Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($)		3 Months Ended			9 Months Ended		12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Mar. 23, 2016	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							$ 20,000,000				$ 2,000,000
Asset Retirement Obligation, Accretion Expense	[1]						489,000,000		$ 468,000,000		446,000,000
Asset Retirement Obligation, Revision of Estimate							20,000,000				2,000,000
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate		$ 203,000,000	$ 84,000,000		$ 138,000,000		0				0
Asset Retirement Obligation, Accretion Expense	[1]						489,000,000		468,000,000		446,000,000
Asset Retirement Obligation, Period Increase (Decrease)					180,000,000						34,000,000
Asset Retirement Obligation, Revision of Estimate		203,000,000	84,000,000		138,000,000		0				0
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]						0		0
Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate						$ 2,000,000	20,000,000
Asset Retirement Obligation, Accretion Expense	[1]					0
Asset Retirement Obligation, Revision of Estimate						2,000,000	20,000,000
Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate				$ 0
Asset Retirement Obligation, Accretion Expense	[1]			0
Asset Retirement Obligation, Revision of Estimate				0
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							22,000,000				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							22,000,000				0
Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				1,000,000
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				1,000,000
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				2,000,000
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							(1,000,000)				2,000,000
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate							0				0
Asset Retirement Obligation, Accretion Expense	[1]						0		0		0
Asset Retirement Obligation, Revision of Estimate							0				0
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)							(3,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					199,000,000		197,000,000		199,000,000
Asset Retirement Obligation, Revision of Estimate							35,000,000		(1,000,000)
Development projects	[2]								1,000,000
Asset Retirement Obligation, Accretion Expense							10,000,000		10,000,000
Asset Retirement Obligation, Period Increase (Decrease)							(3,000,000)		(7,000,000)
Payments							(1,000,000)		(5,000,000)
ARO ending balance		238,000,000				199,000,000	238,000,000		197,000,000		199,000,000
Asset Retirement Obligation, Revision of Estimate							35,000,000		(1,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					28,000,000		27,000,000		28,000,000
Asset Retirement Obligation, Revision of Estimate							0		(1,000,000)
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						1,000,000		1,000,000
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		(1,000,000)
ARO ending balance		28,000,000				28,000,000	28,000,000		27,000,000		28,000,000
Asset Retirement Obligation, Revision of Estimate							0		(1,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					24,000,000		24,000,000		24,000,000
Asset Retirement Obligation, Revision of Estimate							2,000,000		2,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						1,000,000		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							(2,000,000)		(2,000,000)
ARO ending balance		25,000,000				24,000,000	25,000,000		24,000,000		24,000,000
Asset Retirement Obligation, Revision of Estimate							2,000,000		2,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					14,000,000		16,000,000		14,000,000
Asset Retirement Obligation, Revision of Estimate							36,000,000		2,000,000
Development projects	[2]			$ 0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)									0
Payments							0		0
ARO ending balance		52,000,000				14,000,000	52,000,000		16,000,000		14,000,000
Asset Retirement Obligation, Revision of Estimate							36,000,000		2,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)							0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					2,000,000		3,000,000		2,000,000
Asset Retirement Obligation, Revision of Estimate			22,000,000				34,000,000		1,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		37,000,000				2,000,000	37,000,000		3,000,000		2,000,000
Asset Retirement Obligation, Revision of Estimate			22,000,000				34,000,000		1,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					9,000,000		10,000,000		9,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		1,000,000
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		11,000,000				9,000,000	11,000,000		10,000,000		9,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		1,000,000
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					3,000,000		3,000,000		3,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		0
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense							0		0
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							0		0
ARO ending balance		4,000,000				3,000,000	4,000,000		3,000,000		3,000,000
Asset Retirement Obligation, Revision of Estimate							1,000,000		0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)									(7,000,000)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					121,000,000		113,000,000		121,000,000
Asset Retirement Obligation, Revision of Estimate							7,000,000		(13,000,000)
Development projects	[2]								0
Asset Retirement Obligation, Accretion Expense	[3]						4,000,000		7,000,000
Asset Retirement Obligation, Period Increase (Decrease)							0		0
Payments							(3,000,000)		(2,000,000)
ARO ending balance		121,000,000				121,000,000	121,000,000		113,000,000		121,000,000
Asset Retirement Obligation, Revision of Estimate							7,000,000		(13,000,000)
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					8,734,000,000		9,662,000,000	[4]	8,734,000,000
Asset Retirement Obligation, Revision of Estimate			772,000,000						444,000,000
Development projects							(58,000,000)		8,000,000
Asset Retirement Obligation, Accretion Expense							478,000,000		458,000,000
Asset Retirement Obligation, Period Increase (Decrease)							(77,000,000)		34,000,000
ARO ending balance		10,005,000,000				8,734,000,000	10,005,000,000		9,662,000,000	[4]	8,734,000,000
Asset Retirement Obligation, Revision of Estimate			$ 772,000,000						444,000,000
Asset Retirement Obligation, Current		22,000,000					22,000,000		13,000,000
Nuclear decommissioning | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					$ 393,000,000		384,000,000		393,000,000
Asset Retirement Obligation, Revision of Estimate							80,000,000		(11,000,000)
Development projects	[2]								1,000,000
Asset Retirement Obligation, Accretion Expense							16,000,000		18,000,000
Payments							(6,000,000)		(10,000,000)
ARO ending balance		$ 471,000,000				$ 393,000,000	471,000,000		384,000,000		$ 393,000,000
Asset Retirement Obligation, Revision of Estimate							$ 80,000,000		$ (11,000,000)

[1] Included in Operating and maintenance expense in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[2] .

[3] (b)In 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.

[4] Includes $22 million and $13 million as the current portion of the ARO at December 31, 2018 and 2017, respectively, which is included in Other current liabilities in Exelon’s and Generation’s Consolidated Balance Sheets.