Jointly Owned Electric Utility Plant (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
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	$ 874.00	$ 822.00
Accumulated depreciation	187.00	156.00
Construction work in progress	44.00	37.00
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	75.00%
Plant	874.00	822.00
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	796.00	650.00
Accumulated depreciation	302.00	285.00
Construction work in progress	115.00	111.00
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	50.00%
Plant	796.00	650.00
Exelon Generation Co L L C [Member] | Nuclear Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	PSEG Nuclear
Ownership interest	42.59%
Plant	494.00	420.00
Accumulated depreciation	119.00	103.00
Construction work in progress	11.00	61.00
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	42.59%
Plant	494.00	420.00
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Salem [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Plant	3.00	3.00
Jointly Owned Utility Plant Footnote [Abstract]
Plant	3.00	3.00
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Keystone [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	GenOn
Ownership interest	41.98%
Plant	624.00	366.00
Accumulated depreciation	153.00	137.00
Construction work in progress	10.00	5.00
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	41.98%
Plant	624.00	366.00
Exelon Generation Co L L C [Member] | Fossil Fuel Generation [Member] | Conemaugh [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	GenOn
Ownership interest	31.28%
Plant	322.00	271.00
Accumulated depreciation	158.00	154.00
Construction work in progress	57.00	15.00
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	31.28%
Plant	322.00	271.00
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	3.00	3.00
Accumulated depreciation	3.00	3.00
Construction work in progress	0	0
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	5.89%
Plant	3.00	3.00
Exelon Generation Co L L C [Member] | Other Service [Member] | Other Locations [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator
Ownership interest	44.24%
Plant	1.00	1.00
Accumulated depreciation	0	0
Construction work in progress	0	0
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	44.24%
Plant	1.00	1.00
PECO Energy Co [Member] | Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	First Energy
Plant	13.00	5.00
Accumulated depreciation	7.00	3.00
Construction work in progress	1.00	0
Jointly Owned Utility Plant Footnote [Abstract]
Plant	13.00	5.00
Miles of transmission voltage lines	127
Transmission line capacity	500
PECO Energy Co [Member] | Electric Transmission [Member] | Delaware And New Jersey [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Operator	PSEG
Ownership interest	42.55%
Plant	65.00	66.00
Accumulated depreciation	33.00	33.00
Construction work in progress	0	0
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	42.55%
Plant	$ 65.00	$ 66.00
Miles of transmission voltage lines	131
Transmission line capacity	500
PECO Energy Co [Member] | Electric Transmission [Member] | PA Transmission Lines [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	22.00%
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	22.00%
PECO Energy Co [Member] | Electric Transmission [Member] | Conemaugh Substation [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	20.70%
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	20.70%
Transmission line capacity	500
Substation capacity	500
Baltimore Gas and Electric Company [Member] | Conemaugh Substation [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	10.56%
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	10.56%
Baltimore Gas and Electric Company [Member] | Electric Transmission [Member] | Pennsylvania [Member]
Schedule Of Jointly Owned Utility Plant Net Ownership [Abstract]
Ownership interest	7.00%
Jointly Owned Utility Plant Footnote [Abstract]
Ownership interest	7.00%