ComEd 323 321 PECO 28 27 BGE 6 4 PHI 27 — Pepco 25 — DPL 1 — ACE 1 — December 31, 2017 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 466 $ 315 Generation 117 — ComEd 285 283 PECO 30 28 BGE 5 4 PHI 29 — Pepco 27 — DPL 1 — ACE 1 — Solid and Hazardous Waste Cotter Corporation (Exelon and Generation) The EPA has advised Cotter Corporation (Cotter), a former ComEd subsidiary, that it is potentially liable in connection with radiological contamination at a site known as the West Lake Landfill in Missouri. In 2000, ComEd sold Cotter to an unaffiliated third-party. As part of the sale, ComEd agreed to indemnify Cotter for any liability arising in connection with the West Lake Landfill. In connection with Exelon’s 2001 corporate restructuring, this responsibility to indemnify Cotter was transferred to Generation. On May 29, 2008, the EPA issued a Record of Decision (ROD) approving a landfill cover remediation approach. 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 final Remedial Investigation and Feasibility Study (RI/FS) to the EPA in January 2018, which formed the basis for EPA’s final remedy selection, as 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 September 27, 2018 the EPA issued its ROD Amendment for the selection of the final remedy for the West Lake Landfill Superfund site. The ROD modifies the EPA’s previously proposed plan for partial excavation of the radiological materials by reducing the depths of the excavation. The ROD also allows for variation in depths of excavation depending on radiological concentrations. The EPA estimates that the ROD will result in a reduction of both radiological and non-radiological waste excavated, with corresponding reductions in the cost and schedule for the remedy. The next step is the negotiation of a Consent Agreement by the EPA with the PRPs to implement the ROD, a process that is expected to be completed in the first quarter of 2020. 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 $280 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 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. In September 2018, the PRPs agreed to 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 2019 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. In the event of a finding of liability against Cotter, it is probable 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, which has been upheld on appeal. Cotter and the remaining plaintiffs have engaged in settlement discussions pursuant to court-ordered mediation. During the second quarter of 2018, Generation determined a loss was probable based on the advancement of settlement proceedings and recorded an immaterial liability. Benning Road Site (Exelon, Generation, PHI and Pepco) 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 (Exelon, PHI and Pepco) 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. In April 2018, DOEE released a draft remedial investigation report for public review and comment. Pepco submitted written comments to the draft RI and participated in a public hearing. Pepco continues outreach efforts as appropriate to the agencies, governmental officials, community organizations and other key stakeholders. In May 2018 the District of Columbia Council extended the deadline for completion of the Record of Decision from June 30, 2018 until December 31, 2019. 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. A draft Feasibility Study of potential remedies and their estimated costs is being prepared by the agencies and is expected to be released in early 2019, at which time Pepco will likely be in a better position to estimate the range of loss. In addition to the activities associated with the remedial process outlined above, there is a complementary statutory program that requires an assessment to determine if any natural resources have been damaged as a result of the contamination that is being remediated, and, if so, that a plan be developed by the federal, state and local Trustees responsible for those resources to restore them to their condition before injury from the environmental contaminants. If natural resources are not restored, then compensation for the injury can be sought from the party responsible for the release of the contaminants. The assessment of Natural Resource Damages (NRD) typically takes place following cleanup because cleanups sometimes also effectively restore habitat. During the second quarter of 2018, Pepco became aware that the Trustees are in the beginning stages of this process that often takes many years beyond

Supplemental Financial Informat

Supplemental Financial Information (All Registrants)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2018 and 2017 . Three Months Ended September 30, 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 $ 214 $ 214 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 58 58 — — — — — — — Net unrealized (losses) gains on decommissioning trust funds Regulatory agreement units (66 ) (66 ) — — — — — — — Non-regulatory agreement units 72 72 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (9 ) (9 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (110 ) (110 ) — — — — — — — Total decommissioning-related activities 159 159 — $ — — — — — — Investment income 9 5 — — — 2 1 1 — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 16 — 4 1 5 6 6 — — Non-service net periodic benefit cost (12 ) — — — — — — — — Other 21 15 3 1 — 3 — 1 1 Other, net $ 194 $ 179 $ 7 2 $ 5 $ 11 $ 7 $ 2 $ 1 Nine Months Ended September 30, 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 $ 476 $ 476 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 257 257 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (335 ) (335 ) — — — — — — — Non-regulatory agreement units (143 ) (143 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (7 ) (7 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (110 ) (110 ) — — — — — — — Total decommissioning-related activities 138 138 — — — — — — — Investment income 19 12 — — — 3 1 1 — Interest income related to uncertain income tax positions 5 1 — — — — — — — AFUDC — Equity 47 — 12 3 13 19 17 2 — Non-service net periodic benefit cost (33 ) — — — — — — — — Other 36 13 9 1 1 11 5 4 2 Other, net $ 212 $ 164 $ 21 $ 4 $ 14 $ 33 $ 23 $ 7 $ 2 Three Months Ended September 30, 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 $ 159 $ 159 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 59 59 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 44 44 — — — — — — — Non-regulatory agreement units 111 111 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (4 ) (4 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (161 ) (161 ) — — — — — — — Total decommissioning-related activities 208 208 — — — — — — — Investment income 2 1 — — — 1 1 — — Interest expense related to uncertain income tax positions 4 — — — — — — — — AFUDC — Equity 17 — 2 2 4 9 6 2 1 Non-service net periodic benefit cost (27 ) — — — — — — — — Other 6 — 3 — — 3 — 2 — Other, net $ 210 $ 209 $ 5 $ 2 $ 4 $ 13 $ 7 $ 4 $ 1 Nine Months Ended September 30, 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 $ 439 $ 439 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 165 165 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 253 253 — — — — — — — Non-regulatory agreement units 347 347 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (5 ) (5 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (558 ) (558 ) — — — — — — — Total decommissioning-related activities 641 641 — — — — — — — Investment income 6 4 — — — 2 1 — — Interest income related to uncertain income tax positions 3 — — — — — — — — Penalty income related to uncertain income tax positions 2 — — — — — — — — AFUDC — Equity 51 — 6 6 12 27 17 5 5 Non-service net periodic benefit cost (82 ) — — — — — — — — Other 22 3 8 — — 11 4 5 1 Other, net $ 643 $ 648 $ 14 $ 6 $ 12 $ 40 $ 22 $ 10 $ 6 _________ (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 and nine months ended September 30, 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 September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 253 $ 32 $ 67 $ 39 $ 23 $ 92 $ 87 $ 5 $ — Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 705 $ 92 $ 188 $ 102 $ 70 $ 253 $ 238 $ 15 $ — Three Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 245 $ 35 $ 65 $ 35 $ 22 $ 88 $ 83 $ 5 $ — Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 682 $ 97 $ 181 $ 95 $ 69 $ 240 $ 226 $ 14 $ — Supplemental Cash Flow Information The following tables provide additional information regarding the Registrants’ Consolidated Statements of Cash Flows for the nine months ended September 30, 2018 and 2017 . Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 2,829 $ 1,347 $ 613 $ 204 $ 249 $ 355 $ 161 $ 97 $ 70 Amortization of regulatory assets (a) 412 — 83 20 109 200 125 38 37 Amortization of intangible assets, net (a) 43 36 — — — — — — — Amortization of energy contract assets and liabilities (b) 8 8 — — — — — — — Nuclear fuel (c) 852 852 — — — — — — — ARO accretion (d) 367 365 — — — — — — — Total depreciation, amortization and accretion $ 4,511 $ 2,608 $ 696 $ 224 $ 358 $ 555 $ 286 $ 135 $ 107 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 2,416 $ 1,010 $ 579 $ 194 $ 233 $ 342 $ 153 $ 92 $ 66 Amortization of regulatory assets (a) 355 — 52 19 115 169 89 32 47 Amortization of intangible assets, net (a) 43 36 — — — — — — — Amortization of energy contract assets and liabilities (b) 19 19 — — — — — — — Nuclear fuel (c) 816 816 — — — — — — — ARO accretion (d) 350 350 — — — — — — — Total depreciation, amortization and accretion $ 3,999 $ 2,231 $ 631 $ 213 $ 348 $ 511 $ 242 $ 124 $ 113 _________ (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. Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 435 $ 151 $ 133 $ 14 $ 43 $ 51 $ 10 $ 5 $ 10 Loss (gain) from equity method investments 22 23 — — — (1 ) — — — Provision for uncollectible accounts 133 38 30 25 6 32 12 6 14 Stock-based compensation costs 64 — — — — — — — — Other decommissioning-related activity (a) (39 ) (39 ) — — — — — — — Energy-related options (b) 4 4 — — — — — — — Amortization of regulatory asset related to debt costs 6 — 2 — — 3 1 1 1 Amortization of rate stabilization deferral — — — — — — — — — Amortization of debt fair value adjustment (12 ) (9 ) — — — (3 ) — — — Discrete impacts from EIMA and FEJA (c) 27 — 27 — — — — — — Amortization of debt costs 26 10 4 1 1 3 2 1 — Provision for excess and obsolete inventory 15 13 2 — — — — — — Long-term incentive plan 84 — — — — — — — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Other 19 (4 ) (11 ) 1 (8 ) 4 (5 ) 4 — Total other non-cash operating activities $ 804 $ 187 $ 187 $ 41 $ 42 $ 109 $ 42 $ 16 $ 24 Non-cash investing and financing activities: (Decrease) increase in capital expenditures not paid $ (175 ) $ (226 ) $ (28 ) $ 4 $ 44 $ 54 $ 15 $ 20 $ 16 Increase in PPE related to ARO update 67 47 4 — 1 15 12 2 1 Dividends on stock compensation 4 — — — — — — — — Acquisition of land 3 — — — — 3 — — 3 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 482 $ 170 $ 131 $ 21 $ 47 $ 72 $ 19 $ 10 $ 10 Loss from equity method investments 26 26 — — — — — — — Provision for uncollectible accounts 103 31 25 17 4 26 11 1 14 Stock-based compensation costs 76 — — — — — — — — Other decommissioning-related activity (a) (213 ) (213 ) — — — — — — — Energy-related options (b) 15 15 — — — — — — — Amortization of regulatory asset related to debt costs 7 — 3 1 — 3 1 1 1 Amortization of rate stabilization deferral (7 ) — — — 7 (14 ) (12 ) (2 ) — Amortization of debt fair value adjustment (13 ) (9 ) — — — (4 ) — — — Discrete impacts from EIMA and FEJA (c) (61 ) — (61 ) — — — — — — Amortization of debt costs 57 33 3 1 1 1 1 — — Provision for excess and obsolete inventory 52 50 1 — — 1 — 1 — Merger-related commitments (d) — — — — — (8 ) (6 ) (2 ) — Severance costs 33 25 — — — 3 — — — Other 46 4 10 (2 ) (7 ) (14 ) (6 ) (3 ) (4 ) Total other non-cash operating activities $ 603 $ 132 $ 112 $ 38 $ 52 $ 66 $ 8 $ 6 $ 21 Non-cash investing and financing activities: (Decrease) increase in capital expenditures not paid $ (101 ) $ 20 $ (79 ) $ (29 ) $ 16 $ (6 ) $ 7 $ 14 $ (18 ) Fair value of pension obligation transferred in connection with the FitzPatrick acquisition — 33 — — — — — — — Decrease in PPE related to ARO update (141 ) (141 ) — — — — — — — Indemnification of like-kind exchange tax position (e) — — 21 — — — — — — Non-cash financing of capital projects 16 16 — — — — — — — Dividends on stock compensation 5 — — — — — — — — Dissolution of financing trust due to long-term debt retirement 8 — — — 8 — — — — Fair value adjustment of long-term debt due to retirement (5 ) — — — — — — — — _________ (a) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations 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 and expenses. (c) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information. (d) See Note 4 - Mergers, Acquisitions and Dispositions for additional information. (e) See Note 12 - Income Taxes for additional information on the like-kind exchange tax position. 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. September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,918 $ 1,187 $ 124 $ 102 $ 113 $ 153 $ 12 $ 110 $ 11 Restricted cash 240 152 12 5 3 42 35 — 7 Restricted cash included in other long-term assets 163 — 144 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 2,321 $ 1,339 $ 280 $ 107 $ 116 $ 214 $ 47 $ 110 $ 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 $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,203 $ 360 $ 257 $ 330 $ 29 $ 137 $ 117 $ 3 $ 5 Restricted cash 320 186 52 4 1 43 34 — 9 Restricted cash included in other long-term assets 22 — — — — 22 — — 22 Total cash, cash equivalents and restricted cash $ 1,545 $ 546 $ 309 $ 334 $ 30 $ 202 $ 151 $ 3 $ 36 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 $ 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 addit i onal information about assets and liabilities of the Registrants as of September 30, 2018 and December 31, 2017 . September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 23,122 (a) $ 12,753 (a) $ 4,557 $ 3,521 $ 3,579 $ 759 $ 3,311 $ 1,315 $ 1,121 Accounts receivable: Allowance for uncollectible accounts $ 354 $ 112 $ 93 $ 61 $ 22 $ 66 $ 25 $ 16 $ 25 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 $3,278 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 $11 million as of September 30, 2018 and December 31, 2017 . The allowance for uncollectible accounts balance associated with these receivables at September 30, 2018 and December 31, 2017 of $11 million consists of $3 million and $8 million for medium risk and high risk segments, respectively. See Note 1 — Significant Accounting Policies of the Exelon 2017 Form 10-K for additional information regarding uncollectible accounts reserve methodology and assessment of the credit quality of the installment plan receivables.

Segment Information (All Regist

Segment Information (All Registrants)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2018 and 2017 is as follows: Three Months Ended September 30, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 4,741 $ — — $ — $ — $ — $ (306 ) $ 4,435 Competitive businesses natural gas revenues 397 — — — — — — 397 Competitive businesses other revenues 140 — — — — — (1 ) 139 Rate-regulated electric revenues — 1,598 700 645 1,334 — (7 ) 4,270 Rate-regulated natural gas revenues — — 57 86 24 — (5 ) 162 Shared service and other revenues — — — — 3 458 (461 ) — Total operating revenues $ 5,278 $ 1,598 $ 757 $ 731 $ 1,361 $ 458 $ (780 ) $ 9,403 2017 Competitive businesses electric revenues $ 4,041 $ — $ — $ — $ — $ — $ (295 ) $ 3,746 Competitive businesses natural gas revenues 460 — — — — — — 460 Competitive businesses other revenues 249 — — — — — — 249 Rate-regulated electric revenues — 1,571 662 658 1,280 — (7 ) 4,164 Rate-regulated natural gas revenues — — 53 80 18 — (2 ) 149 Shared service and other revenues — — — — 12 446 (458 ) — Total operating revenues $ 4,750 $ 1,571 $ 715 $ 738 $ 1,310 $ 446 $ (762 ) $ 8,768 Intersegment revenues (d) : 2018 $ 308 $ 4 $ 2 $ 6 $ 3 $ 456 $ (779 ) $ — 2017 294 3 2 3 12 445 (759 ) — Net income (loss): 2018 $ 300 $ 193 $ 126 $ 63 $ 187 $ (69 ) $ — $ 800 2017 346 189 112 62 153 3 — 865 Total assets: September 30, 2018 $ 48,207 $ 31,119 $ 10,621 $ 9,541 $ 21,957 $ 8,418 $ (10,378 ) $ 119,485 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 September 30, 2018 include revenue from sales to PECO of $35 million , sales to BGE of $69 million , sales to Pepco of $46 million , sales to DPL of $26 million and sales to ACE of $10 million in the Mid-Atlantic region, and sales to ComEd of $122 million in the Midwest region, which eliminate upon consolidation. For the three months ended September 30, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $31 million , sales to BGE of $98 million , sales to Pepco of $57 million , sales to DPL of $47 million and sales to ACE of $7 million in the Mid-Atlantic region, and sales to ComEd of $54 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 September 30, 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 September 30, 2018 Rate-regulated electric revenues $ 628 $ 304 $ 406 $ — $ (4 ) $ 1,334 Rate-regulated natural gas revenues — 24 — — — 24 Shared service and other revenues — — — 103 (100 ) 3 Total operating revenues $ 628 $ 328 $ 406 $ 103 $ (104 ) $ 1,361 Three Months Ended September 30, 2017 Rate-regulated electric revenues $ 604 $ 309 $ 370 $ — $ (3 ) $ 1,280 Rate-regulated natural gas revenues — 18 — — — 18 Shared service and other revenues — — — 12 — 12 Total operating revenues $ 604 $ 327 $ 370 $ 12 $ (3 ) $ 1,310 Intersegment revenues: Three Months Ended September 30, 2018 $ 2 $ 2 $ 1 $ 103 $ (105 ) $ 3 Three Months Ended September 30, 2017 1 2 — 13 (4 ) 12 Net income (loss): Three Months Ended September 30, 2018 $ 89 $ 33 $ 61 $ 1 $ 3 $ 187 Three Months Ended September 30, 2017 87 31 41 (18 ) 12 153 Total assets: September 30, 2018 $ 8,199 $ 4,601 $ 3,694 $ 10,763 $ (5,300 ) $ 21,957 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 September 30, 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 September 30, 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 September 30, 2018 Revenues from external parties (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,397 $ 52 $ 1,449 $ 7 $ 1,456 Midwest 1,095 26 1,121 (4 ) 1,117 New England 666 33 699 — 699 New York 475 (6 ) 469 — 469 ERCOT 156 289 445 (1 ) 444 Other Power Regions 293 265 558 (45 ) 513 Total Competitive Businesses Electric Revenues 4,082 659 4,741 (43 ) 4,698 Competitive Businesses Natural Gas Revenues 200 197 397 43 440 Competitive Businesses Other Revenues (c) 130 10 140 — 140 Total Generation Consolidated Operating Revenues $ 4,412 $ 866 $ 5,278 $ — $ 5,278 Three Months Ended September 30, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,397 $ 24 $ 1,421 $ 11 $ 1,432 Midwest 982 67 1,049 (11 ) 1,038 New England 504 (22 ) 482 (1 ) 481 New York 454 (21 ) 433 (6 ) 427 ERCOT 164 144 308 6 314 Other Power Regions 167 181 348 (13 ) 335 Total Competitive Businesses Electric Revenues 3,668 373 4,041 (14 ) 4,027 Competitive Businesses Natural Gas Revenues 226 234 460 20 480 Competitive Businesses Other Revenues (c) 207 42 249 (6 ) 243 Total Generation Consolidated Operating Revenues $ 4,101 $ 649 $ 4,750 $ — $ 4,750 __________ (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 $13 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 September 30, 2017 , unrealized mark-to-market gains of $6 million and $52 million for the three months ended September 30, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 RNF (a) Intersegment RNF Total RNF RNF (a) Intersegment RNF Total RNF Mid-Atlantic $ 746 $ 17 $ 763 $ 817 $ 38 $ 855 Midwest 763 5 768 697 — 697 New England 83 (2 ) 81 151 (6 ) 145 New York 290 2 292 295 — 295 ERCOT 161 (63 ) 98 229 (111 ) 118 Other Power Regions 143 (44 ) 99 118 (50 ) 68 Total Revenues net of purchased power and fuel for Reportable Segments 2,186 (85 ) 2,101 2,307 (129 ) 2,178 Other (b) 112 85 197 112 129 241 Total Generation Revenues net of purchased power and fuel expense $ 2,298 $ — $ 2,298 $ 2,419 $ — $ 2,419 __________ (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 $19 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended September 30, 2017 , unrealized mark-to-market gains of $71 million and $73 million for the three months ended September 30, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $18 million and $6 million decrease to revenue net of purchased power and fuel expense for the three months ended September 30, 2018 , and 2017 , respectively, and the elimination of intersegment revenue net of purchased power and fuel expense. Electric and Gas Revenue by Customer Class (the Utility Registrants): Three Months Ended September 30, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 861 $ 458 $ 366 $ 726 $ 306 $ 180 $ 240 Small commercial & industrial 391 108 68 140 39 48 53 Large commercial & industrial 131 64 117 303 230 25 48 Public authorities & electric railroads 11 7 7 14 8 3 3 Other (a) 212 59 91 156 47 47 63 Total rate-regulated electric revenues (b) 1,606 696 649 1,339 630 303 407 Rate-regulated natural gas revenues Residential — 36 46 8 — 8 — Small commercial & industrial — 15 8 5 — 5 — Large commercial & industrial — — 17 2 — 2 — Transportation — 5 — 3 — 3 — Other (c) — 1 12 6 — 6 — Total rate-regulated natural gas revenues (d) — 57 83 24 — 24 — Total rate-regulated revenues from contracts with customers 1,606 753 732 1,363 630 327 407 Other revenues Revenues from alternative revenue programs (15 ) 1 (6 ) (5 ) (4 ) — (1 ) Other rate-regulated electric revenues (e) 7 3 4 3 2 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Total other revenues (8 ) 4 (1 ) (2 ) (2 ) 1 (1 ) Total rate-regulated revenues for reportable segments $ 1,598 $ 757 $ 731 $ 1,361 $ 628 $ 328 $ 406 Three Months Ended September 30, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 816 $ 434 $ 352 $ 687 $ 291 $ 185 $ 211 Small commercial & industrial 366 106 65 140 37 50 53 Large commercial & industrial 119 59 114 288 211 28 49 Public authorities & electric railroads 11 7 8 14 8 3 3 Other (a) 235 53 85 147 52 43 54 Total rate-regulated electric revenues (b) 1,547 659 624 1,276 599 309 370 Rate-regulated natural gas revenues Residential — 33 44 8 — 8 — Small commercial & industrial — 14 8 3 — 3 — Large commercial & industrial — — 19 1 — 1 — Transportation — 5 — 3 — 3 — Other (c) — 1 3 3 — 3 — Total rate-regulated natural gas revenues (d) — 53 74 18 — 18 — Total rate-regulated revenues from contracts with customers 1,547 712 698 1,294 599 327 370 Other revenues Revenues from alternative revenue programs 16 — 36 2 3 (1 ) — Other rate-regulated electric revenues (e) 8 3 3 3 2 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Other revenues (f) — — — 11 — — — Total other revenues 24 3 40 16 5 — — Total rate-regulated revenues for reportable segments $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $4 million , $2 million , $1 million , $3 million , $2 million , $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2018 and $3 million , $1 million , $1 million , $1 million $1 million , $2 million and less than $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $5 million at PECO and BGE, respectively, for the three months ended September 30, 2018 and less than $1 million and $2 million at PECO and BGE, respectively, for the three months ended September 30, 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $11 million at PHI for the three months ended September 30, 2017 . Nine Months Ended September 30, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 13,190 $ — $ — $ — $ — $ — $ (969 ) $ 12,221 Competitive businesses natural gas revenues 1,839 — — — — — (8 ) 1,831 Competitive businesses other revenues 339 — — — — — (4 ) 335 Rate-regulated electric revenues — 4,508 1,893 1,850 3,549 — (34 ) 11,766 Rate-regulated natural gas revenues — — 382 519 129 — (13 ) 1,017 Shared service and other revenues — — — — 10 1,398 (1,408 ) — Total operating revenues $ 15,368 $ 4,508 $ 2,275 $ 2,369 $ 3,688 $ 1,398 $ (2,436 ) $ 27,170 2017 Competitive businesses electric revenues $ 11,514 $ — $ — $ — $ — $ — $ (888 ) $ 10,626 Competitive businesses natural gas revenues 1,807 — — — — — — 1,807 Competitive businesses other revenues 522 — — — — — — 522 Rate-regulated electric revenues — 4,227 1,802 1,895 3,417 — (23 ) 11,318 Rate-regulated natural gas revenues — — 339 468 105 — (6 ) 906 Shared service and other revenues — — — — 35 1,316 (1,350 ) 1 Total operating revenues $ 13,843 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,316 $ (2,267 ) $ 25,180 Intersegment revenues (d) : 2018 $ 981 $ 23 $ 5 $ 18 $ 11 $ 1,392 $ (2,430 ) $ — 2017 888 12 5 12 35 1,312 (2,262 ) 2 Net income (loss): 2018 $ 667 $ 523 $ 336 $ 242 $ 336 $ (125 ) $ — $ 1,979 2017 508 447 327 231 359 58 (2 ) 1,928 __________ (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 nine months ended September 30, 2018 include revenue from sales to PECO of $97 million , sales to BGE of $198 million , sales to Pepco of $143 million , sales to DPL of $103 million and sales to ACE of $21 million in the Mid-Atlantic region, and sales to ComEd of $419 million in the Midwest region, which eliminate upon consolidation. For the nine months ended September 30, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $111 million , sales to BGE of $330 million , sales to Pepco of $209 million , sales to DPL of $138 million and sales to ACE of $23 million in the Mid-Atlantic region, and sales to ComEd of $77 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 nine months ended September 30, 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) : Nine Months Ended September 30, 2018 Rate-regulated electric revenues $ 1,708 $ 872 $ 981 $ — $ (12 ) $ 3,549 Rate-regulated natural gas revenues — 129 — — — 129 Shared service and other revenues — — — 326 (316 ) 10 Total operating revenues $ 1,708 $ 1,001 $ 981 $ 326 $ (328 ) $ 3,688 Nine Months Ended September 30, 2017 Rate-regulated electric revenues $ 1,649 $ 866 $ 915 $ — $ (13 ) $ 3,417 Rate-regulated natural gas revenues — 105 — — — 105 Shared service and other revenues — — — 37 (2 ) 35 Total operating revenues $ 1,649 $ 971 $ 915 $ 37 $ (15 ) $ 3,557 Intersegment revenues: Nine Months Ended September 30, 2018 $ 5 $ 6 $ 2 $ 325 $ (327 ) $ 11 Nine Months Ended September 30, 2017 4 6 2 37 (14 ) 35 Net income (loss): Nine Months Ended September 30, 2018 $ 174 $ 90 $ 76 $ (15 ) $ 11 $ 336 Nine Months Ended September 30, 2017 188 107 77 (48 ) 35 359 __________ (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 nine months ended September 30, 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 nine months ended September 30, 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): Nine Months Ended September 30, 2018 Revenues from external parties (a) Intersegment Revenues Total Revenues Contracts with customers Other (b) Total Mid-Atlantic $ 3,971 $ 191 $ 4,162 $ 17 $ 4,179 Midwest 3,432 169 3,601 (8 ) 3,593 New England 1,943 87 2,030 (4 ) 2,026 New York 1,305 (37 ) 1,268 1 1,269 ERCOT 470 459 929 1 930 Other Power Regions 713 487 1,200 (112 ) 1,088 Total Competitive Businesses Electric Revenues 11,834 1,356 13,190 (105 ) 13,085 Competitive Businesses Natural Gas Revenues 1,016 823 1,839 105 1,944 Competitive Businesses Other Revenues (c) 385 (46 ) 339 — 339 Total Generation Consolidated Operating Revenues $ 13,235 $ 2,133 $ 15,368 $ — $ 15,368 Nine Months Ended September 30, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 4,260 $ (53 ) $ 4,207 $ 15 $ 4,222 Midwest 2,948 210 3,158 (17 ) 3,141 New England 1,555 (86 ) 1,469 (8 ) 1,461 New York 1,161 (37 ) 1,124 (14 ) 1,110 ERCOT 520 229 749 4 753 Other Power Regions 439 368 807 (28 ) 779 Total Competitive Businesses Electric Revenues 10,883 631 11,514 (48 ) 11,466 Competitive Businesses Natural Gas Revenues 1,237 570 1,807 52 1,859 Competitive Businesses Other Revenues (c) 588 (66 ) 522 (4 ) 518 Total Generation Consolidated Operating Revenues $ 12,708 $ 1,135 $ 13,843 $ — $ 13,843 __________ (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 $30 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the nine months ended September 30, 2017 , unrealized mark-to-market losses of $96 million and $47 million for the nine months ended September 30, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 RNF from external customers (a) Intersegment RNF Total RNF RNF from external customers (a) Intersegment RNF Total RNF Mid-Atlantic $ 2,303 $ 45 $ 2,348 $ 2,330 $ 81 $ 2,411 Midwest 2,381 19 2,400 2,129 11 2,140 New England 310 (12 ) 298 423 (20 ) 403 New York 832 9 841 708 (1 ) 707 ERCOT 396 (180 ) 216 446 (188 ) 258 Other Power Regions 430 (121 ) 309 359 (139 ) 220 Total Revenues net of purchased power and fuel expense for Reportable Segments 6,652 (240 ) 6,412 6,395 (256 ) 6,139 Other (b) 164 240 404 162 256 418 Total Generation Revenues net of purchased power and fuel expense $ 6,816 $ — $ 6,816 $ 6,557 $ — $ 6,557 __________ (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 $41 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the nine months ended September 30, 2017 , unrealized mark-to-market losses of $104 million and $161 million for the nine months ended September 30, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $53 million and $8 million decrease to revenue net of purchased power and fuel expense for the nine months ended September 30, 2018 and 2017 , respectively, and the elimination of intersegment revenue net of purchased power and fuel expense. Electric and Gas Revenue by Customer Class (the Utility Registrants): Nine Months Ended September 30, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,277 $ 1,199 $ 1,054 $ 1,839 $ 792 $ 513 $ 534 Small commercial & industrial 1,132 306 196 370 104 138 128 Large commercial & industrial 411 174 325 845 632 74 139 Public authorities & electric railroads 36 21 21 44 24 10 10 Other (a) 656 181 246 446 145 129 174 Total rate-regulated electric revenues (b) 4,512 1,881 1,842 3,544 1,697 864 985 Rate-regulated natural gas revenues Residential — 259 345 68 — 68 — Small commercial & industrial — 102 55 31 — 31 — Large commercial & industrial — 1 88 7 — 7 — Transportation — 16 — 12 — 12 — Other (c) — 4 49 11 — 11 — Total rate-regulated natural gas revenues (d) — 382 537 129 — 129 — Total rate-regulated revenues from contracts with customers 4,512 2,263 2,379 3,673 1,697 993 985 Other revenues Revenues from alternative revenue programs (27 ) 2 (23 ) 7 6 5 (4 ) Other rate-regulated electric revenues (e) 23 10 10 8 5 3 — Other rate-regulated natural gas revenues (e) — — 3 — — — — Total other revenues (4 ) 12 (10 ) 15 11 8 (4 ) Total rate-regulated revenues for reportable segments $ 4,508 $ 2,275 $ 2,369 $ 3,688 $ 1,708 $ 1,001 $ 981 Nine Months Ended September 30, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,071 $ 1,147 $ 1,038 $ 1,740 $ 751 $ 505 $ 484 Small commercial & industrial 1,035 303 193 373 105 139 129 Large commercial & industrial 346 168 329 814 593 78 143 Public authorities & electric railroads 33 23 23 45 24 11 10 Other (a) 671 151 222 398 148 121 140 Total rate-regulated electric revenues (b) 4,156 1,792 1,805 3,370 1,621 854 906 Rate-regulated natural gas revenues Residential — 225 289 57 — 57 — Small commercial & industrial — 90 51 25 — 25 — Large commercial & industrial — — 82 5 — 5 — Transportation — 16 — 11 — 11 — Other (c) — 8 20 7 — 7 — Total rate-regulated natural gas revenues (d) — 339 442 105 — 105 — Total rate-regulated revenues from contracts with customers 4,156 2,131 2,247 3,475 1,621 959 906 Other revenues Revenues from alternative revenue programs 48 — 102 41 23 9 9 Other rate-regulated electric revenues (e) 23 10 11 8 5 3 — Other rate-regulated natural gas revenues (e) — — 3 — — — — Other revenues (f) — — — 33 — — — Total other revenues 71 10 116 82 28 12 9 Total rate-regulated revenues for reportable segments $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $23 million , $5 million , $5 million , $11 million , $5 million , $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2018 and $12 million , $4 million , $5 million , $2 million , $4 million , $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $13 million at PECO and BGE, respectively, for the nine months ended September 30, 2018 and less than $1 million and $7 million at PECO and BGE, respectively, for the nine months ended September 30, 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $33 million at PHI for the nine months ended September 30, 2017 .

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 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 R egistrant’s Consolidated Financial Statements includes the accounts of its subsidiaries. All intercompany transactions have been eliminated. The accompanying consolidated financial statements as of September 30, 2018 and 2017 and for the three and nine 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 f or 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.
Reclassifications [Text Block]	Prior Period Adjustments and Reclassifications (All Registrants) Certain prior year amounts in the Registrants' Consolidated Statements of Operations and Comprehensive Incom e, Consolidated Statements of Cash Flows, Consolidated Balance Sheets and Consolidated Statements of Changes in Shareholders' Equity have been recasted to reflect new accounting standards issued by the FASB and adopted as of January 1, 2018. 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 additional 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 additional 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 additional 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 additional 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 additional 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. See Note 6 — Regulatory Matters and Note 10 — Derivative Financial Instruments for additional information. Taxes Directly Imposed on Revenue-Producing Transactions. The Registrants collect certain taxes from customers such as sales and gross receipts taxes, along with other taxes, surcharges and fees that are levied by state or local governments on the sale or distribution of 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 (All Registrants). 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 September 30, 2018 , Generation has outstanding commitments to invest in fixed income, middle market lending, private equity and real estate investments of approximately $135 million , $208 million , $349 million , and $227 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 September 30, 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 September 30, 2018 , there were no significant concentrations (generally defined as greater than 10 percent) of risk in Generation's NDT assets. See Note 13 — Asset Retirement Obligations for additional information on the NDT fund investments. Rabbi Trust Investments (Exelon, Generation, PECO, BGE, PHI, and Pepco). 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 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. 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 additional information on mark-to-market derivatives. Deferred Compensation Obligations (All Registrants). 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.
Earnings Per Share, Policy [Policy Text Block]	Basic earnings per share is computed by dividing net income attributable to common shareholders by the weighted average number of common shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to common shareholders by the weighted average number of common shares outstanding, including the effect of issuing common stock assuming (i) stock options are exercised, and (ii) performance share awards and restricted stock awards are fully vested under the treasury stock method.

Significant Accounting Polici_3

Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Cummulative Effect of New Accounting Pronouncement Adoption Revenue from Contract with Customer [Table Text Block]	Three Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 4,456 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,313 — — — — — — — — Operating revenues — 4,455 — — — — — — — Electric operating revenues — — 1,568 660 657 1,280 603 307 370 Natural gas operating revenues — — — 53 78 18 — 18 — Operating revenues from affiliates — 296 3 2 3 12 1 2 — Total operating revenues $ 8,769 $ 4,751 $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 Operating Revenues - Adjustments Competitive business revenues $ (1 ) $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (54 ) — — — — — — — — Operating revenues — (1 ) — — — — — — — Electric operating revenues — — (16 ) — (31 ) (2 ) (3 ) 1 — Natural gas operating revenues — — — — (5 ) — — — — Revenues from alternative revenue programs 54 — 16 — 36 2 3 (1 ) — Operating revenues from affiliates — — — — — — — — — Total operating revenues $ (1 ) $ (1 ) $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 4,455 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 4,259 — — — — — — — — Operating revenues — 4,454 — — — — — — — Electric operating revenues — — 1,552 660 626 1,278 600 308 370 Natural gas operating revenues — — — 53 73 18 — 18 — Revenues from alternative revenue programs 54 — 16 — 36 2 3 (1 ) — Operating revenues from affiliates — 296 3 2 3 12 1 2 — Total operating revenues $ 8,768 $ 4,750 $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Operating Revenues - As reported Competitive business revenues $ 12,924 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 12,225 — — — — — — — — Operating revenues — 12,918 — — — — — — — Electric operating revenues — — 4,215 1,798 1,890 3,417 1,645 860 913 Natural gas operating revenues — — — 338 461 105 — 105 — Operating revenues from affiliates — 894 12 5 12 35 4 6 2 Total operating revenues $ 25,149 $ 13,812 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915 Operating Revenues - Adjustments Competitive business revenues $ 31 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues (191 ) — — — — — — — — Operating revenues — 31 — — — — — — — Electric operating revenues — — (48 ) — (79 ) (41 ) (23 ) (9 ) (9 ) Natural gas operating revenues — — — — (23 ) — — — — Revenues from alternative revenue programs 191 — 48 — 102 41 23 9 9 Operating revenues from affiliates — — — — — — — — — Total operating revenues $ 31 $ 31 $ — $ — $ — $ — $ — $ — $ — Operating Revenues - Retrospective application Competitive business revenues $ 12,955 $ — $ — $ — $ — $ — $ — $ — $ — Rate-regulated utility revenues 12,034 — — — — — — — — Operating revenues — 12,949 — — — — — — — Electric operating revenues — — 4,167 1,798 1,811 3,376 1,622 851 904 Natural gas operating revenues — — — 338 438 105 — 105 — Revenues from alternative revenue programs 191 — 48 — 102 41 23 9 9 Operating revenues from affiliates — 894 12 5 12 35 4 6 2 Total operating revenues $ 25,180 $ 13,843 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	9 Months Ended
	Sep. 30, 2018
Variable Interest Entity [Abstract]
Schedule of Variable Interest Entities	As of September 30, 2018 and December 31, 2017 , these assets and liabilities primarily consisted of the following: September 30, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Cash and cash equivalents $ 316 $ 316 $ — $ — $ 126 $ 126 $ — $ — Restricted cash 77 70 7 7 64 58 6 6 Accounts receivable, net Customer 165 165 — — 170 170 — — Other 30 30 — — 25 25 — — Inventory, net Materials and supplies 214 214 — — 205 205 — — Other current assets 65 62 3 — 45 41 4 — Total current assets 867 857 10 7 635 625 10 6 Property, plant and equipment, net 6,158 6,158 — — 6,186 6,186 — — Nuclear decommissioning trust funds 2,523 2,523 — — 2,502 2,502 — — Other noncurrent assets 256 230 26 19 274 243 31 23 Total noncurrent assets 8,937 8,911 26 19 8,962 8,931 31 23 Total assets $ 9,804 $ 9,768 $ 36 $ 26 $ 9,597 $ 9,556 $ 41 $ 29 Long-term debt due within one year $ 97 $ 72 $ 25 $ 22 $ 102 $ 67 $ 35 $ 31 Accounts payable 128 128 — — 114 114 — — Accrued expenses 73 72 1 1 67 66 1 1 Unamortized energy contract liabilities 16 16 — — 18 18 — — Other current liabilities 14 14 — — 7 7 — — Total current liabilities 328 302 26 23 308 272 36 32 Long-term debt 1,087 1,035 52 45 1,154 1,088 66 58 Asset retirement obligations 2,116 2,116 — — 2,035 2,035 — — Other noncurrent liabilities 75 75 — — 121 121 — — Total noncurrent liabilities 3,278 3,226 52 45 3,310 3,244 66 58 Total liabilities $ 3,606 $ 3,528 $ 78 $ 68 $ 3,618 $ 3,516 $ 102 $ 90 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. The carrying amounts and classification of the consolidated VIEs’ assets and liabilities included in the Registrants' consolidated financial statements at September 30, 2018 and December 31, 2017 are as follows: September 30, 2018 December 31, 2017 Exelon (a) Generation PHI (a) ACE Exelon (a) Generation PHI (a) ACE Current assets $ 891 $ 881 $ 10 $ 7 $ 662 $ 652 $ 10 $ 6 Noncurrent assets 9,259 9,233 26 19 9,317 9,286 31 23 Total assets $ 10,150 $ 10,114 $ 36 $ 26 $ 9,979 $ 9,938 $ 41 $ 29 Current liabilities $ 329 $ 303 $ 26 $ 23 $ 308 $ 272 $ 36 $ 32 Noncurrent liabilities 3,284 3,232 52 45 3,316 3,250 66 58 Total liabilities $ 3,613 $ 3,535 $ 78 $ 68 $ 3,624 $ 3,522 $ 102 $ 90 _________ (a) Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity. The following tables present summary information about Exelon's and Generation’s significant unconsolidated VIE entities: September 30, 2018 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 606 $ 481 $ 1,087 Total liabilities (a) 36 221 257 Exelon's ownership interest in VIE (a) — 232 232 Other ownership interests in VIE (a) 570 28 598 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 232 232 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) — — — December 31, 2017 Commercial Agreement VIEs Equity Investment VIEs Total Total assets (a) $ 625 $ 509 $ 1,134 Total liabilities (a) 37 228 265 Exelon's ownership interest in VIE (a) — 251 251 Other ownership interests in VIE (a) 588 30 618 Registrants’ maximum exposure to loss: Carrying amount of equity method investments — 251 251 Contract intangible asset 8 — 8 Net assets pledged for Zion Station decommissioning (b) 2 — 2 _________ (a) These items represent amounts on the unconsolidated VIE balance sheets, not 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 $9 million and $39 million as of September 30, 2018 and December 31, 2017 , respectively; offset by payables to ZionSolutions, LLC of $9 million and $37 million as of September 30, 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 — Asset Retirement Obligations for additional information.

