Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2016	Mar. 24, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (17,966)		$ (13,393)
Accrual based contracts	434		(136)
Derivatives and other financial instruments	(179)		(203)
Deferred pension and postretirement obligation	2,287		1,801
Nuclear decommissioning activities	(509)		(592)
Deferred debt refinancing costs	325		133
Deferred Tax Liabilities, Regulatory Assets and Liabilities	3,319		1,706
Tax loss carryforward	189		103
Tax credit carryforward	446		327
Investment in CENG	(650)		(595)
Other, net	1,485	$ (59)	1,112
Deferred income tax liabilities (net)	(17,457)		(13,149)
Unamortized investment tax credits	(658)		(622)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(18,115)		(13,771)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,192)		(4,269)
Accrual based contracts	(115)		(136)
Derivatives and other financial instruments	(162)		(181)
Deferred pension and postretirement obligation	(316)		(371)
Nuclear decommissioning activities	(509)		(592)
Deferred debt refinancing costs	44		48
Regulatory assets and liabilities			0
Deferred Tax Liabilities, Regulatory Assets and Liabilities	0
Tax loss carryforward	61		56
Tax credit carryforward	493		374
Investment in CENG	(650)		(595)
Other, net	403		425
Deferred income tax liabilities (net)	(4,943)		(5,241)
Unamortized investment tax credits	(626)		(598)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(5,569)		(5,839)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(5,034)		(4,424)
Accrual based contracts	0		0
Derivatives and other financial instruments	(3)		(4)
Deferred pension and postretirement obligation	(453)		(505)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	13		15
Deferred Tax Liabilities, Regulatory Assets and Liabilities	226		219
Tax loss carryforward	29		0
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	351		270
Deferred income tax liabilities (net)	(5,349)		(4,897)
Unamortized investment tax credits	(15)		(17)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(5,364)		(4,914)
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(3,095)		(2,901)
Accrual based contracts	0		0
Derivatives and other financial instruments	0		0
Deferred pension and postretirement obligation	(18)		(9)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	1		1
Deferred Tax Liabilities, Regulatory Assets and Liabilities	10		(16)
Tax loss carryforward	0		0
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	99		105
Deferred income tax liabilities (net)	(3,005)		(2,790)
Unamortized investment tax credits	(1)		(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(3,006)		(2,792)
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,977)		(1,821)
Accrual based contracts	0		0
Derivatives and other financial instruments	0		0
Deferred pension and postretirement obligation	(43)		(47)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	3		4
Deferred Tax Liabilities, Regulatory Assets and Liabilities	240		264
Tax loss carryforward	22		33
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	27		27
Deferred income tax liabilities (net)	(2,214)		(2,076)
Unamortized investment tax credits	(5)		(5)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,219)		(2,081)
Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,678)		(1,599)
Accrual based contracts	0		0
Derivatives and other financial instruments	0		0
Deferred pension and postretirement obligation	(122)		(95)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	7		8
Deferred Tax Liabilities, Regulatory Assets and Liabilities	194		202
Tax loss carryforward	27		141
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	66		42
Deferred income tax liabilities (net)	(1,908)		(1,721)
Unamortized investment tax credits	(2)		(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,910)		(1,723)
Delmarva Power and Light Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(973)		(915)
Accrual based contracts	0		0
Derivatives and other financial instruments	0		0
Deferred pension and postretirement obligation	(74)		(82)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	4		4
Deferred Tax Liabilities, Regulatory Assets and Liabilities	75		91
Tax loss carryforward	39		122
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	34		29
Deferred income tax liabilities (net)	(1,053)		(941)
Unamortized investment tax credits	(3)		(4)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(1,056)		(945)
Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(869)		(791)
Accrual based contracts	0		0
Derivatives and other financial instruments	0		0
Deferred pension and postretirement obligation	(21)		(20)
Nuclear decommissioning activities	0		0
Deferred debt refinancing costs	2		3
Deferred Tax Liabilities, Regulatory Assets and Liabilities	69		93
Tax loss carryforward	14		8
Tax credit carryforward	0		0
Investment in CENG	0		0
Other, net	34		18
Deferred income tax liabilities (net)	(913)		(881)
Unamortized investment tax credits	(4)		(4)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(917)		(885)
Pepco Holdings LLC [Member] | Successor [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(3,586)
Accrual based contracts	548
Derivatives and other financial instruments	(1)
Deferred pension and postretirement obligation	(111)
Nuclear decommissioning activities	0
Deferred debt refinancing costs	293
Deferred Tax Liabilities, Regulatory Assets and Liabilities	1,205
Tax loss carryforward	77
Tax credit carryforward	0
Investment in CENG	0
Other, net	225
Deferred income tax liabilities (net)	(3,760)
Unamortized investment tax credits	(9)
Total deferred income tax liabilities (net) and unamortized investment tax credits	$ (3,769)
Pepco Holdings LLC [Member] | Predecessor [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences			(3,342)
Accrual based contracts			0
Derivatives and other financial instruments			(1)
Deferred pension and postretirement obligation			(92)
Nuclear decommissioning activities			0
Deferred debt refinancing costs			15
Deferred Tax Liabilities, Regulatory Assets and Liabilities			414
Tax loss carryforward			378
Tax credit carryforward			6
Investment in CENG			0
Other, net		$ (8)	103
Deferred income tax liabilities (net)			(3,377)
Unamortized investment tax credits			(15)
Total deferred income tax liabilities (net) and unamortized investment tax credits			$ (3,392)