Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - Nuclear Decommissioning Asset Retirement Obligation [Member] - Exelon Generation Co L L C [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear Decommissioning ARO, Beginning Balance	[1]	$ 8,246
Net increase due to changes in, and timing of, estimated cash flows		106
Asset Retirement Obligation, Period Increase (Decrease)		60
Nuclear Decommissioning ARO, Ending Balance	[1]	8,412
Current portion of ARO		$ 6	$ 7

[1] Includes $6 million and $7 million as the current portion of the ARO at March 31, 2016 and December 31, 2015 which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.