Mergers, Acquisitions and Dispo

Mergers, Acquisitions and Dispositions (Tables)	9 Months Ended
	Sep. 30, 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 information regarding SNF obligations to the DOE.

Revenue from Contracts with C_2

Revenue from Contracts with Customers Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 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 liabilities reflected on Exelon's and Generation's Consolidated Balance Sheet from January 1, 2018 to September 30, 2018 : Contract Liabilities Exelon and Generation Balance as of January 1, 2018 $ 35 Increases as a result of additional cash received or due 389 Amounts recognized into revenues (387 ) Balance at September 30, 2018 $ 37 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 September 30, 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 34 Amounts reclassified to receivables (120 ) Balance at September 30, 2018 $ 197
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	2019 2020 2021 2022 2023 and thereafter Total Exelon $ 647 $ 302 $ 119 $ 47 $ 137 $ 1,252 Generation 647 302 119 47 137 1,252

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2018
Regulated Operations [Abstract]
Public Utilities General Disclosures [Table Text Block]	The following table presents authorized amounts capitalized for ratemaking purposes related to earnings on shareholders’ investment that are not recognized for financial reporting purposes on Exelon's and the Utility Registrant's Consolidated Balance Sheets. These amounts will be recognized as revenues in the related 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 September 30, 2018 $ 67 $ 8 $ — $ 50 $ 9 $ 5 $ 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. 2018 Annual Transmission Updates (a)(b) ComEd BGE Pepco DPL ACE Initial revenue requirement (decrease) increase $ (44 ) $ 10 $ 6 $ 14 $ 4 Annual reconciliation increase (decrease) 18 4 2 13 (4 ) Dedicated facilities increase (c) — 12 — — — Total revenue requirement (decrease) increase $ (26 ) $ 26 $ 8 $ 27 $ — Allowed return on rate base (d) 8.32 % 7.61 % 7.82 % 7.29 % 8.02 % Allowed ROE (e) 11.50 % 10.50 % 10.50 % 10.50 % 10.50 %
Schedule of Regulatory Assets	he following tables provide information about the regulatory assets and liabilities of Exelon and the Utility Registrants as of September 30, 2018 and December 31, 2017 . See Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K for additional information on the specific regulatory assets and liabilities. September 30, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,710 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 391 — 381 — 10 10 — — AMI programs (c) 583 142 27 198 216 144 72 — Electric distribution formula rate (d) 228 228 — — — — — — Energy efficiency costs 357 357 — — — — — — Debt costs 102 34 1 11 68 15 7 6 Fair value of long-term debt 716 — — — 581 — — — Fair value of PHI's unamortized energy contracts 600 — — — 600 — — — Asset retirement obligations 114 76 22 15 1 1 — — MGP remediation costs 318 299 19 — — — — — Under-recovered uncollectible accounts 71 71 — — — — — — Renewable energy 260 259 — — 1 — — 1 Energy and transmission programs (e)(f)(g)(h)(i)(j) 251 7 50 72 122 93 15 14 Deferred storm costs 45 — — — 45 11 5 29 Energy efficiency and demand response programs 561 — 2 291 268 194 74 — Merger integration costs (k)(l)(m) 44 — — 4 40 18 12 10 Under-recovered revenue decoupling (n) 64 — — — 64 64 — — COPCO acquisition adjustment 3 — — — 3 — 3 — Workers compensation and long-term disability costs 36 — — — 36 36 — — Vacation accrual 24 — 11 — 13 — 8 5 Securitized stranded costs 57 — — — 57 — — 57 CAP arrearage 10 — 10 — — — — — Removal costs 555 — — — 555 156 97 302 DC PLUG charge 168 — — — 168 168 — — Other 74 12 9 6 47 36 8 3 Total regulatory assets 9,342 1,485 532 597 2,895 946 301 427 Less: current portion 1,340 256 84 195 521 284 66 44 Total noncurrent regulatory assets $ 8,002 $ 1,229 $ 448 $ 402 $ 2,374 $ 662 $ 235 $ 383 September 30, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 20 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,054 2,418 — 1,015 1,621 734 493 394 Nuclear decommissioning 2,958 2,469 489 — — — — — Removal costs 1,566 1,370 — 67 129 20 109 — Deferred rent 34 — — — 34 — — — Energy efficiency and demand response programs 10 3 5 — 2 — — 2 DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 10 — 10 — — — — — Gas distribution tax repairs 4 — 4 — — — — — Energy and transmission programs (e)(f)(g)(h)(i)(j) 372 204 143 7 18 — 14 4 Over-recovered revenue decoupling (n) 21 — — 17 4 — 4 — Renewable portfolio standards costs 140 140 — — — — — — Zero emission credit costs 18 18 — — — — — — Over-recovered uncollectible accounts 2 — — — 2 — — 2 Merger integration costs (l) 3 — — — 3 — 3 — TCJA income tax benefit over-recoveries (o) 108 — 61 19 28 6 8 14 Other 118 16 21 40 41 4 23 12 Total regulatory liabilities 10,445 6,638 740 1,165 1,882 764 654 428 Less: current portion 689 320 159 95 99 5 67 27 Total noncurrent regulatory liabilities $ 9,756 $ 6,318 $ 581 $ 1,070 $ 1,783 $ 759 $ 587 $ 401 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 assets established at the Constellation and PHI merger dates of $401 million and $897 million , respectively, as of September 30, 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 September 30, 2018 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $464 million , $135 million , $136 million , $145 million and $141 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 September 30, 2018 , BGE's regulatory asset of $198 million includes $117 million of unamortized incremental deployment costs under the program, $48 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $33 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 September 30, 2018 , ComEd’s regulatory asset of $228 million was comprised of $165 million for the 2016, 2017 and 2018 annual reconciliations and $63 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 September 30, 2018 , ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018 , ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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 September 30, 2018 , PECO’s regulatory asset of $50 million represents the under-recovered natural gas costs under the PGC. As of December 31, 2017 , PECO’s regulatory asset of $1 million is related to under-recovered costs under the TSC program. As of September 30, 2018 , PECO's regulatory liability of $143 million included $85 million related to the PJM Transmission Rate Design Settlement, $43 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $12 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 September 30, 2018 , BGE's regulatory asset of $72 million included $48 million related to the PJM Transmission Rate Design Settlement, $14 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $7 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of September 30, 2018 , BGE's regulatory liability of $7 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 September 30, 2018 , Pepco's regulatory asset of $93 million included $74 million related to the PJM Transmission Rate Design Settlement, $7 million of transmission costs recoverable through its FERC approved formula rate and $12 million related to under-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 September 30, 2018 , DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018 , DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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 September 30, 2018 , ACE's regulatory asset of $14 million included $7 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2018 , ACE's regulatory liability of $4 million included $3 million related to the PJM Transmission Rate Design Settlement and $1 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 September 30, 2018 , Pepco’s regulatory asset of $18 million represents previously incurred PHI integration costs, including $9 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. As of 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 September 30, 2018 , DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $1 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of September 30, 2018 , DPL’s regulatory liability of $3 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 September 30, 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 September 30, 2018 , BGE had a regulatory asset of less than $1 million related to under-recovered electric revenue decoupling and a regulatory liability of $17 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 and the Utility Registrants as of September 30, 2018 and December 31, 2017 . See Note 3 — Regulatory Matters of the Exelon 2017 Form 10-K for additional information on the specific regulatory assets and liabilities. September 30, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory assets Pension and other postretirement benefits (a) $ 3,710 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes 391 — 381 — 10 10 — — AMI programs (c) 583 142 27 198 216 144 72 — Electric distribution formula rate (d) 228 228 — — — — — — Energy efficiency costs 357 357 — — — — — — Debt costs 102 34 1 11 68 15 7 6 Fair value of long-term debt 716 — — — 581 — — — Fair value of PHI's unamortized energy contracts 600 — — — 600 — — — Asset retirement obligations 114 76 22 15 1 1 — — MGP remediation costs 318 299 19 — — — — — Under-recovered uncollectible accounts 71 71 — — — — — — Renewable energy 260 259 — — 1 — — 1 Energy and transmission programs (e)(f)(g)(h)(i)(j) 251 7 50 72 122 93 15 14 Deferred storm costs 45 — — — 45 11 5 29 Energy efficiency and demand response programs 561 — 2 291 268 194 74 — Merger integration costs (k)(l)(m) 44 — — 4 40 18 12 10 Under-recovered revenue decoupling (n) 64 — — — 64 64 — — COPCO acquisition adjustment 3 — — — 3 — 3 — Workers compensation and long-term disability costs 36 — — — 36 36 — — Vacation accrual 24 — 11 — 13 — 8 5 Securitized stranded costs 57 — — — 57 — — 57 CAP arrearage 10 — 10 — — — — — Removal costs 555 — — — 555 156 97 302 DC PLUG charge 168 — — — 168 168 — — Other 74 12 9 6 47 36 8 3 Total regulatory assets 9,342 1,485 532 597 2,895 946 301 427 Less: current portion 1,340 256 84 195 521 284 66 44 Total noncurrent regulatory assets $ 8,002 $ 1,229 $ 448 $ 402 $ 2,374 $ 662 $ 235 $ 383 September 30, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Regulatory liabilities Other postretirement benefits $ 20 $ — $ — $ — $ — $ — $ — $ — Deferred income taxes (b) 5,054 2,418 — 1,015 1,621 734 493 394 Nuclear decommissioning 2,958 2,469 489 — — — — — Removal costs 1,566 1,370 — 67 129 20 109 — Deferred rent 34 — — — 34 — — — Energy efficiency and demand response programs 10 3 5 — 2 — — 2 DLC program costs 7 — 7 — — — — — Electric distribution tax repairs 10 — 10 — — — — — Gas distribution tax repairs 4 — 4 — — — — — Energy and transmission programs (e)(f)(g)(h)(i)(j) 372 204 143 7 18 — 14 4 Over-recovered revenue decoupling (n) 21 — — 17 4 — 4 — Renewable portfolio standards costs 140 140 — — — — — — Zero emission credit costs 18 18 — — — — — — Over-recovered uncollectible accounts 2 — — — 2 — — 2 Merger integration costs (l) 3 — — — 3 — 3 — TCJA income tax benefit over-recoveries (o) 108 — 61 19 28 6 8 14 Other 118 16 21 40 41 4 23 12 Total regulatory liabilities 10,445 6,638 740 1,165 1,882 764 654 428 Less: current portion 689 320 159 95 99 5 67 27 Total noncurrent regulatory liabilities $ 9,756 $ 6,318 $ 581 $ 1,070 $ 1,783 $ 759 $ 587 $ 401 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 assets established at the Constellation and PHI merger dates of $401 million and $897 million , respectively, as of September 30, 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 September 30, 2018 , includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $464 million , $135 million , $136 million , $145 million and $141 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 September 30, 2018 , BGE's regulatory asset of $198 million includes $117 million of unamortized incremental deployment costs under the program, $48 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $33 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 September 30, 2018 , ComEd’s regulatory asset of $228 million was comprised of $165 million for the 2016, 2017 and 2018 annual reconciliations and $63 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 September 30, 2018 , ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018 , ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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 September 30, 2018 , PECO’s regulatory asset of $50 million represents the under-recovered natural gas costs under the PGC. As of December 31, 2017 , PECO’s regulatory asset of $1 million is related to under-recovered costs under the TSC program. As of September 30, 2018 , PECO's regulatory liability of $143 million included $85 million related to the PJM Transmission Rate Design Settlement, $43 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $12 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 September 30, 2018 , BGE's regulatory asset of $72 million included $48 million related to the PJM Transmission Rate Design Settlement, $14 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $7 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of September 30, 2018 , BGE's regulatory liability of $7 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 September 30, 2018 , Pepco's regulatory asset of $93 million included $74 million related to the PJM Transmission Rate Design Settlement, $7 million of transmission costs recoverable through its FERC approved formula rate and $12 million related to under-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 September 30, 2018 , DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018 , DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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 September 30, 2018 , ACE's regulatory asset of $14 million included $7 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2018 , ACE's regulatory liability of $4 million included $3 million related to the PJM Transmission Rate Design Settlement and $1 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 September 30, 2018 , Pepco’s regulatory asset of $18 million represents previously incurred PHI integration costs, including $9 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. As of 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 September 30, 2018 , DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $1 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of September 30, 2018 , DPL’s regulatory liability of $3 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 September 30, 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 September 30, 2018 , BGE had a regulatory asset of less than $1 million related to under-recovered electric revenue decoupling and a regulatory liability of $17 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 September 30, 2018 and December 31, 2017 . As of September 30, 2018 Exelon ComEd PECO BGE PHI Pepco DPL ACE Purchased receivables $ 379 $ 120 $ 91 $ 60 $ 108 $ 69 $ 11 $ 28 Allowance for uncollectible accounts (a) (37 ) (19 ) (5 ) (3 ) (10 ) (5 ) (1 ) (4 ) Purchased receivables, net $ 342 $ 101 $ 86 $ 57 $ 98 $ 64 $ 10 $ 24 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 Plant Retirements Early_2

Early Plant Retirements Early Plant Retirements (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	During the three and nine months ended September 30, 2018 , both Exelon's and Generation's results include a net incremental $174 million and $525 million , respectively, 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) Q3 2018 YTD 2018 Depreciation and amortization (a) Accelerated depreciation (b) $ 152 $ 441 Accelerated nuclear fuel amortization 18 52 Operating and maintenance (c) 4 32 Total $ 174 $ 525 _________ (a) Reflects incremental accelerated depreciation and amortization for TMI and Oyster Creek for the three and nine months ended September 30, 2018 . The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 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. It does not include remeasurement of the Oyster Creek ARO. Refer to Note 13 - Asset Retirement Obligations for additional detail. 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.
Implications of Potential Early Plant Retirement [Table Text Block]	The following table provides the balance sheet amounts as of September 30, 2018 for Generation’s ownership share of the significant assets and liabilities associated with Salem that would potentially be impacted by a decision to permanently cease generation operations. September 30, 2018 Asset Balances Materials and supplies inventory $ 45 Nuclear fuel inventory, net 114 Completed plant, net 605 Construction work in progress 34 Liability Balances Asset retirement obligation (455 ) NRC License Renewal Term 2036 (unit 1) 2040 (unit 2) The following table provides the balance sheet amounts as of September 30, 2018 for Generation’s significant assets and liabilities associated with the Mystic Generating Station assets that would potentially be impacted by a decision to permanently cease generation operations. September 30, 2018 Asset Balances Materials and supplies inventory $ 21 Fuel inventory 18 Completed plant, net 877 Construction work in progress 5 Prepaid expenses (a) 15 Liability Balances Asset retirement obligation (5 ) Accrued expenses (a) (2 ) _________ (a) Reflects ending balances only as they relate to Mystic's Long-term Service Agreement.

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair value of financial liabilities recorded at the carrying amount	The following tables present the carrying amounts and fair values of the Registrants’ short-term liabilities, long-term debt, SNF obligation and trust preferred securities (long-term debt to financing trusts or junior subordinated debentures) as of September 30, 2018 and December 31, 2017 : Exelon September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 834 $ — $ 834 $ — $ 834 Long-term debt (including amounts due within one year) (b)(c) 35,290 — 33,608 2,079 35,687 Long-term debt to financing trusts (d) 390 — — 411 411 SNF obligation 1,164 — 993 — 993 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 8,842 $ — $ 7,563 $ 1,461 $ 9,024 SNF obligation 1,164 — 993 — 993 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 8,100 — 8,317 — 8,317 Long-term debt to financing trusts (d) 205 — — 214 214 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 3,083 — 3,130 50 3,180 Long-term debt to financing trusts 184 — — 196 196 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 184 — — 204 204 BGE September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) 2,876 — 2,933 — 2,933 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 334 $ — $ 334 $ — $ 334 Long-term debt (including amounts due within one year) (b)(c) 6,089 — 5,323 568 5,891 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 64 $ — $ 64 $ — $ 64 Long-term debt (including amounts due within one year) (b)(c) $ 2,625 $ — $ 2,890 $ 101 $ 2,991 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Long-term debt (including amounts due within one year) (b)(c) $ 1,494 $ — $ 1,299 $ 196 $ 1,495 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 September 30, 2018 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total Short-term liabilities (a) $ 270 $ — $ 270 $ — $ 270 Long-term debt (including amounts due within one year) (b)(c) 1,100 — 887 271 1,158 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 $219 million , $53 million , $64 million , $23 million , $19 million , $11 million , $34 million , $12 million and $4 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of September 30, 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, government-backed fixed rate non-recourse debt and loan agreements. (d) Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of September 30, 2018 and December 31, 2017
Assets and liabilities measured and recorded at fair value on recurring basis	The following tables present assets and liabilities measured and recorded at fair value on Exelon's and Generation’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of September 30, 2018 and December 31, 2017 : Generation Exelon As of September 30, 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) $ 1,099 $ — $ — $ — $ 1,099 $ 1,906 $ — $ — $ — $ 1,906 NDT fund investments Cash equivalents (b) 278 92 — — 370 278 92 — — 370 Equities 3,206 1,608 1 1,942 6,757 3,206 1,608 1 1,942 6,757 Fixed income Corporate debt — 1,629 231 — 1,860 — 1,629 231 — 1,860 U.S. Treasury and agencies 2,031 99 — — 2,130 2,031 99 — — 2,130 Foreign governments — 49 — — 49 — 49 — — 49 State and municipal debt — 165 — — 165 — 165 — — 165 Other (c) — 29 — 854 883 — 29 — 854 883 Fixed income subtotal 2,031 1,971 231 854 5,087 2,031 1,971 231 854 5,087 Middle market lending — — 334 235 569 — — 334 235 569 Private equity — — — 303 303 — — — 303 303 Real estate — — — 490 490 — — — 490 490 NDT fund investments subtotal (d) 5,515 3,671 566 3,824 13,576 5,515 3,671 566 3,824 13,576 Pledged assets for Zion Station decommissioning Cash equivalents 9 — — — 9 9 — — — 9 Pledged assets for Zion Station (e) 9 — — — 9 9 — — — 9 Rabbi trust investments Cash equivalents 5 — — — 5 48 — — — 48 Mutual funds 25 — — — 25 76 — — — 76 Fixed income — — — — — — 16 — — 16 Life insurance contracts — 23 — — 23 — 73 37 — 110 Rabbi trust investments subtotal (f) 30 23 — — 53 124 89 37 — 250 Generation Exelon As of September 30, 2018 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Commodity derivative assets Economic hedges 234 2,117 2,019 — 4,370 234 2,117 2,019 — 4,370 Proprietary trading — 84 90 — 174 — 84 90 — 174 Effect of netting and allocation of collateral (g) (h) (230 ) (1,887 ) (1,302 ) — (3,419 ) (230 ) (1,887 ) (1,302 ) — (3,419 ) Commodity derivative assets subtotal 4 314 807 — 1,125 4 314 807 — 1,125 Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — — — — — — — — — — Economic hedges — 21 — — 21 — 21 — — 21 Effect of netting and allocation of collateral — (1 ) — — (1 ) — (1 ) — — (1 ) Interest rate and foreign currency derivative assets subtotal — 20 — — 20 — 20 — — 20 Other investments — — 52 — 52 — — 52 — 52 Total assets 6,657 4,028 1,425 3,824 15,934 7,558 4,094 1,462 3,824 16,938 Liabilities Commodity derivative liabilities Economic hedges (329 ) (2,056 ) (1,660 ) — (4,045 ) (329 ) (2,056 ) (1,919 ) — (4,304 ) Proprietary trading — (95 ) (32 ) — (127 ) — (95 ) (32 ) — (127 ) Effect of netting and allocation of collateral (g) (h) 247 1,987 1,397 — 3,631 247 1,987 1,397 — 3,631 Commodity derivative liabilities subtotal (82 ) (164 ) (295 ) — (541 ) (82 ) (164 ) (554 ) — (800 ) Interest rate and foreign currency derivative liabilities Derivatives designated as hedging instruments — — — — — — (10 ) — — (10 ) Economic hedges — (2 ) — — (2 ) — (2 ) — — (2 ) Effect of netting and allocation of collateral — 1 — — 1 — 1 — — 1 Interest rate and foreign currency derivative liabilities subtotal — (1 ) — — (1 ) — (11 ) — — (11 ) Deferred compensation obligation — (36 ) — — (36 ) — (142 ) — — (142 ) Total liabilities (82 ) (201 ) (295 ) — (578 ) (82 ) (317 ) (554 ) — (953 ) Total net assets $ 6,575 $ 3,827 $ 1,130 $ 3,824 $ 15,356 $ 7,476 $ 3,777 $ 908 $ 3,824 $ 15,985 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 Generation Exelon As of December 31, 2017 Level 1 Level 2 Level 3 Not subject to leveling Total Level 1 Level 2 Level 3 Not subject to leveling Total Interest rate and foreign currency derivative assets Derivatives designated as hedging instruments — 3 — — 3 — 6 — — 6 Economic hedges — 10 — — 10 — 10 — — 10 Effect of netting and allocation of collateral (2 ) (5 ) — — (7 ) (2 ) (5 ) — — (7 ) Interest rate and foreign currency derivative assets subtotal (2 ) 8 — — 6 (2 ) 11 — — 9 Other investments — — 37 — 37 — — 37 — 37 Total assets 6,385 3,729 1,387 3,534 15,035 6,980 3,793 1,409 3,534 15,716 Liabilities Commodity derivative liabilities Economic hedges (712 ) (2,226 ) (845 ) — (3,783 ) (713 ) (2,226 ) (1,101 ) — (4,040 ) Proprietary trading (2 ) (42 ) (9 ) — (53 ) (2 ) (42 ) (9 ) — (53 ) Effect of netting and allocation of 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 $183 million and $259 million at September 30, 2018 and December 31, 2017 and restricted cash of $57 million and $127 million at September 30, 2018 and December 31, 2017 . Exelon excludes cash of $330 million and $389 million at September 30, 2018 and December 31, 2017 and restricted cash of $85 million and $145 million at September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $163 million and $85 million at September 30, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. (b) Includes $37 million and $77 million of cash received from outstanding repurchase agreements at September 30, 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 $ (4) million and less than $1 million, which have a total notional amount of $915 million and $811 million at September 30, 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 Exelon and Generation's exposure to credit or market loss. (d) Excludes net liabilities of $89 million and $82 million at September 30, 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 less than $1 million at September 30, 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 for the three months ended September 30, 2018 and September 30, 2017 . The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the nine months ended September 30, 2018 and September 30, 2017 , respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended September 30, 2018 and September 30, 2017 . The amount of unrealized gains/(losses) at Exelon totaled $2 million and $3 million for the nine months ended September 30, 2018 and September 30, 2017 , respectively. (g) Collateral posted/(received) from counterparties totaled $18 million , $100 million and $94 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of September 30, 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), $(166) million represents variation margin on the exchanges as of September 30, 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 $71 million as of September 30, 2018 . Changes were immaterial in fair value, cumulative adjustments and impairments for the three and nine months ended September 30, 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 September 30, 2018 and December 31, 2017 : ComEd PECO BGE As of September 30, 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) $ 211 $ — $ — $ 211 $ 84 $ — $ — $ 84 $ 100 $ — $ — $ 100 Rabbi trust investments Mutual funds — — — — 7 — — 7 6 — — 6 Life insurance contracts — — — — — 11 — 11 — — — — Rabbi trust investments subtotal (b) — — — — 7 11 — 18 6 — — 6 Total assets 211 — — 211 91 11 — 102 106 — — 106 Liabilities Deferred compensation obligation — (7 ) — (7 ) — (10 ) — (10 ) — (5 ) — (5 ) Mark-to-market derivative liabilities (c) — — (259 ) (259 ) — — — — — — — — Total liabilities — (7 ) (259 ) (266 ) — (10 ) — (10 ) — (5 ) — (5 ) Total net assets (liabilities) $ 211 $ (7 ) $ (259 ) $ (55 ) $ 91 $ 1 $ — $ 92 $ 106 $ (5 ) $ — $ 101 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 September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $144 million and $62 million at September 30, 2018 and December 31, 2017 , which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $23 million and $47 million at September 30, 2018 and December 31, 2017 . BGE excludes cash of $13 million and $17 million at September 30, 2018 and December 31, 2017 and restricted cash of $3 million and $1 million at September 30, 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 and nine months ended September 30, 2018 and September 30, 2017 , respectively. (c) The Level 3 balance consists of the current and noncurrent liability of $24 million and $235 million , respectively, at September 30, 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 September 30, 2018 and December 31, 2017 : As of September 30, 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) $ 182 $ — $ — $ 182 $ 83 $ — $ — $ 83 Rabbi trust investments Cash equivalents 42 — — 42 72 — — 72 Mutual funds 15 — — 15 — — — — Fixed income — 16 — 16 — 12 — 12 Life insurance contracts — 22 37 59 — 23 22 45 Rabbi trust investments subtotal (b) 57 38 37 132 72 35 22 129 Total assets 239 38 37 314 155 35 22 212 Liabilities Deferred compensation obligation — (22 ) — (22 ) — (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 — (22 ) — (22 ) — (25 ) — (25 ) Total net assets $ 239 $ 16 $ 37 $ 292 $ 155 $ 10 $ 22 $ 187 Pepco DPL ACE As of September 30, 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) $ 35 $ — $ — $ 35 $ 102 $ — $ — $ 102 $ 26 $ — $ — $ 26 Rabbi trust investments Cash equivalents 41 — — 41 — — — — — — — — Fixed income — 6 — 6 — — — — — — — — Life insurance contracts — 22 36 58 — — — — — — — — Rabbi trust investments subtotal (b) 41 28 36 105 — — — — — — — — Total assets 76 28 36 140 102 — — 102 26 — — 26 Liabilities Deferred compensation obligation — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total liabilities — (3 ) — (3 ) — (1 ) — (1 ) — — — — Total net assets (liabilities) $ 76 $ 25 $ 36 $ 137 $ 102 $ (1 ) $ — $ 101 $ 26 $ — $ — $ 26 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 $33 million and $12 million at September 30, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 2018 and December 31, 2017 , respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $12 million and $4 million at September 30, 2018 and December 31, 2017 , respectively. DPL excludes cash of $8 million and $2 million at September 30, 2018 and December 31, 2017 , respectively. ACE excludes cash of $11 million and $2 million at September 30, 2018 and December 31, 2017 , respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 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 totaled less than $1 million for the three months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Pepco totaled $1 million and less than $1 million for the three months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at PHI totaled $1 million and less than $1 million for the nine months ended September 30, 2018 and 2017 , respectively. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for the nine months ended September 30, 2018 and 2017 , respectively. (c) Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.
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 and nine months ended September 30, 2018 and 2017 : Generation ComEd PHI Exelon Three Months Ended September 30, 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 June 30, 2018 $ 585 $ 18 $ 737 $ 36 $ 1,376 $ (252 ) $ 36 $ — $ 1,160 Total realized / unrealized gains (losses) Included in net income (1 ) — (259 ) (a) 13 (247 ) — 1 — (246 ) Included in noncurrent payables to affiliates (4 ) — — — (4 ) — — 4 — Included in payable for Zion Station decommissioning — 2 — — 2 — — — 2 Included in regulatory assets/liabilities — — — — — (7 ) (b) — (4 ) (11 ) Change in collateral — — (44 ) — (44 ) — — — (44 ) Purchases, sales, issuances and settlements Purchases 15 — 81 3 99 — — — 99 Sales — (20 ) — — (20 ) — — — (20 ) Settlements (29 ) — — — (29 ) — — — (29 ) Transfers into Level 3 — — 3 — 3 — — — 3 Transfers out of Level 3 — — (6 ) — (6 ) — — — (6 ) Balance at September 30, 2018 $ 566 $ — $ 512 $ 52 $ 1,130 $ (259 ) $ 37 $ — $ 908 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2018 $ (1 ) $ — $ (104 ) $ 13 $ (92 ) $ — $ — $ — $ (92 ) Generation ComEd PHI Exelon Nine Months Ended September 30, 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 (1 ) — (188 ) (a) 14 (175 ) — 3 — (172 ) Included in noncurrent payables to affiliates — — — — — — — — — Included in payable for Zion Station decommissioning — 7 — — 7 — — — 7 Included in regulatory assets — — — — — (3 ) (b) — — (3 ) Change in collateral — — 14 — 14 — — — 14 Purchases, sales, issuances and settlements Purchases 34 1 181 3 219 — — — 219 Sales — (20 ) (3 ) — (23 ) — — — (23 ) Settlements (115 ) — — — (115 ) — 12 — (103 ) Transfers into Level 3 — — (21 ) — (21 ) — — — (21 ) Transfers out of Level 3 — — (23 ) (2 ) (25 ) — — — (25 ) Balance as of September 30, 2018 $ 566 $ — $ 512 $ 52 $ 1,130 $ (259 ) $ 37 $ — $ 908 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2018 $ (5 ) $ — $ 159 $ 14 $ 168 $ — $ — $ — $ 168 __________ (a) Includes a reduction for the reclassification of $155 million and $347 million of realized losses due to the settlement of derivative contracts for the three and nine months ended September 30, 2018 , respectively. (b) Includes $4 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2018 . Includes $9 million of decreases in fair value and an increase for realized losses due to settlements of $12 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 2018 . (c) The amounts represented are life insurance contracts at Pepco. Generation ComEd PHI Exelon Three Months Ended September 30, 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) Total Balance as of June 30, 2017 $ 683 $ 21 $ 589 $ 41 $ 1,334 $ (256 ) $ 20 $ 1,098 Total realized / unrealized gains (losses) Included in net income — — (82 ) (a) 1 (81 ) — 1 (80 ) Included in noncurrent payables to affiliates — — — — — — — — Included in payable for Zion Station decommissioning — (4 ) — — (4 ) — — (4 ) Included in regulatory assets — — — — — (21 ) (b) — (21 ) Change in collateral — — 11 — 11 — — 11 Purchases, sales, issuances and settlements Purchases 19 — 57 1 77 — — 77 Sales — — — — — — — — Settlements (31 ) — 10 — (21 ) — — (21 ) Transfers into Level 3 — — — — — — — — Transfers out of Level 3 — — 10 — 10 — — 10 Balance as of September 30, 2017 $ 671 $ 17 $ 595 $ 43 $ 1,326 $ (277 ) $ 21 $ 1,070 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2017 $ — $ — $ 24 $ 1 $ 25 $ — $ 1 $ 26 Generation ComEd PHI Exelon Nine Months Ended September 30, 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 4 — (110 ) (a) 2 (104 ) — 2 — (102 ) Included in noncurrent payables to affiliates 13 — — — 13 — — (13 ) — Included in payable for Zion Station decommissioning — (3 ) — — (3 ) — — — (3 ) Included in regulatory assets — — — — — (19 ) (b) — 13 (6 ) Change in collateral — — 81 — 81 — — — 81 Purchases, sales, issuances and settlements Purchases 54 1 146 4 205 — — — 205 Sales — — (15 ) — (15 ) — — — (15 ) Issuances — — — — — — (1 ) — (1 ) Settlements (77 ) (8 ) (85 ) — — — (85 ) Transfers into Level 3 — — (9 ) — (9 ) — — — (9 ) Transfers out of Level 3 — — 17 (5 ) 12 — — — 12 Balance as of September 30, 2017 $ 671 $ 17 $ 595 $ 43 $ 1,326 $ (277 ) $ 21 $ — $ 1,070 The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities as of September 30, 2017 $ 2 $ — $ 161 $ 2 $ 165 $ — $ 2 $ — $ 167 __________ (a) Includes a reduction for the reclassification of $96 million and $279 million of realized gains due to the settlement of derivative contracts for the three and nine months ended September 30, 2017 , respectively. (b) Includes $24 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2017 . Includes $32 million of decreases in fair value and an increase for realized losses due to settlements of $13 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 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 and nine months ended September 30, 2018 and 2017 : Generation PHI Exelon Operating Purchased Other, net Operating and Maintenance Operating Purchased Operating and Maintenance Other, net Total gains (losses) included in net income for the three months ended September 30, 2018 $ (176 ) $ (83 ) $ 12 $ 1 $ (176 ) $ (83 ) $ 1 $ 12 Total gains (losses) included in net income for the nine months ended September 30, 2018 (32 ) (156 ) 13 3 (32 ) (156 ) 3 13 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended September 30, 2018 (64 ) (40 ) 12 — (64 ) (40 ) — 12 Change in the unrealized gains (losses) relating to assets and liabilities held for the nine months ended September 30, 2018 174 (15 ) 9 — 174 (15 ) — 9 Generation PHI Exelon Operating Revenues Purchased Power and Fuel Other, net Other, net (a) Operating Revenues Purchased Power and Fuel Other, net Total gains (losses) included in net income for the three months ended September 30, 2017 $ (3 ) $ (69 ) $ 1 $ 1 $ (3 ) $ (69 ) $ 2 Total gains (losses) included in net income for the nine months ended September 30, 2017 34 (152 ) 6 2 34 (152 ) 8 Change in the unrealized gains (losses) relating to assets and liabilities held for the three months ended September 30, 2017 47 (23 ) 1 1 47 (23 ) 2 Change in the unrealized gains (losses) relating to assets and liabilities held for the nine months ended September 30, 2017 222 (61 ) 4 2 222 (61 ) 6
Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis, valuation technique	The table below discloses the significant inputs to the forward curve used to value these positions. Type of trade Fair Value at September 30, 2018 Valuation Technique Unobservable Input Range Mark-to-market derivatives — Economic Hedges (Exelon and Generation) (a)(b) $ 359 Discounted Forward power $9 - $158 Forward gas $1.10 - $12.57 Option Model Volatility 8% - 211% Mark-to-market derivatives — Proprietary trading (Exelon and Generation) (a)(b) $ 58 Discounted Forward power $17 - $158 Mark-to-market derivatives (Exelon and ComEd) $ (259 ) Discounted Forward heat (c) 10x - 11x Marketability 4% - 8% Renewable 86% - 121% 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 $94 million and $81 million as of September 30, 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.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Summary of the derivative fair value	The following table provides a summary of the derivative fair value balances recorded by the Registrants as of September 30, 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) $ 2,987 $ 113 $ (2,406 ) $ 694 $ — $ — $ — $ — $ 694 Mark-to-market derivative assets (noncurrent assets) 1,383 61 (1,013 ) 431 — — — — 431 Total mark-to-market derivative assets 4,370 174 (3,419 ) 1,125 — — — — 1,125 Mark-to-market derivative liabilities (current liabilities) (2,761 ) (86 ) 2,543 (304 ) (24 ) — — — (328 ) Mark-to-market derivative liabilities (noncurrent liabilities) (1,284 ) (41 ) 1,088 (237 ) (235 ) — — — (472 ) Total mark-to-market derivative liabilities (4,045 ) (127 ) 3,631 (541 ) (259 ) — — — (800 ) Total mark-to-market derivative net assets (liabilities) $ 325 $ 47 $ 212 $ 584 $ (259 ) $ — $ — $ — $ 325 _________ (a) Exelon, G eneration 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 $71 million and $28 million , respectively, and current and noncurrent liabilities are shown net of collateral of $66 million and $47 million , respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $212 million at September 30, 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 p osted/(received), $(166) 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 al l 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/(rece ived), $(117) million represents variation margin on the exchanges. Below is a summary of the interest rate and foreign exchange hedge balances as of September 30, 2018 : Generation Exelon Corporate Exelon Description Economic Hedges Collateral and Netting (a) Subtotal Economic Hedges Total Mark-to-market derivative assets (current assets) $ 3 $ (1 ) $ 2 $ — $ 2 Mark-to-market derivative assets (noncurrent assets) 18 — 18 — 18 Total mark-to-market derivative assets 21 (1 ) 20 — 20 Mark-to-market derivative liabilities (current liabilities) (2 ) 1 (1 ) — (1 ) Mark-to-market derivative liabilities (noncurrent liabilities) — — — (10 ) (10 ) Total mark-to-market derivative liabilities (2 ) 1 (1 ) (10 ) (11 ) Total mark-to-market derivative net assets (liabilities) $ 19 $ — $ 19 $ (10 ) $ 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 $ 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 and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ 8 $ 55 $ (99 ) $ (41 ) Purchased power and fuel 66 21 (4 ) (114 ) Total Exelon and Generation $ 74 $ 76 $ (103 ) $ (155 ) 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 September 30, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ — $ (2 ) $ — $ 6 Nine Months Ended September 30, Income Statement Location 2018 2017 2018 2017 Loss on Swaps Gain on Borrowings Exelon Interest expense $ (11 ) $ (6 ) $ 20 $ 17 For the three and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Generation Operating Revenues $ (2 ) $ (3 ) $ 3 $ (6 ) Generation Purchased Power and Fuel (1 ) — (4 ) — Generation Interest Expense 4 — 4 — Total Generation $ 1 $ (3 ) $ 3 $ (6 ) Three Months Ended Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Exelon Operating Revenues $ (2 ) $ (3 ) $ 3 $ (6 ) Exelon Purchased Power and Fuel (1 ) — (4 ) — Exelon Interest Expense 2 — 2 — Total Exelon $ (1 ) $ (3 ) $ 1 $ (6 ) The tables below provide the activity of OCI related to cash flow hedges for the three and nine months ended September 30, 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 September 30, 2018 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at June 30, 2018 $ (4 ) $ (2 ) Reclassifications from AOCI to net income Interest Expense — — AOCI derivative loss at September 30, 2018 $ (4 ) $ (2 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Nine Months Ended September 30, 2018 Income Statement Location Total Cash Total Cash AOCI derivative loss at December 31, 2017 $ (16 ) $ (14 ) Effective portion of changes in fair value 11 11 Reclassifications from AOCI to net income Interest Expense 1 1 AOCI derivative loss at September 30, 2018 $ (4 ) $ (2 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Three Months Ended September 30, 2017 Income Statement Location Total Cash Total Cash Flow Hedges AOCI derivative loss at June 30, 2017 $ (14 ) $ (12 ) Effective portion of changes in fair value 1 1 Reclassifications from AOCI to net income Interest Expense (1 ) (a) (1 ) (a) AOCI derivative loss at September 30, 2017 $ (14 ) $ (12 ) Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Nine Months Ended September 30, 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 3 (b) 3 (b) AOCI derivative loss at September 30, 2017 $ (14 ) $ (12 ) _________ (a) Amount is net of related income tax benefit of $1 million for the three months ended September 30, 2017 . (b) Amount is net of related income tax expense of $2 million for the nine months ended September 30, 2017 .
Schedule of Derivative Instruments Included in Trading Activities [Table Text Block]	For the three and nine months ended September 30, 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 Nine Months Ended 2018 2017 2018 2017 Income Statement Location Gain (Loss) Operating revenues $ (3 ) $ 5 $ 14 $ 4 For the nine months ended September 30, 2017 , Exelon and Generation recognized a $1 million net pre-tax commodity mark-to-market loss.
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 September 30, 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 $47 million , $26 million , $23 million , $39 million , $8 million , and $6 million as of September 30, 2018 , respectively. Rating as of September 30, 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 $ 647 $ — $ 647 1 $ 176 Non-investment grade 101 20 81 No external ratings Internally rated — investment grade 179 1 178 Internally rated — non-investment grade 139 17 122 Total $ 1,066 $ 38 $ 1,028 1 $ 176 Net Credit Exposure by Type of Counterparty As of Financial institutions $ 19 Investor-owned utilities, marketers, power producers 572 Energy cooperatives and municipalities 357 Other 80 Total $ 1,028 _________ (a) As of September 30, 2018 , credit collateral held from counterparties where Generation had credit exposure included $4 million of cash and $34 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 i n the table below: Credit-Risk Related Contingent Features September 30, 2018 December 31, 2017 Gross fair value of derivative contracts containing this feature (a) $ (1,704 ) $ (926 ) Offsetting fair value of in-the-money contracts under master netting arrangements (b) 1,249 577 Net fair value of derivative contracts containing this feature (c) $ (455 ) $ (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 following table provides notional amounts outstanding held by Exelon and Generation at September 30, 2018 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 88 $ — $ 88 Interest rate swaps 625 800 1,425 Total $ 713 $ 800 $ 1,513 The following table provides notional amounts outstanding held by Exelon and Generation at December 31, 2017 related to interest rate swaps and foreign currency exchange rate swaps. Generation Exelon Corporate Exelon Foreign currency exchange rate swaps $ 94 $ — $ 94 Interest rate swaps (a) 1 — 1 Total $ 95 $ — $ 95 __________ (a) On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017.

