Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		$ 346	[1]	$ 351
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(10)		(1)
Development projects	[3]	10		11
Accretion expense	[4]	16		15
Payments		(5)		(6)
Reclassified to liabilities held for sale	[5]			(4)
Asset Divestitures	[6]	(2)		(20)
ARO ending balance	[1]	355		346
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Net increase (decrease) resulting from updates to estimated future cash flows		8		16
Reduction to operating and maintenance expense due to updates to estimated future cash flows		(2)		(2)
Asset Retirement Obligation, Current		5		1
Exelon Generation Co L L C [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		194	[1]	201
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(12)		(2)
Development projects	[3]	10		11
Accretion expense	[4]	10		11
Payments		(3)		(3)
Reclassified to liabilities held for sale	[5]			(4)
Asset Divestitures	[6]	(2)		(20)
ARO ending balance	[1]	197		194
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Reduction to operating and maintenance expense due to updates to estimated future cash flows				1
Asset Retirement Obligation, Current		2		1
Commonwealth Edison Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		104	[1]	101
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	6		2
Development projects	[3]	0		0
Accretion expense	[4]	5		3
Payments		(2)		(2)
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	113		104
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Current		0		1
PECO Energy Co [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		30	[1]	30
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	(4)		0
Development projects	[3]	0		0
Accretion expense	[4]	1		1
Payments		0		(1)
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	27		30
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Current		1		1
Baltimore Gas and Electric Company [Member] | Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance		18	[1]	19
Net increase (decrease) resulting from updates to estimated future cash flows	[2]	0		(1)
Development projects	[3]	0		0
Accretion expense	[4]	0		0
Payments		0		0
Reclassified to liabilities held for sale	[5]			0
Asset Divestitures	[6]	0		0
ARO ending balance	[1]	$ 18		$ 18

[1] Excludes $1 million, $1 million, $1 million and $1 million as the current portion of the ARO at December 31, 2014 for Generation, ComEd, PECO and BGE, respectively. This is included in Other current liabilities on the Registrants' respective Consolidated Balance Sheets.

[2] 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. During the year ended December 31, 2014, Generation recorded a decrease of $(2) million and ComEd recorded an increase of $1 million in Operating and maintenance expense. PECO and BGE did not record any adjustments in Operating and maintenance expense for the year ended December 31, 2014.

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

[4] 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.

[5] Represents AROs related to generating stations classified as held for sale. See Note 4 — Mergers, Acquisitions, and Dispositions for further information.

[6] Reflects a reduction to the ARO resulting primarily from the sales of Schuylkill generating station in 2015 and Keystone and Conemaugh generating stations in 2014. See Note 4 — Mergers, Acquisitions, and Dispositions for further information.