Intangible Assets - Schedule of Other Intangible Assets (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2015
Finite-Lived Intangible Assets [Line Items]
Gross		$ 1,228	$ 1,244
Accumulated Amortization		(1,255)	(1,502)
Net		(27)	(258)
Finite-Lived Intangible Assets, Gross		1,228	1,244
Exelon Enterprise [Member]
Finite-Lived Intangible Assets [Line Items]
2018	[1]	10
2019	[1]	10
2020	[1]	10
2021	[1]	10
2022	[1]	10
Exelon Enterprise [Member] | Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[1]	95	95
Accumulated Amortization	[1]	(25)	(15)
Net	[1]	70	80
Finite-Lived Intangible Assets, Gross	[1]	95	95
Exelon Generation Consolidated [Member]
Finite-Lived Intangible Assets [Line Items]
2018	[1]	62
2019	[1]	57
2020	[1]	68
2021	[1]	77
2022	[1]	54
Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	[2],[3]	1,938	1,926
Accumulated Amortization	[2],[3]	(1,574)	(1,543)
Net	[2],[3]	364	383
Finite-Lived Intangible Assets, Gross	[2],[3]	1,938	1,926
Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		305	299
Accumulated Amortization		(133)	(109)
Net		172	190
Finite-Lived Intangible Assets, Gross		305	299
Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		243	243
Accumulated Amortization		(148)	(125)
Net		95	118
Finite-Lived Intangible Assets, Gross		243	243
Exelon Generation Co L L C [Member] | Order or Production Backlog [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		0	9
Accumulated Amortization		0	(7)
Net		0	2
Finite-Lived Intangible Assets, Gross		0	9
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
2018	[1]	7
2019	[1]	7
2020	[1]	7
2021	[1]	0
2022	[1]	0
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		162	162
Accumulated Amortization		(141)	(133)
Net		21	29
Finite-Lived Intangible Assets, Gross		162	162
PHI Service Co Affiliate [Member]
Finite-Lived Intangible Assets [Line Items]
2018	[1]	(189)
2019	[1]	(119)
2020	[1]	(115)
2021	[1]	(92)
2022	[1]	(89)
Pepco Holdings LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Gross				$ 25
Finite-Lived Intangible Assets, Gross				$ 25
Pepco Holdings LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		(1,515)	(1,515)
Accumulated Amortization		766	430
Net		(749)	(1,085)
Finite-Lived Intangible Assets, Gross		(1,515)	(1,515)
Potomac Electric Power Company [Member] | DC Sponsorship Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Gross		0	25
Accumulated Amortization		0	0
Net		0	25
Finite-Lived Intangible Assets, Gross		$ 0	$ 25

[1] On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.

[2] In March 1999 and February 2003, ComEd entered into separate agreements with the City of Chicago and Midwest Generation, LLC. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement.

[3] Includes unamortized energy contract assets and liabilities on Exelon's, Generations and PHI's Consolidated Balance Sheets.