Debt and Credit Agreements (Tab

Debt and Credit Agreements (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Commercial Paper Borrowings	The Registrants had the following amounts of commercial paper borrowings outstanding as of September 30, 2018 and December 31, 2017 : Commercial Paper Borrowings September 30, 2018 December 31, 2017 Exelon $ 209 $ 427 BGE — 77 PHI (a) 209 350 Pepco 64 26 DPL — 216 ACE 145 108 _________ (a) PHI reflects the commercial paper borrowings outstanding of Pepco, DPL and ACE.
Schedule of Long-term Debt Instruments [Table Text Block]	During the nine months ended September 30, 2018 , the following long-term debt was issued: Company Type Interest Rate Maturity Amount Use of Proceeds Generation Energy Efficiency Project Financing 3.72 % November 30, 2018 $ 4 Funding to install energy conservation measures for the Smithsonian Zoo project. Generation Energy Efficiency Project Financing 3.17 % October 31, 2018 $ 1 Funding to install energy conservation measures in Brooklyn, NY. Generation Energy Efficiency Project Financing 2.61 % September 30, 2018 $ 5 Funding to install energy conservation measures for the Pensacola project. Generation Energy Efficiency Project Financing 4.17 % January 1, 2019 $ 1 Funding to install energy conservation measures for the General Services Administration Philadelphia project. Generation Energy Efficiency Project Financing 4.26 % May 1, 2019 $ 3 Funding to install energy conservation measures for the National Institutes of Health Multi-Buildings Phase II 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. ComEd First Mortgage Bonds, Series 125 3.70 % August 15, 2028 $ 550 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. PECO Loan Agreement 2.00 % June 20, 2023 $ 50 Funding to implement Electric Long-term Infrastructure Improvement Plan. PECO First and Refunding Mortgage Bonds 3.90 % March 1, 2048 $ 325 Satisfy short-term borrowings from the Exelon intercompany money pool and for general corporate purposes. BGE Senior Notes 4.25 % September 15, 2048 $ 300 Repay commercial paper obligations and for general corporate purposes. Pepco First Mortgage Bonds 4.27 % June 15, 2048 $ 100 Repay existing indebtedness and for general corporate purposes. DPL First Mortgage Bonds 4.27 % June 15, 2048 $ 200 Repay existing indebtedness and for general corporate purposes.

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Schedule Of Remeasurements Of Deferred Income Taxes Due To Tax Reform [Table Text Block]	The one-time impacts recorded by the Registrants to remeasure their deferred income tax balances at the 21% corporate federal income tax rate as of December 31, 2017 are presented below. The impact of the August 3, 2018 proposed regulations to these balances is not material. 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 was in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. See Note 6 - 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 September 30, 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 (1.2) (9.0) 8.3 (3.6) 7.3 0.2 1.0 6.6 7.3 Qualified nuclear decommissioning trust fund income 2.4 5.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.6) (1.1) (0.2) (0.1) — (0.2) (0.1) (0.3) (0.3) Plant basis differences (2.5) — (0.3) (15.2) (0.8) (2.0) (3.4) (0.7) (1.3) Production tax credits and other credits (1.2) (2.9) (0.1) — — — — — — Noncontrolling interests (1.1) (2.8) — — — — — — — Excess deferred tax amortization (6.8) — (7.8) (4.6) (7.9) (17.7) (21.2) (14.0) (15.4) Tax Cuts and Jobs Act of 2017 1.3 3.5 — — — 0.2 0.1 — — Other 3.2 5.6 0.3 0.9 2.6 0.6 0.3 0.6 0.3 Effective income tax rate 14.5% 20.1% 21.2% (1.6)% 22.2% 2.1% (2.3)% 13.2% 11.6% Three Months Ended September 30, 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 2.2 5.6 6.6 (0.1) 5.3 5.1 2.2 5.3 5.6 Qualified nuclear decommissioning trust fund income 2.6 5.8 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (1.1) (2.2) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.4) Plant basis differences (2.6) — (0.3) (14.6) (0.8) (4.9) (6.7) (1.9) (3.4) Production tax credits and other credits (2.2) (4.9) — — — — — — — Noncontrolling interests 0.5 1.1 — — — — — — — Fitzpatrick bargain purchase gain (0.2) (0.4) — — — — — — — Other (0.1) 0.3 (0.2) (0.2) (0.2) 0.2 — (0.2) 0.1 Effective income tax rate 34.1% 40.3% 40.9% 20.0% 39.2% 35.2% 30.4% 38.0% 36.9% Nine Months Ended September 30, 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 1.7 (2.6) 8.2 (3.6) 6.6 2.7 2.4 6.5 7.3 Qualified nuclear decommissioning trust fund income 0.9 2.6 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9) (2.2) (0.2) (0.1) (0.1) (0.2) (0.1) (0.3) (0.3) Plant basis differences (2.7) — (0.1) (15.4) (0.7) (1.9) (2.9) (0.7) (1.3) Production tax credits and other credits (1.8) (5.1) (0.1) — — — — — — Noncontrolling interests (1.1) (3.2) — — — — — — — Excess deferred tax amortization (6.1) — (7.6) (3.4) (8.1) (14.5) (16.5) (11.0) (14.0) Tax Cuts and Jobs Act of 2017 0.2 1.3 (0.2) — — 0.3 — — — Other 0.4 2.0 0.1 — 0.9 0.3 — 0.4 0.9 Effective income tax rate 11.6% 13.8% 21.1% (1.5)% 19.6% 7.7% 3.9% 15.9% 13.6% Nine Months Ended September 30, 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 0.7 2.2 5.9 (0.1) 5.2 4.9 3.0 5.1 5.6 Qualified nuclear decommissioning trust fund income 4.0 13.6 — — — — — — — Amortization of investment tax credit, including deferred taxes on basis difference (0.9) (2.7) (0.2) (0.1) (0.1) (0.2) (0.1) (0.2) (0.4) Plant basis differences (3.4) — (0.3) (14.4) (0.8) (4.6) (6.3) (1.8) (3.4) Production tax credits and other credits (1.8) (6.0) — — — — — — — Noncontrolling interests 0.1 0.3 — — — — — — — Merger expenses (c) (5.4) (2.4) — — — (11.8) (8.0) (10.0) (23.0) FitzPatrick bargain purchase gain (3.2) (10.9) — — — — — — — Like-Kind Exchange (b) (1.7) — 1.7 — — — — — — Other 0.1 (0.4) 0.2 — 0.2 — (0.3) 0.6 (0.3) Effective income tax rate 23.5% 28.7% 42.3% 20.4% 39.5% 23.3% 23.3% 28.7% 13.5% _________ (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) Exelon and ComEd recorded the impact of the IRS's finalization of the LKE computation in the second quarter of 2017. (c) Includes a remeasurement of uncertain federal and state income tax positions.
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The Registrants have the following unrecognized tax benefits as of September 30, 2018 and December 31, 2017 : Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE September 30, 2018 $ 804 $ 527 $ 2 $ — $ 120 $ 134 $ 67 $ 21 $ 14 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE December 31, 2017 $ 743 $ 468 $ 2 $ — $ 120 $ 125 $ 59 $ 21 $ 14

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2018 and December 31, 2017 : Exelon and Generation September 30, 2018 December 31, 2017 Carrying value of Zion Station pledged assets (a) $ 9 $ 39 Payable to Zion Solutions (b)(c) 9 37 Cumulative withdrawals by Zion Solutions to pay decommissioning costs (d) 965 942 _________ (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 September 30, 2018 : Nuclear decommissioning ARO at December 31, 2017 (a) $ 9,662 Oyster Creek transferred to Liabilities held for sale (783 ) Accretion expense 357 Net increase due to changes in, and timing of, estimated future cash flows 116 Costs incurred related to decommissioning plants (35 ) Nuclear decommissioning ARO at September 30, 2018 (a) $ 9,317 _________ (a) Includes $12 million and $13 million for the current portion of the ARO at September 30, 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 and nine months ended September 30, 2018 and 2017 : Exelon and Generation Exelon and Generation Three Months Ended Nine Months Ended 2018 2017 2018 2017 Net unrealized gains (losses) on decommissioning trust funds — Regulatory Agreement Units (a) $ (66 ) $ 44 $ (335 ) $ 253 Net unrealized gains (losses) on decommissioning trust funds — Non-Regulatory Agreement Units (b)(c) 72 111 (143 ) 347 _________ (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 $9 million and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2018 and 2017 , respectively. Excludes $7 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 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. (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 $12 million and $13 million for the current portion of the ARO at September 30, 2018 and December 31, 2017, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.
[6]	Excludes $9 million and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2018 and 2017, respectively. Excludes $7 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 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.
[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)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2018 and 2017 . Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 100 $ 98 $ 28 $ 26 Interest cost 201 211 43 45 Expected return on assets (312 ) (300 ) (43 ) (39 ) Amortization of: Prior service cost (benefit) — (1 ) (47 ) (47 ) Actuarial loss 158 152 18 15 Settlement charges — 1 — — Net periodic benefit cost $ 147 $ 161 $ (1 ) $ — Pension Benefits Other Postretirement Benefits 2018 2017 (a) 2018 2017 (a) Components of net periodic benefit cost: Service cost $ 303 $ 290 $ 84 $ 79 Interest cost 602 632 131 136 Expected return on assets (939 ) (898 ) (130 ) (121 ) Amortization of: Prior service cost (benefit) 1 — (140 ) (140 ) Actuarial loss 472 455 50 46 Settlement charges 1 3 — — Net periodic benefit cost $ 440 $ 482 $ (5 ) $ — _________ (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 and nine months ended September 30, 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, net, for the three and nine months ended September 30, 2018 and 2017, while the non-service cost components are included in Other, net and Regulatory assets for the three and nine months ended September 30, 2018 and in Other, net and Property, plant and equipment, net, for the three and nine months ended September 30, 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, net on their consolidated financial statements for the three and nine months ended September 30, 2018 and 2017. Three Months Ended September 30, Nine Months Ended September 30, Pension and Other Postretirement Benefit Costs 2018 2017 2018 2017 Exelon (a)(b) $ 145 $ 161 $ 435 $ 482 Generation (b) 50 57 151 170 ComEd 45 44 133 131 PECO 5 7 14 21 BGE 15 16 44 48 BSC (c) 13 13 42 40 PHI (a) 17 24 51 72 Pepco 3 6 10 19 DPL 2 3 5 10 ACE 3 3 10 10 PHISCO (d) 9 12 26 33 _________ (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, ACE or PHISCO 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 and nine months ended September 30, 2018 and 2017 , respectively. Three Months Ended September 30, Nine Months Ended Savings Plan Matching Contributions 2018 2017 2018 2017 Exelon (a)(b) $ 44 $ 34 $ 126 $ 97 Generation (b) 23 14 65 42 ComEd 8 9 23 24 PECO 2 3 7 7 BGE 2 3 5 7 BSC (c) 5 2 16 7 PHI (a) 4 3 10 10 Pepco 1 1 2 3 DPL 1 1 2 2 ACE 1 — 2 1 PHISCO (d) 1 1 4 4 _________ (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, 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, ACE or PHISCO 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.

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 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 nine months ended September 30, 2018 and 2017 : Nine Months Ended September 30, 2018 Gains (Losses) on Cash Flow Hedges Unrealized gains (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 11 — 22 (4 ) 1 30 Amounts reclassified from AOCI (b) 1 — 136 — — 137 Net current-period OCI 12 — 158 (4 ) 1 167 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (10 ) (c) — — — (10 ) Ending balance $ (2 ) $ — $ (2,840 ) $ (27 ) $ — $ (2,869 ) Generation (a) Beginning balance $ (16 ) $ 3 $ — $ (23 ) $ (1 ) $ (37 ) OCI before reclassifications 11 — — (4 ) 1 8 Amounts reclassified from AOCI (b) 1 — — — — 1 Net current-period OCI 12 — — (4 ) 1 9 Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard — (3 ) (c) — — — (3 ) Ending balance $ (4 ) $ — $ — $ (27 ) $ — $ (31 ) 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 $ — $ — $ — $ — $ — $ — Nine Months Ended September 30, 2017 Gains (Losses) on Cash Flow Hedges Unrealized gains (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 2 (55 ) 7 7 (37 ) Amounts reclassified from AOCI (b) 3 — 105 — — 108 Net current-period OCI 5 2 50 7 7 71 Ending balance $ (12 ) $ 6 $ (2,560 ) $ (23 ) $ — $ (2,589 ) Generation (a) Beginning balance $ (19 ) $ 2 $ — $ (30 ) $ (7 ) $ (54 ) OCI before reclassifications 2 — — 7 6 15 Amounts reclassified from AOCI (b) 3 — — — — 3 Net current-period OCI 5 — — 7 6 18 Ending balance $ (14 ) $ 2 $ — $ (23 ) $ (1 ) $ (36 ) PECO (a) Beginning balance $ — $ 1 $ — $ — $ — $ 1 OCI before reclassifications — — — — — — Amounts reclassified from AOCI (b) — — — — — — Net current-period OCI — — — — — — Ending balance $ — $ 1 $ — $ — $ — $ 1 _________ (a) All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI. (b) See next tables for details about these reclassifications. (c) Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and 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 and nine months ended September 30, 2018 and 2017 . Three Months Ended September 30, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ — $ — Interest expense — — Total before tax — — Tax benefit $ — $ — Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (83 ) — (60 ) — Total before tax 15 — Tax benefit $ (45 ) $ — Net of tax Total Reclassifications $ (45 ) $ — Net of tax Nine Months Ended September 30, 2018 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (1 ) $ (1 ) Interest expense (1 ) (1 ) Total before tax — — Tax benefit $ (1 ) $ (1 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 68 $ — Actuarial losses (b) (251 ) — (183 ) — Total before tax 47 — Tax benefit $ (136 ) $ — Net of tax Total Reclassifications $ (137 ) $ (1 ) Net of tax Three Months Ended September 30, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ 2 $ 2 Interest expense 2 2 Total before tax (1 ) (1 ) Tax expense $ 1 $ 1 Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 23 $ — Actuarial losses (b) (81 ) — (58 ) — Total before tax 23 — Tax benefit $ (35 ) $ — Net of tax Total Reclassifications $ (34 ) $ 1 Net of tax Nine Months Ended September 30, 2017 Details about AOCI components Items reclassified out of AOCI (a) Affected line item in the Statement of Operations and Comprehensive Income Exelon Generation Gains (Losses) on cash flow hedges Other cash flow hedges $ (5 ) $ (5 ) Interest expense (5 ) (5 ) Total before tax 2 2 Tax benefit $ (3 ) $ (3 ) Net of tax Amortization of pension and other postretirement benefit plan items Prior service costs (b) $ 69 $ — Actuarial losses (b) (243 ) — (174 ) — Total before tax 69 — Tax benefit $ (105 ) $ — Net of tax Total Reclassifications $ (108 ) $ (3 ) Net of tax _________ (a) Amounts in parenthesis represent a decrease in AOCI. (b) This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional information).
Schedule Of Other Comprehensive Income Loss Tax	The following table presents income tax benefit (expense) allocated to each component of other comprehensive income (loss) during the three and nine months ended September 30, 2018 and 2017 : Three Months Ended September 30, Nine Months Ended 2018 2017 2018 2017 Exelon Pension and non-pension postretirement benefit plans: Prior service benefit reclassified to periodic benefit cost $ 6 $ 9 $ 18 $ 27 Actuarial loss reclassified to periodic benefit cost (21 ) (32 ) (65 ) (96 ) Pension and non-pension postretirement benefit plans valuation adjustment (2 ) — (8 ) 2 Change in unrealized gains on cash flow hedges — — (5 ) (3 ) Change in unrealized gains (losses) on investments in unconsolidated affiliates — 1 (1 ) (2 ) Change in unrealized gains on marketable securities — — — (2 ) Total $ (17 ) $ (22 ) $ (61 ) $ (74 ) Generation Change in unrealized gains on cash flow hedges $ — $ — $ (4 ) $ (3 ) Change in unrealized gains on investments in unconsolidated affiliates — — (1 ) (2 ) Change in unrealized gains on marketable securities — — — (1 ) Total $ — $ — $ (5 ) $ (6 )

Earnings Per Share and Equity_2

Earnings Per Share and Equity (Tables)	9 Months Ended
	Sep. 30, 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 September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Exelon Net income attributable to common shareholders $ 733 $ 823 $ 1,858 $ 1,907 Weighted average common shares outstanding — basic 968 962 967 941 Assumed exercise and/or distributions of stock-based awards 2 3 2 2 Weighted average common shares outstanding — diluted 970 965 969 943

Commitments and Contingencies_2

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Tables Disclosure [Line Items]
Other Commitments	The Registrants’ commercial commitments as of September 30, 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) $ 1,584 $ 1,565 $ 2 $ — $ 3 $ 4 $ 4 $ — $ — Surety bonds (b) 1,402 1,201 9 9 25 65 32 4 3 Financing trust guarantees 378 — 200 178 — — — — — Guaranteed lease residual values (c) 22 — — — — 22 7 9 6 Total commercial commitments $ 3,386 $ 2,766 $ 211 $ 187 $ 28 $ 91 $ 43 $ 13 $ 9 _________ (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 $60 million , $17 million of which is a guarantee by Pepco, $25 million by DPL and $17 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. 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 September 30, 2018 : Description Expected Payment Period Exelon PHI Pepco DPL ACE Rate credits 2016 - 2021 $ 259 $ 259 $ 91 $ 67 $ 101 Energy efficiency 2016 - 2021 122 — — — — Charitable contributions 2016 - 2026 50 50 28 12 10 Delivery system modernization Q2 2017 22 — — — — Green sustainability fund Q2 2017 14 — — — — Workforce development 2016 - 2020 17 — — — — Other 29 6 1 5 — Total commitments $ 513 $ 315 $ 120 $ 84 $ 111 Remaining commitments $ 138 $ 94 $ 75 $ 12 $ 7
Accrued environmental liabilities	As of September 30, 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: September 30, 2018 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 486 $ 352 Generation 102 — ComEd 323 321 PECO 28 27 BGE 6 4 PHI 27 — Pepco 25 — DPL 1 — ACE 1 — December 31, 2017 Total environmental investigation and remediation reserve Portion of total related to MGP investigation and remediation Exelon $ 466 $ 315 Generation 117 — ComEd 285 283 PECO 30 28 BGE 5 4 PHI 29 — Pepco 27 — DPL 1 — ACE 1 —

