Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended			12 Months Ended
		Dec. 31, 2017		Sep. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016		Sep. 30, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										$ 468		$ 446		$ 398
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate										$ 61	1		1
Asset Retirement Obligation, Accretion Expense	[1]										468		446		397
Asset Retirement Obligation, Period Increase (Decrease)		$ 180		$ 165						288			488
Payments	[2]										(942)		(878)
Asset Retirement Obligation, Revision of Estimate										61	1		1
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		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
Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]							$ 0			0
Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]						$ 0								0
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Delmarva Power and Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]										0		0		0
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					$ 197		197			197	199	[3]	197
Asset Retirement Obligation, Revision of Estimate					1	[4]					(1)	[5]	8	[5]
Development projects	[6]										1		11
Asset Retirement Obligation, Accretion Expense											10		10
Asset Retirement Obligation, Period Increase (Decrease)											7		(22)	[7]
Payments											(5)		(6)
ARO ending balance		197	[3]					199	[3]		197	[3]	199	[3]	197
Asset Retirement Obligation, Revision of Estimate					1	[4]					(1)	[5]	8	[5]
Asset Retirement Obligation, Current		1						1			1		1
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					27		27			27	28		27
Asset Retirement Obligation, Revision of Estimate					0	[4]					(1)	[5]	1	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										1		1
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(1)		(1)
ARO ending balance		27						28			27		28		27
Asset Retirement Obligation, Revision of Estimate					0	[4]					(1)	[5]	1	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					18		18			18	24	[3]	18
Asset Retirement Obligation, Revision of Estimate					0	[4]					2	[5]	7	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(2)		(1)
ARO ending balance		24	[3]					24	[3]		24	[3]	24	[3]	18
Asset Retirement Obligation, Revision of Estimate					0	[4]					2	[5]	7	[5]
Asset Retirement Obligation, Current		2						3			2		3
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	[9]				0		0			0	14		0
Asset Retirement Obligation, Revision of Estimate	[9]				0	[4]					2	[5]	14	[5]
Development projects	[6],[9]						0				0
Asset Retirement Obligation, Accretion Expense	[9]										0		0
Asset Retirement Obligation, Period Increase (Decrease)	[9]										0	[10]	0	[7]
Payments	[9]										0		0
ARO ending balance	[9]	16						14			16		14		0
Asset Retirement Obligation, Revision of Estimate	[9]				0	[4]					2	[5]	14	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	[9]				8		8	8		8			8
ARO ending balance	[9]						8								8
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	2		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	2	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		3						2			3		2		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	2	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Delmarva Power and Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	9		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	9	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		10						9			10		9		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					1	[5]	9	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					0		0			0	3		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					0	[5]	3	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense											0		0
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											0		0
ARO ending balance		3						3			3		3		0
Asset Retirement Obligation, Revision of Estimate					0	[4]					0	[5]	3	[5]
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Increase (Decrease)	[7]												(22)
Nonnuclear Decommissioning Asset Retirement Obligation [Member] | Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					113		113			113	121	[3]	113
Asset Retirement Obligation, Revision of Estimate					0	[4]					(13)	[5]	4	[5]
Development projects	[6]										0		0
Asset Retirement Obligation, Accretion Expense	[8]										7		7
Asset Retirement Obligation, Period Increase (Decrease)											0		0	[7]
Payments											(2)		(3)
ARO ending balance		113	[3]					121	[3]		113	[3]	121	[3]	113
Asset Retirement Obligation, Revision of Estimate					0	[4]					(13)	[5]	4	[5]
Asset Retirement Obligation, Current		2						2			2		2
Nuclear decommissioning | Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					8,246		8,246			8,246	8,734	[11]	8,246
Asset Retirement Obligation, Revision of Estimate											444
Asset Retirement Obligation, Accretion Expense											458		436
Asset Retirement Obligation, Period Increase (Decrease)											34		61
ARO ending balance		9,662						8,734	[11]		9,662		8,734	[11]	8,246
Asset Retirement Obligation, Revision of Estimate											444
Asset Retirement Obligation, Current		13						10			13		10
Nuclear decommissioning | Exelon Enterprise [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance					355		$ 355			$ 355	393		355
Asset Retirement Obligation, Revision of Estimate					8	[4]					(11)	[5]	34	[5]
Development projects	[6]										1		11
Asset Retirement Obligation, Accretion Expense											18		18
Asset Retirement Obligation, Period Increase (Decrease)											7
Payments											(10)		(11)
ARO ending balance		$ 384						$ 393			384		393		$ 355
Asset Retirement Obligation, Revision of Estimate					$ 8	[4]					$ (11)	[5]	$ 34	[5]

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

[2] Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.

[3] Excludes the current portion of the ARO at December 31, 2017 for Generation, ComEd and BGE of $1 million, $2 million and $2 million, respectively. Excludes the current portion of the ARO at December 31, 2016 for Generation, ComEd and BGE of $1 million, $2 million and $3 million, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

[4] Following the completion of the PHI merger on March 23, 2016, PHI's AROs related to its unregulated business interests were transferred to Exelon and Generation.

[5] During the year ended December 31, 2017, ComEd recorded a decrease of $1 million in Operating and maintenance expense. Generation, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2017. During the year ended December 31, 2016, Generation recorded a increase of $1 million in Operating and maintenance expense. ComEd, PECO, BGE, Pepco, DPL and ACE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2016.

[6] Net unrealized gains (losses) related to Generation’s NDT funds with Non-Regulatory Agreement Units are included within Other, net in Exelon’s and Generation’s Consolidated Statements of Operations and Comprehensive Income.

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

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

[9] For PHI, the successor period includes activity for the year ended December 31, 2017 and the period of March 24, 2016 through December 31, 2016. The PHI predecessor periods include activity for the period of January 1, 2016 through March 23, 2016.

[10] See Note 4—Mergers, Acquisitions and Dispositions for additional information.

[11] Includes $13 million and $10 million as the current portion of the ARO at December 31, 2017 and 2016, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.