Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended				12 Months Ended
		Dec. 31, 2016		Mar. 23, 2016		Dec. 31, 2016		Sep. 30, 2016		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										$ 2
Asset Retirement Obligation, Accretion Expense	[1]									446		$ 398		$ 345
Asset Retirement Obligation, Revision of Estimate										2
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				$ 355	[2]			$ 355	[2]	355	[2]	346
Asset Retirement Obligation, Revision of Estimate	[3]					$ 8				34		(10)
Development projects	[4]									11		10
Asset Retirement Obligation, Accretion Expense	[5]									18		16
Payments										(11)		(5)
ARO ending balance		$ 393	[2]			393	[2]			393	[2]	355	[2]	346
Asset Retirement Obligation, Revision of Estimate	[3]					8				34		(10)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									22		2
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate								285				1,300
Asset Retirement Obligation, Accretion Expense	[1]									446		397		345
Asset Retirement Obligation, Period Increase (Decrease)		165								288
Asset Retirement Obligation, Revision of Estimate								285				1,300
Asset Retirement Obligation, Current		10				10				10		7
Exelon Generation Co L L C [Member] | Operating Expense [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										1		(2)
Asset Retirement Obligation, Revision of Estimate										1		(2)
Exelon Generation Co L L C [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				197	[2]			197	[2]	197	[2]	194
Asset Retirement Obligation, Revision of Estimate	[3]					1				8		(12)
Development projects	[4]									11		10
Asset Retirement Obligation, Accretion Expense	[5]									10		10
Payments										(6)		(3)
ARO ending balance		199	[2]			199	[2]			199	[2]	197	[2]	194
Asset Retirement Obligation, Revision of Estimate	[3]					1				8		(12)
Asset Retirement Obligation, Current		1				1				1		5
Exelon Generation Co L L C [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									22		2
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]									0		0		0
PECO Energy Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				27	[2]			27	[2]	27	[2]	30
Asset Retirement Obligation, Revision of Estimate	[3]									1		(4)
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									1		1
Payments										(1)		0
ARO ending balance		28	[2]			28	[2]			28	[2]	27	[2]	30
Asset Retirement Obligation, Revision of Estimate	[3]									1		(4)
PECO Energy Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									0		0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]									0		0		0
Baltimore Gas and Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				18	[2]			18	[2]	18	[2]	18
Asset Retirement Obligation, Revision of Estimate	[3]									7		0
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									0		0
Payments										(1)		0
ARO ending balance		24	[2]			24	[2]			24	[2]	18	[2]	18
Asset Retirement Obligation, Revision of Estimate	[3]									7		0
Asset Retirement Obligation, Current		3				3				3		1
Baltimore Gas and Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									0		0
Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate						2
Asset Retirement Obligation, Accretion Expense	[1]					0
Asset Retirement Obligation, Revision of Estimate						2
Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]			0
Pepco Holdings LLC [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				0	[2]			0	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate										14	[3]	0
Development projects										0	[4]	0
Asset Retirement Obligation, Accretion Expense										0	[5]	0
Payments										0		0
ARO ending balance		14	[2]			14	[2]			14	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate										14	[3]	0
Pepco Holdings LLC [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Successor [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)										0	[6]	0
Pepco Holdings LLC [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				8	[2]	8	[2]	8	[2]	8	[2]	7
Asset Retirement Obligation, Accretion Expense	[5]											1
ARO ending balance				8	[2]							8	[2]	7
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]									0		0		0
Potomac Electric Power Company [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]											0		0
Potomac Electric Power Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				0	[2]			0	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									2		0
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									0		0
Payments										0		0
ARO ending balance		2	[2]			2	[2]			2	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									2		0
Potomac Electric Power Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									0		0
Delmarva Power and Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										1
Asset Retirement Obligation, Accretion Expense	[1]									0		0		0
Asset Retirement Obligation, Revision of Estimate										1
Delmarva Power and Light Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				0	[2]			0	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									9		0
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									0		0
Payments										0		0
ARO ending balance		9	[2]			9	[2]			9	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									9		0
Delmarva Power and Light Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									0		0
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										2
Asset Retirement Obligation, Accretion Expense	[1]									0
Asset Retirement Obligation, Revision of Estimate										2
Atlantic City Electric Company [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]											0		0
Atlantic City Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				0	[2]			0	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									3		0
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									0		0
Payments										0		0
ARO ending balance		3	[2]			3	[2]			3	[2]	0	[2]	0
Asset Retirement Obligation, Revision of Estimate	[3]									3		0
Atlantic City Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									0		0
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]									0		0		0
Commonwealth Edison Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance				$ 113	[2]			$ 113	[2]	113	[2]	104
Asset Retirement Obligation, Revision of Estimate	[3]									4		6
Development projects	[4]									0		0
Asset Retirement Obligation, Accretion Expense	[5]									7		5
Payments										(3)		(2)
ARO ending balance		121	[2]			121	[2]			121	[2]	113	[2]	$ 104
Asset Retirement Obligation, Revision of Estimate	[3]									4		6
Asset Retirement Obligation, Current		$ 2				$ 2				2		2
Commonwealth Edison Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[6]									$ 0		$ 0

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

[2] Excludes $1 million, $2 million and $3 million as the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE, respectively. Excludes $5 million, $2 million and $1 million as the current portion of the ARO at December 31, 2015 for Generation, ComEd and BGE, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

[3] During the year ended December 31, 2016, Generation recorded an increase of $1 million in Operating and maintenance expense. ComEd, PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016. During the year ended December 31, 2015, Generation recorded a decrease of $(2) million in Operating and maintenance expense. ComEd, PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2015.

[4] Relates to new AROs recorded due to the construction of solar, wind and other non-nuclear generating sites.

[5] For ComEd, PECO, and BGE, the majority of the accretion is recorded as an increase to a regulatory asset due to the associated regulatory treatment.

[6] Reflects a reduction to the ARO resulting primarily from the sales of the New Boston generating site and Upstream business in 2016 and Schuylkill generating station in 2015. See Note 4 — Mergers, Acquisitions, and Dispositions for further information.