Jointly Owned Electric Utility Plant - Ownership Interests in Jointly Owned Electric Plants and Transmission Facilities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity	500,000
Salem [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity	500,000
Conemaugh [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Substation capacity	500,000
Pennsylvania [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines	127
Transmission line capacity	500,000
Delaware And New Jersey [Member]
Jointly Owned Utility Plant Footnote [Abstract]
Miles of transmission voltage lines	131
Substation capacity	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	$ 995	[1]	$ 941	[2]
Accumulated depreciation	266	[1]	226	[2]
Construction work in progress	15		27
Jointly Owned Utility Plant Footnote [Abstract]
Plant	995	[1]	941	[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	1,095	[1]	883	[2]
Accumulated depreciation	343	[1]	326	[2]
Construction work in progress	133		174
Jointly Owned Utility Plant Footnote [Abstract]
Plant	1,095	[1]	883	[2]
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	PSEG Nuclear	[3]
Ownership interest	42.59%	[3]
Plant	531	[2],[3]	501	[2],[3]
Accumulated depreciation	150	[2],[3]	134	[2],[3]
Construction work in progress	29	[3]	24	[3]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	531	[2],[3]	501	[2],[3]
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] | Keystone [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	GenOn	[2]
Ownership interest	0.00%	[2]
Plant	0	[1],[2]	725	[1],[2]
Accumulated depreciation	0	[1],[2]	268	[1],[2]
Construction work in progress	0	[2]	6	[2]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	0	[1],[2]	725	[1],[2]
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	GenOn	[2]
Ownership interest	0.00%	[2]
Plant	0	[1],[2]	399	[1],[2]
Accumulated depreciation	0	[1],[2]	220	[1],[2]
Construction work in progress	0	[2]	121	[2]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	0	[1],[2]	399	[1],[2]
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	3	[1],[2]	3	[1],[2]
Accumulated depreciation	3	[1],[2]	3	[1],[2]
Construction work in progress	0		0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	3	[1],[2]	3	[1],[2]
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	44.24%	[1]
Plant	2	[1],[2]	2	[1],[2]
Accumulated depreciation	1	[1],[2]	1	[1],[2]
Construction work in progress	0	[1]	0	[1]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	2	[1],[2]	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	First Energy	[4]
Plant	14	[2],[4]	14	[2],[4]
Accumulated depreciation	7	[2],[4]	7	[2],[4]
Construction work in progress	0	[4]	0	[4]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	14	[2],[4]	14	[2],[4]
PECO Energy Co [Member] | Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	PSEG	[5]
Ownership interest	42.55%	[5]
Plant	64	[2],[5]	64	[2],[5]
Accumulated depreciation	34	[2],[5]	34	[2],[5]
Construction work in progress	0	[5]	0	[5]
Jointly Owned Utility Plant Footnote [Abstract]
Plant	$ 64	[2],[5]	$ 64	[2],[5]
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] As of December 31, 2014, Generation sold its ownership interest in Keystone and Conemaugh. At December 31, 2013, Generation held 41.98% and 31.28% ownership interest in Keystone and Conemaugh, respectively. See Note 4—Mergers, Acquisitions, and Dispositions for additional information.

[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, 2014 and 2013.

[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.