Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - Nuclear Decommissioning Asset Retirement Obligation [Member] - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear Decommissioning ARO, Beginning Balance	[1]	$ 6,961
Accretion expense		189
Costs incurred to decommission retired plants		(1)
Nuclear Decommissioning ARO, Ending Balance	[1]	7,204
Asset Retirement Obligation, Revision of Estimate	[2]	55
Current portion of ARO		$ 7	$ 8

[1] Includes $7 million and $8 million as the current portion of the ARO at June 30, 2015 and December 31, 2014 respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.

[2] the fair value of the CENG ARO liability as of April 1, 2014, the date of consolidation. See Note 6 — Investment in Constellation Energy Nuclear Group, LLC for additional information.