Mezzanine Equity Mezzanine Equity (Details) - USD ($) $ in Millions		3 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross		$ 0	$ 212
Exelon Generation Co L L C [Member]
Preferred Stock, Shares Subscribed but Unissued, Value [Abstract]
Payments to Acquire Businesses, Gross	$ 87	$ 0	$ 212