Investment in Constellation Energy Nuclear Group, LLC (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended						3 Months Ended								12 Months Ended	3 Months Ended				0 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Apr. 02, 2014 CENG [Member] Subsequent Event [Member] FinancialGuaranteeMember	Apr. 02, 2014 CENG [Member] Subsequent Event [Member] Payment Guarantee [Member]	Mar. 31, 2014 Constellation Energy Nuclear Group [Member]	Mar. 31, 2013 Constellation Energy Nuclear Group [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member]		Apr. 02, 2014 Exelon Generation Co L L C [Member] CENG [Member] Subsequent Event [Member]	Apr. 02, 2014 Exelon Generation Co L L C [Member] CENG [Member] Subsequent Event [Member] Payment Guarantee [Member]	Dec. 31, 2013 Exelon Generation Co L L C [Member] First Distribution [Member] CENG [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member] Second Distribution [Member] CENG [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member] Minimum [Member]	Mar. 31, 2014 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Constellation Energy Nuclear Group [Member]	Apr. 02, 2014 Constellation Energy Group LLC [Member] EDFI [Member] Subsequent Event [Member]	Apr. 02, 2014 Constellation Energy Group LLC [Member] GenerationCoMember [Member] Subsequent Event [Member]	Apr. 02, 2014 Electricite De France LLC [Member] CENG [Member] Subsequent Event [Member] FinancialGuaranteeMember
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)									50.01%
CENG							$ 93	$ 53										$ (2)	$ 15
Amortization of basis difference in CENG							(88)	(131)										(17)	(27)
Total equity investment earnings (losses) - CENG							5	(78)										(19)	(12)
Basis difference in investment in CENG									204
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 by EDF (as a percent)									49.99%
Impact Of Transactions Under Agreements [Abstract]
Increase (Decrease) in earnings									334		392
Amortization of energy contract assets and liabilities	42	[1]	176	[1]					44	[1]	176	[1]
Distribution From Affiliates															115	13
Loan Recievable from CENG													400
Special and Preferred Distributions by CENG									30		211									400	400
Debt Instrument Interest Rate Stated Percentage													5.25%
InterestRateOnDistribution																					8.50%
Maximum exposure related to guarantees	9,890								6,491													145
Due To Affiliate Current And Noncurrent					$ 165	$ 245								$ 205

[1] Included in Operating revenues or Purchased power and fuel expense on the Registrants' Consolidated Statements of Operations and Comprehensive Income.