Income Taxes - Tax Effects of Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Plant basis differences	$ (13,393)	$ (12,143)
Accrual based contracts	(136)	(178)
Derivatives and other financial instruments	(203)	(46)
Deferred pension and postretirement obligation	1,801	1,914
Nuclear decommissioning activities	(592)	(726)
Deferred debt refinancing costs	133	112
Regulatory assets and liabilities	(1,706)	(1,824)
Tax loss carryforward	103	111
Tax credit carryforward	327	97
Investment in CENG	(595)	(563)
Other, net	1,112	1,029
Deferred income tax liabilities (net)	13,149	12,217
Unamortized investment tax credits	(622)	(555)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(13,771)	(12,772)
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,269)	(3,834)
Accrual based contracts	(136)	(178)
Derivatives and other financial instruments	(181)	(79)
Deferred pension and postretirement obligation	(371)	(390)
Nuclear decommissioning activities	(592)	(726)
Deferred debt refinancing costs	48	57
Regulatory assets and liabilities	0	0
Tax loss carryforward	56	48
Tax credit carryforward	374	143
Investment in CENG	(595)	(563)
Other, net	425	346
Deferred income tax liabilities (net)	5,241	5,176
Unamortized investment tax credits	(598)	(528)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(5,839)	(5,704)
Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(4,424)	(3,945)
Accrual based contracts	0	0
Derivatives and other financial instruments	(4)	(4)
Deferred pension and postretirement obligation	(505)	(543)
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(15)	(18)
Regulatory assets and liabilities	(219)	(286)
Tax loss carryforward	0	0
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	270	255
Deferred income tax liabilities (net)	4,897	4,541
Unamortized investment tax credits	(17)	(20)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(4,914)	(4,561)
PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(2,901)	(2,749)
Accrual based contracts	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(9)	2
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(1)	(2)
Regulatory assets and liabilities	16	27
Tax loss carryforward	0	11
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	105	111
Deferred income tax liabilities (net)	2,790	2,600
Unamortized investment tax credits	(2)	(2)
Total deferred income tax liabilities (net) and unamortized investment tax credits	(2,792)	(2,602)
Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Plant basis differences	(1,821)	(1,660)
Accrual based contracts	0	0
Derivatives and other financial instruments	0	0
Deferred pension and postretirement obligation	(47)	(53)
Nuclear decommissioning activities	0	0
Deferred debt refinancing costs	(4)	(4)
Regulatory assets and liabilities	(264)	(258)
Tax loss carryforward	33	39
Tax credit carryforward	0	0
Investment in CENG	0	0
Other, net	27	30
Deferred income tax liabilities (net)	2,076	1,906
Unamortized investment tax credits	(5)	(5)
Total deferred income tax liabilities (net) and unamortized investment tax credits	$ (2,081)	$ (1,911)