Severance Severance - Narrative (Details) - USD ($) $ in Millions		1 Months Ended			3 Months Ended
		Nov. 30, 2017	Jun. 30, 2017	Aug. 31, 2015	Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs					$ 8	$ 4
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Effect on Future Earnings, Amount		$ 250		$ 400
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]				$ 2	$ 3
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			$ 17

[1] The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.