Supplemental Financial Inform_2

Supplemental Financial Information (Tables)	9 Months Ended
	Sep. 30, 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 and nine months ended September 30, 2018 and 2017 . Three Months Ended September 30, 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 $ 214 $ 214 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 58 58 — — — — — — — Net unrealized (losses) gains on decommissioning trust funds Regulatory agreement units (66 ) (66 ) — — — — — — — Non-regulatory agreement units 72 72 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (9 ) (9 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (110 ) (110 ) — — — — — — — Total decommissioning-related activities 159 159 — $ — — — — — — Investment income 9 5 — — — 2 1 1 — Interest income related to uncertain income tax positions 1 — — — — — — — — AFUDC — Equity 16 — 4 1 5 6 6 — — Non-service net periodic benefit cost (12 ) — — — — — — — — Other 21 15 3 1 — 3 — 1 1 Other, net $ 194 $ 179 $ 7 2 $ 5 $ 11 $ 7 $ 2 $ 1 Nine Months Ended September 30, 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 $ 476 $ 476 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 257 257 — — — — — — — Net unrealized losses on decommissioning trust funds Regulatory agreement units (335 ) (335 ) — — — — — — — Non-regulatory agreement units (143 ) (143 ) — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (7 ) (7 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (110 ) (110 ) — — — — — — — Total decommissioning-related activities 138 138 — — — — — — — Investment income 19 12 — — — 3 1 1 — Interest income related to uncertain income tax positions 5 1 — — — — — — — AFUDC — Equity 47 — 12 3 13 19 17 2 — Non-service net periodic benefit cost (33 ) — — — — — — — — Other 36 13 9 1 1 11 5 4 2 Other, net $ 212 $ 164 $ 21 $ 4 $ 14 $ 33 $ 23 $ 7 $ 2 Three Months Ended September 30, 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 $ 159 $ 159 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 59 59 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 44 44 — — — — — — — Non-regulatory agreement units 111 111 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (4 ) (4 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (161 ) (161 ) — — — — — — — Total decommissioning-related activities 208 208 — — — — — — — Investment income 2 1 — — — 1 1 — — Interest expense related to uncertain income tax positions 4 — — — — — — — — AFUDC — Equity 17 — 2 2 4 9 6 2 1 Non-service net periodic benefit cost (27 ) — — — — — — — — Other 6 — 3 — — 3 — 2 — Other, net $ 210 $ 209 $ 5 $ 2 $ 4 $ 13 $ 7 $ 4 $ 1 Nine Months Ended September 30, 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 $ 439 $ 439 $ — $ — $ — $ — $ — $ — $ — Non-regulatory agreement units 165 165 — — — — — — — Net unrealized gains on decommissioning trust funds Regulatory agreement units 253 253 — — — — — — — Non-regulatory agreement units 347 347 — — — — — — — Net unrealized losses on pledged assets Zion Station decommissioning (5 ) (5 ) — — — — — — — Regulatory offset to decommissioning trust fund-related activities (b) (558 ) (558 ) — — — — — — — Total decommissioning-related activities 641 641 — — — — — — — Investment income 6 4 — — — 2 1 — — Interest income related to uncertain income tax positions 3 — — — — — — — — Penalty income related to uncertain income tax positions 2 — — — — — — — — AFUDC — Equity 51 — 6 6 12 27 17 5 5 Non-service net periodic benefit cost (82 ) — — — — — — — — Other 22 3 8 — — 11 4 5 1 Other, net $ 643 $ 648 $ 14 $ 6 $ 12 $ 40 $ 22 $ 10 $ 6 _________ (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 and nine months ended September 30, 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 September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 253 $ 32 $ 67 $ 39 $ 23 $ 92 $ 87 $ 5 $ — Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 705 $ 92 $ 188 $ 102 $ 70 $ 253 $ 238 $ 15 $ — Three Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 245 $ 35 $ 65 $ 35 $ 22 $ 88 $ 83 $ 5 $ — Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Utility taxes $ 682 $ 97 $ 181 $ 95 $ 69 $ 240 $ 226 $ 14 $ —
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 nine months ended September 30, 2018 and 2017 . Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 2,829 $ 1,347 $ 613 $ 204 $ 249 $ 355 $ 161 $ 97 $ 70 Amortization of regulatory assets (a) 412 — 83 20 109 200 125 38 37 Amortization of intangible assets, net (a) 43 36 — — — — — — — Amortization of energy contract assets and liabilities (b) 8 8 — — — — — — — Nuclear fuel (c) 852 852 — — — — — — — ARO accretion (d) 367 365 — — — — — — — Total depreciation, amortization and accretion $ 4,511 $ 2,608 $ 696 $ 224 $ 358 $ 555 $ 286 $ 135 $ 107 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Depreciation, amortization and accretion Property, plant and equipment (a) $ 2,416 $ 1,010 $ 579 $ 194 $ 233 $ 342 $ 153 $ 92 $ 66 Amortization of regulatory assets (a) 355 — 52 19 115 169 89 32 47 Amortization of intangible assets, net (a) 43 36 — — — — — — — Amortization of energy contract assets and liabilities (b) 19 19 — — — — — — — Nuclear fuel (c) 816 816 — — — — — — — ARO accretion (d) 350 350 — — — — — — — Total depreciation, amortization and accretion $ 3,999 $ 2,231 $ 631 $ 213 $ 348 $ 511 $ 242 $ 124 $ 113 _________ (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	Nine Months Ended September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 435 $ 151 $ 133 $ 14 $ 43 $ 51 $ 10 $ 5 $ 10 Loss (gain) from equity method investments 22 23 — — — (1 ) — — — Provision for uncollectible accounts 133 38 30 25 6 32 12 6 14 Stock-based compensation costs 64 — — — — — — — — Other decommissioning-related activity (a) (39 ) (39 ) — — — — — — — Energy-related options (b) 4 4 — — — — — — — Amortization of regulatory asset related to debt costs 6 — 2 — — 3 1 1 1 Amortization of rate stabilization deferral — — — — — — — — — Amortization of debt fair value adjustment (12 ) (9 ) — — — (3 ) — — — Discrete impacts from EIMA and FEJA (c) 27 — 27 — — — — — — Amortization of debt costs 26 10 4 1 1 3 2 1 — Provision for excess and obsolete inventory 15 13 2 — — — — — — Long-term incentive plan 84 — — — — — — — — Asset retirement costs 20 — — — — 20 22 (1 ) (1 ) Other 19 (4 ) (11 ) 1 (8 ) 4 (5 ) 4 — Total other non-cash operating activities $ 804 $ 187 $ 187 $ 41 $ 42 $ 109 $ 42 $ 16 $ 24 Non-cash investing and financing activities: (Decrease) increase in capital expenditures not paid $ (175 ) $ (226 ) $ (28 ) $ 4 $ 44 $ 54 $ 15 $ 20 $ 16 Increase in PPE related to ARO update 67 47 4 — 1 15 12 2 1 Dividends on stock compensation 4 — — — — — — — — Acquisition of land 3 — — — — 3 — — 3 Nine Months Ended September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Other non-cash operating activities: Pension and non-pension postretirement benefit costs $ 482 $ 170 $ 131 $ 21 $ 47 $ 72 $ 19 $ 10 $ 10 Loss from equity method investments 26 26 — — — — — — — Provision for uncollectible accounts 103 31 25 17 4 26 11 1 14 Stock-based compensation costs 76 — — — — — — — — Other decommissioning-related activity (a) (213 ) (213 ) — — — — — — — Energy-related options (b) 15 15 — — — — — — — Amortization of regulatory asset related to debt costs 7 — 3 1 — 3 1 1 1 Amortization of rate stabilization deferral (7 ) — — — 7 (14 ) (12 ) (2 ) — Amortization of debt fair value adjustment (13 ) (9 ) — — — (4 ) — — — Discrete impacts from EIMA and FEJA (c) (61 ) — (61 ) — — — — — — Amortization of debt costs 57 33 3 1 1 1 1 — — Provision for excess and obsolete inventory 52 50 1 — — 1 — 1 — Merger-related commitments (d) — — — — — (8 ) (6 ) (2 ) — Severance costs 33 25 — — — 3 — — — Other 46 4 10 (2 ) (7 ) (14 ) (6 ) (3 ) (4 ) Total other non-cash operating activities $ 603 $ 132 $ 112 $ 38 $ 52 $ 66 $ 8 $ 6 $ 21 Non-cash investing and financing activities: (Decrease) increase in capital expenditures not paid $ (101 ) $ 20 $ (79 ) $ (29 ) $ 16 $ (6 ) $ 7 $ 14 $ (18 ) Fair value of pension obligation transferred in connection with the FitzPatrick acquisition — 33 — — — — — — — Decrease in PPE related to ARO update (141 ) (141 ) — — — — — — — Indemnification of like-kind exchange tax position (e) — — 21 — — — — — — Non-cash financing of capital projects 16 16 — — — — — — — Dividends on stock compensation 5 — — — — — — — — Dissolution of financing trust due to long-term debt retirement 8 — — — 8 — — — — Fair value adjustment of long-term debt due to retirement (5 ) — — — — — — — — _________ (a) Includes the elimination of decommissioning-related activities for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations 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 and expenses. (c) Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information. (d) See Note 4 - Mergers, Acquisitions and Dispositions for additional information. (e) See Note 12 - Income Taxes for additional information on the like-kind exchange tax position.
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. September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,918 $ 1,187 $ 124 $ 102 $ 113 $ 153 $ 12 $ 110 $ 11 Restricted cash 240 152 12 5 3 42 35 — 7 Restricted cash included in other long-term assets 163 — 144 — — 19 — — 19 Total cash, cash equivalents and restricted cash $ 2,321 $ 1,339 $ 280 $ 107 $ 116 $ 214 $ 47 $ 110 $ 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 $ 1,190 $ 554 $ 144 $ 275 $ 18 $ 95 $ 40 $ 2 $ 31 September 30, 2017 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Cash and cash equivalents $ 1,203 $ 360 $ 257 $ 330 $ 29 $ 137 $ 117 $ 3 $ 5 Restricted cash 320 186 52 4 1 43 34 — 9 Restricted cash included in other long-term assets 22 — — — — 22 — — 22 Total cash, cash equivalents and restricted cash $ 1,545 $ 546 $ 309 $ 334 $ 30 $ 202 $ 151 $ 3 $ 36 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 $ 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 addit i onal information about assets and liabilities of the Registrants as of September 30, 2018 and December 31, 2017 . September 30, 2018 Exelon Generation ComEd PECO BGE PHI Pepco DPL ACE Property, plant and equipment: Accumulated depreciation and amortization $ 23,122 (a) $ 12,753 (a) $ 4,557 $ 3,521 $ 3,579 $ 759 $ 3,311 $ 1,315 $ 1,121 Accounts receivable: Allowance for uncollectible accounts $ 354 $ 112 $ 93 $ 61 $ 22 $ 66 $ 25 $ 16 $ 25 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 $3,278 million . (b) Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Analysis and reconciliation of reportable segment information	Nine Months Ended September 30, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 13,190 $ — $ — $ — $ — $ — $ (969 ) $ 12,221 Competitive businesses natural gas revenues 1,839 — — — — — (8 ) 1,831 Competitive businesses other revenues 339 — — — — — (4 ) 335 Rate-regulated electric revenues — 4,508 1,893 1,850 3,549 — (34 ) 11,766 Rate-regulated natural gas revenues — — 382 519 129 — (13 ) 1,017 Shared service and other revenues — — — — 10 1,398 (1,408 ) — Total operating revenues $ 15,368 $ 4,508 $ 2,275 $ 2,369 $ 3,688 $ 1,398 $ (2,436 ) $ 27,170 2017 Competitive businesses electric revenues $ 11,514 $ — $ — $ — $ — $ — $ (888 ) $ 10,626 Competitive businesses natural gas revenues 1,807 — — — — — — 1,807 Competitive businesses other revenues 522 — — — — — — 522 Rate-regulated electric revenues — 4,227 1,802 1,895 3,417 — (23 ) 11,318 Rate-regulated natural gas revenues — — 339 468 105 — (6 ) 906 Shared service and other revenues — — — — 35 1,316 (1,350 ) 1 Total operating revenues $ 13,843 $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,316 $ (2,267 ) $ 25,180 Intersegment revenues (d) : 2018 $ 981 $ 23 $ 5 $ 18 $ 11 $ 1,392 $ (2,430 ) $ — 2017 888 12 5 12 35 1,312 (2,262 ) 2 Net income (loss): 2018 $ 667 $ 523 $ 336 $ 242 $ 336 $ (125 ) $ — $ 1,979 2017 508 447 327 231 359 58 (2 ) 1,928 __________ (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 nine months ended September 30, 2018 include revenue from sales to PECO of $97 million , sales to BGE of $198 million , sales to Pepco of $143 million , sales to DPL of $103 million and sales to ACE of $21 million in the Mid-Atlantic region, and sales to ComEd of $419 million in the Midwest region, which eliminate upon consolidation. For the nine months ended September 30, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $111 million , sales to BGE of $330 million , sales to Pepco of $209 million , sales to DPL of $138 million and sales to ACE of $23 million in the Mid-Atlantic region, and sales to ComEd of $77 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 nine months ended September 30, 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) : Nine Months Ended September 30, 2018 Rate-regulated electric revenues $ 1,708 $ 872 $ 981 $ — $ (12 ) $ 3,549 Rate-regulated natural gas revenues — 129 — — — 129 Shared service and other revenues — — — 326 (316 ) 10 Total operating revenues $ 1,708 $ 1,001 $ 981 $ 326 $ (328 ) $ 3,688 Nine Months Ended September 30, 2017 Rate-regulated electric revenues $ 1,649 $ 866 $ 915 $ — $ (13 ) $ 3,417 Rate-regulated natural gas revenues — 105 — — — 105 Shared service and other revenues — — — 37 (2 ) 35 Total operating revenues $ 1,649 $ 971 $ 915 $ 37 $ (15 ) $ 3,557 Intersegment revenues: Nine Months Ended September 30, 2018 $ 5 $ 6 $ 2 $ 325 $ (327 ) $ 11 Nine Months Ended September 30, 2017 4 6 2 37 (14 ) 35 Net income (loss): Nine Months Ended September 30, 2018 $ 174 $ 90 $ 76 $ (15 ) $ 11 $ 336 Nine Months Ended September 30, 2017 188 107 77 (48 ) 35 359 __________ (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 nine months ended September 30, 2018 and 2017 . (b) Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities An analysis and reconciliation of the Registrants’ reportable segment information to the respective information in the consolidated financial statements for the three and nine months ended September 30, 2018 and 2017 is as follows: Three Months Ended September 30, 2018 and 2017 Generation (a) ComEd PECO BGE PHI Other (b) Intersegment Exelon Operating revenues (c) : 2018 Competitive businesses electric revenues $ 4,741 $ — — $ — $ — $ — $ (306 ) $ 4,435 Competitive businesses natural gas revenues 397 — — — — — — 397 Competitive businesses other revenues 140 — — — — — (1 ) 139 Rate-regulated electric revenues — 1,598 700 645 1,334 — (7 ) 4,270 Rate-regulated natural gas revenues — — 57 86 24 — (5 ) 162 Shared service and other revenues — — — — 3 458 (461 ) — Total operating revenues $ 5,278 $ 1,598 $ 757 $ 731 $ 1,361 $ 458 $ (780 ) $ 9,403 2017 Competitive businesses electric revenues $ 4,041 $ — $ — $ — $ — $ — $ (295 ) $ 3,746 Competitive businesses natural gas revenues 460 — — — — — — 460 Competitive businesses other revenues 249 — — — — — — 249 Rate-regulated electric revenues — 1,571 662 658 1,280 — (7 ) 4,164 Rate-regulated natural gas revenues — — 53 80 18 — (2 ) 149 Shared service and other revenues — — — — 12 446 (458 ) — Total operating revenues $ 4,750 $ 1,571 $ 715 $ 738 $ 1,310 $ 446 $ (762 ) $ 8,768 Intersegment revenues (d) : 2018 $ 308 $ 4 $ 2 $ 6 $ 3 $ 456 $ (779 ) $ — 2017 294 3 2 3 12 445 (759 ) — Net income (loss): 2018 $ 300 $ 193 $ 126 $ 63 $ 187 $ (69 ) $ — $ 800 2017 346 189 112 62 153 3 — 865 Total assets: September 30, 2018 $ 48,207 $ 31,119 $ 10,621 $ 9,541 $ 21,957 $ 8,418 $ (10,378 ) $ 119,485 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 September 30, 2018 include revenue from sales to PECO of $35 million , sales to BGE of $69 million , sales to Pepco of $46 million , sales to DPL of $26 million and sales to ACE of $10 million in the Mid-Atlantic region, and sales to ComEd of $122 million in the Midwest region, which eliminate upon consolidation. For the three months ended September 30, 2017 , intersegment revenues for Generation include revenue from sales to PECO of $31 million , sales to BGE of $98 million , sales to Pepco of $57 million , sales to DPL of $47 million and sales to ACE of $7 million in the Mid-Atlantic region, and sales to ComEd of $54 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 September 30, 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 September 30, 2018 Rate-regulated electric revenues $ 628 $ 304 $ 406 $ — $ (4 ) $ 1,334 Rate-regulated natural gas revenues — 24 — — — 24 Shared service and other revenues — — — 103 (100 ) 3 Total operating revenues $ 628 $ 328 $ 406 $ 103 $ (104 ) $ 1,361 Three Months Ended September 30, 2017 Rate-regulated electric revenues $ 604 $ 309 $ 370 $ — $ (3 ) $ 1,280 Rate-regulated natural gas revenues — 18 — — — 18 Shared service and other revenues — — — 12 — 12 Total operating revenues $ 604 $ 327 $ 370 $ 12 $ (3 ) $ 1,310 Intersegment revenues: Three Months Ended September 30, 2018 $ 2 $ 2 $ 1 $ 103 $ (105 ) $ 3 Three Months Ended September 30, 2017 1 2 — 13 (4 ) 12 Net income (loss): Three Months Ended September 30, 2018 $ 89 $ 33 $ 61 $ 1 $ 3 $ 187 Three Months Ended September 30, 2017 87 31 41 (18 ) 12 153 Total assets: September 30, 2018 $ 8,199 $ 4,601 $ 3,694 $ 10,763 $ (5,300 ) $ 21,957 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 September 30, 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	Competitive Business Revenues (Generation): Three Months Ended September 30, 2018 Revenues from external parties (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,397 $ 52 $ 1,449 $ 7 $ 1,456 Midwest 1,095 26 1,121 (4 ) 1,117 New England 666 33 699 — 699 New York 475 (6 ) 469 — 469 ERCOT 156 289 445 (1 ) 444 Other Power Regions 293 265 558 (45 ) 513 Total Competitive Businesses Electric Revenues 4,082 659 4,741 (43 ) 4,698 Competitive Businesses Natural Gas Revenues 200 197 397 43 440 Competitive Businesses Other Revenues (c) 130 10 140 — 140 Total Generation Consolidated Operating Revenues $ 4,412 $ 866 $ 5,278 $ — $ 5,278 Three Months Ended September 30, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 1,397 $ 24 $ 1,421 $ 11 $ 1,432 Midwest 982 67 1,049 (11 ) 1,038 New England 504 (22 ) 482 (1 ) 481 New York 454 (21 ) 433 (6 ) 427 ERCOT 164 144 308 6 314 Other Power Regions 167 181 348 (13 ) 335 Total Competitive Businesses Electric Revenues 3,668 373 4,041 (14 ) 4,027 Competitive Businesses Natural Gas Revenues 226 234 460 20 480 Competitive Businesses Other Revenues (c) 207 42 249 (6 ) 243 Total Generation Consolidated Operating Revenues $ 4,101 $ 649 $ 4,750 $ — $ 4,750 __________ (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 $13 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 September 30, 2017 , unrealized mark-to-market gains of $6 million and $52 million for the three months ended September 30, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Three Months Ended September 30, 2018 Three Months Ended September 30, 2017 RNF (a) Intersegment RNF Total RNF RNF (a) Intersegment RNF Total RNF Mid-Atlantic $ 746 $ 17 $ 763 $ 817 $ 38 $ 855 Midwest 763 5 768 697 — 697 New England 83 (2 ) 81 151 (6 ) 145 New York 290 2 292 295 — 295 ERCOT 161 (63 ) 98 229 (111 ) 118 Other Power Regions 143 (44 ) 99 118 (50 ) 68 Total Revenues net of purchased power and fuel for Reportable Segments 2,186 (85 ) 2,101 2,307 (129 ) 2,178 Other (b) 112 85 197 112 129 241 Total Generation Revenues net of purchased power and fuel expense $ 2,298 $ — $ 2,298 $ 2,419 $ — $ 2,419 __________ (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 $19 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended September 30, 2017 , unrealized mark-to-market gains of $71 million and $73 million for the three months ended September 30, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $18 million and $6 million decrease to revenue net of purchased power and fuel expense for the three months ended September 30, 2018 , and 2017 , respectively, and the elimination of intersegment revenue net of purchased power and fuel expense. 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 nine months ended September 30, 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): Nine Months Ended September 30, 2018 Revenues from external parties (a) Intersegment Revenues Total Revenues Contracts with customers Other (b) Total Mid-Atlantic $ 3,971 $ 191 $ 4,162 $ 17 $ 4,179 Midwest 3,432 169 3,601 (8 ) 3,593 New England 1,943 87 2,030 (4 ) 2,026 New York 1,305 (37 ) 1,268 1 1,269 ERCOT 470 459 929 1 930 Other Power Regions 713 487 1,200 (112 ) 1,088 Total Competitive Businesses Electric Revenues 11,834 1,356 13,190 (105 ) 13,085 Competitive Businesses Natural Gas Revenues 1,016 823 1,839 105 1,944 Competitive Businesses Other Revenues (c) 385 (46 ) 339 — 339 Total Generation Consolidated Operating Revenues $ 13,235 $ 2,133 $ 15,368 $ — $ 15,368 Nine Months Ended September 30, 2017 Revenues from external customers (a) Intersegment Total Contracts with customers Other (b) Total Mid-Atlantic $ 4,260 $ (53 ) $ 4,207 $ 15 $ 4,222 Midwest 2,948 210 3,158 (17 ) 3,141 New England 1,555 (86 ) 1,469 (8 ) 1,461 New York 1,161 (37 ) 1,124 (14 ) 1,110 ERCOT 520 229 749 4 753 Other Power Regions 439 368 807 (28 ) 779 Total Competitive Businesses Electric Revenues 10,883 631 11,514 (48 ) 11,466 Competitive Businesses Natural Gas Revenues 1,237 570 1,807 52 1,859 Competitive Businesses Other Revenues (c) 588 (66 ) 522 (4 ) 518 Total Generation Consolidated Operating Revenues $ 12,708 $ 1,135 $ 13,843 $ — $ 13,843 __________ (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 $30 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the nine months ended September 30, 2017 , unrealized mark-to-market losses of $96 million and $47 million for the nine months ended September 30, 2018 and 2017 , respectively, and elimination of intersegment revenues. Revenues net of purchased power and fuel expense (Generation): Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 RNF from external customers (a) Intersegment RNF Total RNF RNF from external customers (a) Intersegment RNF Total RNF Mid-Atlantic $ 2,303 $ 45 $ 2,348 $ 2,330 $ 81 $ 2,411 Midwest 2,381 19 2,400 2,129 11 2,140 New England 310 (12 ) 298 423 (20 ) 403 New York 832 9 841 708 (1 ) 707 ERCOT 396 (180 ) 216 446 (188 ) 258 Other Power Regions 430 (121 ) 309 359 (139 ) 220 Total Revenues net of purchased power and fuel expense for Reportable Segments 6,652 (240 ) 6,412 6,395 (256 ) 6,139 Other (b) 164 240 404 162 256 418 Total Generation Revenues net of purchased power and fuel expense $ 6,816 $ — $ 6,816 $ 6,557 $ — $ 6,557 __________ (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 $41 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the nine months ended September 30, 2017 , unrealized mark-to-market losses of $104 million and $161 million for the nine months ended September 30, 2018 and 2017 , respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $53 million and $8 million decrease to revenue net of purchased power and fuel expense for the nine months ended September 30, 2018 and 2017 , respectively, 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 (the Utility Registrants): Nine Months Ended September 30, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,277 $ 1,199 $ 1,054 $ 1,839 $ 792 $ 513 $ 534 Small commercial & industrial 1,132 306 196 370 104 138 128 Large commercial & industrial 411 174 325 845 632 74 139 Public authorities & electric railroads 36 21 21 44 24 10 10 Other (a) 656 181 246 446 145 129 174 Total rate-regulated electric revenues (b) 4,512 1,881 1,842 3,544 1,697 864 985 Rate-regulated natural gas revenues Residential — 259 345 68 — 68 — Small commercial & industrial — 102 55 31 — 31 — Large commercial & industrial — 1 88 7 — 7 — Transportation — 16 — 12 — 12 — Other (c) — 4 49 11 — 11 — Total rate-regulated natural gas revenues (d) — 382 537 129 — 129 — Total rate-regulated revenues from contracts with customers 4,512 2,263 2,379 3,673 1,697 993 985 Other revenues Revenues from alternative revenue programs (27 ) 2 (23 ) 7 6 5 (4 ) Other rate-regulated electric revenues (e) 23 10 10 8 5 3 — Other rate-regulated natural gas revenues (e) — — 3 — — — — Total other revenues (4 ) 12 (10 ) 15 11 8 (4 ) Total rate-regulated revenues for reportable segments $ 4,508 $ 2,275 $ 2,369 $ 3,688 $ 1,708 $ 1,001 $ 981 Nine Months Ended September 30, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 2,071 $ 1,147 $ 1,038 $ 1,740 $ 751 $ 505 $ 484 Small commercial & industrial 1,035 303 193 373 105 139 129 Large commercial & industrial 346 168 329 814 593 78 143 Public authorities & electric railroads 33 23 23 45 24 11 10 Other (a) 671 151 222 398 148 121 140 Total rate-regulated electric revenues (b) 4,156 1,792 1,805 3,370 1,621 854 906 Rate-regulated natural gas revenues Residential — 225 289 57 — 57 — Small commercial & industrial — 90 51 25 — 25 — Large commercial & industrial — — 82 5 — 5 — Transportation — 16 — 11 — 11 — Other (c) — 8 20 7 — 7 — Total rate-regulated natural gas revenues (d) — 339 442 105 — 105 — Total rate-regulated revenues from contracts with customers 4,156 2,131 2,247 3,475 1,621 959 906 Other revenues Revenues from alternative revenue programs 48 — 102 41 23 9 9 Other rate-regulated electric revenues (e) 23 10 11 8 5 3 — Other rate-regulated natural gas revenues (e) — — 3 — — — — Other revenues (f) — — — 33 — — — Total other revenues 71 10 116 82 28 12 9 Total rate-regulated revenues for reportable segments $ 4,227 $ 2,141 $ 2,363 $ 3,557 $ 1,649 $ 971 $ 915 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $23 million , $5 million , $5 million , $11 million , $5 million , $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2018 and $12 million , $4 million , $5 million , $2 million , $4 million , $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $13 million at PECO and BGE, respectively, for the nine months ended September 30, 2018 and less than $1 million and $7 million at PECO and BGE, respectively, for the nine months ended September 30, 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $33 million at PHI for the nine months ended September 30, 2017 . Electric and Gas Revenue by Customer Class (the Utility Registrants): Three Months Ended September 30, 2018 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 861 $ 458 $ 366 $ 726 $ 306 $ 180 $ 240 Small commercial & industrial 391 108 68 140 39 48 53 Large commercial & industrial 131 64 117 303 230 25 48 Public authorities & electric railroads 11 7 7 14 8 3 3 Other (a) 212 59 91 156 47 47 63 Total rate-regulated electric revenues (b) 1,606 696 649 1,339 630 303 407 Rate-regulated natural gas revenues Residential — 36 46 8 — 8 — Small commercial & industrial — 15 8 5 — 5 — Large commercial & industrial — — 17 2 — 2 — Transportation — 5 — 3 — 3 — Other (c) — 1 12 6 — 6 — Total rate-regulated natural gas revenues (d) — 57 83 24 — 24 — Total rate-regulated revenues from contracts with customers 1,606 753 732 1,363 630 327 407 Other revenues Revenues from alternative revenue programs (15 ) 1 (6 ) (5 ) (4 ) — (1 ) Other rate-regulated electric revenues (e) 7 3 4 3 2 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Total other revenues (8 ) 4 (1 ) (2 ) (2 ) 1 (1 ) Total rate-regulated revenues for reportable segments $ 1,598 $ 757 $ 731 $ 1,361 $ 628 $ 328 $ 406 Three Months Ended September 30, 2017 Revenues from contracts with customers ComEd PECO BGE PHI Pepco DPL ACE Rate-regulated electric revenues Residential $ 816 $ 434 $ 352 $ 687 $ 291 $ 185 $ 211 Small commercial & industrial 366 106 65 140 37 50 53 Large commercial & industrial 119 59 114 288 211 28 49 Public authorities & electric railroads 11 7 8 14 8 3 3 Other (a) 235 53 85 147 52 43 54 Total rate-regulated electric revenues (b) 1,547 659 624 1,276 599 309 370 Rate-regulated natural gas revenues Residential — 33 44 8 — 8 — Small commercial & industrial — 14 8 3 — 3 — Large commercial & industrial — — 19 1 — 1 — Transportation — 5 — 3 — 3 — Other (c) — 1 3 3 — 3 — Total rate-regulated natural gas revenues (d) — 53 74 18 — 18 — Total rate-regulated revenues from contracts with customers 1,547 712 698 1,294 599 327 370 Other revenues Revenues from alternative revenue programs 16 — 36 2 3 (1 ) — Other rate-regulated electric revenues (e) 8 3 3 3 2 1 — Other rate-regulated natural gas revenues (e) — — 1 — — — — Other revenues (f) — — — 11 — — — Total other revenues 24 3 40 16 5 — — Total rate-regulated revenues for reportable segments $ 1,571 $ 715 $ 738 $ 1,310 $ 604 $ 327 $ 370 __________ (a) Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue. (b) Includes operating revenues from affiliates of $4 million , $2 million , $1 million , $3 million , $2 million , $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2018 and $3 million , $1 million , $1 million , $1 million $1 million , $2 million and less than $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2017 . (c) Includes revenues from off-system natural gas sales. (d) Includes operating revenues from affiliates of less than $1 million and $5 million at PECO and BGE, respectively, for the three months ended September 30, 2018 and less than $1 million and $2 million at PECO and BGE, respectively, for the three months ended September 30, 2017 . (e) Includes late payment charge revenues. (f) Includes operating revenues from affiliates of $11 million at PHI for the three months ended September 30, 2017 .

Significant Accounting Polici_4

Significant Accounting Policies Revenue Initial Application Period Cumulative Effect Transition (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues	$ 4,971		$ 4,455		$ 14,387		$ 12,955
Rate-regulated utility revenues	4,457		4,259		12,824		12,034
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(25)		54		(41)		191
Operating revenues from affiliates	0	[1]	0	[1]	0	[2]	0
Total operating revenues	9,403		8,768		27,170		25,180
Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			4,456				12,924
Rate-regulated utility revenues			4,313				12,225
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Operating revenues from affiliates			0				0
Total operating revenues			8,769				25,149
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			(1)				31
Rate-regulated utility revenues			(54)				(191)
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			54				191
Operating revenues from affiliates			0				0
Total operating revenues			(1)				31
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Exelon Generation Co L L C [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues	4,970		4,454		14,389		12,949
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates	308		296		979		894
Total operating revenues	5,278		4,750		15,368		13,843
Exelon Generation Co L L C [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			4,455				12,918
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Operating revenues from affiliates			296				894
Total operating revenues			4,751				13,812
Exelon Generation Co L L C [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			(1)				31
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates			0				0
Total operating revenues			(1)				31
Exelon Generation Co L L C [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Commonwealth Edison Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	1,609		1,552		4,512		4,167
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(15)		16		(27)		48
Operating revenues from affiliates	4		3		23		12
Total operating revenues	1,598		1,571		4,508		4,227
Commonwealth Edison Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1,568				4,215
Natural gas operating revenues			0				0
Operating revenues from affiliates			3				12
Total operating revenues			1,571				4,227
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(16)				(48)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			16				48
Operating revenues from affiliates			0				0
Total operating revenues			0				0
PECO Energy Co [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	697		660		1,886		1,798
Natural gas operating revenues	57		53		382		338
Revenues from alternative revenue programs	1		0		2		0
Operating revenues from affiliates	2		2		5		5
Total operating revenues	757		715		2,275		2,141
PECO Energy Co [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			660				1,798
Natural gas operating revenues			53				338
Operating revenues from affiliates			2				5
Total operating revenues			715				2,141
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			0				0
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				0
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Baltimore Gas and Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	652		626		1,847		1,811
Natural gas operating revenues	79		73		527		438
Revenues from alternative revenue programs	(6)		36		(23)		102
Operating revenues from affiliates	6		3		18		12
Total operating revenues	731		738		2,369		2,363
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			657				1,890
Natural gas operating revenues			78				461
Operating revenues from affiliates			3				12
Total operating revenues			738				2,363
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(31)				(79)
Natural gas operating revenues			(5)				(23)
Revenues from alternative revenue programs			36				102
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Pepco Holdings LLC [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	1,340		1,278		3,541		3,376
Natural gas operating revenues	23		18		129		105
Revenues from alternative revenue programs	(5)		2		7		41
Operating revenues from affiliates	3		12		11		35
Total operating revenues	1,361		1,310		3,688		3,557
Pepco Holdings LLC [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1,280				3,417
Natural gas operating revenues			18				105
Operating revenues from affiliates			12				35
Total operating revenues			1,310				3,557
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(2)				(41)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			2				41
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Potomac Electric Power Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	630		600		1,697		1,622
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(4)		3		6		23
Operating revenues from affiliates	2		1		5		4
Total operating revenues	628		604		1,708		1,649
Potomac Electric Power Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			603				1,645
Natural gas operating revenues			0				0
Operating revenues from affiliates			1				4
Total operating revenues			604				1,649
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			(3)				(23)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			3				23
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Delmarva Power and Light Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	302		308		861		851
Natural gas operating revenues	24		18		129		105
Revenues from alternative revenue programs	0		(1)		5		9
Operating revenues from affiliates	2		2		6		6
Total operating revenues	328		327		1,001		971
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			307				860
Natural gas operating revenues			18				105
Operating revenues from affiliates			2				6
Total operating revenues			327				971
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			1				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			(1)				9
Operating revenues from affiliates			0				0
Total operating revenues			0				0
Atlantic City Electric Company [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues	406		370		983		904
Natural gas operating revenues			0				0
Revenues from alternative revenue programs	(1)		0		(4)		9
Operating revenues from affiliates	1		0		2		2
Total operating revenues	$ 406		370		$ 981		915
Atlantic City Electric Company [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			370				913
Natural gas operating revenues			0				0
Operating revenues from affiliates			0				2
Total operating revenues			370				915
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]
Competitive business revenues			0				0
Rate-regulated utility revenues			0				0
Electric operating revenues			0				(9)
Natural gas operating revenues			0				0
Revenues from alternative revenue programs			0				9
Operating revenues from affiliates			0				0
Total operating revenues			$ 0				$ 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.
[2]	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.

New Accounting Standards New Ac

New Accounting Standards New Accounting Standards - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings	$ 539

Variable Interest Entities - Na

Variable Interest Entities - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018USD ($)VIE	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)VIE	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)VIE	Apr. 01, 2014USD ($)
Variable Interest Entity [Line Items]
Number Of Variable Interest Entities Consolidated | VIE		5		5		5
Number of Variable Interest Entities not consolidated by equity holders | VIE		7		7		7
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 60		$ 60
Other Nonconsolidated Variable Interest Entity Ownership Interests	[1]	598		598		$ 618
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		15		15
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				$ 34
Related Party Purchase Of Nuclear Output By Third Party Percentage				50.01%
Other Nonconsolidated Variable Interest Entity Ownership Interests		15		$ 15
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Variable Interest Entity [Line Items]
Receivables from affiliates		194		194			$ 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		637
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		17		17
Atlantic City Electric Company [Member] | ATF [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Financial or Other Support, Amount		$ 9	$ 11	$ 23	$ 39
[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		Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 891	$ 662
Noncurrent assets	[1]	9,259	9,317
Total assets	[1]	10,150	9,979
Current liabilities	[1]	329	308
Noncurrent liabilities	[1]	3,284	3,316
Total liabilities	[1]	3,613	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		881	652
Noncurrent assets		9,233	9,286
Total assets		10,114	9,938
Current liabilities		303	272
Noncurrent liabilities		3,232	3,250
Total liabilities		3,535	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	10	10
Noncurrent assets	[1]	26	31
Total assets	[1]	36	41
Current liabilities	[1]	26	36
Noncurrent liabilities	[1]	52	66
Total liabilities	[1]	78	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		7	6
Noncurrent assets		19	23
Total assets		26	29
Current liabilities		23	32
Noncurrent liabilities		45	58
Total liabilities		$ 68	$ 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		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents		$ 1,918	$ 898	$ 1,203	$ 635
Restricted cash		240	207	320	253
Accounts receivable, net
Customer		4,239	4,445
Other		1,246	1,132
Inventory, net
Materials and Supplies		1,316	1,311
Other current assets		1,177	1,260
Total current assets		13,473	11,896
Property, plant and equipment, net		75,840	74,202
Nuclear decommissioning trust funds		12,464	13,272
Goodwill		6,677	6,677
Mark-to-market derivative assets		449	337
Other noncurrent assets		1,560	1,330
Total assets	[1]	119,485	116,770
Long-term debt due within one year		771	2,088
Accounts payable		3,348	3,532
Accrued expenses		1,964	1,837
Unamortized energy contract liabilities		158	231
Other		935	982
Total current liabilities		10,140	10,798
Long-term debt		34,519	32,176
Asset retirement obligations		9,747	10,029
Pension obligation		3,385	3,736
Unamortized energy contract liabilities		497	609
Other noncurrent liabilities		2,160	2,097
Total liabilities	[1]	86,097	84,583
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents	[2]	316	126
Restricted cash	[2]	77	64
Accounts receivable, net
Customer	[2]	165	170
Other	[2]	30	25
Inventory, net
Materials and Supplies	[2]	214	205
Other current assets	[2]	65	45
Total current assets	[2]	867	635
Property, plant and equipment, net	[2]	6,158	6,186
Nuclear decommissioning trust funds	[2]	2,523	2,502
Other noncurrent assets	[2]	256	274
Total noncurrent assets	[2]	8,937	8,962
Total assets	[2]	9,804	9,597
Long-term debt due within one year	[2]	97	102
Accounts payable	[2]	128	114
Accrued expenses	[2]	73	67
Unamortized energy contract liabilities	[2]	16	18
Other	[2]	14	7
Total current liabilities	[2]	328	308
Long-term debt	[2]	1,087	1,154
Asset retirement obligations	[2]	2,116	2,035
Other noncurrent liabilities	[2]	75	121
Total noncurrent liabilities	[2]	3,278	3,310
Total liabilities	[2]	3,606	3,618
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		1,187	416	360	290
Restricted cash		152	138	186	158
Accounts receivable, net
Customer		2,545	2,697
Other		278	321
Inventory, net
Materials and Supplies		948	937
Other current assets		854	933
Total current assets		8,049	6,882
Property, plant and equipment, net		24,168	24,906
Nuclear decommissioning trust funds		12,464	13,272
Goodwill		47	47
Mark-to-market derivative assets		449	334
Other noncurrent assets		730	670
Total assets	[3]	48,207	48,457
Long-term debt due within one year		336	346
Accounts payable		1,450	1,773
Accrued expenses		1,200	1,022
Unamortized energy contract liabilities		33	43
Other		255	265
Total current liabilities		4,767	4,191
Long-term debt		7,605	7,734
Asset retirement obligations		9,521	9,844
Unamortized energy contract liabilities		23	48
Other noncurrent liabilities		635	658
Total liabilities	[3]	32,247	32,498
Exelon Generation Co L L C [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		316	126
Restricted cash		70	58
Accounts receivable, net
Customer		165	170
Other		30	25
Inventory, net
Materials and Supplies		214	205
Other current assets		62	41
Total current assets		857	625
Property, plant and equipment, net		6,158	6,186
Nuclear decommissioning trust funds		2,523	2,502
Other noncurrent assets		230	243
Total noncurrent assets		8,911	8,931
Total assets		9,768	9,556
Long-term debt due within one year		72	67
Accounts payable		128	114
Accrued expenses		72	66
Unamortized energy contract liabilities		16	18
Other		14	7
Total current liabilities		302	272
Long-term debt		1,035	1,088
Asset retirement obligations		2,116	2,035
Other noncurrent liabilities		75	121
Total noncurrent liabilities		3,226	3,244
Total liabilities		3,528	3,516
Baltimore Gas and Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		113	17	29	23
Restricted cash		3	1	1	24
Accounts receivable, net
Customer		296	375
Other		96	94
Inventory, net
Materials and Supplies		39	40
Other current assets		10	3
Total current assets		798	811
Property, plant and equipment, net		8,039	7,602
Other noncurrent assets		7	4
Total assets		9,541	9,104
Accounts payable		277	265
Accrued expenses		146	164
Other		23	24
Total current liabilities		707	760
Long-term debt		2,876	2,577
Asset retirement obligations		24	23
Other noncurrent liabilities		75	56
Total liabilities		6,297	5,963
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		153	30	137	170
Restricted cash		42	42	43	43
Accounts receivable, net
Customer		500	486
Other		266	206
Inventory, net
Materials and Supplies		149	151
Other current assets		60	75
Total current assets		1,700	1,551
Property, plant and equipment, net		13,167	12,498
Goodwill		4,005	4,005
Other noncurrent assets		67	70
Total assets	[4]	21,957	21,247
Long-term debt due within one year		117	396
Accounts payable		505	348
Accrued expenses		269	261
Unamortized energy contract liabilities		125	188
Other		57	81
Total current liabilities		1,769	1,931
Long-term debt		5,972	5,478
Asset retirement obligations		53	16
Unamortized energy contract liabilities		474	561
Other noncurrent liabilities		395	389
Total liabilities	[4]	12,791	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, net
Materials and Supplies	[2]	0	0
Other current assets	[2]	3	4
Total current assets	[2]	10	10
Property, plant and equipment, net	[2]	0	0
Nuclear decommissioning trust funds	[2]	0	0
Other noncurrent assets	[2]	26	31
Total noncurrent assets	[2]	26	31
Total assets	[2]	36	41
Long-term debt due within one year	[2]	25	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]	26	36
Long-term debt	[2]	52	66
Asset retirement obligations	[2]	0	0
Other noncurrent liabilities	[2]	0	0
Total noncurrent liabilities	[2]	52	66
Total liabilities	[2]	78	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		11	2	5	101
Restricted cash		7	6	$ 9	$ 9
Accounts receivable, net
Customer		144	92
Other		59	56
Inventory, net
Other current assets		21	2
Total current assets		317	258
Property, plant and equipment, net		2,883	2,706
Other noncurrent assets		41	45
Total assets	[5]	3,694	3,445
Long-term debt due within one year		22	281
Accounts payable		149	118
Accrued expenses		38	33
Other		9	8
Total current liabilities		566	619
Long-term debt		1,078	840
Other noncurrent liabilities		26	25
Total liabilities	[5]	2,621	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, net
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		19	23
Total noncurrent assets		19	23
Total assets		26	29
Long-term debt due within one year		22	31
Accounts payable		0	0
Accrued expenses		1	1
Unamortized energy contract liabilities		0	0
Other		0	0
Total current liabilities		23	32
Long-term debt		45	58
Asset retirement obligations		0	0
Other noncurrent liabilities		0	0
Total noncurrent liabilities		45	58
Total liabilities		$ 68	$ 90
[1]	Exelon’s consolidated assets include $9,804 million and $9,597 million at September 30, 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 $3,606 million and $3,618 million at September 30, 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 for additional information.
[2]	Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.
[3]	Generation’s consolidated assets include $9,768 million and $9,556 million at September 30, 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 $3,528 million and $3,516 million at September 30, 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 for additional information.
[4]	PHI’s consolidated total assets include $36 million and $41 million at September 30, 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 $78 million and $102 million at September 30, 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 for additional information.
[5]	ACE’s consolidated total assets include $26 million and $29 million at September 30, 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 $68 million and $90 million at September 30, 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 for additional information.

Variable Interest Entities - Su

Variable Interest Entities - Summary of Significant Unconsolidated VIEs (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total assets	[1]	$ 1,087	$ 1,134
Total liabilities	[1]	257	265
Exelon's ownership interest in VIE	[1]	232	251
Other ownership interests in VIE	[1]	598	618
Registrants' maximum exposure to loss		15
Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		232	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]	0	2
Commercial Agreement Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	606	625
Total liabilities	[1]	36	37
Exelon's ownership interest in VIE	[1]	0	0
Other ownership interests in VIE	[1]	570	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]	0	2
Equity Investment VIE [Member]
Variable Interest Entity [Line Items]
Total assets	[1]	481	509
Total liabilities	[1]	221	228
Exelon's ownership interest in VIE	[1]	232	251
Other ownership interests in VIE	[1]	28	30
Equity Investment VIE [Member] | Carrying amount of equity method investments
Variable Interest Entity [Line Items]
Registrants' maximum exposure to loss		232	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		15
Held-to-maturity Securities Pledged as Collateral	[3]	9	39
Payables to ZionSolutions, LLC	[4],[5]	$ 9	$ 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 $9 million and $39 million as of September 30, 2018 and December 31, 2017, respectively; offset by payables to ZionSolutions, LLC of $9 million and $37 million as of September 30, 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 — Asset Retirement Obligations for additional information.
[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 Di_2

Mergers, Acquisitions, and Dispositions - Narrative (Details) - USD ($) $ in Millions	Jul. 09, 2018	Apr. 04, 2018	Feb. 28, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross								$ 57	$ 208
Bargain Purchase Gain					$ 0	$ 7		0	233
Disposal Group, Including Discontinued Operation, Assets, Current					910			910		$ 0
Disposal Group, Including Discontinued Operation, Liabilities, Current					788			788		0
Asset Retirement Obligation, Revision of Estimate								(20)
Fitzpatrick [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs					0			0
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross								57	208
Bargain Purchase Gain					0	7		0	233
Disposal Group, Including Discontinued Operation, Assets, Current					910			910		0
Disposal Group, Including Discontinued Operation, Liabilities, Current					788			788		0
Asset Retirement Obligation, Revision of Estimate					84			0
Proceeds from Divestiture of Businesses			$ 87
Exelon Generation Co L L C [Member] | FirstEnergy [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 140
Exelon Generation Co L L C [Member] | Handley [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 62
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross										110
Business Combination, Consideration Transferred				$ 289						289
Business Combination, Consideration Transferred, Other				179						54
Bargain Purchase Gain						7	$ 226			233
Business Combination, Integration Related Costs					$ 0	$ 16		$ 0	$ 47
Exelon Generation Co L L C [Member] | Fitzpatrick [Member] | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross										$ 125
Business Combination, Consideration Transferred				$ 110

Mergers, Acquisitions, and Di_3

Mergers, Acquisitions, and Dispositions Purchase Price Allocation Table - FitzPatrick (Details) - USD ($) $ in Millions		Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						$ 57	$ 208
Bargain Purchase Gain			$ 0	$ 7		0	233
Exelon Generation Co L L C [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross						57	208
Bargain Purchase Gain			$ 0	7		$ 0	$ 233
Exelon Generation Co L L C [Member] | Fitzpatrick [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross								$ 110
Business Combination, Consideration Transferred		$ 289						289
Business Combination, Consideration Transferred, Other		179						54
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]
Payments to Acquire Businesses, Gross								$ 125
Business Combination, Consideration Transferred		$ 110
[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 information regarding SNF obligations to the DOE.

