Investment in Constellation Energy Nuclear Group, LLC (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
CENG	$ 123	$ 73
Amortization of basis difference in CENG	(114)	(172)
Total equity investment earnings (losses) - CENG	9	(99)
Related Party Transaction [Line Items]
Required purchases of power from CENG's nuclear plants not sold to third parties (as a percent)	85.00%
Purchase of nuclear output of CENG (as a percent)	50.01%
Purchase of nuclear output by EDF (as a percent)	49.99%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings		48	9
Amortization of energy contract assets and liabilities	430	1,110
Distribution From Affiliates	115
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	20.00%
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	50.00%
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	50.01%
Basis difference in investment in CENG	204
Related Party Transaction [Line Items]
Purchase of nuclear output by EDF (as a percent)	49.99%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings	1,423	1,702	1,161
Amortization of energy contract assets and liabilities	507	1,110
Loan to CENG/Distribution to EDF/ Repayment to Generation	400
Interest rate on loan to CENG	5.25%
Return on distributions (CENG)	8.50%
Distribution From Affiliates	$ 115