Impairment of Long-Lived Assets (Details) - Electricity Generation Plant, Non-Nuclear [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2018
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Impairment of Long-Lived Assets to be Disposed of	$ 41	$ 418	$ 460
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset				$ 41
Exelon Generation Co L L C [Member]
Capital Leases, Net Investment in Direct Financing Leases [Abstract]
Impairment of Long-Lived Assets to be Disposed of	$ 41	$ 418	$ 460
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset				$ 41