Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 1,697	$ 1,021
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 940	$ 304
Salem [Member] | Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Ownership interest	42.59%
Midwest Asset Group [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 20
Generation New England [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	20
Facility Closing [Member] | Midwest Asset Group [Member]
Property, Plant and Equipment [Line Items]
Severance Liability	81
Severance Costs			$ 81
Facility Closing [Member] | Midwest Asset Group [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Severance Liability	$ 81
Severance Costs			$ 81