Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) V mi		Dec. 31, 2014 USD ($)
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Salem [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Conemaugh [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity | V		500,000
Pennsylvania [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines | mi		127
Transmission line capacity | V		500,000
Delaware And New Jersey [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines | mi		131
Substation capacity | V		500,000
Exelon Generation Co L L C [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		44.24%
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Quad Cities [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		Generation
Ownership interest		75.00%
Plant		$ 1,035	[1]	$ 995	[2]
Accumulated depreciation		309	[1]	266	[2]
Construction work in progress		11		15
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 1,035	[1]	995	[2]
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Peach Bottom [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		Generation
Ownership interest		50.00%
Plant		$ 1,345	[1]	1,095	[2]
Accumulated depreciation		368	[1]	343	[2]
Construction work in progress		18		133
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 1,345	[1]	1,095	[2]
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[3]	PSEG Nuclear
Ownership interest	[3]	42.59%
Plant	[2],[3]	$ 566		531
Accumulated depreciation	[2],[3]	167		150
Construction work in progress	[3]	40		29
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[3]	566		531
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant		3		3
Jointly Owned Utility Plant Footnote [Abstract]
Plant		$ 3		3
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Wyman [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator		FP&L
Ownership interest		5.89%
Plant	[1],[2]	$ 3		3
Accumulated depreciation	[1],[2]	3		3
Construction work in progress		0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[1],[2]	$ 3		3
Exelon Generation Co L L C [Member] | Other Service [Member] | Other Locations [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[1]
Ownership interest	[1]	44.24%
Plant	[1],[2]	$ 1		2
Accumulated depreciation	[1],[2]	1		1
Construction work in progress	[1]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[1],[2]	$ 1		2
PECO Energy Co [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		20.70%
PECO Energy Co [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		22.00%
PECO Energy Co [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		42.55%
PECO Energy Co [Member] | Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[4]	First Energy
Plant	[2],[4]	$ 15		14
Accumulated depreciation	[2],[4]	7		7
Construction work in progress	[4]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[4]	$ 15		14
PECO Energy Co [Member] | Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	[5]	PSEG
Ownership interest	[5]	42.55%
Plant	[2],[5]	$ 65		64
Accumulated depreciation	[2],[5]	35		34
Construction work in progress	[5]	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	[2],[5]	$ 65		$ 64
Baltimore Gas and Electric Company [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		10.56%
Baltimore Gas and Electric Company [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest		7.00%

[1] Excludes asset retirement costs.

[2] .

[3] Generation also owns a proportionate share in the fossil fuel combustion turbine at Salem, which is fully depreciated. The gross book value was $3 million at December 31, 2015 and 2014.

[4] PECO owns a 42.55% share in 131 miles of 500kV lines located in Delaware and New Jersey as well as a 42.55% share in a 500kV substation immediately outside of the Salem nuclear generating station in New Jersey which supplies power to the 500kV lines including, but not limited to, the lines noted above.

[5] Generation has a 44.24% ownership interest in assets located at Merrill Creek Reservoir located in New Jersey.