Revenue from Contracts with C_3

Revenue from Contracts with Customers Revenue from Contracts with Customers - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Gross	$ 30		$ 30		$ 26
Capitalized Contract Cost, Amortization	6	$ 7	16	$ 24
Exelon Generation Co L L C [Member]
Capitalized Contract Cost [Line Items]
Capitalized Contract Cost, Gross	30		30		$ 26
Capitalized Contract Cost, Amortization	$ 6	$ 7	$ 16	$ 24

Revenue from Contracts with C_4

Revenue from Contracts with Customers Contract Assets and Liabilites (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net, Current	$ 197	$ 283
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	34
Contract with Customer, Asset, Reclassified to Receivable	(120)
Contract with Customer, Liability, Current	37	35
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	389
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	(387)
Exelon Generation Co L L C [Member]
Change in Contract with Customer, Asset and Liability [Abstract]
Contract with Customer, Asset, Net, Current	197	283
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	34
Contract with Customer, Asset, Reclassified to Receivable	(120)
Contract with Customer, Liability, Current	37	$ 35
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	389
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized	$ (387)

Revenue from Contracts with C_5

Revenue from Contracts with Customers Revenue Remaining Performance Obligation (Details) $ in Millions	Sep. 30, 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	$ 647
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	302
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	119
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	47
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	137
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	1,252
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	647
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	302
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	119
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	47
Exelon Generation Co L L C [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	137
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	$ 1,252

Regulatory Matters - Narrative

Regulatory Matters - Narrative (Details) - USD ($) $ in Millions		Sep. 07, 2018	Aug. 29, 2018	Aug. 28, 2018	Aug. 21, 2018	Aug. 13, 2018	Jul. 01, 2018	Jun. 27, 2018	Jun. 15, 2018	Jun. 08, 2018	Jun. 02, 2018	May 22, 2018	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	Oct. 18, 2017	Aug. 17, 2017	Jul. 14, 2017	May 01, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2018		Dec. 31, 2022	Dec. 31, 2023	Jun. 30, 2018	Apr. 21, 2016
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	$ 9,342			$ 9,288	$ 9,342
Regulatory Liabilities																																	10,445			10,388	10,445
Revenues																																	9,403		$ 8,768		27,170		$ 25,180
Payments to Acquire Property, Plant, and Equipment																																					5,497		5,556
Other Receivables																																	1,246			1,132	1,246
Accounts Payable, Current																																	3,348			3,532	3,348
PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												$ 220
Accounts Payable, Current																																												176
Maximum [Member] | One-Time Revenue Adjustment [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets																																	73				73
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																																	5,278		4,750		15,368		13,843
Payments to Acquire Property, Plant, and Equipment																																					1,660		1,654
License Costs																																					35
Other Receivables																																	278			321	278
Accounts Payable, Current																																	1,450			1,773	1,450
Exelon Generation Co L L C [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												0
Accounts Payable, Current																																												41
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																																	1,485			1,279	1,485
Regulatory Liabilities																																	6,638			6,577	6,638
Tax Savings From Tax Cuts and Jobs Act																								$ 201
Revenues																																	1,598		1,571		$ 4,508		4,227
Public Utilities, Requested Increase (Decrease), Amount											$ 38																													$ (44)	[1],[2]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											1																													(26)	[1],[2]
Prior Year Revenue Adjustment																																								$ 18
Public Utilities, Approved Rate Increase (Decrease), Amount											$ (39)
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[3]																																				11.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[4]																																							8.32%
Payments to Acquire Property, Plant, and Equipment																																					$ 1,540		1,698
Other Receivables																																	450			266	450
Accounts Payable, Current																																	576			568	$ 576
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Increase (Decrease), Amount																																								$ 58
Public Utilities, Requested Rate Increase (Decrease), Percentage																																								8.69%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																																								$ 23
Public Utilities, Requested Equity Capital Structure, Percentage																																								6.52%
Commonwealth Edison Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												122
Accounts Payable, Current																																												0
Commonwealth Edison Co [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 69
Public Utilities, Approved Return on Equity, Percentage																																					55.00%
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																																	51				$ 51
Commonwealth Edison Co [Member] | Subsequent Event [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																																								$ (35)
Public Utilities, Approved Rate Increase (Decrease), Percentage																																								8.69%
Public Utilities, Approved Equity Capital Structure, Percentage																																								6.52%
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	532			410	532
Regulatory Liabilities																																	740			690	740
Tax Savings From Tax Cuts and Jobs Act															$ 71
Revenues																																	757		715		2,275		2,141
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																																$ 22
Public Utilities, Requested Equity Capital Structure, Percentage																																11.00%
Prior Year Revenue Adjustment																																					6
Payments to Acquire Property, Plant, and Equipment																																					615		537
Other Receivables																																	190			105	190
Accounts Payable, Current																																	387			370	387
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				$ 25											$ 82
Public Utilities, Requested Equity Capital Structure, Percentage															10.95%
PECO Energy Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												85
Accounts Payable, Current																																												0
PECO Energy Co [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																					20
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	597			571	597
Regulatory Liabilities																																	1,165			1,163	1,165
Tax Savings From Tax Cuts and Jobs Act																							103
Revenues																																	731		738		$ 2,369		2,363
Public Utilities, Requested Increase (Decrease), Amount	[1],[2]																																							$ 10
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]																																							26
Prior Year Revenue Adjustment	[1],[2]																																							$ 4
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[3]																																				10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[4]																																							7.61%
Payments to Acquire Property, Plant, and Equipment																																					$ 667		615
Other Receivables																																	96			94	96
Accounts Payable, Current																																	277			265	277
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
Public Utilities, Requested Increase (Decrease), Amount										$ 61
Public Utilities, Requested Return on Equity, Percentage										10.50%
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] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												0
Accounts Payable, Current																																												51
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 18
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																																	13				13
Baltimore Gas and Electric Company [Member] | Subsequent Event [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																																											$ (200)
Payments to Acquire Property, Plant, and Equipment																																											$ 732
Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	2,895			3,047	2,895
Regulatory Liabilities																																	1,882			1,928	1,882
Revenues																																	1,361		1,310		3,688		3,557
Payments to Acquire Property, Plant, and Equipment																																					988		995
Other Receivables																																	266			206	266
Accounts Payable, Current																																	505			348	505
Pepco Holdings LLC [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												13
Accounts Payable, Current																																												84
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																																	9				9
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	946			891	946
Regulatory Liabilities																																	764			832	764
Revenues																																	628		604		1,708		1,649
Public Utilities, Requested Increase (Decrease), Amount	[1],[2]																																							6
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]																																							8
Prior Year Revenue Adjustment	[1],[2]																																							$ 2
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[3]																																							10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[4]																																							7.82%
Payments to Acquire Property, Plant, and Equipment																																					475		439
Other Receivables																																	102			87	102
Accounts Payable, Current																																	234			139	234
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																					$ 39
Tax Savings From Tax Cuts and Jobs Act Through Effective Date		$ (20)				$ (19)
Public Utilities, Requested Increase (Decrease), Amount																						$ 11			$ 41	$ 66
Public Utilities, Requested Rate Increase (Decrease), Percentage													9.50%												10.10%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount													$ 15	$ (24)				$ 3
Public Utilities, Requested Return on Equity, Percentage														9.525%												10.10%
Public Utilities, Rate Credit													$ 10
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												0
Accounts Payable, Current																																												84
Potomac Electric Power Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 13
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																																	3				3
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	301			314	301
Regulatory Liabilities																																	654			635	654
Revenues																																	328		327		1,001		971
Public Utilities, Requested Increase (Decrease), Amount	[1],[2]																																							14
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]																																							27
Public Utilities, Requested Return on Equity, Percentage																														10.10%
Prior Year Revenue Adjustment	[1],[2]																																							$ 13
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[3]																																							10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[4]																																							7.29%
Public Utilities, Interim Rate Increase (Decrease), Amount																													$ 2.5
Payments to Acquire Property, Plant, and Equipment																																					254		294
Other Receivables																																	53			38	53
Accounts Payable, Current																																	104			82	104
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
Tax Savings From Tax Cuts and Jobs Act Through Effective Date		(1)
Public Utilities, Requested Increase (Decrease), Amount		$ (4)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				4
Public Utilities, Requested Return on Equity, Percentage		9.70%
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
Tax Savings From Tax Cuts and Jobs Act Through Effective Date								$ 3
Public Utilities, Requested Increase (Decrease), Amount								$ (7)																							$ 27
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																				12								$ 19
Public Utilities, Requested Return on Equity, Percentage								9.70%																							10.10%
Public Utilities, Approved Rate Increase (Decrease), Amount																											$ (13)
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] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												10
Accounts Payable, Current																																												0
Delmarva Power and Light Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 12
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																																	5				5
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	427			430	427
Regulatory Liabilities																																	428			422	428
Tax Savings From Tax Cuts and Jobs Act																			$ 23
Revenues																																	406		$ 370		981		915
Public Utilities, Requested Increase (Decrease), Amount					$ 40				$ 40																															4	[1],[2]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]																																							0
Prior Year Revenue Adjustment	[1],[2]																																							$ (4)
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[3]																																							10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[4]																																							8.02%
Payments to Acquire Property, Plant, and Equipment																																					247		$ 242
Other Receivables																																	59			56	59
Accounts Payable, Current																																	149			118	149
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act Through Effective Date			$ 6
Public Utilities, Requested Increase (Decrease), Amount					$ 109				$ 99.7
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount																$ 13						$ 19
Public Utilities, Requested Return on Equity, Percentage					10.10%				10.10%
Public Utilities, Approved Rate Increase (Decrease), Amount												$ 33
Atlantic City Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Receivables																																												3
Accounts Payable, Current																																												0
Atlantic City Electric Company [Member] | Electric Transmission [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Tax Savings From Tax Cuts and Jobs Act																																								$ 11
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																																	1				1
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																																	18			112	18
Zero Emission Standard [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Revenues																																	61				315
Other Revenue, Net																																				150
Zero Emission Standard [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	18			112	18
Zero Emission Standard [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
Zero Emission Standard [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
Zero Emission Standard [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
Zero Emission Standard [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
Zero Emission Standard [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
Zero Emission Standard [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	0			0	0
PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																												221
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																												0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	101				101							122
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	85				85							85
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																												0
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																												14
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																												0
PJM Transmission Rate Design Settlement [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	10	[5]			10	[5]						10
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Liabilities																																	3	[5]			3	[5]						4
Under Recovered Electric Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[6]																																1				1
Under-Recovered Natural Gas Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																				8
Pension and Other Postretirement Plans Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																3,710			3,848	3,710
Pension and Other Postretirement Plans Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			0	0
Pension and Other Postretirement Plans Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]																																0			$ 0	0
PJM Transmission Rate Design Settlement [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												136
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												0
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												0
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												0
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	48				48							51
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												85
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																	$ 74				$ 74							84
PJM Transmission Rate Design Settlement [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												0
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets																																												$ 1
[1]	All rates are effective June 2018, subject to review by the FERC and other parties, which is due by fourth quarter 2018.
[2]	The initial revenue requirement changes reflect the annual benefit of lower income tax rates effective January 1, 2018 resulting from the enactment of the TCJA of $69 million, $18 million, $13 million, $12 million and $11 million for ComEd, BGE, Pepco, DPL and ACE, respectively. They do not reflect the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. See further discussion above.
[3]	As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50 basis point incentive adder for being a member of a regional transmission organization.
[4]	Represents the weighted average debt and equity return on transmission rate bases.
[5]	As of September 30, 2018, DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018, DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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 September 30, 2018, ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018, ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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]	Includes regulatory assets established at the Constellation and PHI merger dates of $401 million and $897 million, respectively, as of September 30, 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.

Regulatory Matters Regulatory M

Regulatory Matters Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions		Aug. 21, 2018	Jun. 15, 2018	Jun. 02, 2018	Mar. 02, 2018	Jan. 31, 2018	Jan. 18, 2018	Sep. 30, 2018	Dec. 31, 2018
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase				$ 38					$ (44)	[1],[2]
Annual reconciliation increase (decrease)									18
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount				$ 1					$ (26)	[1],[2]
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								8.32%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]							11.50%
Tax Savings From Tax Cuts and Jobs Act							$ 201
Commonwealth Edison Co [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage								55.00%
Tax Savings From Tax Cuts and Jobs Act									$ 69
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]								10
Annual reconciliation increase (decrease)	[1],[2]								4
Proposed Capital Expenditure	[1],[2],[5]								12
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 26
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.61%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]							10.50%
Tax Savings From Tax Cuts and Jobs Act						$ 103
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 18
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]								6
Annual reconciliation increase (decrease)	[1],[2]								2
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 8
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.82%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
Potomac Electric Power Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 13
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase	[1],[2]								14
Annual reconciliation increase (decrease)	[1],[2]								13
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 27
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								7.29%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
Delmarva Power and Light Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 12
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Initial revenue requirement (decrease) increase		$ 40	$ 40						4	[1],[2]
Annual reconciliation increase (decrease)	[1],[2]								(4)
Proposed Capital Expenditure									0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1],[2]								$ 0
Public Utilities, Approved Equity Capital Structure, Percentage	[1],[2],[3]								8.02%
Public Utilities, Approved Return on Equity, Percentage	[1],[2],[4]								10.50%
Tax Savings From Tax Cuts and Jobs Act					$ 23
Atlantic City Electric Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 11
[1]	All rates are effective June 2018, subject to review by the FERC and other parties, which is due by fourth quarter 2018.
[2]	The initial revenue requirement changes reflect the annual benefit of lower income tax rates effective January 1, 2018 resulting from the enactment of the TCJA of $69 million, $18 million, $13 million, $12 million and $11 million for ComEd, BGE, Pepco, DPL and ACE, respectively. They do not reflect the pass back or recovery of income tax-related regulatory liabilities or assets, including those established upon enactment of the TCJA. See further discussion above.
[3]	Represents the weighted average debt and equity return on transmission rate bases.
[4]	As part of the FERC-approved settlement of ComEd’s 2007 transmission rate case, the rate of return on common equity is 11.50% and the common equity component of the ratio used to calculate the weighted average debt and equity return for the transmission formula rate is currently capped at 55%. As part of the FERC-approved settlement of the ROE complaint against BGE, Pepco, DPL and ACE, the rate of return on common equity is 10.50%, inclusive of a 50 basis point incentive adder for being a member of a regional transmission organization.
[5]	BGE's transmission revenues include a FERC-approved dedicated facilities charge to recover the costs of providing transmission service to a specifically designated load by BGE.

Regulatory Matters Regulatory_2

Regulatory Matters Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in Millions		Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Regulatory Assets		$ 9,342		$ 9,288
Current		1,340		1,267
Regulatory Assets, Noncurrent		8,002		8,021
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	3,710		3,848
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		391		306
Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	583		640
Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	228		244
Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		357		166
Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		102		116
Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		716		758
Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		600		750
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		114		109
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		318		295
Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71		61
Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		260		258
Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	251		82
Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		45		27
Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		561		596
Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	44		45
Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		55
COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		5
Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		35
Recoverable Vacation Pay [Member]
Regulatory Assets [Line Items]
Regulatory Assets		24		19
Stranded Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		57		79
CAP Arrearage [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		8
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		555		529
DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		74		67
Under funded Benefit Post Retirement Obligation [Member] | Constellation Energy Group LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		401		440
Under funded Benefit Post Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		897		953
PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			$ 136
Exelon Generation Co L L C [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
Commonwealth Edison Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1,485		1,279
Current		256		225
Regulatory Assets, Noncurrent		1,229		1,054
Commonwealth Edison Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	142		155
Commonwealth Edison Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	228		244
Commonwealth Edison Co [Member] | Energy Efficiency Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		357		166
Commonwealth Edison Co [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		34		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		76		73
Commonwealth Edison Co [Member] | Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		299		273
Commonwealth Edison Co [Member] | Under Recovered Uncollectible Accounts Expense [Member]
Regulatory Assets [Line Items]
Regulatory Assets		71		61
Commonwealth Edison Co [Member] | Renewable Energy Program [Member]
Regulatory Assets [Line Items]
Regulatory Assets		259		256
Commonwealth Edison Co [Member] | Under Recovered Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[4],[5],[6],[7],[8]	7		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	[9],[10],[11]	0		0
Commonwealth Edison Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		12		8
Commonwealth Edison Co [Member] | Annual Reconciliations [Member]
Regulatory Assets [Line Items]
Regulatory Assets		165		186
Commonwealth Edison Co [Member] | Recoverable Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		63		58
Commonwealth Edison Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
PECO Energy Co [Member]
Regulatory Assets [Line Items]
Regulatory Assets		532		410
Current		84		29
Regulatory Assets, Noncurrent		448		381
PECO Energy Co [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	0		0
PECO Energy Co [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		381		297
PECO Energy Co [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	27		36
PECO Energy Co [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		19		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	[4],[5],[6],[7],[8]	50		1
PECO Energy Co [Member] | Under Recovered Electric Energy And Transmission Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[6]	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		2		1
PECO Energy Co [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	0		0
PECO Energy Co [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		11		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		10		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		9		16
PECO Energy Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
Baltimore Gas and Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		597		571
Current		195		174
Regulatory Assets, Noncurrent		402		397
Baltimore Gas and Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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]	198		214
Baltimore Gas and Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		15		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	[4],[5],[6],[7],[8]	72		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		291		285
Baltimore Gas and Electric Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	4		6
Baltimore Gas and Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	0		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		117		129
Baltimore Gas and Electric Company [Member] | Legacy AMI [Member]
Regulatory Assets [Line Items]
Regulatory Assets		48		53
Baltimore Gas and Electric Company [Member] | Recoverable Smart Meter Related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		33		32
Baltimore Gas and Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		5
Baltimore Gas and Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14		7
Baltimore Gas and Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets		48	51
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		1		10
Baltimore Gas and Electric Company [Member] | UnderRecoveredNaturalGasDecouplingRevenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets		17		4
Pepco Holdings LLC [Member]
Regulatory Assets [Line Items]
Regulatory Assets		2,895		3,047
Current		521		554
Regulatory Assets, Noncurrent		2,374		2,493
Pepco Holdings LLC [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	0		0
Pepco Holdings LLC [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		9
Pepco Holdings LLC [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	216		235
Pepco Holdings LLC [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		68		73
Pepco Holdings LLC [Member] | Fair Value Of Long Term Debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets		581		619
Pepco Holdings LLC [Member] | Fair Value Of Supply Contract [Member]
Regulatory Assets [Line Items]
Regulatory Assets		600		750
Pepco Holdings LLC [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1		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],[5],[6],[7],[8]	122		52
Pepco Holdings LLC [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		45		27
Pepco Holdings LLC [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		268		310
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	40		39
Pepco Holdings LLC [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		41
Pepco Holdings LLC [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		5
Pepco Holdings LLC [Member] | Workers Compensation and Long-Term Disability [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		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		57		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		555		529
Pepco Holdings LLC [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Pepco Holdings LLC [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		47		39
Pepco Holdings LLC [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			85
Potomac Electric Power Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		946		891
Current		284		213
Regulatory Assets, Noncurrent		662		678
Potomac Electric Power Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	0		0
Potomac Electric Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		10		9
Potomac Electric Power Company [Member] | Advanced Metering Infrastructure Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[2]	144		158
Potomac Electric Power Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		1		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	[4],[5],[6],[7],[8]	93		11
Potomac Electric Power Company [Member] | Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		11		7
Potomac Electric Power Company [Member] | Energy Efficiency And Demand Response Programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets		194		229
Potomac Electric Power Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	18		20
Potomac Electric Power Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	64		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		36		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		156		150
Potomac Electric Power Company [Member] | DC PLUG Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets		168		190
Potomac Electric Power Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets		36		29
Potomac Electric Power Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		12		8
Potomac Electric Power Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		3
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets		74	84
Potomac Electric Power Company [Member] | MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member]
Regulatory Assets [Line Items]
Regulatory Assets		9		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		301		314
Current		66		69
Regulatory Assets, Noncurrent		235		245
Delmarva Power and Light Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	72		77
Delmarva Power and Light Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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	[4],[5],[6],[7],[8]	15		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		74		81
Delmarva Power and Light Company [Member] | Merger Integration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[9],[10],[11]	12		10
Delmarva Power and Light Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	0		3
Delmarva Power and Light Company [Member] | COPCO Acquisition Adjustment [Member]
Regulatory Assets [Line Items]
Regulatory Assets		3		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		97		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		8		8
Delmarva Power and Light Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		1		7
Delmarva Power and Light Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		14		8
Delmarva Power and Light Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			0
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		1
Atlantic City Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets		427		430
Current		44		71
Regulatory Assets, Noncurrent		383		359
Atlantic City Electric Company [Member] | Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[1]	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	[2]	0		0
Atlantic City Electric Company [Member] | Electric Distribution Formula Rate [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[3]	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		6		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],[5],[6],[7],[8]	14		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	[9],[10],[11]	10		9
Atlantic City Electric Company [Member] | Under Recovered Decoupling Revenue [Member]
Regulatory Assets [Line Items]
Regulatory Assets	[12]	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		57		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		302		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		3		4
Atlantic City Electric Company [Member] | UnderRecoveredElectricEnergyCosts [Member]
Regulatory Assets [Line Items]
Regulatory Assets		7		15
Atlantic City Electric Company [Member] | TransmissionCost [Member]
Regulatory Assets [Line Items]
Regulatory Assets		$ 7		$ 11
Atlantic City Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Assets [Line Items]
Regulatory Assets			$ 1
[1]	Includes regulatory assets established at the Constellation and PHI merger dates of $401 million and $897 million, respectively, as of September 30, 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 September 30, 2018, BGE's regulatory asset of $198 million includes $117 million of unamortized incremental deployment costs under the program, $48 million of unamortized costs of the non-AMI meters replaced under the AMI program, and $33 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.
[3]	As of September 30, 2018, ComEd’s regulatory asset of $228 million was comprised of $165 million for the 2016, 2017 and 2018 annual reconciliations and $63 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 September 30, 2018, ACE's regulatory asset of $14 million included $7 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2018, ACE's regulatory liability of $4 million included $3 million related to the PJM Transmission Rate Design Settlement and $1 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 September 30, 2018, BGE's regulatory asset of $72 million included $48 million related to the PJM Transmission Rate Design Settlement, $14 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $7 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of September 30, 2018, BGE's regulatory liability of $7 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 September 30, 2018, ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018, ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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 September 30, 2018, DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018, DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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 September 30, 2018, Pepco's regulatory asset of $93 million included $74 million related to the PJM Transmission Rate Design Settlement, $7 million of transmission costs recoverable through its FERC approved formula rate and $12 million related to under-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.
[9]	As of September 30, 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.
[10]	As of September 30, 2018, DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $1 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of September 30, 2018, DPL’s regulatory liability of $3 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.
[11]	As of September 30, 2018, Pepco’s regulatory asset of $18 million represents previously incurred PHI integration costs, including $9 million authorized for recovery in Maryland and $9 million expected to be recovered in the District of Columbia service territory. As of 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]	Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2018, BGE had a regulatory asset of less than $1 million related to under-recovered electric revenue decoupling and a regulatory liability of $17 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 Regulatory_3

Regulatory Matters Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Millions		Sep. 30, 2018		Jun. 30, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 10,445			$ 10,388
Regulatory Liability, Current		689			523
Regulatory Liability, Noncurrent		9,756			9,865
Pension and Other Postretirement Plans Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		20			30
Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	5,054			5,241
Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2,958			3,064
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,566			1,573
Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		34			36
Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		10			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		10			35
Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4			9
Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2],[4],[5]	372	[3],[6]		111	[7]
Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	21
Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		140			63
Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		18			112
Over Recovered Uncollectible Accounts Expense [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2			2
Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[9]	3
TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	108
Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		118			82
PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities				$ 221
Commonwealth Edison Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		6,638			6,577
Regulatory Liability, Current		320			249
Regulatory Liability, Noncurrent		6,318			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]	2,418			2,479
Commonwealth Edison Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2,469			2,528
Commonwealth Edison Co [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,370			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		3			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	[2],[4],[5]	204	[3],[6]		47	[7]
Commonwealth Edison Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	0
Commonwealth Edison Co [Member] | Renewable Portfolio Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		140			63
Commonwealth Edison Co [Member] | Zero Emission Standard [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		18			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	[9]	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		16			6
Commonwealth Edison Co [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		464			484
Commonwealth Edison Co [Member] | Over Recovered Electric Supply Cost [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		72			14
Commonwealth Edison Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		101		122
Commonwealth Edison Co [Member] | Renewable energy Requirements [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		31			33
PECO Energy Co [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		740			690
Regulatory Liability, Current		159			141
Regulatory Liability, Noncurrent		581			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	[1]
PECO Energy Co [Member] | Nuclear Decommissioning [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		489			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		5			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		10			35
PECO Energy Co [Member] | Gas Distribution Tax Repairs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4			9
PECO Energy Co [Member] | Over Recovered Energy And Transmission Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2],[4],[5]	143	[3],[6]		60	[7]
PECO Energy Co [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	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	[9]	0
PECO Energy Co [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	61
PECO Energy Co [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		21			24
PECO Energy Co [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		85		85
PECO Energy Co [Member] | Default Service Provider Program [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		43			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		12			12
Baltimore Gas and Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,165			1,163
Regulatory Liability, Current		95			62
Regulatory Liability, Noncurrent		1,070			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]	1,015			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		67			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	[2],[4],[5]	7	[3],[6]		0	[7]
Baltimore Gas and Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	17
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	[9]	0
Baltimore Gas and Electric Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	19
Baltimore Gas and Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		40			26
Baltimore Gas and Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		135			137
Baltimore Gas and Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities				0
Pepco Holdings LLC [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		1,882			1,928
Regulatory Liability, Current		99			56
Regulatory Liability, Noncurrent		1,783			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]	1,621			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		129			130
Pepco Holdings LLC [Member] | Deferred Lease Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		34			36
Pepco Holdings LLC [Member] | Energy Efficiency Demand Response Programs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2			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],[4],[5]	18	[3],[6]		4	[7]
Pepco Holdings LLC [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	4
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		2			2
Pepco Holdings LLC [Member] | Merger Integration Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[9]	3
Pepco Holdings LLC [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	28
Pepco Holdings LLC [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		41			26
Pepco Holdings LLC [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities				14
Potomac Electric Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		764			832
Regulatory Liability, Current		5			3
Regulatory Liability, Noncurrent		759			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]	734			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	[2],[4],[5]	0	[3],[6]		0	[7]
Potomac Electric Power Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	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	[9]	0
Potomac Electric Power Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	6
Potomac Electric Power Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		4			3
Potomac Electric Power Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		136			147
Potomac Electric Power Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities				0
Delmarva Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		654			635
Regulatory Liability, Current		67			42
Regulatory Liability, Noncurrent		587			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]	493			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		109			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	[2],[4],[5]	14	[3],[6]		1	[7]
Delmarva Power and Light Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	4
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	[9]	3
Delmarva Power and Light Company [Member] | TCJA income tax benefit over-recoveries [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[10]	8
Delmarva Power and Light Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		23			14
Delmarva Power and Light Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		145			148
Delmarva Power and Light Company [Member] | Over Recovered Electric Energy and Gas Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[5]	4
Delmarva Power and Light Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		10	[5]	10
Atlantic City Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		428			422
Regulatory Liability, Current		27			11
Regulatory Liability, Noncurrent		401			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]	394			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		2			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],[4],[5]	4	[3],[6]		3	[7]
Atlantic City Electric Company [Member] | Over Recovered Decoupling Revenue [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[8]	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		2			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]	14
Atlantic City Electric Company [Member] | Regulatory Liabilities Other [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		12			6
Atlantic City Electric Company [Member] | Deferred Income Tax Transmission Related [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		141			$ 147
Atlantic City Electric Company [Member] | PJM Transmission Rate Design Settlement [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		3	[5]	$ 4
Atlantic City Electric Company [Member] | Over Recovered Electric Energy Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2]	$ 1
[1]	As of September 30, 2018, includes transmission-related income tax regulatory liabilities that require FERC approval separate from the transmission formula rate of $464 million, $135 million, $136 million, $145 million and $141 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 September 30, 2018, ACE's regulatory asset of $14 million included $7 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2018, ACE's regulatory liability of $4 million included $3 million related to the PJM Transmission Rate Design Settlement and $1 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 September 30, 2018, BGE's regulatory asset of $72 million included $48 million related to the PJM Transmission Rate Design Settlement, $14 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $7 million related to under-recovered electric energy costs and $3 million of abandonment costs to be recovered upon FERC approval. As of September 30, 2018, BGE's regulatory liability of $7 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 September 30, 2018, ComEd’s regulatory asset of $7 million represents transmission costs recoverable through its FERC approved formula rate. As of September 30, 2018, ComEd’s regulatory liability of $204 million included $101 million related to the PJM Transmission Rate Design Settlement, $72 million related to over-recovered energy costs and $31 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 September 30, 2018, DPL's regulatory asset of $15 million included $14 million of transmission costs recoverable through its FERC approved formula rate and $1 million related to under-recovered electric energy costs. As of September 30, 2018, DPL's regulatory liability of $14 million included $10 million related to the PJM Transmission Rate Design Settlement and $4 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 September 30, 2018, Pepco's regulatory asset of $93 million included $74 million related to the PJM Transmission Rate Design Settlement, $7 million of transmission costs recoverable through its FERC approved formula rate and $12 million related to under-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.
[7]	As of September 30, 2018, PECO’s regulatory asset of $50 million represents the under-recovered natural gas costs under the PGC. As of December 31, 2017, PECO’s regulatory asset of $1 million is related to under-recovered costs under the TSC program. As of September 30, 2018, PECO's regulatory liability of $143 million included $85 million related to the PJM Transmission Rate Design Settlement, $43 million related to over-recovered costs under the DSP program, $3 million related to the over-recovered transmission service charges and $12 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.
[8]	Represents the electric and natural gas distribution costs recoverable from customers under BGE’s decoupling mechanism. As of September 30, 2018, BGE had a regulatory asset of less than $1 million related to under-recovered electric revenue decoupling and a regulatory liability of $17 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 September 30, 2018, DPL’s regulatory asset of $12 million represents previously incurred PHI integration costs, including $4 million authorized for recovery in Maryland, $5 million authorized for recovery in Delaware electric rates, $2 million authorized for recovery in Delaware gas rates and $1 million expected to be recovered in electric rates in the Delaware and Maryland service territories. As of September 30, 2018, DPL’s regulatory liability of $3 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.
[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 additional information on the regulatory proceedings.

Regulatory Matters Regulatory_4

Regulatory Matters Regulatory Matters - Capitalized Ratemaking Amount Not Recognized (Details) - USD ($) $ in Millions		Sep. 30, 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		$ 67	$ 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]	8	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]	50	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		9	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]	5	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 Regulatory_5

Regulatory Matters Regulatory Matters - Purchase of Receivables Programs (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		$ 379	$ 298
Allowance for Doubtful Accounts Receivable	[1]	(37)	(31)
Payments to Acquire Other Receivables, Net		342	267
Commonwealth Edison Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		120	87
Allowance for Doubtful Accounts Receivable	[1]	(19)	(14)
Payments to Acquire Other Receivables, Net		101	73
PECO Energy Co [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		91	70
Allowance for Doubtful Accounts Receivable	[1]	(5)	(5)
Payments to Acquire Other Receivables, Net		86	65
Baltimore Gas and Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		60	58
Allowance for Doubtful Accounts Receivable	[1]	(3)	(3)
Payments to Acquire Other Receivables, Net		57	55
Pepco Holdings LLC [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		108	83
Allowance for Doubtful Accounts Receivable	[1]	(10)	(9)
Payments to Acquire Other Receivables, Net		98	74
Potomac Electric Power Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		69	56
Allowance for Doubtful Accounts Receivable	[1]	(5)	(5)
Payments to Acquire Other Receivables, Net		64	51
Delmarva Power and Light Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		11	9
Allowance for Doubtful Accounts Receivable	[1]	(1)	(1)
Payments to Acquire Other Receivables, Net		10	8
Atlantic City Electric Company [Member]
Purchase Of Receivables [Line Items]
Payments to Acquire Other Receivables		28	18
Allowance for Doubtful Accounts Receivable	[1]	(4)	(3)
Payments to Acquire Other Receivables, Net		$ 24	$ 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 Asse_2

Impairment of Long-Lived Assets (Details) - Electricity Generation Plant, Non-Nuclear [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2018
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Impairment of Long-Lived Assets to be Disposed of	$ 41	$ 418	$ 460
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset				$ 41
Exelon Generation Co L L C [Member]
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Impairment of Long-Lived Assets to be Disposed of	$ 41	$ 418	$ 460
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset				$ 41

Early Plant Retirements Early_3

Early Plant Retirements Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
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%				42.59%
Facility Closing [Member] | TMI,OysterCreek [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Incurred Cost	$ 174				$ 525
Facility Closing [Member] | TMI,OysterCreek [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Incurred Cost	$ 174				$ 525
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] | Three Mile Island [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Restructuring and Related Cost, Incurred Cost		$ 114	$ 117	$ 108		$ 339

Early Plant Retirements Early_4

Early Plant Retirements Early Plant Retirements - Pretax Expense (Details) - Facility Closing [Member] - USD ($) $ in Millions		3 Months Ended				9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Three Mile Island [Member]
Restructuring and Related Cost, Accelerated Depreciation	[1],[2]		$ 109	$ 106	$ 35		$ 250
Accelerated Nuclear Fuel Amortization	[2]		4	6	2		12
Operating and maintenance	[3]		1	5	71		77
Restructuring and Related Cost, Incurred Cost			114	117	108		339
TMI,OysterCreek [Member]
Restructuring and Related Cost, Incurred Cost		$ 174				$ 525
Exelon Generation Co L L C [Member] | Three Mile Island [Member]
Restructuring and Related Cost, Accelerated Depreciation	[1],[2]		109	106	35		250
Accelerated Nuclear Fuel Amortization	[2]		4	6	2		12
Operating and maintenance	[3]		1	5	71		77
Restructuring and Related Cost, Incurred Cost			$ 114	$ 117	$ 108		$ 339
Exelon Generation Co L L C [Member] | TMI,OysterCreek [Member]
Restructuring and Related Cost, Accelerated Depreciation	[4],[5]	152				441
Accelerated Nuclear Fuel Amortization	[4]	18				52
Operating and maintenance	[6]	4				32
Restructuring and Related Cost, Incurred Cost		$ 174				$ 525
[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 and Oyster Creek for the three and nine months ended September 30, 2018. The Oyster Creek year-to-date amounts are from February 2, 2018 through September 17, 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. It does not include remeasurement of the Oyster Creek ARO. Refer to Note 13 - Asset Retirement Obligations for additional detail.

Early Plant Retirements Early_5

Early Plant Retirements Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Implications of Potential Early Plant Retirement [Line Items]
Completed plant, net		$ 75,840	$ 74,202
Salem [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and Supplies Inventory		45
Nuclear Fuel Inventory, Net of Amortization		114
Completed plant, net		605
Construction Work in Progress		34
Asset Retirement Obligation		(455)
Mystic Generating Station [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and Supplies Inventory		21
Nuclear Fuel Inventory, Net of Amortization		18
Completed plant, net		877
Construction Work in Progress		5
Prepaid Expense	[1]	15
Asset Retirement Obligation		(5)
Accrued Expenses	[1]	$ (2)
[1]	Reflects ending balances only as they relate to Mystic's Long-term Service Agreement.

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Narrative (Details)	Sep. 30, 2018USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	$ 71,000,000
Forward Power Basis	3.38
Forward Gas Basis	0.46
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	135,000,000
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	208,000,000
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	349,000,000
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	$ 227,000,000

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		$ 390	$ 389
Spent Nuclear Fuel Obligation, Noncurrent		1,164	1,147
Unamortized debt issuance costs		219	201
Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		1
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	834	929
Long-term debt (including amounts due within one year)	[2],[3]	35,290	34,264
Long-term debt to financing trust	[4]	390	389
Spent Nuclear Fuel Obligation, Noncurrent		1,164	1,147
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	834	929
Long-term debt (including amounts due within one year)	[2],[3]	35,687	36,705
Long-term debt to financing trust	[4]	411	431
Spent Nuclear Fuel Obligation, Noncurrent		993	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	0	0
Long-term debt to financing trust	[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 liabilities	[1]	834	929
Long-term debt (including amounts due within one year)	[2],[3]	33,608	34,735
Long-term debt to financing trust	[4]	0	0
Spent Nuclear Fuel Obligation, Noncurrent		993	936
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	2,079	1,970
Long-term debt to financing trust	[4]	411	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		1,164	1,147
Unamortized debt issuance costs		53	60
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]		2
Long-term debt (including amounts due within one year)	[2],[3]	8,842	8,990
Spent Nuclear Fuel Obligation, Noncurrent		1,164	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 liabilities	[1]		2
Long-term debt (including amounts due within one year)	[2],[3]	9,024	9,512
Spent Nuclear Fuel Obligation, Noncurrent		993	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[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 liabilities	[1]		2
Long-term debt (including amounts due within one year)	[2],[3]	7,563	7,839
Spent Nuclear Fuel Obligation, Noncurrent		993	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[2],[3]	1,461	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
Unamortized debt issuance costs		64	52
Commonwealth Edison Co [Member] | Financing Trusts [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		1
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[2],[3]	8,100	7,601
Long-term debt to financing trust	[4]	205	205
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[2],[3]	8,317	8,418
Long-term debt to financing trust	[4]	214	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]
Long-term debt (including amounts due within one year)	[2],[3]	0	0
Long-term debt to financing trust	[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]
Long-term debt (including amounts due within one year)	[2],[3]	8,317	8,418
Long-term debt to financing trust	[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]
Long-term debt (including amounts due within one year)	[2],[3]	0	0
Long-term debt to financing trust	[4]	214	227
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt to financing trust		184	184
Unamortized debt issuance costs		23	17
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	[2],[3]	3,083	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]
Long-term debt (including amounts due within one year)	[2],[3]	3,180	3,194
Long-term debt to financing trust	[4]	196	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]
Long-term debt (including amounts due within one year)	[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]
Long-term debt (including amounts due within one year)	[2],[3]	3,130	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]
Long-term debt (including amounts due within one year)	[2],[3]	50	0
Long-term debt to financing trust	[4]	196	204
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		19	17
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]		77
Long-term debt (including amounts due within one year)	[2],[3]	2,876	2,577
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]		77
Long-term debt (including amounts due within one year)	[2],[3]	2,933	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[2],[3]	0	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 liabilities	[1]		77
Long-term debt (including amounts due within one year)	[2],[3]	2,933	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[2],[3]	0	0
Pepco Holdings LLC [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		11	6
Pepco Holdings LLC [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	334	350
Long-term debt (including amounts due within one year)	[2],[3]	6,089	5,874
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	334	350
Long-term debt (including amounts due within one year)	[2],[3]	5,891	6,019
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	0	0
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	334	350
Long-term debt (including amounts due within one year)	[2],[3]	5,323	5,722
Pepco Holdings LLC [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	568	297
Potomac Electric Power Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		34	32
Potomac Electric Power Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	64	26
Long-term debt (including amounts due within one year)	[2],[3]	2,625	2,540
Potomac Electric Power Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	64	26
Long-term debt (including amounts due within one year)	[2],[3]	2,991	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 liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[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 liabilities	[1]	64	26
Long-term debt (including amounts due within one year)	[2],[3]	2,890	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 liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	101	9
Delmarva Power and Light Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		12	11
Delmarva Power and Light Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]		216
Long-term debt (including amounts due within one year)	[2],[3]	1,494	1,300
Delmarva Power and Light Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]		216
Long-term debt (including amounts due within one year)	[2],[3]	1,495	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[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 liabilities	[1]		216
Long-term debt (including amounts due within one year)	[2],[3]	1,299	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 liabilities	[1]		0
Long-term debt (including amounts due within one year)	[2],[3]	196	0
Atlantic City Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Unamortized debt issuance costs		4	5
Atlantic City Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	270	108
Long-term debt (including amounts due within one year)	[2],[3]	1,100	1,121
Atlantic City Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	[1]	270	108
Long-term debt (including amounts due within one year)	[2],[3]	1,158	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 liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[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 liabilities	[1]	270	108
Long-term debt (including amounts due within one year)	[2],[3]	887	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 liabilities	[1]	0	0
Long-term debt (including amounts due within one year)	[2],[3]	$ 271	$ 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 $219 million, $53 million, $64 million, $23 million, $19 million, $11 million, $34 million, $12 million and $4 million for Exelon, Generation, ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, as of September 30, 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, government-backed fixed rate non-recourse debt and loan agreements.
[4]	Includes unamortized debt issuance costs which are not fair valued of $1 million and $1 million for Exelon and ComEd, respectively, as of September 30, 2018 and December 31, 2017.

