Nuclear Decommissioning - Rollforward of Nuclear Decommissioning ARO (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]	$ 112	$ 109
Asset Retirement Obligation, Revision of Estimate			0
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]	110	$ 109
Current portion of ARO				$ 10
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Nuclear Decommissioning ARO, Beginning Balance	[2]	8,734
Asset Retirement Obligation, Accretion Expense		109
Asset Retirement Obligation, Liabilities Settled		(1)
Asset Retirement Obligation, Period Increase (Decrease)		525
Asset Retirement Obligation, Revision of Estimate		417
Nuclear Decommissioning ARO, Ending Balance	[2]	9,259
Current portion of ARO		$ 11

[1] Included in Operating and maintenance expense on the Registrants’ Consolidated Statements of Operations and Comprehensive Income

[2] Includes $11 million and $10 million for the current portion of the ARO at March 31, 2017 and December 31, 2016, respectively, which is included in Other current liabilities on Exelon’s and Generation’s Consolidated Balance Sheets.