Asset Retirement Obligations - Nuclear Decommissioning Asset Retirement Obligation Rollforward (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]			$ 446	$ 398	$ 345
Asset Retirement Obligation, Revision of Estimate				2
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Accretion Expense	[1]			446	397	345
Asset Retirement Obligation, Revision of Estimate			$ 285		1,300
Asset Retirement Obligation, Current		$ 10		10	7
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance			$ 8,246	8,246	6,961
Asset Retirement Obligation, Accretion Expense				436	387
Asset Retirement Obligation, Revision of Estimate		89		61	901
Costs incurred to decommission retired plants				(9)	(3)
ARO ending balance		8,734		8,734	8,246	$ 6,961
Asset Retirement Obligation, Current	[2]	$ 90		$ 90	$ 99

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

[2] Included in Other current liabilities within Exelon’s and Generation’s Consolidated Balance Sheets.