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		$ 329			$ 329				$ 232
Derivative Liability, Noncurrent		(482)			(482)				(409)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative, Collateral, Right to Reclaim Cash		37			37				77
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		4			4				0
Derivative Asset, Notional Amount		915			915				811
Margin Deposit Assets		(166)			(166)				117
Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		330			330				389
Restricted cash member [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		85			85				145
Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		163			163				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		89			89				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		0			0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[1]	1,906			1,906				656
Total Assets		16,938			16,938				15,716
Deferred Compensation Liability, Current and Noncurrent		(142)			(142)				(145)
Total Liabilities		(953)			(953)				(786)
Total net assets (liabilities)		15,985			15,985				14,930
Alternative Investment, Fair Value Disclosure		3,824			3,824				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		(800)			(800)				(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		(4,304)			(4,304)				(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		(127)			(127)				(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]	3,631			3,631				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		(11)			(11)				(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		(10)			(10)				(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		(2)			(2)				(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		1			1				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]	13,576			13,576				13,431
Alternative Investment, Fair Value Disclosure	[4]	3,824			3,824				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]	370			370				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		6,757			6,757				7,254
Alternative Investment, Fair Value Disclosure		1,942			1,942				2,176
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5,087			5,087				4,736
Alternative Investment, Fair Value Disclosure		854			854				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		1,860			1,860				1,865
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,130			2,130				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		49			49				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		165			165				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]	883			883				557
Alternative Investment, Fair Value Disclosure	[6]	854			854				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		569			569				528
Alternative Investment, Fair Value Disclosure		235			235				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		303			303				222
Alternative Investment, Fair Value Disclosure		303			303				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		490			490				471
Alternative Investment, Fair Value Disclosure		490			490				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	[7]	9			9				39
Alternative Investment, Fair Value Disclosure	[7]	0			0				24
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		9			9				2
Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure									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									36
Alternative Investment, Fair Value Disclosure									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]	250			250				240
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48			48				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		76			76				58
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		110			110				93
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		4,370			4,370				4,225
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		174			174				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]	(3,419)			(3,419)				(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		1,125			1,125				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		20			20				9
Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				6
Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		21			21				10
Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		(1)			(1)				(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		52			52				37
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		16			16				12
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		18			18				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]	1,906			1,906				656
Total Assets		7,558			7,558				6,980
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		(82)			(82)				(63)
Total net assets (liabilities)		7,476			7,476				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		(82)			(82)				(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		(329)			(329)				(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			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]	247			247				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			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				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		0			0				(1)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		0			0				2
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	5,515			5,515				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]	278			278				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		3,206			3,206				4,163
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,031			2,031				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				0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,031			2,031				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				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				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				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				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				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				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	[7]	9			9				2
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		9			9				2
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure									0
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
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]	124			124				135
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		48			48				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		76			76				58
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				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		234			234				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			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]	(230)			(230)				(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		4			4				(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		0			0				(2)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				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				0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				(2)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
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				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		100			100				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				0
Total Assets		4,094			4,094				3,793
Deferred Compensation Liability, Current and Noncurrent		(142)			(142)				(145)
Total Liabilities		(317)			(317)				(329)
Total net assets (liabilities)		3,777			3,777				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		(164)			(164)				(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		(2,056)			(2,056)				(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		(95)			(95)				(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]	1,987			1,987				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		(11)			(11)				(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		(10)			(10)				(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		(2)			(2)				(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		1			1				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]	3,671			3,671				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]	92			92				85
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,608			1,608				915
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,971			1,971				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		1,629			1,629				1,614
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		99			99				52
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49			49				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		165			165				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]	29			29				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				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				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				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	[7]	0			0				1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			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
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]	89			89				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				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				0
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		73			73				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		2,117			2,117				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		84			84				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]	(1,887)			(1,887)				(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		314			314				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		20			20				11
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				6
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		21			21				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		(1)			(1)				(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				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		16			16				12
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		94			94				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				0
Total Assets		1,462			1,462				1,409
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		(554)			(554)				(394)
Total net assets (liabilities)		908			908				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		(554)			(554)				(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		(1,919)			(1,919)				(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		(32)			(32)				(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]	1,397			1,397				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				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				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				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				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]	566			566				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				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		1			1				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		231			231				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		231			231				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				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				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				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				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		334			334				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				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				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	[7]	0			0				12
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			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									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]	37			37				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				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				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		37			37				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		2,019			2,019				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		90			90				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]	(1,302)			(1,302)				(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		807			807				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				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				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				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				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		52			52				37
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				0
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)		305			305				211
Derivative Liability, Noncurrent		(237)			(237)				(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		183			183				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		57			57				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]	1,099			1,099				168
Total Assets		15,934			15,934				15,035
Deferred Compensation Liability, Current and Noncurrent		(36)			(36)				(38)
Total Liabilities		(578)			(578)				(423)
Total net assets (liabilities)		15,356			15,356				14,612
Alternative Investment, Fair Value Disclosure		3,824			3,824				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		(541)			(541)				(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		(4,045)			(4,045)				(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		(127)			(127)				(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]	3,631			3,631				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)			(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			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		(2)			(2)				(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		1			1				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]	13,576			13,576				13,431
Alternative Investment, Fair Value Disclosure	[4]	3,824			3,824				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]	370			370				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		6,757			6,757				7,254
Alternative Investment, Fair Value Disclosure		1,942			1,942				2,176
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		5,087			5,087				4,736
Alternative Investment, Fair Value Disclosure		854			854				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		1,860			1,860				1,865
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,130			2,130				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		49			49				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		165			165				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]	883			883				557
Alternative Investment, Fair Value Disclosure	[6]	854			854				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		569			569				528
Alternative Investment, Fair Value Disclosure		235			235				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		303			303				222
Alternative Investment, Fair Value Disclosure		303			303				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		490			490				471
Alternative Investment, Fair Value Disclosure		490			490				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	[7]	9			9				39
Alternative Investment, Fair Value Disclosure	[7]	0			0				24
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		9			9				2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure									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									36
Alternative Investment, Fair Value Disclosure									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]	53			53				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				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		25			25				23
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		23			23				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		4,370			4,370				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		174			174				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]	(3,419)			(3,419)				(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		1,125			1,125				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		20			20				6
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				3
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		21			21				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		(1)			(1)				(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		52			52				37
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				0
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]	1,099			1,099				168
Total Assets		6,657			6,657				6,385
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		(82)			(82)				(63)
Total net assets (liabilities)		6,575			6,575				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		(82)			(82)				(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		(329)			(329)				(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			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]	247			247				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			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				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		0			0				(1)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total mark-to-market derivative liabilities		0			0				2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[4]	5,515			5,515				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]	278			278				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		3,206			3,206				4,163
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,031			2,031				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				0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		2,031			2,031				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				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				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				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				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				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				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	[7]	9			9				2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		9			9				2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure									0
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
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]	30			30				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				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		25			25				23
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				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		234			234				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			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]	(230)			(230)				(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		4			4				(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		0			0				(2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				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				0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effectsofnettingandallocationofcollateral1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				(2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
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				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				0
Total Assets		4,028			4,028				3,729
Deferred Compensation Liability, Current and Noncurrent		(36)			(36)				(38)
Total Liabilities		(201)			(201)				(222)
Total net assets (liabilities)		3,827			3,827				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		(164)			(164)				(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		(2,056)			(2,056)				(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		(95)			(95)				(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]	1,987			1,987				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)			(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			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		(2)			(2)				(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		1			1				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]	3,671			3,671				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]	92			92				85
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,608			1,608				915
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		1,971			1,971				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		1,629			1,629				1,614
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		99			99				52
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		49			49				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		165			165				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]	29			29				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				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				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				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	[7]	0			0				1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			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
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]	23			23				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				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				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		23			23				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		2,117			2,117				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		84			84				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]	(1,887)			(1,887)				(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		314			314				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		20			20				8
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		0			0				3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Asset		21			21				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		(1)			(1)				(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				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				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				0
Total Assets		1,425			1,425				1,387
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		(295)			(295)				(138)
Total net assets (liabilities)		1,130			1,130				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		(295)			(295)				(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		(1,660)			(1,660)				(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		(32)			(32)				(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]	1,397			1,397				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				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				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				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				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]	566			566				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				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		1			1				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		231			231				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		231			231				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				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				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				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				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		334			334				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				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				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	[7]	0			0				12
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			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									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				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				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				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				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		2,019			2,019				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		90			90				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]	(1,302)			(1,302)				(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		807			807				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				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				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				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				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		52			52				37
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				0
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)		24			24				21
Derivative Liability, Noncurrent		(235)			(235)				(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			69				45
Commonwealth Edison Co [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		144			144				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]	211			211				98
Total Assets		211			211				98
Total mark-to-market derivative liabilities	[10]	259			259				256
Deferred Compensation Liability, Current and Noncurrent		(7)			(7)				(8)
Total Liabilities		(266)			(266)				(264)
Total net assets (liabilities)		(55)			(55)				(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				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				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				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]	211			211				98
Total Assets		211			211				98
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)								$ 211	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				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				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				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				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		(7)			(7)				(8)
Total Liabilities		(7)			(7)				(8)
Total net assets (liabilities)								(7)	(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				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				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				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				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities	[10]	259			259				256
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		(259)			(259)				(256)
Total net assets (liabilities)		(259)			(259)				(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				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				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				0
PECO Energy Co [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		23			23				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]	84			84				228
Total Assets		102			102				245
Total mark-to-market derivative liabilities	[10]	0			0				0
Deferred Compensation Liability, Current and Noncurrent		(10)			(10)				(11)
Total Liabilities		(10)			(10)				(11)
Total net assets (liabilities)		92			92				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]	18			18				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				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		11			11				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]	84			84				228
Total Assets		91			91				235
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)								91	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				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				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				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				0
Total Assets		11			11				10
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		(10)			(10)				(11)
Total Liabilities		(10)			(10)				(11)
Total net assets (liabilities)								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]	11			11				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				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		11			11				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				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		0			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				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				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				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		13			13				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		3			3				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]	100			100				0
Total Assets		106			106				6
Total mark-to-market derivative liabilities	[10]	0			0				0
Deferred Compensation Liability, Current and Noncurrent		(5)			(5)				(5)
Total Liabilities		(5)			(5)				(5)
Total net assets (liabilities)		101			101				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				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				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				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]	100			100				0
Total Assets		106			106				6
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)								106	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				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				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				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				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		(5)			(5)				(5)
Total Liabilities		(5)			(5)				(5)
Total net assets (liabilities)								$ (5)	(5)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[11]	0			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				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				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				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities		0	[10]		0	[10]			0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		0			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				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				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				0
Pepco Holdings LLC [Member] | Cash and Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		33			33				12
Pepco Holdings LLC [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		19			19				23
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	182			182				83
Total Assets		314			314				212
Total mark-to-market derivative liabilities		0			0				0
Deferred Compensation Liability, Current and Noncurrent		(22)			(22)				(25)
Total Liabilities		(22)			(22)				(25)
Total net assets (liabilities)		292			292				187
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total Liabilities	[13]	0			0				(1)
Pepco Holdings LLC [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			0				1
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	132			132				129
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42			42				72
Pepco Holdings LLC [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		15			15				0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		59			59				45
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		16			16				12
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	182			182				83
Total Assets		239			239				155
Total mark-to-market derivative liabilities		0			0				0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		239			239				155
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total Liabilities	[13]	0			0				(1)
Pepco Holdings LLC [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			0				1
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	57			57				72
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		42			42				72
Pepco Holdings LLC [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		15			15				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0			0				0
Total Assets		38			38				35
Total mark-to-market derivative liabilities		0			0				0
Deferred Compensation Liability, Current and Noncurrent		(22)			(22)				(25)
Total Liabilities		(22)			(22)				(25)
Total net assets (liabilities)		16			16				10
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total Liabilities	[13]	0			0				0
Pepco Holdings LLC [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			0				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	38			38				35
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
Pepco Holdings LLC [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				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22			22				23
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		16			16				12
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	0			0				0
Total Assets		37			37				22
Total mark-to-market derivative liabilities		0			0				0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		37			37				22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Total Liabilities	[13]	0			0				0
Pepco Holdings LLC [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			0				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure	[14]	37			37				22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				0
Pepco Holdings LLC [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				0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		37			37				22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		0			0				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		12			12				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]	35			35				36
Total Assets		140			140				137
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		(3)			(3)				(4)
Total Liabilities		(3)			(3)				(4)
Total net assets (liabilities)		137			137				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]
Total Liabilities	[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]	105			105				101
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		41			41				44
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		58			58				45
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		6			6				12
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]	35			35				36
Investments, Fair Value Disclosure		0			0
Total Assets		76			76				80
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		76			76				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]
Total Liabilities	[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]	41			41				44
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		41			41				44
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				0
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				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				0
Investments, Fair Value Disclosure									0
Total Assets		28			28				35
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		(3)			(3)				(4)
Total Liabilities		(3)			(3)				(4)
Total net assets (liabilities)		25			25				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]
Total Liabilities	[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]	28			28				35
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Investments, Fair Value Disclosure		22			22				23
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		6			6				12
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				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		36			36				22
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		36			36				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]
Total Liabilities	[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]	36			36				22
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		36			36				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				0
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		8			8				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]	102			102				0
Total Assets		102			102				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		(1)			(1)				(1)
Total Liabilities		(1)			(1)				(1)
Total net assets (liabilities)		101			101				(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]
Total Liabilities	[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				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				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				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				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]	102			102				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		102			102				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		102			102				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]
Total Liabilities	[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				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				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				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				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		(1)			(1)				(1)
Total Liabilities		(1)			(1)				(1)
Total net assets (liabilities)		(1)			(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]
Total Liabilities	[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				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				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				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				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		0			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]
Total Liabilities	[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				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				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				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		11			11				2
Atlantic City Electric Company [Member] | Other Assets [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents		19			19				23
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	[12]	26			26				29
Total Assets		26			26				29
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		26			26				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]
Total Liabilities	[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				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				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				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				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]	26			26				29
Investments, Fair Value Disclosure		0			0				0
Total Assets		26			26				29
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		26			26				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]
Total Liabilities	[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				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				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				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				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		0			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]
Total Liabilities	[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				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				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				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				0
Investments, Fair Value Disclosure		0			0				0
Total Assets		0			0				0
Total mark-to-market derivative liabilities									0
Deferred Compensation Liability, Current and Noncurrent		0			0				0
Total Liabilities		0			0				0
Total net assets (liabilities)		0			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]
Total Liabilities	[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				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				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				$ 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] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		1		$ 1	2		$ 3
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)		0		0	0		1
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0		0	0		0
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)
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0		0	0		0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0		0	0		0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Pepco Holdings LLC [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		0		0	1		0
Accounting Standards Update 2016-01 [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Potomac Electric Power Company [Member] | Rabbi Trust Investments [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Marketable Securities, Unrealized Gain (Loss)		$ 1		$ 0	$ 0		$ 0
[1]	Generation excludes cash of $183 million and $259 million at September 30, 2018 and December 31, 2017 and restricted cash of $57 million and $127 million at September 30, 2018 and December 31, 2017. Exelon excludes cash of $330 million and $389 million at September 30, 2018 and December 31, 2017 and restricted cash of $85 million and $145 million at September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $163 million and $85 million at September 30, 2018 and December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[2]	Collateral posted/(received) from counterparties totaled $18 million, $100 million and $94 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of September 30, 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), $(166) million represents variation margin on the exchanges as of September 30, 2018. Of the collateral posted/(received), $(117) million represents variation margin on the exchanges as of December 31, 2017.
[4]	Excludes net liabilities of $89 million and $82 million at September 30, 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 $37 million and $77 million of cash received from outstanding repurchase agreements at September 30, 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 $(4) million and less than $1 million, which have a total notional amount of $915 million and $811 million at September 30, 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 Exelon and Generation's exposure to credit or market loss.
[7]	Excludes net assets of less than $1 million at September 30, 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 for the three months ended September 30, 2018 and September 30, 2017. The amount of unrealized gains/(losses) at Generation totaled less than $1 million and $1 million for the nine months ended September 30, 2018 and September 30, 2017, respectively. The amount of unrealized gains/(losses) at Exelon totaled $1 million for the three months ended September 30, 2018 and September 30, 2017. The amount of unrealized gains/(losses) at Exelon totaled $2 million and $3 million for the nine months ended September 30, 2018 and September 30, 2017, respectively.
[9]	ComEd excludes cash of $69 million and $45 million at September 30, 2018 and December 31, 2017 and includes long-term restricted cash of $144 million and $62 million at September 30, 2018 and December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $23 million and $47 million at September 30, 2018 and December 31, 2017. BGE excludes cash of $13 million and $17 million at September 30, 2018 and December 31, 2017 and restricted cash of $3 million and $1 million at September 30, 2018 and December 31, 2017.
[10]	The Level 3 balance consists of the current and noncurrent liability of $24 million and $235 million, respectively, at September 30, 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 and nine months ended September 30, 2018 and September 30, 2017, respectively.
[12]	PHI excludes cash of $33 million and $12 million at September 30, 2018 and December 31, 2017, respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 2018 and December 31, 2017, respectively, which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $12 million and $4 million at September 30, 2018 and December 31, 2017, respectively. DPL excludes cash of $8 million and $2 million at September 30, 2018 and December 31, 2017, respectively. ACE excludes cash of $11 million and $2 million at September 30, 2018 and December 31, 2017, respectively, and includes long-term restricted cash of $19 million and $23 million at September 30, 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]	The amount of unrealized gains/(losses) at PHI totaled less than $1 million for the three months ended September 30, 2018 and 2017, respectively. The amount of unrealized gains/(losses) at Pepco totaled $1 million and less than $1 million for the three months ended September 30, 2018 and 2017, respectively. The amount of unrealized gains/(losses) at PHI totaled $1 million and less than $1 million for the nine months ended September 30, 2018 and 2017, respectively. The amount of unrealized gains/(losses) at Pepco totaled less than $1 million for the nine months ended September 30, 2018 and 2017, respectively.
[15]	All amounts are net of tax and noncontrolling interests. 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 Asset_6

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				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Jun. 30, 2018		Dec. 31, 2017		Jun. 30, 2017		Dec. 31, 2016
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																$ 0
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		$ 908		$ 1,070		$ 908		$ 1,070		$ 1,160		$ 1,015		$ 1,098		993
Total realized / unrealized gains (losses)
Included in net income		(246)		(80)		(172)		(102)
Included in noncurrent payables to affiliates		0		0		0		0
Included in payable for Zion Station decommissioning		2		(4)		7		(3)
Included in regulatory assets		(11)		(21)		(3)		(6)
Change in collateral		(44)		11		14		81
Purchases, sales, issuances and settlements
Purchases		99		77		219		205
Sales		(20)		0		(23)		(15)
Issuances								(1)
Settlements		(29)		(21)		(103)		(85)
Transfers into Level 3		3		0		(21)		(9)
Transfers out of Level 3		(6)		10		(25)		12
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(92)		26		168		167
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [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		0		0		0		0				0
Total realized / unrealized gains (losses)
Included in net income		0				0		0
Included in noncurrent payables to affiliates		4				0		(13)
Included in payable for Zion Station decommissioning		0				0		0
Included in regulatory assets		(4)				0		13
Change in collateral		0				0		0
Purchases, sales, issuances and settlements
Purchases		0				0		0
Sales		0				0		0
Issuances								0
Settlements		0				0		0
Transfers into Level 3		0				0		0
Transfers out of Level 3		0				0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0				0		0
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		(155)		96		(347)		279
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		1,130		1,326		1,130		1,326		1,376		1,249		1,334		1,231
Total realized / unrealized gains (losses)
Included in net income		(247)		(81)		(175)		(104)
Included in noncurrent payables to affiliates		(4)		0		0		13
Included in payable for Zion Station decommissioning		2		(4)		7		(3)
Included in regulatory assets		0		0		0		0
Change in collateral		(44)		11		14		81
Purchases, sales, issuances and settlements
Purchases		99		77		219		205
Sales		(20)		0		(23)		(15)
Issuances								0
Settlements		(29)		(21)		(115)		(85)
Transfers into Level 3		3		0		(21)		(9)
Transfers out of Level 3		(6)		10		(25)		12
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(92)		25		168		165
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		566		671		566		671		585		648		683		677
Total realized / unrealized gains (losses)
Included in net income		(1)		0		(1)		4
Included in noncurrent payables to affiliates		(4)		0		0		13
Included in payable for Zion Station decommissioning		0		0		0		0
Included in regulatory assets				0				0
Change in collateral		0		0		0		0
Purchases, sales, issuances and settlements
Purchases		15		19		34		54
Sales		0		0		0		0
Issuances								0
Settlements		(29)		(31)		(115)		(77)
Transfers into Level 3		0		0		0		0
Transfers out of Level 3		0		0		0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(1)		0		(5)		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		0		17		0		17		18		12		21		19
Total realized / unrealized gains (losses)
Included in net income		0		0		0		0
Included in noncurrent payables to affiliates		0		0		0		0
Included in payable for Zion Station decommissioning		2		(4)		7		(3)
Included in regulatory assets				0				0
Change in collateral		0		0		0		0
Purchases, sales, issuances and settlements
Purchases		0		0		1		1
Sales		(20)		0		(20)		0
Issuances								0
Settlements		0		0		0
Transfers into Level 3		0		0		0		0
Transfers out of Level 3		0		0		0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0		0		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		512		595		512		595		737		552		589		493
Total realized / unrealized gains (losses)
Included in net income		(259)	[1]	(82)	[2]	(188)	[1]	(110)	[2]
Included in noncurrent payables to affiliates		0		0		0		0
Included in payable for Zion Station decommissioning		0		0		0		0
Included in regulatory assets				0				0
Change in collateral		(44)		11		14		81
Purchases, sales, issuances and settlements
Purchases		81		57		181		146
Sales		0		0		(3)		(15)
Issuances								0
Settlements		0		10		0		(8)
Transfers into Level 3		3		0		(21)		(9)
Transfers out of Level 3		(6)		10		(23)		17
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		(104)		24		159		161
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		52		43		52		43		36		37		41		42
Total realized / unrealized gains (losses)
Included in net income		13		1		14		2
Included in noncurrent payables to affiliates		0		0		0		0
Included in payable for Zion Station decommissioning		0		0		0		0
Included in regulatory assets				0				0
Change in collateral		0		0		0		0
Purchases, sales, issuances and settlements
Purchases		3		1		3		4
Sales		0		0		0		0
Issuances								0
Settlements		0		0		0
Transfers into Level 3		0		0		0		0
Transfers out of Level 3		0		0		(2)		(5)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		13		1		14		2
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)		(3)		(3)		(12)		(13)
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		(259)		(277)		(259)		(277)		(252)		(256)		(256)		(258)
Total realized / unrealized gains (losses)
Included in net income		0		0		0		0
Included in noncurrent payables to affiliates		0		0		0		0
Included in payable for Zion Station decommissioning		0		0		0		0
Included in regulatory assets		(7)	[3]	21	[4]	(3)	[3]	(19)	[4]
Change in collateral		0		0		0		0
Purchases, sales, issuances and settlements
Purchases		0		0		0		0
Sales		0		0		0		0
Issuances								0
Settlements		0		0		0		0
Transfers into Level 3		0		0		0		0
Transfers out of Level 3		0		0		0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0		0		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)		4		24		(9)		32
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [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		37	[5]	21	[6]	37	[5]	21	[6]	$ 36	[5]	$ 22	[5]	$ 20	[6]	$ 20	[6]
Total realized / unrealized gains (losses)
Included in net income		(1)	[5]	(1)	[6]	(3)	[5]	(2)	[6]
Included in noncurrent payables to affiliates		0	[5]	0	[6]	0	[5]	0	[6]
Included in payable for Zion Station decommissioning		0	[5]	0	[6]	0	[5]	0	[6]
Included in regulatory assets		0	[5]	0	[6]	0	[5]	0	[6]
Change in collateral		0	[5]	0	[6]	0	[5]	0
Purchases, sales, issuances and settlements
Purchases		0	[5]	0	[6]	0	[5]	0	[6]
Sales		0	[5]	0	[6]	0	[5]	0	[6]
Issuances	[6]							(1)
Settlements		0	[5]	0	[6]	(12)	[5]	0	[6]
Transfers into Level 3		0	[5]	0	[6]	0	[5]	0	[6]
Transfers out of Level 3		0	[5]	0	[6]	0	[5]	0	[6]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		$ 0	[5]	$ 1	[6]	$ 0	[5]	$ 2	[6]
[1]	Includes a reduction for the reclassification of $155 million and $347 million of realized losses due to the settlement of derivative contracts for the three and nine months ended September 30, 2018, respectively.
[2]	Includes a reduction for the reclassification of $96 million and $279 million of realized gains due to the settlement of derivative contracts for the three and nine months ended September 30, 2017, respectively.
[3]	Includes $4 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2018. Includes $9 million of decreases in fair value and an increase for realized losses due to settlements of $12 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 2018.
[4]	Includes $24 million of increases in fair value and an increase for realized losses due to settlements of $3 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2017. Includes $32 million of decreases in fair value and an increase for realized losses due to settlements of $13 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the nine months ended September 30, 2017.
[5]	The amounts represented are life insurance contracts at Pepco.
[6]	The amounts represented are life insurance contracts at Pepco.

Fair Value of Financial Asset_7

Fair Value of Financial Assets and Liabilities - Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Pepco Holdings LLC [Member] | Operating and Maintenance [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				$ 3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0				0
Fair Value, Inputs, Level 3 [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	246		$ 80		172		$ 102
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(92)		26		168		167
Fair Value, Inputs, Level 3 [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	(176)		(3)		(32)		34
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(64)		47		174		222
Fair Value, Inputs, Level 3 [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	(83)		(69)		(156)		(152)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(40)		(23)		(15)		(61)
Fair Value, Inputs, Level 3 [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	12		2		13		8
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	12		2		9		6
Fair Value, Inputs, Level 3 [Member] | Operating and Maintenance [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				3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0				0
Fair Value, Inputs, Level 3 [Member] | 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	247		81		175		104
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(92)		25		168		165
Fair Value, Inputs, Level 3 [Member] | 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	(176)		(3)		(32)		34
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(64)		47		174		222
Fair Value, Inputs, Level 3 [Member] | 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	(83)		(69)		(156)		(152)
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	(40)		(23)		(15)		(61)
Fair Value, Inputs, Level 3 [Member] | 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	12		1		13		6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	12		1		9		4
Fair Value, Inputs, Level 3 [Member] | Pepco Holdings LLC [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				2
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)			1				2
Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Pepco Holdings LLC [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	[2]	3	[1]	2	[2]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0	[1]	$ 1	[2]	$ 0	[1]	$ 2	[2]
[1]	The amounts represented are life insurance contracts at Pepco.
[2]	The amounts represented are life insurance contracts at Pepco.

Fair Value of Financial Asset_8

Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		$ 4,000,000
Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		536,000,000	$ 445,000,000	[1],[2]
Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		$ (252,000,000)	$ (256,000,000)
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[2]	9	3
Forward gas price assets	[2]	1.10	1.27
Forward heat rate		1000.00%	900.00%	[3]
Fair Value Inputs, Discount for Lack of Marketability		4.00%	4.00%
Fair Value Inputs Renewable Factor		88.00%	88.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	[2]	158	124
Forward gas price assets	[2]	12.57	12.80
Forward heat rate		1100.00%	1000.00%	[3]
Fair Value Inputs, Discount for Lack of Marketability		8.00%	8.00%
Fair Value Inputs Renewable Factor		120.00%	120.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[2]	8.00%	11.00%
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	[2]	211.00%	139.00%
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		$ (63,000,000)	$ 26,000,000	[1],[2]
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		9	14	[2]
Fair Value, Inputs, Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets		139	94	[2]
Exelon Generation Co L L C [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		$ 255,000,000	$ 497,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash Collateral Posted		94,000,000	81,000,000
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Economic Hedges [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[1],[2]	359,000,000	$ 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	[2]		3
Forward gas price assets	[2]		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	[2]		124
Forward gas price assets	[2]		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	[2]		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	[2]		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]	$ (58,000,000)	$ 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	[2]	17	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	[2]	158	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		$ (259,000,000)	$ (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	[3]	1000.00%	900.00%
Fair Value Inputs, Discount for Lack of Marketability		4.00%	4.00%
Fair Value Inputs Renewable Factor		86.00%	88.00%
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward heat rate	[3]	1100.00%	1000.00%
Fair Value Inputs, Discount for Lack of Marketability		8.00%	8.00%
Fair Value Inputs Renewable Factor		121.00%	120.00%
[1]	The fair values do not include cash collateral posted on level three positions of $94 million and $81 million as of September 30, 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 Instrume_3

Derivative Financial Instruments Derivative Financial Instruments - Summary of Derivative Fair Value Balances (Details) - USD ($) $ in Millions		Sep. 30, 2018		Dec. 31, 2017
Derivative [Line Items]
Mark-to-market derivatives assets		$ 696		$ 976
Derivative Asset, Noncurrent		449		337
Derivative Liability, Current		(329)		(232)
Derivative Liability, Noncurrent		(482)		(409)
Derivative, Collateral, Right to Reclaim Cash		37		77
Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		694		973
Derivative Asset, Noncurrent		431		331
Total mark-to-market derivative assets		1,125		1,304
Derivative Liability, Current		(328)		(230)
Derivative Liability, Noncurrent		(472)		(407)
Total mark-to-market derivative liabilities		(800)		(637)
Total mark-to-market derivative net assets (liabilities)		325		667
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		696		976
Derivative Asset, Noncurrent		449		334
Derivative Liability, Current		(305)		(211)
Derivative Liability, Noncurrent		(237)		(174)
Derivative Liability, Fair Value, Amount Offset Against Collateral	[1]	(1,249)		(577)
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		694	[2]	973	[3]
Derivative Asset, Noncurrent		431	[2]	331	[3]
Total mark-to-market derivative assets		1,125	[2]	1,304	[3]
Derivative Liability, Current		(304)	[2]	(209)	[3]
Derivative Liability, Noncurrent		(237)	[2]	(172)	[3]
Total mark-to-market derivative liabilities		(541)	[2]	(381)	[3]
Total mark-to-market derivative net assets (liabilities)		584	[2]	923	[3]
Commonwealth Edison Co [Member]
Derivative [Line Items]
Derivative Liability, Current		(24)		(21)
Derivative Liability, Noncurrent		(235)		(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]	(2,406)	[5]	(2,144)	[6]
Derivative Asset, Noncurrent	[4]	(1,013)	[5]	(845)	[6]
Total mark-to-market derivative assets	[4]	(3,419)	[5]	(2,989)	[6]
Derivative Liability, Current	[4]	2,543	[5]	2,480	[6]
Derivative Liability, Noncurrent	[4]	1,088	[5]	975	[6]
Total mark-to-market derivative liabilities	[4]	3,631	[5]	3,455	[6]
Total mark-to-market derivative net assets (liabilities)	[4]	212	[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		2,987		3,061
Derivative Asset, Noncurrent		1,383		1,164
Total mark-to-market derivative assets		4,370		4,225
Derivative Liability, Current		(2,761)		(2,646)
Derivative Liability, Noncurrent		(1,284)		(1,137)
Total mark-to-market derivative liabilities		(4,045)		(3,783)
Total mark-to-market derivative net assets (liabilities)		325		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]	(235)		(235)
Total mark-to-market derivative liabilities	[7]	(259)		(256)
Total mark-to-market derivative net assets (liabilities)	[7]	(259)		(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		113		56
Derivative Asset, Noncurrent		61		12
Total mark-to-market derivative assets		174		68
Derivative Liability, Current		(86)		(43)
Derivative Liability, Noncurrent		(41)		(10)
Total mark-to-market derivative liabilities		(127)		(53)
Total mark-to-market derivative net assets (liabilities)		47		15
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		(212)		(466)
Current liabilities collateral offset		66		167
Noncurrent liabilities collateral offset		47		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		71		169
Derivative Liability, Fair Value, Amount Offset Against Collateral		(166)		(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		$ 28		$ 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 $71 million and $28 million, respectively, and current and noncurrent liabilities are shown net of collateral of $66 million and $47 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $212 million at September 30, 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), $(166) 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 Instrume_4

Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			$ (67)	$ (149)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			(73)	(160)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (1)	$ (3)	1	(6)
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	(3)	3	(6)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(2)	(3)	3	(6)
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)	(3)	3	(6)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(1)	0	(4)	0
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	(4)	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	2	0	2	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	4	0	4	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	74	76	(103)	(155)
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	8	55	(99)	(41)
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	$ 66	$ 21	$ (4)	$ (114)

Derivative Financial Instrume_5

Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			$ (67)	$ (149)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			(73)	(160)
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	$ (3)	$ 5	14	4
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	$ 0	$ 0	$ (1)

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Interest Rate and Foreign Currency Hedges (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Mark-to-market derivatives assets		$ 696	$ 976
Derivative Asset, Noncurrent		449	337
Derivative Liability, Current		(329)	(232)
Derivative Liability, Noncurrent		(482)	(409)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		696	976
Derivative Asset, Noncurrent		449	334
Derivative Liability, Current		(305)	(211)
Derivative Liability, Noncurrent		(237)	(174)
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		2	3
Derivative Asset, Noncurrent		18	6
Total mark-to-market derivative assets		20	9
Derivative Liability, Current		(1)	(2)
Derivative Liability, Noncurrent		(10)	(2)
Total mark-to-market derivative liabilities		(11)	(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		18	3
Total mark-to-market derivative assets		20	6
Derivative Liability, Current		(1)	(2)
Derivative Liability, Noncurrent		0	(2)
Total mark-to-market derivative liabilities		(1)	(4)
Total mark-to-market derivative net assets (liabilities)		19	2
Collateral And Netting [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets	[1]	(1)	(7)
Derivative Asset, Noncurrent	[1]	0	0
Total mark-to-market derivative assets	[1]	(1)	(7)
Derivative Liability, Current	[1]	1	7
Derivative Liability, Noncurrent	[1]	0	0
Total mark-to-market derivative liabilities	[1]	1	7
Total mark-to-market derivative net assets (liabilities)	[1]	0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Mark-to-market derivatives assets		0
Derivative Asset, Noncurrent		0
Total mark-to-market derivative assets		0
Derivative Liability, Current		0
Derivative Liability, Noncurrent		(10)
Total mark-to-market derivative liabilities		(10)
Total mark-to-market derivative net assets (liabilities)		(10)
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivatives assets			0
Derivative Asset, Noncurrent			3
Total mark-to-market derivative assets			3
Derivative Liability, Current			(2)
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			(2)
Total mark-to-market derivative net assets (liabilities)			1
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Mark-to-market derivatives assets			0
Derivative Asset, Noncurrent			3
Total mark-to-market derivative assets			3
Derivative Liability, Current			0
Derivative Liability, Noncurrent			0
Total mark-to-market derivative liabilities			0
Total mark-to-market derivative net assets (liabilities)			3
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		3	10
Derivative Asset, Noncurrent		18	0
Total mark-to-market derivative assets		21	10
Derivative Liability, Current		(2)	(7)
Derivative Liability, Noncurrent		0	(2)
Total mark-to-market derivative liabilities		(2)	(9)
Total mark-to-market derivative net assets (liabilities)		$ 19	$ 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 Instrume_7

Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Beginning Balance					$ (3,026)
Ending Balance		$ (2,869)			(2,869)
Income taxes		137	$ 451		262	$ 601
Amounts reclassified from AOCI	[1]	(45)	(34)		(137)	(108)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Derivative [Line Items]
Amounts reclassified from AOCI	[2],[3]				(1)	(3)
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(2)	(12)		(14)	(17)
Ending Balance		(2)	(12)		(2)	(12)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			1		11	2
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Beginning Balance					(37)
Ending Balance		(31)			(31)
Income taxes		78	239		110	215
Amounts reclassified from AOCI	[1]	0	1		(1)	(3)
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	[2],[3]				(1)	(3)
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning Balance		(4)	(14)		(16)	(19)
Ending Balance		(4)	(14)		(4)	(14)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net			1		11	2
Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Amounts reclassified from AOCI		0	(1)	[4]	1	3	[5]
Interest Expense [Member] | Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Amounts reclassified from AOCI		0	(1)	[4]	1	3	[5]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Income taxes			1			2
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	[1]	0	(1)		0	2
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	[1]	$ 0	$ (1)		$ 0	$ 2
[1]	Amounts in parenthesis represent a decrease in AOCI.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	Amount is net of related income tax benefit of $1 million for the three months ended September 30, 2017.
[5]	Amount is net of related income tax expense of $2 million for the nine months ended September 30, 2017.

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - Interest Expense [Member] - Fair Value Hedging [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest Rate Swap [Member]
Derivative [Line Items]
Gain (loss) on Swaps	$ 0	$ (2)	$ (11)	$ (6)
Price Risk Derivative [Member]
Derivative [Line Items]
Gain on Borrowings	$ 0	$ 6	$ 20	$ 17

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Cash Collateral Posted		$ 4
Letters Of Credit Posted		34
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Financial institutions		19
Investor-owned utilities, marketers and power producers		572
Energy Cooperatives And Municipalities		357
Other		80
Cash Collateral Posted		255	$ 497
Letters Of Credit Posted		283	$ 293
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Investment grade		647
Non-investment grade		101
No external ratings - internally rated - investment grade		179
No external ratings - internally rated - non-investment grade		139
Total		1,066
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Derivative [Line Items]
Investment grade		0
Non-investment grade		20
No external ratings - internally rated - investment grade		1
No external ratings - internally rated - non-investment grade		17
Total	[1]	38
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Derivative [Line Items]
Investment grade		647
Non-investment grade		81
No external ratings - internally rated - investment grade		178
No external ratings - internally rated - non-investment grade		122
Total		1,028
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		1
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		1
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Investment grade		176
Non-investment grade
No external ratings - internally rated - investment grade
No external ratings - internally rated - non-investment grade
Total		$ 176
[1]	As of September 30, 2018, credit collateral held from counterparties where Generation had credit exposure included $4 million of cash and $34 million of letters of credit. The credit collateral does not include non-liquid collateral.

Derivative Financial Instrum_10

Derivative Financial Instruments - Summary of Credit Risk Related Contingent Features (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Aggregate fair value of derivatives with credit-risk-related contingent features	[1]	$ (1,704)	$ (926)
Contractual right of offset related to derivative assets	[2]	1,249	577
Net liability position after contractual right of offset	[3]	$ (455)	$ (349)
[1]	Amount represents the gross fair value of out-of-the-money derivative contracts containing credit-risk related contingent features ignoring the effects of master netting agreements.
[2]	Amount represents the offsetting fair value of in-the-money derivative contracts under legally enforceable master netting agreements with the same counterparty, which reduces the amount of any liability for which a Registrant could potentially be required to post collateral.
[3]	Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.

Derivative Financial Instrum_11

Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Ineffective portion recognized in income	$ 0	$ 4,000	$ 9,000	$ 11,000
Cash Collateral Posted	4,000		4,000
Letters of credit posted	34,000		34,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	23,000		23,000		$ 4,000
Cash Collateral Posted	255,000		255,000		497,000
Letters of credit held	48,000		48,000		33,000
Letters of credit posted	283,000		283,000		293,000
Cash collateral held	20,000		20,000		35,000
Incremental collateral for loss of investment grade credit rating	1,800,000		1,800,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	19,000		19,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	8,000		8,000
Credit Exposure Under Off System Sales	2,000		$ 2,000
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	22,000		$ 22,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	31,000		31,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	10,000		$ 10,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months			98.00%
Expected Generation Hedged In Year Two			82.00%
Expected generation hedged in year three			48.00%
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			101.00%
Expected Generation Hedged In Year Two			85.00%
Expected generation hedged in year three			51.00%
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
Energy Related Derivative [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties			6
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			20
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	9,000		$ 9,000		5,000
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	19,000		19,000		2,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	47,000		47,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	26,000		26,000
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	23,000		23,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	39,000		39,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	8,000		8,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 6,000		$ 6,000
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net					1,000
Corporate, Non-Segment [Member] | Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net					$ 3,000

Derivative Financial Instrum_12

Derivative Financial Instruments Schedule of Notional Amounts Outstanding (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Fair Value Hedging [Member] | Corporate, Non-Segment [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 0	$ 800	[1]
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	[1]	0	636
Not Designated as Hedging Instrument, Economic Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,513	95
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		88	94
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		1,425	1	[1]
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount		713	95
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		88	94
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		625	1
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member]
Derivative [Line Items]
Derivative, Notional Amount		800	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount		0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Corporate, Non-Segment [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 800	$ 0
[1]	On July 1, 2018, Exelon and Generation de-designated its fair value and cash flow hedges. The table excludes amounts of $800 million of fixed-to-floating hedges that were previously designated as fair value hedges by Exelon and $636 million of floating-to-fixed hedges that were previously designated as cash flow hedges by Exelon and Generation as of December 31, 2017.

Debt and Credit Agreements - Co

Debt and Credit Agreements - Commercial Paper Borrowings (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Commercial paper borrowings		$ 209	$ 427
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		0	77
Pepco Holdings LLC [Member]
Short-term Debt [Line Items]
Commercial paper borrowings	[1]	209	350
Potomac Electric Power Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		64	26
Delmarva Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		0	216
Atlantic City Electric Company [Member]
Short-term Debt [Line Items]
Commercial paper borrowings		$ 145	$ 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) $ in Millions	Sep. 30, 2018USD ($)
Exelon Generation Co L L C [Member] | EEPF372Nov2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.72%
Debt Instrument, Face Amount	$ 4
Exelon Generation Co L L C [Member] | EEPF317Oct2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.17%
Debt Instrument, Face Amount	$ 1
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	$ 5
Exelon Generation Co L L C [Member] | EEPF417Jan2019 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	4.17%
Debt Instrument, Face Amount	$ 1
Exelon Generation Co L L C [Member] | EEPF426May2019 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	4.26%
Debt Instrument, Face Amount	$ 3
Commonwealth Edison Co [Member] | FMB400Mar2048Member | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.00%
Debt Instrument, Face Amount	$ 800
Commonwealth Edison Co [Member] | FMB370Aug2028 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.70%
Debt Instrument, Face Amount	$ 550
PECO Energy Co [Member] | FRMB390Mar2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 325
PECO Energy Co [Member] | PIDC200Jun2023 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	2.00%
Debt Instrument, Face Amount	$ 50
PECO Energy Co [Member] | FRMB390Mar2048B [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 325
Baltimore Gas and Electric Company [Member] | SN425Sep2048 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	4.25%
Debt Instrument, Face Amount	$ 300
Potomac Electric Power Company [Member] | FMB427Jun2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.27%
Debt Instrument, Face Amount	$ 100
Delmarva Power and Light Company [Member] | FMB427Jun2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.27%
Debt Instrument, Face Amount	$ 200

Debt and Credit Agreements - Na

Debt and Credit Agreements - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Nov. 01, 2018	Oct. 16, 2018
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%
Atlantic City Electric Company [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	$ 125
Debt Instrument, Interest Rate Terms	LIBOR plus 0.55%
FMB400Oct2028 [Member] | Atlantic City Electric Company [Member] | First Mortgage [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 350
Interest Rate			4.00%
FMB775Nov2018 [Member] | Atlantic City Electric Company [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	7.75%
FMB431Nov2048 [Member] | Potomac Electric Power Company [Member] | First Mortgage [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 100
Interest Rate		4.31%

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended			12 Months Ended
		Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	[1]	Sep. 30, 2018	Sep. 30, 2017	[1]	Dec. 31, 2017	Jul. 27, 2018	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%		35.00%
Allowable Expensing For Cost Of Qualified Property						30.00%
Limitation on Deductible Interest Expense						100.00%
Net Regulatory Liabilities		$ 10,445				$ 10,445			$ 10,388
Unrecognized tax benefits that if recognized would affect the effective tax rate		473				473				$ 20
Decrease in Unrecognized Tax Benefits is Reasonably Possible		515				515
Regulatory Assets		9,342				9,342			9,288
Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 33				33
Deferred Gain on Sale of Property											$ 1,200
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%		21.00%	35.00%
Increase in Unrecognized Tax Benefits is Reasonably Possible										71
Unrecognized tax benefits that if recognized would affect the effective tax rate		$ 473				$ 473				$ 20
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 501				$ 501
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 6,638				$ 6,638			6,577
Regulatory Assets		1,485				1,485			1,279
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 2				$ 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%		21.00%	35.00%
Net Regulatory Liabilities		$ 740				$ 740			690
Regulatory Assets		$ 532				$ 532			410
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 1,165				$ 1,165			1,163
Regulatory Assets		$ 597				$ 597			571
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 1,882				$ 1,882			1,928
Decrease in Unrecognized Tax Benefits is Reasonably Possible		14				14
Regulatory Assets		$ 2,895				$ 2,895			3,047
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 764				$ 764			832
Regulatory Assets		$ 946				$ 946			891
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 654				$ 654			635
Regulatory Assets		$ 301				$ 301			314
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%		21.00%	35.00%
Net Regulatory Liabilities		$ 428				$ 428			422
Decrease in Unrecognized Tax Benefits is Reasonably Possible		14				14
Regulatory Assets		427				427			430
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									3,040
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									1,400
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[2]								533
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									459
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									648
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									299
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									195
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To IRS Normalization Rules | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									153
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									1,694
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									573
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[2]								43
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									324
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									754
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									391
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									194
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers Subject To Rate Regulator Determinations | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									170
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									4,734
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									1,973
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities	[2]								576
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									783
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									1,402
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									690
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									389
Net Regulatory Liabilities Associated With Ultimate Settlement To Customers | Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities									$ 323
State and Local Jurisdiction [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized tax benefits that if recognized would affect the effective tax rate		26				26
Decrease in Unrecognized Tax Benefits is Reasonably Possible		241				241
Increase (Decrease) in Deferred Income Taxes		(50)	$ 16
Increase (Decrease) in Income Tax Expense		(50)
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		26				26
Decrease in Unrecognized Tax Benefits is Reasonably Possible		33				33
Increase (Decrease) in Deferred Income Taxes		(53)	5
Increase (Decrease) in Income Tax Expense		(53)
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				120
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		88				88
Increase (Decrease) in Deferred Income Taxes		(4)	17
Increase (Decrease) in Income Tax Expense		(3)
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible		67				67
Increase (Decrease) in Deferred Income Taxes		1	16
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				21
Increase (Decrease) in Deferred Income Taxes		(2)	$ 1
State and Local Jurisdiction [Member] | Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities		1				1
State and Local Jurisdiction [Member] | Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities		1				1
State and Local Jurisdiction [Member] | Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Net Regulatory Liabilities		2				2
State and Local Jurisdiction [Member] | Net Regulatory Assets Associated With Marginal State Income Tax Rates [Member] | Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Regulatory Assets		$ 1				$ 1
[1]	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.
[2]	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. See Note 6 - Regulatory Matters for additional information.

Income Taxes Deferred Tax Revis

Income Taxes Deferred Tax Revision (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Sep. 30, 2018
Net Regulatory Liability Recorded		$ 10,388	$ 10,445
Commonwealth Edison Co [Member]
Net Regulatory Liability Recorded		6,577	6,638
PECO Energy Co [Member]
Net Regulatory Liability Recorded		690	740
Baltimore Gas and Electric Company [Member]
Net Regulatory Liability Recorded		1,163	1,165
Pepco Holdings LLC [Member]
Net Regulatory Liability Recorded		1,928	1,882
Potomac Electric Power Company [Member]
Net Regulatory Liability Recorded		832	764
Delmarva Power and Light Company [Member]
Net Regulatory Liability Recorded		635	654
Atlantic City Electric Company [Member]
Net Regulatory Liability Recorded		422	$ 428
Remeasurement Of Deferred Income Taxes Due To Tax Reform
Net Decrease to Deferred Income Tax Liability Balances	[1]	8,624
Net Regulatory Liability Recorded	[2]	7,315
Net Deferred Income Tax Benefit/(Expense) Recorded	[1]	1,309
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Exelon Generation Co L L C [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,895
Net Deferred Income Tax Benefit/(Expense) Recorded		1,895
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Commonwealth Edison Co [Member]
Net Decrease to Deferred Income Tax Liability Balances		2,819
Net Regulatory Liability Recorded	[2]	2,818
Net Deferred Income Tax Benefit/(Expense) Recorded		1
Remeasurement Of Deferred Income Taxes Due To Tax Reform | PECO Energy Co [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,407
Net Regulatory Liability Recorded	[2],[3]	1,394
Net Deferred Income Tax Benefit/(Expense) Recorded		13
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Baltimore Gas and Electric Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,120
Net Regulatory Liability Recorded	[2]	1,124
Net Deferred Income Tax Benefit/(Expense) Recorded		(4)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Pepco Holdings LLC [Member]
Net Decrease to Deferred Income Tax Liability Balances		1,944
Net Regulatory Liability Recorded	[2]	1,979
Net Deferred Income Tax Benefit/(Expense) Recorded		(35)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Potomac Electric Power Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		968
Net Regulatory Liability Recorded	[2]	976
Net Deferred Income Tax Benefit/(Expense) Recorded		(8)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Delmarva Power and Light Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		540
Net Regulatory Liability Recorded	[2]	545
Net Deferred Income Tax Benefit/(Expense) Recorded		(5)
Remeasurement Of Deferred Income Taxes Due To Tax Reform | Atlantic City Electric Company [Member]
Net Decrease to Deferred Income Tax Liability Balances		456
Net Regulatory Liability Recorded	[2]	458
Net Deferred Income Tax Benefit/(Expense) Recorded		$ (2)
[1]	Amounts do not sum across due to deferred tax adjustments recorded at the Exelon Corporation parent company, primarily related to certain employee compensation plans.
[2]	Reflects the net regulatory liabilities recorded on a pre-tax basis before taking into consideration the income tax benefits associated with the ultimate settlement with customers.
[3]	Given the regulatory treatment of income tax benefits related to electric and gas distribution repairs, PECO was in an overall net regulatory asset position as of December 31, 2017 after recording the impacts related to the TCJA. See Note 6 - Regulatory Matters for additional information.

Income Taxes - Reconciliation t

Income Taxes - Reconciliation to Effective Tax Rate (Details)		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(1.20%)	2.20%	[1]	1.70%	0.70%	[1]
Qualified nuclear decommissioning trust fund income		2.40%	2.60%	[1]	0.90%	4.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.60%)	(1.10%)	[1]	(0.90%)	(0.90%)	[1]
Plant basis differences		(2.50%)	(2.60%)	[1]	(2.70%)	(3.40%)	[1]
Production tax credits and other credits		(1.20%)	(2.20%)	[1]	(1.80%)	(1.80%)	[1]
Noncontrolling interests		(1.10%)	0.50%	[1]	(1.10%)	0.10%	[1]
Excess deferred tax amortization		(6.80%)			(6.10%)
Merger expenses	[1],[2]					(5.40%)
FitzPatrick bargain purchase gain	[1]		(0.20%)			(3.20%)
Tax Cuts and Jobs Act of 2017		1.30%			0.20%
Like-Kind Exchange	[1],[3]					(1.70%)
Other		3.20%	(0.10%)	[1]	0.40%	0.10%	[1]
Effective income tax rate		14.50%	34.10%		11.60%	23.50%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(9.00%)	5.60%	[1]	(2.60%)	2.20%	[1]
Qualified nuclear decommissioning trust fund income		5.80%	5.80%	[1]	2.60%	13.60%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(1.10%)	(2.20%)	[1]	(2.20%)	(2.70%)	[1]
Plant basis differences		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Production tax credits and other credits		(2.90%)	(4.90%)	[1]	(5.10%)	(6.00%)	[1]
Noncontrolling interests		(2.80%)	1.10%	[1]	(3.20%)	0.30%	[1]
Excess deferred tax amortization		0.00%			0.00%
Merger expenses	[1],[2]					(2.40%)
FitzPatrick bargain purchase gain	[1]		(0.40%)			(10.90%)
Tax Cuts and Jobs Act of 2017		3.50%			1.30%
Like-Kind Exchange	[1]					0.00%
Other		5.60%	0.30%	[1]	2.00%	(0.40%)	[1]
Effective income tax rate		20.10%	40.30%		13.80%	28.70%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		8.30%	6.60%	[1]	8.20%	5.90%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.20%)	(0.20%)	[1]	(0.20%)	(0.20%)	[1]
Plant basis differences		(0.30%)	(0.30%)	[1]	(0.10%)	(0.30%)	[1]
Production tax credits and other credits		(0.10%)	(0.00%)	[1]	(0.10%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(7.80%)			(7.60%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			(0.20%)
Like-Kind Exchange	[1],[3]					1.70%
Other		0.30%	(0.20%)	[1]	0.10%	0.20%	[1]
Effective income tax rate		21.20%	40.90%		21.10%	42.30%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(3.60%)	(0.10%)	[1]	(3.60%)	(0.10%)	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(15.20%)	(14.60%)	[1]	(15.40%)	(14.40%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(4.60%)			(3.40%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.90%	(0.20%)	[1]	0.00%	0.00%	[1]
Effective income tax rate		(1.60%)	20.00%		(1.50%)	20.40%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		7.30%	5.30%	[1]	6.60%	5.20%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.00%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(0.80%)	(0.80%)	[1]	(0.70%)	(0.80%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(7.90%)			(8.10%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		2.60%	(0.20%)	[1]	0.90%	0.20%	[1]
Effective income tax rate		22.20%	39.20%		19.60%	39.50%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		0.20%	5.10%	[1]	2.70%	4.90%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.20%)	(0.20%)	[1]	(0.20%)	(0.20%)	[1]
Plant basis differences		(2.00%)	(4.90%)	[1]	(1.90%)	(4.60%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(17.70%)			(14.50%)
Merger expenses	[1],[2]					(11.80%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.20%			0.30%
Like-Kind Exchange	[1]					0.00%
Other		0.60%	0.20%	[1]	0.30%	0.00%	[1]
Effective income tax rate		2.10%	35.20%		7.70%	23.30%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		1.00%	2.20%	[1]	2.40%	3.00%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(3.40%)	(6.70%)	[1]	(2.90%)	(6.30%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(21.20%)			(16.50%)
Merger expenses	[1],[2]					(8.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.10%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.30%	0.00%	[1]	0.00%	(0.30%)	[1]
Effective income tax rate		(2.30%)	30.40%		3.90%	23.30%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		6.60%	5.30%	[1]	6.50%	5.10%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.30%)	(0.20%)	[1]	(0.30%)	(0.20%)	[1]
Plant basis differences		(0.70%)	(1.90%)	[1]	(0.70%)	(1.80%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(14.00%)			(11.00%)
Merger expenses	[1],[2]					(10.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.60%	(0.20%)	[1]	0.40%	0.60%	[1]
Effective income tax rate		13.20%	38.00%		15.90%	28.70%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		7.30%	5.60%	[1]	7.30%	5.60%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.30%)	(0.40%)	[1]	(0.30%)	(0.40%)	[1]
Plant basis differences		(1.30%)	(3.40%)	[1]	(1.30%)	(3.40%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(15.40%)			(14.00%)
Merger expenses	[1],[2]					(23.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.30%	0.10%	[1]	0.90%	(0.30%)	[1]
Effective income tax rate		11.60%	36.90%		13.60%	13.50%
[1]	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.
[2]	Includes a remeasurement of uncertain federal and state income tax positions.
[3]	Exelon and ComEd recorded the impact of the IRS's finalization of the LKE computation in the second quarter of 2017

Income Taxes Income Tax Unrecog

Income Taxes Income Tax Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 804	$ 743
Exelon Generation Co L L C [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	527	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	134	125
Potomac Electric Power Company [Member]
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	67	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

Asset Retirement Obligations -

Asset Retirement Obligations - Narrative (Details) - USD ($) $ in Millions		Jan. 02, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate					$ (20)
Decommissioning Fund Investments			$ 12,464		12,464	$ 13,272
Disposal Group, Including Discontinued Operation, Assets, Current			910		910	0
Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate			84		0
Recovery Stranded Costs		$ 4
Asset Retirement Obligation, Period Increase (Decrease)					345
Decommissioning Fund Investments			12,464		12,464	13,272
Disposal Group, Including Discontinued Operation, Assets, Current			910		910	0
Oyster Creek [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current			903		903
Potomac Electric Power Company [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate					(22)
Nuclear Decommissioning [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Current			12		12	13
Asset Retirement Obligation, Period Increase (Decrease)			84	$ 32	116
Proceeds from Customers			9,317		9,317	9,662	[1]
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Liability, Noncurrent			118		118
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Asset Retirement Obligation, Revision of Estimate	[1]		22
Proceeds from Customers	[1]		38		38	3
Assets, Total [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments			12,584		12,584	13,349
Other Current Assets [Member] | Exelon Generation Co L L C [Member]
Nuclear Decommissioning Additional Narrative Information [Line Items]
Decommissioning Fund Investments			$ 120		$ 120	$ 77
[1]	Includes $12 million and $13 million for the current portion of the ARO at September 30, 2018 and December 31, 2017, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.

Asset Retirement Obligations _2

Asset Retirement Obligations - Rollforward of Nuclear Decommissioning ARO (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current		$ 910		$ 910		$ 0
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion Expense	[1]			367	$ 350
Exelon Generation Co L L C [Member]
Asset Retirement Obligation Roll Forward Analysis [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current		910		910		0
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion Expense	[1]			365	$ 350
Net increase due to changes in, and timing of, estimated future cash flows				345
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear Decommissioning ARO, Beginning Balance	[2]		$ 9,662	9,662
Asset Retirement Obligation, Liabilities Settled				(783)
Accretion Expense				357
Net increase due to changes in, and timing of, estimated future cash flows		84	$ 32	116
Costs incurred related to decommissioning plants				(35)
Nuclear Decommissioning ARO, Ending Balance		9,317		9,317
Current portion of ARO		$ 12		$ 12		$ 13
[1]	Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.
[2]	Includes $12 million and $13 million for the current portion of the ARO at September 30, 2018 and December 31, 2017, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.

Asset Retirement Obligations _3

Asset Retirement Obligations - Unrealized Gains on NDT Funds (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments		$ 9	$ 4	$ 7	$ 5
Collateral Pledged [Member] | Regulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[1]	(66)	44	(335)	253
Collateral Pledged [Member] | Unregulated Operation [Member]
Unrealized Losses On Nuclear Decommissioning Trust Fund Investment [Line Items]
Unrealized Gain (Loss) on Investments	[2],[3]	$ 72	$ 111	$ (143)	$ 347
[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 $9 million and $4 million of net unrealized losses related to the Zion Station pledged assets for the three months ended September 30, 2018 and 2017, respectively. Excludes $7 million and $5 million of net unrealized losses related to the Zion Station pledged assets for the nine months ended September 30, 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.
[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.

Asset Retirement Obligations _4

Asset Retirement Obligations - Assets, Payables and Withdrawals by ZionSolutions (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Nuclear Decommissioning Additional Narrative Information [Line Items]
Held-to-maturity Securities Pledged as Collateral	[1]	$ 9	$ 39
Accounts Payable, Interest-bearing, Noncurrent	[2],[3]	9	37
Accounts Payable, Interest-bearing, Current	[4]	$ 965	$ 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			9 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2018
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			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Amortization of:
Net periodic benefit cost	$ 12	$ 27		$ 33	$ 82
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	100	98		303	290
Interest cost	201	211		602	632
Expected return on assets	(312)	(300)		(939)	(898)
Amortization of:
Prior service cost (benefit)	0	(1)		1	0
Actuarial loss	158	152		472	455
Settlement charges	0	(1)		(1)	(3)
Net periodic benefit cost	147	161	[1]	440	482	[1]
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	28	26		84	79
Interest cost	43	45		131	136
Expected return on assets	(43)	(39)		(130)	(121)
Amortization of:
Prior service cost (benefit)	(47)	(47)		(140)	(140)
Actuarial loss	18	15		50	46
Settlement charges	0	0		0	0
Net periodic benefit cost	(1)	0	[1]	(5)	0	[1]
Pepco Holdings LLC [Member]
Amortization of:
Net periodic benefit cost	$ 0	$ 0		$ 0	$ 0
[1]	FitzPatrick net benefit costs are included for the period after the acquisition date of March 31, 2017.

Retirement Benefits - Allocated

Retirement Benefits - Allocated Portion of Pension and Postretirement Benefit Plan Costs (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						$ 435		$ 482
Pension and other post retirement benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	[1]	$ 145		$ 161	[2]	435		482	[2]
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]	13		13		42		40
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						151		170
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)		50		57	[2]	151		170	[2]
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						133		131
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		133		131
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						14		21
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		14		21
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						43		47
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		44		48
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						10		19
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)		3		6		10		19
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						5		10
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)		2		3		5		10
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						10		10
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		10		10
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)						51		72
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]	17		24		51		72
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)		$ 9	[3]	$ 12	[3]	$ 26	[4]	$ 33	[4]
[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, ACE or PHISCO 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			9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[1]	$ 44	$ 34	[2]	$ 126	$ 97	[2]
Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[3]	5	2		16	7
Exelon Generation Co L L C [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		23	14	[2]	65	42	[2]
Commonwealth Edison Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		8	9		23	24
PECO Energy Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		2	3		7	7
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		2	3		5	7
Potomac Electric Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	1		2	3
Delmarva Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	1		2	2
Atlantic City Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions		1	0		2	1
Pepco Holdings LLC [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[1]	4	3		10	10
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Defined Benefit Plan Disclosure [Line Items]
Savings Plan Matching Contributions	[4]	$ 1	$ 1		$ 4	$ 4
[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, 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, ACE or PHISCO 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.

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				$ 32,187
Beginning Balance				29,896
Amounts reclassified from AOCI(b)	[1]	$ 45	$ 34	137		$ 108
Other comprehensive income		52	44	169		69
Ending balance		33,388		33,388
Ending Balance		31,020		31,020
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings				539
Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(14)		(17)
OCI before reclassifications	[2]			11		2
Amounts reclassified from AOCI(b)	[2],[3]			1		3
Other comprehensive income	[2]			12		5
Ending balance	[2]	(2)	(12)	(2)		(12)
Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
Unrealized gains (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			10		4
OCI before reclassifications	[2]			0		2
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		2
Ending balance	[2]	0	6	0		6
Unrealized gains (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]			(10)
Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(2,998)	[5]	(2,610)
OCI before reclassifications	[2]			22		(55)
Amounts reclassified from AOCI(b)	[1]	45	35	136	[2],[3]	105	[2],[3]
Other comprehensive income	[2]			158		50
Ending balance	[2]	(2,840)	(2,560)	(2,840)		(2,560)
Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(23)		(30)
OCI before reclassifications	[2]			(4)		7
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			(4)		7
Ending balance	[2]	(27)	(23)	(27)		(23)
Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(1)		(7)
OCI before reclassifications	[2]			1		7
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			1		7
Ending balance	[2]	0	0	0		0
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	[2]			0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[2]			(3,026)		(2,660)
OCI before reclassifications	[2]			30		(37)
Amounts reclassified from AOCI(b)	[2],[3]			137		108
Other comprehensive income	[2]			167		71
Ending balance	[2]	(2,869)	(2,589)	(2,869)		(2,589)
Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			(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)	[1]	0	(1)	1		3
Other comprehensive income		2	4	11		16
Ending Balance		15,960		15,960
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			(16)		(19)
OCI before reclassifications	[2]			11		2
Amounts reclassified from AOCI(b)	[2],[3]			1		3
Other comprehensive income	[2]			12		5
Ending Balance	[2]	(4)	(14)	(4)		(14)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
Exelon Generation Co L L C [Member] | Unrealized gains (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			3		2
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	2	0		2
Exelon Generation Co L L C [Member] | Unrealized gains (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]			(3)
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			0		0
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[1]	0	0	0	[2],[3]	0	[2],[3]
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	0	0		0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
Exelon Generation Co L L C [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			(23)		(30)
OCI before reclassifications	[2]			(4)		7
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			(4)		7
Ending Balance	[2]	(27)	(23)	(27)		(23)
Exelon Generation Co L L C [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
Exelon Generation Co L L C [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			(1)		(7)
OCI before reclassifications	[2]			1		6
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			1		6
Ending Balance	[2]	0	(1)	0		(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	[2]			0
Exelon Generation Co L L C [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			(37)		(54)
OCI before reclassifications	[2]			8		15
Amounts reclassified from AOCI(b)	[2],[3]			1		3
Other comprehensive income	[2]			9		18
Ending Balance	[2]	(31)	(36)	(31)		(36)
Exelon Generation Co L L C [Member] | Total | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			(3)
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance				3,577
Ending Balance		3,684		3,684
PECO Energy Co [Member] | Gains (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			0		0
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	0	0		0
PECO Energy Co [Member] | Gains (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
PECO Energy Co [Member] | Unrealized gains (losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			1		1
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	1	0		1
PECO Energy Co [Member] | Unrealized gains (losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2],[4]			(1)
PECO Energy Co [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			0		0
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	0	0		0
PECO Energy Co [Member] | Pension and Non-Pension Postretirement Benefit Plan Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
PECO Energy Co [Member] | Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			0		0
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	0	0		0
PECO Energy Co [Member] | Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard	[2]			0
PECO Energy Co [Member] | AOCI of Investments in Unconsolidated Affiliates
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			0		0
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	0	0	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	[2]			0
PECO Energy Co [Member] | Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	[2]			1		1
OCI before reclassifications	[2]			0		0
Amounts reclassified from AOCI(b)	[2],[3]			0		0
Other comprehensive income	[2]			0		0
Ending Balance	[2]	$ 0	$ 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	[2]			$ (1)
[1]	Amounts in parenthesis represent a decrease in AOCI.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	Exelon prospectively adopted the new standard Recognition and Measurement of Financial Assets and 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.
[5]	Exelon early adopted the new standard Reclassification of Certain Tax Effects from AOCI. The standard was adopted retrospectively as of December 31, 2017, which resulted in an increase to Exelon’s Retained earnings and Accumulated other comprehensive loss of $539 million, primarily related to deferred income taxes associated with Exelon’s pension and OPEB obligations. See Note 2 — New Accounting Standards for additional information.

Changes in Accumulated Other _4

Changes in Accumulated Other Comprehensive Income - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		$ 137	$ 451	$ 262		$ 601
Amortization of pension and other postretirement benefit plan items				4
Amounts reclassified from AOCI	[1]	(45)	(34)	(137)		(108)
Gains (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]			(1)		(3)
Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	23	23	68		69
Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	(83)	(81)	(251)		(243)
Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	(60)	(58)	(183)		(174)
Tax benefit	[1]	15	23	47		69
Amounts reclassified from AOCI	[1]	(45)	(35)	(136)	[2],[3]	(105)	[2],[3]
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)			1			2
Cash Flow Hedging [Member] | Gains (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	[1]	0	2	(1)		(5)
Total before tax	[1]	0	2	(1)		(5)
Income Tax Expense (Benefit)	[1]	0	(1)	0		2
Net of tax	[1]	0	1	(1)		(3)
Exelon Generation Co L L C [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense (Benefit)		78	239	110		215
Amortization of pension and other postretirement benefit plan items				3
Amounts reclassified from AOCI	[1]	0	1	(1)		(3)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[2],[3]			(1)		(3)
Exelon Generation Co L L C [Member] | Prior service costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	0	0	0		0
Exelon Generation Co L L C [Member] | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1],[4]	0	0	0		0
Exelon Generation Co L L C [Member] | Pension and Non-Pension Postretirement Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of pension and other postretirement benefit plan items	[1]	0	0	0		0
Tax benefit	[1]	0	0	0		0
Amounts reclassified from AOCI	[1]	0	0	0	[2],[3]	0	[2],[3]
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member] | Gains (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	[1]	0	2	(1)		(5)
Total before tax	[1]	0	2	(1)		(5)
Income Tax Expense (Benefit)	[1]	0	(1)	0		2
Net of tax	[1]	$ 0	$ 1	$ (1)		$ (3)
[1]	Amounts in parenthesis represent a decrease in AOCI.
[2]	All amounts are net of tax and noncontrolling interests. Amounts in parenthesis represent a decrease in AOCI.
[3]	See next tables for details about these reclassifications.
[4]	This AOCI component is included in the computation of net periodic pension and OPEB cost (see Note 14 — Retirement Benefits for additional information).

Changes in Accumulated Other _5

Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	$ (17)	$ (22)	$ (61)	$ (74)
Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	6	9	18	27
Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(21)	(32)	(65)	(96)
Pension and Non-Pension Postretirement Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	(2)	0	(8)	2
Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	0	0	(5)	(3)
Unrealized gains (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in unrealized gains (losses) on investments in unconsolidated affiliates	0	1	(1)	(2)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0	0	0	(2)
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	0	0	(5)	(6)
Exelon Generation Co L L C [Member] | Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	0	0	(4)	(3)
Exelon Generation Co L L C [Member] | Unrealized gains (losses) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Tax	0	0
Change in unrealized gains (losses) on investments in unconsolidated affiliates	$ 0	$ 0	(1)	(2)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax			$ 0	$ (1)

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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 733	$ 823	$ 1,858	$ 1,907
Weighted average common shares outstanding — basic	968	962	967	941
Assumed exercise and/or distributions of stock-based awards	2	3	2	2
Weighted average common shares outstanding — diluted	970	965	969	943

Earnings Per Share and Equity_3

Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Statement Of Equity Line Item [Line Items]
Treasury Stock, Shares	1,832,457		1,832,457		1,832,457
Treasury Stock, Value	$ 123		$ 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	2,000,000	7,000,000	3,000,000	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 - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)MGPSiteOpen_claimgal	Dec. 31, 2016MW	Sep. 30, 2018USD ($)MGPSiteOpen_claimgalMW	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 3,386		$ 3,386
Costs Incurred, Development Costs			$ 458
Power Volume | MW		10	220
Business Acquisition Residual Commitment | MW			55
Loss Contingency, Loss in Period			$ 50
Accrual for Environmental Loss Contingencies, Gross	486		486	$ 466
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	2,766		2,766
Costs Incurred, Development Costs			458
Loss Contingency, Loss in Period			50
Accrued Insurance, Current	13,100		13,100
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability			450
Maximum liability per nuclear incident	12,600		12,600
Prepaid Reinsurance Premiums	345		345
Estimated Insurance Recoveries	3,200		3,200
Site Contingency, Loss Exposure Not Accrued, Best Estimate			90
Accrual for Environmental Loss Contingencies, Gross	102		102	117
Accrual for Environmental Loss Contingencies, Component Amount	90		90
Liability for Asbestos and Environmental Claims, Gross	$ 80		$ 80	78
Open Asbestos Related Personal Injury Claims | Open_claim	241		241
Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 91		$ 91
Accrual for Environmental Loss Contingencies, Gross	$ 27		$ 27	29
Number of Real Estate Properties | MGPSite	9		9
Environmental Remediation Expense			$ 10
Commonwealth Edison Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 211		$ 211
Mgp Site Contingency Approved Cleanup Count | MGPSite	42		42
Mgp Site Contingency Count | MGPSite	20		20
Mgp Site Contingency Monitoring Count | MGPSite	22		22
Other Increase (Decrease) in Environmental Liabilities	$ 48
Accrual for Environmental Loss Contingencies, Gross	323		$ 323	285
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	43		43
Accrual for Environmental Loss Contingencies, Gross	25		25	27
PECO Energy Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 187		$ 187
Mgp Site Contingency Approved Cleanup Count | MGPSite	26		26
Mgp Site Contingency Count | MGPSite	17		17
Mgp Site Contingency Monitoring Count | MGPSite	9		9
Accrual for Environmental Loss Contingencies, Gross	$ 28		$ 28	30
Baltimore Gas and Electric Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 28		$ 28
Mgp Site Contingency Approved Cleanup Count | MGPSite	13		13
Mgp Site Contingency Count | MGPSite	9		9
Mgp Site Contingency Monitoring Count | MGPSite	4		4
Accrual for Environmental Loss Contingencies, Gross	$ 6		$ 6	5
Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 13		$ 13
Mgp Site Contingency Approved Cleanup Count | gal	3		3
Mgp Site Contingency Count | MGPSite	2		2
Accrual for Environmental Loss Contingencies, Gross	$ 1		$ 1	$ 1
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross	24		24
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross	56		$ 56
Maximum [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Business Acquisition, Expected New Generation Mwh | MW			300
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] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Business Acquisition, Expected New Generation Mwh | MW			285
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]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	2,800		$ 2,800
Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Nuclear financial protection pool value	420		420
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Mutual Property Insurance Distribution To Members	31		31
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Mutual Property Insurance Distribution To Members	31		31
Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	513		513
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	315		315
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	120		120
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	84		84
West Lake [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross	280		280
West Lake [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross	20		$ 20
Other Solar Projects [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Business Acquisition, Expected New Generation Mwh | MW			37
Other Non-Financial Commitment | MW			27
Other Commitment	137		$ 137
Other Solar Projects [Member] | Pepco Holdings Inc [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment	$ 137		$ 137
Wind Assets [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Non-Financial Commitment | MW			100
Purchase Commitment | MW			120

Commitments and Contingencies M

Commitments and Contingencies Merger Commitment (Details) $ in Millions	Sep. 30, 2018USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,386
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	91
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	43
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	13
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	9
Pepco Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	513
Pepco Holdings Inc [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings Inc [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	122
Pepco Holdings Inc [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings Inc [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings Inc [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings Inc [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings Inc [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	138
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	315
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	94
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	75
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	84
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	67
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 7

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Sep. 30, 2018USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,386
Guarantor Obligations, Maximum Exposure, Undiscounted	60
Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,584	[1]
Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,402	[2]
Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	378
Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Exelon Generation Co L L C [Member]
Other Commitments [Line Items]
Other Commitment	2,766
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	1,565	[1]
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	1,201	[2]
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] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
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] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
Commonwealth Edison Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	200
Commonwealth Edison Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
PECO Energy Co [Member]
Other Commitments [Line Items]
Other Commitment	187
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
PECO Energy Co [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	9	[2]
PECO Energy Co [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	178
PECO Energy Co [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
Baltimore Gas and Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	28
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	3	[1]
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	25	[2]
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] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	0	[3]
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings LLC [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	4	[1]
Pepco Holdings LLC [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	65	[2]
Pepco Holdings LLC [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings LLC [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	22	[3]
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	43
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Potomac Electric Power Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	4	[1]
Potomac Electric Power Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	32	[2]
Potomac Electric Power Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
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	25
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] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	4	[2]
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] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	9	[3]
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	9
Guarantor Obligations, Maximum Exposure, Undiscounted	17
Atlantic City Electric Company [Member] | Financial Standby Letter of Credit [Member]
Other Commitments [Line Items]
Other Commitment	0	[1]
Atlantic City Electric Company [Member] | Surety Bond [Member]
Other Commitments [Line Items]
Other Commitment	3	[2]
Atlantic City Electric Company [Member] | Guarantee of Indebtedness of Others [Member]
Other Commitments [Line Items]
Other Commitment	0
Atlantic City Electric Company [Member] | Guarantee Obligations [Member]
Other Commitments [Line Items]
Other Commitment	$ 6	[3]
[1]	Letters of credit (non-debt) - Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.
[2]	Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.
[3]	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 $60 million, $17 million of which is a guarantee by Pepco, $25 million by DPL and $17 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 Contingencies_4

Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 486	$ 466
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	102	117
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	323	285
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	28	30
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	6	5
Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	29
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	25	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	352	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	321	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	27	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 LLC [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

Supplemental Financial Inform_3

Supplemental Financial Information - Narrative (Details) - PECO Energy Co [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Net	$ 11	$ 11
Financing Receivable, Allowance for Credit Losses	11
Risk Level, Medium [Member]
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Allowance for Credit Losses	3
Risk Level, High [Member]
Supplemental Financial Information Tables [Line Items]
Financing Receivable, Allowance for Credit Losses	$ 8

Supplemental Financial Inform_4

Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	$ 214	$ 159	$ 476	$ 439
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	58	59	257	165
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(66)	44	(335)	253
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		72	111	(143)	347
Net unrealized income (losses) on pledged assets		(9)	(4)	(7)	(5)
Regulatory offset to decommissioning trust fund-related activities	[2]	(110)	(161)	(110)	(558)
Total decommissioning-related activities		159	208	138	641
Investment income		9	2	19	6
Unrecognized Tax Benefits Interest Income		1	4	5	3
Penalty income related to uncertain income tax positions					2
AFUDC - equity		16	17	47	51
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		(12)	(27)	(33)	(82)
Other Income		21	6	36	22
Other, net		194	210	212	643
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	214	159	476	439
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	58	59	257	165
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		(66)	44	(335)	253
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		72	111	(143)	347
Net unrealized income (losses) on pledged assets		(9)	(4)	(7)	(5)
Regulatory offset to decommissioning trust fund-related activities	[2]	(110)	(161)	(110)	(558)
Total decommissioning-related activities		159	208	138	641
Investment income		5	1	12	4
Unrecognized Tax Benefits Interest Income		0	0	1	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		15	0	13	3
Other, net		179	209	164	648
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		0	0	0	0
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		4	2	12	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		3	3	9	8
Other, net		7	5	21	14
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		0	0	0	0
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		1	2	3	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		1	0	1	0
Other, net		2	2	4	6
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		0	0	0	0
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		5	4	13	12
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		0	0	1	0
Other, net		5	4	14	12
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		2	1	3	2
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		6	9	19	27
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		3	3	11	11
Other, net		11	13	33	40
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		1	1	1	1
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		6	6	17	17
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		0	0	5	4
Other, net		7	7	23	22
Delmarva Power and Light Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		1	0	1	0
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		0	2	2	5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		1	2	4	5
Other, net		2	4	7	10
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	[1]	0	0	0	0
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	[1]	0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units		0	0	0	0
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement		0	0	0	0
Net unrealized income (losses) on pledged assets		0	0	0	0
Regulatory offset to decommissioning trust fund-related activities	[2]	0	0	0	0
Total decommissioning-related activities		0	0	0	0
Investment income		0	0	0	0
Unrecognized Tax Benefits Interest Income		0	0	0	0
Penalty income related to uncertain income tax positions					0
AFUDC - equity		0	1	0	5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		0	0	0	0
Other Income		1	0	2	1
Other, net		$ 1	$ 1	$ 2	$ 6
[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 Inform_5

Supplemental Financial Information Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 253	$ 245	$ 705	$ 682
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	32	35	92	97
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	67	65	188	181
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	39	35	102	95
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	23	22	70	69
Pepco Holdings LLC [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	92	88	253	240
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	87	83	238	226
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	5	5	15	14
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 0	$ 0	$ 0	$ 0

Supplemental Financial Inform_6

Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		$ 2,829	$ 2,416
Regulatory assets	[1]		412	355
Amortization of intangible assets, net	[1]		43	43
Amortization of Power Contracts Emission Credits	[2]		8	19
Amortization of Nuclear Fuel Lease	[3]		852	816
Asset Retirement Obligation, Accretion Expense	[4]		367	350
Total depreciation, amortization and accretion			4,511	3,999
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			435	482
Gain (loss) on equity method investments			22	26
Provision for uncollectible accounts			133	103
Stock-based compensation costs			64	76
Other Decommissioning Related Activity	[5]		(39)	(213)
Energy-related options	[6]		4	15
Amortization of regulatory asset related to debt costs			6	7
Amortization of rate stabilization deferral			0	(7)
Amortization of debt fair value adjustment			(12)	(13)
Discrete impacts from EIMA	[7]		27	(61)
Amortization of debt costs			26	57
Inventory Write-down			15	52
Employee Benefits and Share-based Compensation, Noncash			84
Merger related commitments				0
Restructuring Costs				33
Asset Retirement Obligation, Revision of Estimate			20
Other			19	46
Total other noncash operating activities			804	603
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			175	101
Increase (Decrease) in PPE related to ARO update		$ 67	67	141
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				16
Stock Issued			4	5
Payments to Acquire Land			3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				8
Fair value adjustment of long-term debt due to retirement				(5)
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		1,347	1,010
Regulatory assets	[1]		0	0
Amortization of intangible assets, net	[1]		36	36
Amortization of Power Contracts Emission Credits	[2]		8	19
Amortization of Nuclear Fuel Lease	[3]		852	816
Asset Retirement Obligation, Accretion Expense	[4]		365	350
Total depreciation, amortization and accretion			2,608	2,231
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			151	170
Gain (loss) on equity method investments			23	26
Provision for uncollectible accounts			38	31
Stock-based compensation costs			0	0
Other Decommissioning Related Activity	[5]		(39)	(213)
Energy-related options	[6]		4	15
Amortization of regulatory asset related to debt costs			0	0
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			(9)	(9)
Discrete impacts from EIMA			0	0
Amortization of debt costs			10	33
Inventory Write-down			13	50
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				25
Asset Retirement Obligation, Revision of Estimate		(84)	0
Other			(4)	4
Total other noncash operating activities			187	132
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			226	20
Business Combination, Contingent Consideration, Liability, Noncurrent				33
Increase (Decrease) in PPE related to ARO update		47	47	141
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				16
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		613	579
Regulatory assets	[1]		83	52
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			696	631
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			133	131
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			30	25
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			2	3
Amortization of rate stabilization deferral			0	0
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA	[7]		27	(61)
Amortization of debt costs			4	3
Inventory Write-down			2	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			(11)	10
Total other noncash operating activities			187	112
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			28	79
Increase (Decrease) in PPE related to ARO update		4	4	0
Contribution of Property	[8]			21
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		204	194
Regulatory assets	[1]		20	19
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			224	213
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			14	21
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			25	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	1
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			1	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			1	(2)
Total other noncash operating activities			41	38
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			4	29
Increase (Decrease) in PPE related to ARO update		0	0	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		249	233
Regulatory assets	[1]		109	115
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			358	348
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			43	47
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			6	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			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			1	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			0
Other			(8)	(7)
Total other noncash operating activities			42	52
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			44	16
Increase (Decrease) in PPE related to ARO update		1	1	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				8
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		355	342
Regulatory assets	[1]		200	169
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			555	511
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			51	72
Gain (loss) on equity method investments			(1)	0
Provision for uncollectible accounts			32	26
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			3	3
Amortization of rate stabilization deferral			0	(14)
Amortization of debt fair value adjustment			(3)	(4)
Discrete impacts from EIMA			0	0
Amortization of debt costs			3	1
Inventory Write-down			0	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(8)
Restructuring Costs				3
Asset Retirement Obligation, Revision of Estimate			20
Other			4	(14)
Total other noncash operating activities			109	66
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			54	6
Increase (Decrease) in PPE related to ARO update		15	15
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		161	153
Regulatory assets	[1]		125	89
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			286	242
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			10	19
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			12	11
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	(12)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			2	1
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(6)
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			22
Other			(5)	(6)
Total other noncash operating activities			42	8
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			15	7
Increase (Decrease) in PPE related to ARO update		12	12
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		97	92
Regulatory assets	[1]		38	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			135	124
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			5	10
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			6	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			1	1
Amortization of rate stabilization deferral			0	(2)
Amortization of debt fair value adjustment			0	0
Discrete impacts from EIMA			0	0
Amortization of debt costs			1	0
Inventory Write-down			0	1
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments	[9]			(2)
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			(1)
Other			4	(3)
Total other noncash operating activities			16	6
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			20	14
Increase (Decrease) in PPE related to ARO update		2	2	0
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			0
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Depreciation	[1]		70	66
Regulatory assets	[1]		37	47
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			107	113
Other Non-Cash Operating Activities [Abstract]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)			10	10
Gain (loss) on equity method investments			0	0
Provision for uncollectible accounts			14	14
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			0	0
Amortization of debt costs			0	0
Inventory Write-down			0	0
Employee Benefits and Share-based Compensation, Noncash			0
Merger related commitments				0
Restructuring Costs				0
Asset Retirement Obligation, Revision of Estimate			(1)
Other			0	(4)
Total other noncash operating activities			24	21
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Increase (Decrease) in capital expenditures not paid			16	18
Increase (Decrease) in PPE related to ARO update		$ 1	1
Noncash or Part Noncash Acquisition, Fixed Assets Acquired				0
Stock Issued			0	0
Payments to Acquire Land			$ 3
Non Cash Dissolution of Financing Trust Due to Long-term Debt Retirement				$ 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 decommissioning-related activities for the Regulatory Agreement Units, including the elimination of operating revenues, ARO accretion, ARC amortization, investment income and income taxes related to all NDT fund activity for these units. See Note 15 — Asset Retirement Obligations 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 and expenses.
[7]	Reflects the change in ComEd's distribution and energy efficiency formula rates. See Note 6 — Regulatory Matters for additional information.
[8]	See Note 12 - Income Taxes for additional information on the like-kind exchange tax position.
[9]	See Note 4 - Mergers, Acquisitions and Dispositions for additional information.

Supplemental Financial Inform_7

Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017		Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 23,122	[1]	$ 21,064	[2]
Accounts receivable, net
Allowance for uncollectible accounts	354		322
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	1,918		898		$ 1,203	$ 635
Restricted cash	240		207		320	253
Restricted Cash, Noncurrent	163		85		22	26
Cash, Cash Equivalents and Restricted Cash at End of Period	2,321		1,190		1,545	914
Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,278		3,159
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	12,753	[1]	11,428	[2]
Accounts receivable, net
Allowance for uncollectible accounts	112		114
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	1,187		416		360	290
Restricted cash	152		138		186	158
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	1,339		554		546	448
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,278		3,159
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,557		4,269
Accounts receivable, net
Allowance for uncollectible accounts	93		73
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	124		76		257	56
Restricted cash	12		5		52	2
Restricted Cash, Noncurrent	144		63		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	280		144		309	58
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,521		3,411
Accounts receivable, net
Allowance for uncollectible accounts	61		56
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	102		271		330	63
Restricted cash	5		4		4	4
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	107		275		334	67
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,579		3,405
Accounts receivable, net
Allowance for uncollectible accounts	22		24
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	113		17		29	23
Restricted cash	3		1		1	24
Restricted Cash, Noncurrent	0		0		0	3
Cash, Cash Equivalents and Restricted Cash at End of Period	116		18		30	50
Pepco Holdings LLC [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	759		487
Accounts receivable, net
Allowance for uncollectible accounts	66		55
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	153		30		137	170
Restricted cash	42		42		43	43
Restricted Cash, Noncurrent	19		23		22	23
Cash, Cash Equivalents and Restricted Cash at End of Period	214		95		202	236
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,311		3,177
Accounts receivable, net
Allowance for uncollectible accounts	25		21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	12		5		117	9
Restricted cash	35		35		34	33
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	47		40		151	42
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,315		1,247
Accounts receivable, net
Allowance for uncollectible accounts	16		16
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	110		2		3	46
Restricted cash	0		0		0	0
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	110		2		3	46
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,121		1,066
Accounts receivable, net
Allowance for uncollectible accounts	25		18
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	11		2		5	101
Restricted cash	7		6		9	9
Restricted Cash, Noncurrent	19		23		22	23
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 37		$ 31		$ 36	$ 133
[1]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,278 million.
[2]	Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million.

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Sep. 30, 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				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Segment Reporting Information [Line Items]
Rate-regulated electric revenues				$ 0				$ 0
Rate-regulated natural gas revenues				0				0
Revenues		$ 9,403		8,768		$ 27,170		25,180
Operating revenues from affiliates		0	[1]	0	[1]	0	[2]	0
Net income (loss)		800		865		1,979		1,928
Assets	[3]	119,485				119,485				$ 116,770
Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		1,340		1,278		3,541		3,376
Rate-regulated natural gas revenues		23		18		129		105
Revenues		1,361		1,310		3,688		3,557
Operating revenues from affiliates		3		12		11		35
Net income (loss)		187		153		336		359
Assets	[4]	21,957				21,957				21,247
Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues				0				0
Rate-regulated natural gas revenues				0				0
Revenues		5,278		4,750		15,368		13,843
Operating revenues from affiliates		308		296		979		894
Net income (loss)		300		346		667		508
Assets	[5]	48,207				48,207				48,457
Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		4,435	[6]	3,746	[6]	12,221	[7]	10,626	[7]
Competitive businesses natural gas revenues		397	[6]	460	[6]	1,831	[7]	1,807	[7]
Competitive businesses other revenues		139	[6]	249	[6]	335	[7]	522	[7]
Rate-regulated electric revenues		4,270	[6]	4,164	[6]	11,766	[7]	11,318	[7]
Rate-regulated natural gas revenues		162	[6]	149	[6]	1,017	[7]	906	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	1	[7]
Revenues		9,403	[6]	8,768	[6]	27,170	[7]	25,180	[7]
Net income (loss)		800		865		1,979		1,928
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		(306)	[6]	(295)	[6]	(969)	[7]	(888)	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	(8)	[7]	0	[7]
Competitive businesses other revenues		(1)	[6]	0	[6]	(4)	[7]	0	[7]
Rate-regulated electric revenues		(7)	[6]	(7)	[6]	(34)	[7]	(23)	[7]
Rate-regulated natural gas revenues		(5)	[6]	(2)	[6]	(13)	[7]	(6)	[7]
Shared service and other revenues		(461)	[6]	(458)	[6]	(1,408)	[7]	(1,350)	[7]
Revenues		(780)	[6]	(762)	[6]	(2,436)	[7]	(2,267)	[7]
Operating revenues from affiliates		(779)	[1]	(759)	[1]	(2,430)	[2]	(2,262)	[2]
Net income (loss)		0		0		0		(2)
Assets		(10,378)				(10,378)				(10,552)
Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		(4)	[8]	(3)	[8]	(12)	[9]	(13)	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		(100)	[8]	0	[8]	(316)	[9]	(2)	[9]
Revenues		(104)	[8]	(3)	[8]	(328)	[9]	(15)	[9]
Operating revenues from affiliates		(105)		(4)		(327)		(14)
Net income (loss)		3		12		11		35
Assets		(5,300)				(5,300)				(4,987)
Exelon Generation Co L L C [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		4,741	[6],[10]	4,041	[6],[10]	13,190	[7],[11]	11,514	[7],[11]
Competitive businesses natural gas revenues		397	[6],[10]	460	[6],[10]	1,839	[7],[11]	1,807	[7],[11]
Competitive businesses other revenues		140	[6],[10]	249	[6],[10]	339	[7],[11]	522	[7],[11]
Rate-regulated electric revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Rate-regulated natural gas revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Shared service and other revenues		0	[6],[10]	0	[6],[10]	0	[7],[11]	0	[7],[11]
Revenues		5,278	[6],[10]	4,750	[6],[10]	15,368	[7],[11]	13,843	[7],[11]
Net income (loss)		300	[10]	346	[10]	667	[11]	508	[11]
Assets	[10]	48,207				48,207				48,457
Exelon Generation Co L L C [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		308	[1],[10]	294	[1],[10]	981	[2],[11]	888	[2],[11]
Commonwealth Edison Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		1,598	[6]	1,571	[6]	4,508	[7]	4,227	[7]
Rate-regulated natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		1,598	[6]	1,571	[6]	4,508	[7]	4,227	[7]
Net income (loss)		193		189		523		447
Assets		31,119				31,119				29,726
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		4	[1]	3	[1]	23	[2]	12	[2]
PECO Energy Co [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		700	[6]	662	[6]	1,893	[7]	1,802	[7]
Rate-regulated natural gas revenues		57	[6]	53	[6]	382	[7]	339	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		757	[6]	715	[6]	2,275	[7]	2,141	[7]
Net income (loss)		126		112		336		327
Assets		10,621				10,621				10,170
PECO Energy Co [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2	[1]	2	[1]	5	[2]	5	[2]
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		645	[6]	658	[6]	1,850	[7]	1,895	[7]
Rate-regulated natural gas revenues		86	[6]	80	[6]	519	[7]	468	[7]
Shared service and other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Revenues		731	[6]	738	[6]	2,369	[7]	2,363	[7]
Net income (loss)		63		62		242		231
Assets		9,541				9,541				9,104
Baltimore Gas and Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		6	[1]	3	[1]	18	[2]	12	[2]
Pepco Holdings LLC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses natural gas revenues		0	[6]	0	[6]	0	[7]	0	[7]
Competitive businesses other revenues		0	[6]	0	[6]	0	[7]	0	[7]
Rate-regulated electric revenues		1,334	[6],[8]	1,280	[6],[8]	3,549	[7],[9]	3,417	[7],[9]
Rate-regulated natural gas revenues		24	[6],[8]	18	[6],[8]	129	[7],[9]	105	[7],[9]
Shared service and other revenues		3	[6],[8]	12	[6],[8]	10	[7],[9]	35	[7],[9]
Revenues		1,361	[6],[8]	1,310	[6],[8]	3,688	[7],[9]	3,557	[7],[9]
Net income (loss)		187		153		336		359
Assets		21,957				21,957				21,247
Pepco Holdings LLC [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		3	[1]	12	[1]	11	[2]	35	[2]
Potomac Electric Power Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		628	[8]	604	[8]	1,708	[9]	1,649	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		628	[8]	604	[8]	1,708	[9]	1,649	[9]
Net income (loss)		89		87		174		188
Assets		8,199				8,199				7,832
Potomac Electric Power Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		1		5		4
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		304	[8]	309	[8]	872	[9]	866	[9]
Rate-regulated natural gas revenues		24	[8]	18	[8]	129	[9]	105	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		328	[8]	327	[8]	1,001	[9]	971	[9]
Net income (loss)		33		31		90		107
Assets		4,601				4,601				4,357
Delmarva Power and Light Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		2		2		6		6
Atlantic City Electric Company [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		406	[8]	370	[8]	981	[9]	915	[9]
Rate-regulated natural gas revenues		0	[8]	0	[8]	0	[9]	0	[9]
Shared service and other revenues		0	[8]	0	[8]	0	[9]	0	[9]
Revenues		406	[8]	370	[8]	981	[9]	915	[9]
Net income (loss)		61		41		76		77
Assets		3,694				3,694				3,445
Atlantic City Electric Company [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		1		0		2		2
Corporate and Other [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Competitive businesses electric revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Competitive businesses natural gas revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Competitive businesses other revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Rate-regulated electric revenues		0	[10],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Rate-regulated natural gas revenues		0	[6],[12]	0	[6],[12]	0	[7],[13]	0	[7],[13]
Shared service and other revenues		458	[6],[12]	446	[6],[12]	1,398	[7],[13]	1,316	[7],[13]
Revenues		458	[6],[12]	446	[6],[12]	1,398	[7],[13]	1,316	[7],[13]
Net income (loss)		(69)	[12]	3	[12]	(125)	[13]	58	[13]
Assets	[12]	8,418				8,418				8,618
Corporate and Other [Member] | Corporate, Non-Segment [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Rate-regulated electric revenues		0	[8],[14]	0	[8],[14]	0	[9],[15]	0	[9],[15]
Rate-regulated natural gas revenues		0	[8],[14]	0	[8],[14]	0	[9],[15]	0	[9],[15]
Shared service and other revenues		103	[8],[14]	12	[8],[14]	326	[9],[15]	37	[9],[15]
Revenues		103	[8],[14]	12	[8],[14]	326	[9],[15]	37	[9],[15]
Net income (loss)		1	[14]	(18)	[14]	(15)	[15]	(48)	[15]
Assets	[14]	10,763				10,763				$ 10,600
Corporate and Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		456	[1],[12]	445	[1],[12]	1,392	[2],[13]	1,312	[2],[13]
Corporate and Other [Member] | Intersegment Eliminations [Member] | Pepco Holdings LLC [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		103	[14]	13	[14]	325	[15]	37	[15]
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,456		1,432		4,179		4,222
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		35		31		97		111
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		69		98		198		330
Generation Mid Atlantic [Member] | PotomacElectricPowerCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		46		57		143		209
Generation Mid Atlantic [Member] | DelmarvaPowerandLightCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		26		47		103		138
Generation Mid Atlantic [Member] | AtlanticCityElectricCompanyAffiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		10		7		21		23
Generation Mid Atlantic [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,449	[16]	1,421	[16]	4,162	[17]	4,207	[17]
Generation Mid Atlantic [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		11		17		15
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,117		1,038		3,593		3,141
Generation Midwest [Member] | Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		122		54		419		77
Generation Midwest [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		1,121	[16]	1,049	[16]	3,601	[17]	3,158	[17]
Generation Midwest [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		$ (4)		$ (11)		$ (8)		(17)
Exelon Consolidations [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]	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.
[3]	Exelon’s consolidated assets include $9,804 million and $9,597 million at September 30, 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 $3,606 million and $3,618 million at September 30, 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 for additional information.
[4]	PHI’s consolidated total assets include $36 million and $41 million at September 30, 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 $78 million and $102 million at September 30, 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 for additional information.
[5]	Generation’s consolidated assets include $9,768 million and $9,556 million at September 30, 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 $3,528 million and $3,516 million at September 30, 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 for additional information.
[6]	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 September 30, 2018 and 2017.
[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 nine months ended September 30, 2018 and 2017.
[8]	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 September 30, 2018 and 2017.
[9]	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 nine months ended September 30, 2018 and 2017.
[10]	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 September 30, 2018 include revenue from sales to PECO of $35 million, sales to BGE of $69 million, sales to Pepco of $46 million, sales to DPL of $26 million and sales to ACE of $10 million in the Mid-Atlantic region, and sales to ComEd of $122 million in the Midwest region, which eliminate upon consolidation. For the three months ended September 30, 2017, intersegment revenues for Generation include revenue from sales to PECO of $31 million, sales to BGE of $98 million, sales to Pepco of $57 million, sales to DPL of $47 million and sales to ACE of $7 million in the Mid-Atlantic region, and sales to ComEd of $54 million in the Midwest region, which eliminate upon consolidation.
[11]	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 nine months ended September 30, 2018 include revenue from sales to PECO of $97 million, sales to BGE of $198 million, sales to Pepco of $143 million, sales to DPL of $103 million and sales to ACE of $21 million in the Mid-Atlantic region, and sales to ComEd of $419 million in the Midwest region, which eliminate upon consolidation. For the nine months ended September 30, 2017, intersegment revenues for Generation include revenue from sales to PECO of $111 million, sales to BGE of $330 million, sales to Pepco of $209 million, sales to DPL of $138 million and sales to ACE of $23 million in the Mid-Atlantic region, and sales to ComEd of $77 million in the Midwest region, which eliminate upon consolidation.
[12]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[13]	Other primarily includes Exelon’s corporate operations, shared service entities and other financing and investment activities.
[14]	Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities.
[15]	Other primarily includes PHI’s corporate operations, shared service entities and other financing and investment activities
[16]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.
[17]	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				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues		$ 9,403		$ 8,768		$ 27,170		$ 25,180
Operating revenues from affiliates		0	[1]	0	[1]	0	[2]	0
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,456		1,432		4,179		4,222
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,117		1,038		3,593		3,141
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		699		481		2,026		1,461
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		469		427		1,269		1,110
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		444		314		930		753
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		513		335		1,088		779
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,698		4,027		13,085		11,466
Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		440		480		1,944		1,859
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	140		243		339		518
Unrealized Gain (Loss) on Securities		6		52		(96)		(47)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,278		4,750		15,368		13,843
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues		9,403	[4]	8,768	[4]	27,170	[5]	25,180	[5]
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,449	[6]	1,421	[6]	4,162	[7]	4,207	[7]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,121	[6]	1,049	[6]	3,601	[7]	3,158	[7]
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		699	[6]	482	[6]	2,030	[7]	1,469	[7]
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		469	[6]	433	[6]	1,268	[7]	1,124	[7]
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		445	[6]	308	[6]	929	[7]	749	[7]
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		558	[6]	348	[6]	1,200	[7]	807	[7]
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,741	[6]	4,041	[6]	13,190	[7]	11,514	[7]
Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		397	[6]	460	[6]	1,839	[7]	1,807	[7]
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets related to commodity contracts				(13)				(30)
Unrealized Gain (Loss) on Securities		71		73		(104)		(161)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		5,278	[6]	4,750	[6]	15,368	[7]	13,843	[7]
Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		140	[6],[8]	249	[6],[8]	339	[3],[7]	522	[3],[7]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(780)	[4]	(762)	[4]	(2,436)	[5]	(2,267)	[5]
Operating revenues from affiliates		(779)	[1]	(759)	[1]	(2,430)	[2]	(2,262)	[2]
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		7		11		17		15
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(4)		(11)		(8)		(17)
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		(1)		(4)		(8)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		(6)		1		(14)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(1)		6		1		4
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(45)		(13)		(112)		(28)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		(43)		(14)		(105)		(48)
Intersegment Eliminations [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		43		20		105		52
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates	[3]	0		(6)		0		(4)
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Operating revenues from affiliates		0		0		0		0
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		1,397	[6]	1,397	[6]	3,971	[7]	4,260	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		1,095	[6]	982	[6]	3,432	[7]	2,948	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		666	[6]	504	[6]	1,943	[7]	1,555	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		475	[6]	454	[6]	1,305	[7]	1,161	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		156	[6]	164	[6]	470	[7]	520	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		293	[6]	167	[6]	713	[7]	439	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		4,082	[6]	3,668	[6]	11,834	[7]	10,883	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		200	[6]	226	[6]	1,016	[7]	1,237	[7]
Revenue from Contract with Customer [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		4,412	[6]	4,101	[6]	13,235	[7]	12,708	[7]
Revenue from Contract with Customer [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		130	[6],[8]	207	[6],[8]	385	[3],[7]	588	[3],[7]
Other [Member] | Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenues		52	[6],[9]	24	[6],[9]	191	[7],[10]	(53)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenues		26	[6],[9]	67	[6],[9]	169	[7],[10]	210	[7],[10]
Other [Member] | Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenues		33	[6],[9]	(22)	[6],[9]	87	[7],[10]	(86)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenues		(6)	[6],[9]	(21)	[6],[9]	(37)	[7],[10]	(37)	[7],[10]
Other [Member] | Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenues		289	[6],[9]	144	[6],[9]	459	[7],[10]	229	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenues		265	[6],[9]	181	[6],[9]	487	[7],[10]	368	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues		659	[6],[9]	373	[6],[9]	1,356	[7],[10]	631	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Natural Gas [Member]
Segment Reporting Information [Line Items]
Revenues		197	[6],[9]	234	[6],[9]	823	[7],[10]	570	[7],[10]
Other [Member] | Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenues		866	[6],[9]	649	[6],[9]	2,133	[7],[10]	1,135	[7],[10]
Other [Member] | Corporate, Non-Segment [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues		$ 10	[6],[8],[9]	$ 42	[6],[8],[9]	$ (46)	[3],[7],[10]	$ (66)	[3],[7],[10]
[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]	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.
[3]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $30 million decrease to revenues for the amortization of intangible assets and liabilities related to commodity contracts recorded at fair value for the nine months ended September 30, 2017, unrealized mark-to-market losses of $96 million and $47 million for the nine months ended September 30, 2018 and 2017, respectively, and elimination of intersegment revenues.
[4]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the three months ended September 30, 2018 and 2017.
[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 nine months ended September 30, 2018 and 2017.
[6]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.
[7]	Includes all wholesale and retail electric sales to third parties and affiliated sales to the Utility Registrants.
[8]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $13 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 September 30, 2017, unrealized mark-to-market gains of $6 million and $52 million for the three months ended September 30, 2018 and 2017, respectively, and elimination of intersegment revenues.
[9]	Includes revenues from derivatives and leases.
[10]	Includes revenues from derivatives and leases.

Segment Information - Generat_2

Segment Information - Generation Total Revenues Net of Purchased Power and Fuel Expense (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	$ 763		$ 855		$ 2,348		$ 2,411
Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	768		697		2,400		2,140
Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	81		145		298		403
Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	292		295		841		707
Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	98		118		216		258
Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	99		68		309		220
Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	2,101		2,178		6,412		6,139
Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	197	[1]	241	[1]	404	[2]	418	[2]
Unrealized Gain (Loss) on Securities	6		52		(96)		(47)
Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net of Purchase Power And Fuel	2,298		2,419		6,816		6,557
Operating Segments [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	746	[3]	817	[3]	2,303	[4]	2,330	[4]
Operating Segments [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	763	[3]	697	[3]	2,381	[4]	2,129	[4]
Operating Segments [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	83	[3]	151	[3]	310	[4]	423	[4]
Operating Segments [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	290	[3]	295	[3]	832	[4]	708	[4]
Operating Segments [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	161	[3]	229	[3]	396	[4]	446	[4]
Operating Segments [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	143	[3]	118	[3]	430	[4]	359	[4]
Operating Segments [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	2,186	[3]	2,307	[3]	6,652	[4]	6,395	[4]
Operating Segments [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	112	[1],[3]	112	[1],[3]	164	[2],[4]	162	[2],[4]
Amortization Of Intangible Assets Related To Commodity Contracts For Revenue Net Purchased Power And Fuel			(19)				(41)
Unrealized Gain (Loss) on Securities	71		73		(104)		(161)
Nuclear Fuel Amortization	(18)		(6)		(53)		(8)
Operating Segments [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Revenue Net Of Purchase Power And Fuel From External Customers	2,298	[3]	2,419	[3]	6,816	[4]	6,557	[4]
Intersegment Eliminations [Member] | Generation Mid Atlantic [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	17		38		45		81
Intersegment Eliminations [Member] | Generation Midwest [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	5		0		19		11
Intersegment Eliminations [Member] | Generation New England [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(2)		(6)		(12)		(20)
Intersegment Eliminations [Member] | Generation New York [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	2		0		9		(1)
Intersegment Eliminations [Member] | Generation ERCOT [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(63)		(111)		(180)		(188)
Intersegment Eliminations [Member] | Generation Other Regions [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(44)		(50)		(121)		(139)
Intersegment Eliminations [Member] | Generation Reportable Segments Total [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	(85)		(129)		(240)		(256)
Intersegment Eliminations [Member] | Generation All Other Segments [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	85	[1]	129	[1]	240	[2]	256	[2]
Intersegment Eliminations [Member] | Generation Total Consolidated Group [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue Net Of Purchase Power And Fuel	$ 0		$ 0		$ 0		$ 0
[1]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $19 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the three months ended September 30, 2017, unrealized mark-to-market gains of $71 million and $73 million for the three months ended September 30, 2018 and 2017, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $18 million and $6 million decrease to revenue net of purchased power and fuel expense for the three months ended September 30, 2018, and 2017, respectively, and the elimination of intersegment revenue net of purchased power and fuel expense.
[2]	Other represents activities not allocated to a region. See text above for a description of included activities. Includes a $41 million decrease to RNF for the amortization of intangible assets and liabilities related to commodity contracts for the nine months ended September 30, 2017, unrealized mark-to-market losses of $104 million and $161 million for the nine months ended September 30, 2018 and 2017, respectively, accelerated nuclear fuel amortization associated with announced early plant retirements as discussed in Note 8 - Early Plant Retirements of $53 million and $8 million decrease to revenue net of purchased power and fuel expense for the nine months ended September 30, 2018 and 2017, respectively, and the elimination of intersegment revenue net of purchased power and fuel expense.
[3]	Includes purchases and sales from/to third parties and affiliated sales to the Utility Registrants.
[4]	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				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues			$ 0				$ 0
Rate-regulated natural gas revenues			0				0
Revenues from alternative revenue programs	$ (25)		54		$ (41)		191
Revenues	9,403		8,768		27,170		25,180
Revenue from Related Parties	0	[1]	0	[1]	0	[2]	0
Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	4,270	[3]	4,164	[3]	11,766	[4]	11,318	[4]
Rate-regulated natural gas revenues	162	[3]	149	[3]	1,017	[4]	906	[4]
Revenues	9,403	[3]	8,768	[3]	27,170	[4]	25,180	[4]
Commonwealth Edison Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	1,609		1,552		4,512		4,167
Rate-regulated natural gas revenues			0				0
Revenues from alternative revenue programs	(15)		16		(27)		48
Revenues	1,598		1,571		4,508		4,227
Revenue from Related Parties	4		3		23		12
Commonwealth Edison Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	(15)		16		(27)		48
Revenues			0				0
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	1,606	[5]	1,547	[5]	4,512	[6]	4,156	[6]
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	7	[7]	8	[7]	23	[8]	23	[8]
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	861		816		2,277		2,071
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	391		366		1,132		1,035
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	131		119		411		346
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	11		11		36		33
Commonwealth Edison Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	212	[9]	235	[9]	656	[10]	671	[10]
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[11]	0	[11]	0	[12]	0	[12]
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[7]	0	[7]	0	[8]	0	[8]
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0		0		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		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		0		0
Commonwealth Edison Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[13]	0	[13]	0	[14]	0	[14]
Commonwealth Edison Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	1,606		1,547		4,512		4,156
Commonwealth Edison Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	(8)		24		(4)		71
PECO Energy Co [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	697		660		1,886		1,798
Rate-regulated natural gas revenues	57		53		382		338
Revenues from alternative revenue programs	1		0		2		0
Revenues	757		715		2,275		2,141
Revenue from Related Parties	2		2		5		5
PECO Energy Co [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	1		0		2		0
Revenues			0				0
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	696	[5]	659	[5]	1,881	[6]	1,792	[6]
Revenue from Related Parties	2		1		5		4
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	3	[7]	3	[7]	10	[8]	10	[8]
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	458		434		1,199		1,147
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	108		106		306		303
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	64		59		174		168
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	7		7		21		23
PECO Energy Co [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	59	[9]	53	[9]	181	[10]	151	[10]
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	57	[11]	53	[11]	382	[12]	339	[12]
Revenue from Related Parties	0		0		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	0	[7]	0	[7]	0	[8]	0	[8]
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	36		33		259		225
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	15		14		102		90
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0		0		1		0
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	5		5		16		16
PECO Energy Co [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	1	[13]	1	[13]	4	[14]	8	[14]
PECO Energy Co [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	753		712		2,263		2,131
PECO Energy Co [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	4		3		12		10
Baltimore Gas and Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	652		626		1,847		1,811
Rate-regulated natural gas revenues	79		73		527		438
Revenues from alternative revenue programs	(6)		36		(23)		102
Revenues	731		738		2,369		2,363
Revenue from Related Parties	6		3		18		12
Baltimore Gas and Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	(6)		36		(23)		102
Revenues			0				0
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	649	[5]	624	[5]	1,842	[6]	1,805	[6]
Revenue from Related Parties	1		1		5		5
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	4	[7]	3	[7]	10	[8]	11	[8]
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	366		352		1,054		1,038
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		65		196		193
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	117		114		325		329
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		8		21		23
Baltimore Gas and Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	91	[9]	85	[9]	246	[10]	222	[10]
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	83	[11]	74	[11]	537	[12]	442	[12]
Revenue from Related Parties	5		2		13		7
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	1	[7]	1	[7]	3	[8]	3	[8]
Baltimore Gas and Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	46		44		345		289
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	8		8		55		51
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	17		19		88		82
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		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	12	[13]	3	[13]	49	[14]	20	[14]
Baltimore Gas and Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	732		698		2,379		2,247
Baltimore Gas and Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	(1)		40		(10)		116
Pepco Holdings LLC [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	1,340		1,278		3,541		3,376
Rate-regulated natural gas revenues	23		18		129		105
Revenues from alternative revenue programs	(5)		2		7		41
Revenues	1,361		1,310		3,688		3,557
Revenue from Related Parties	3		12		11		35
Pepco Holdings LLC [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	(5)		2		7		41
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	1,339	[5]	1,276	[5]	3,544	[6]	3,370	[6]
Revenue from Related Parties			1				2
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	3	[7]	3	[7]	8	[8]	8	[8]
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	726		687		1,839		1,740
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	140		140		370		373
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	303		288		845		814
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	14		14		44		45
Pepco Holdings LLC [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	156	[9]	147	[9]	446	[10]	398	[10]
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	24	[11]	18	[11]	129	[12]	105	[12]
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[7]	0	[7]	0	[8]	0	[8]
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	8		8		68		57
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	5		3		31		25
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	2		1		7		5
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	3		3		12		11
Pepco Holdings LLC [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	6	[13]	3	[13]	11	[14]	7	[14]
Pepco Holdings LLC [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	1,363		1,294		3,673		3,475
Pepco Holdings LLC [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	(2)		16		15		82
Revenue from Related Parties			11	[15]			33	[16]
Potomac Electric Power Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	630		600		1,697		1,622
Rate-regulated natural gas revenues			0				0
Revenues from alternative revenue programs	(4)		3		6		23
Revenues	628		604		1,708		1,649
Revenue from Related Parties	2		1		5		4
Potomac Electric Power Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	(4)		3		6		23
Revenues			0				0
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	630	[5]	599	[5]	1,697	[6]	1,621	[6]
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	2	[7]	2	[7]	5	[8]	5	[8]
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	306		291		792		751
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	39		37		104		105
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	230		211		632		593
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Public Authorities & Electric Railroads [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	8		8		24		24
Potomac Electric Power Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	47	[9]	52	[9]	145	[10]	148	[10]
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[11]	0	[11]	0	[12]	0	[12]
Potomac Electric Power Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[7]	0	[7]	0	[8]	0	[8]
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		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		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		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		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	0	[13]	0	[13]	0	[14]	0	[14]
Potomac Electric Power Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	630		599		1,697		1,621
Potomac Electric Power Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	(2)		5		11		28
Delmarva Power and Light Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	302		308		861		851
Rate-regulated natural gas revenues	24		18		129		105
Revenues from alternative revenue programs	0		(1)		5		9
Revenues	328		327		1,001		971
Revenue from Related Parties	2		2		6		6
Delmarva Power and Light Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	0		(1)		5		9
Revenues			0				0
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	303	[5]	309	[5]	864	[6]	854	[6]
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	1	[7]	1	[7]	3	[8]	3	[8]
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	180		185		513		505
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	48		50		138		139
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	25		28		74		78
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	3		3		10		11
Delmarva Power and Light Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	47	[9]	43	[9]	129	[10]	121	[10]
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	24	[11]	18	[11]	129	[12]	105	[12]
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	0	[7]	0	[7]	0	[8]	0	[8]
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	8		8		68		57
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	5		3		31		25
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	2		1		7		5
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Transportation [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	3		3		12		11
Delmarva Power and Light Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	6	[13]	3	[13]	11	[14]	7	[14]
Delmarva Power and Light Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	327		327		993		959
Delmarva Power and Light Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	1		0		8		12
Atlantic City Electric Company [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	406		370		983		904
Rate-regulated natural gas revenues			0				0
Revenues from alternative revenue programs	(1)		0		(4)		9
Revenues	406		370		981		915
Revenue from Related Parties	1		0		2		2
Atlantic City Electric Company [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Revenues from alternative revenue programs	(1)		0		(4)		9
Revenues			0				0
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	407	[5]	370	[5]	985	[6]	906	[6]
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	0	[7]	0	[7]	0	[8]	0	[8]
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Residential [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	240		211		534		484
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Small Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	53		53		128		129
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Large Commercial & Industrial [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	48		49		139		143
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		10		10
Atlantic City Electric Company [Member] | Rate-Regulated Electric Revenues [Member] | Other [Member]
Revenue, Major Customer [Line Items]
Rate-regulated electric revenues	63	[9]	54	[9]	174	[10]	140	[10]
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[11]	0	[11]	0	[12]	0	[12]
Atlantic City Electric Company [Member] | Rate-Regulated Natural Gas Revenues [Member] | Operating Segments [Member]
Revenue, Major Customer [Line Items]
Rate-regulated natural gas revenues	0	[7]	0	[7]	0	[8]	0	[8]
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		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		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		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		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	0	[13]	0	[13]	0	[14]	0	[14]
Atlantic City Electric Company [Member] | Regulated Operation [Member]
Revenue, Major Customer [Line Items]
Revenues	407		370		985		906
Atlantic City Electric Company [Member] | Other Regulated Revenue [Member]
Revenue, Major Customer [Line Items]
Revenues	$ (1)		0		$ (4)		$ 9
Atlantic City Electric Co Affiliate [Member]
Revenue, Major Customer [Line Items]
Revenue from Related Parties			$ 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.
[2]	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.
[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 September 30, 2018 and 2017.
[4]	Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 18 — Supplemental Financial Information for total utility taxes for the nine months ended September 30, 2018 and 2017.
[5]	Includes operating revenues from affiliates of $4 million, $2 million, $1 million, $3 million, $2 million, $2 million and $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2018 and $3 million, $1 million, $1 million, $1 million $1 million, $2 million and less than $1 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the three months ended September 30, 2017.
[6]	Includes operating revenues from affiliates of $23 million, $5 million, $5 million, $11 million, $5 million, $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2018 and $12 million, $4 million, $5 million, $2 million, $4 million, $6 million and $2 million at ComEd, PECO, BGE, PHI, Pepco, DPL and ACE, respectively, for the nine months ended September 30, 2017.
[7]	Includes late payment charge revenues.
[8]	Includes late payment charge revenues.
[9]	Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue.
[10]	Includes revenues from transmission revenue from PJM, wholesale electric revenue and mutual assistance revenue.
[11]	Includes operating revenues from affiliates of less than $1 million and $5 million at PECO and BGE, respectively, for the three months ended September 30, 2018 and less than $1 million and $2 million at PECO and BGE, respectively, for the three months ended September 30, 2017.
[12]	Includes operating revenues from affiliates of less than $1 million and $13 million at PECO and BGE, respectively, for the nine months ended September 30, 2018 and less than $1 million and $7 million at PECO and BGE, respectively, for the nine months ended September 30, 2017.
[13]	Includes revenues from off-system natural gas sales.
[14]	Includes revenues from off-system natural gas sales.
[15]	Includes operating revenues from affiliates of $11 million at PHI for the three months ended September 30, 2017.
[16]	Includes operating revenues from affiliates of $33 million at PHI for the nine months ended September 30, 2017.