Early Plant Retirements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 1,666	$ 1,001	$ 3,363	$ 2,023
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 930	$ 300	$ 1,869	$ 604
Salem [Member] | Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Ownership interest	42.59%		42.59%
Generation New England [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	$ 21		$ 41
Generation New England [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Cost, Depreciation and Amortization	21		41
Facility Closing [Member] | Midwest Asset Group [Member]
Property, Plant and Equipment [Line Items]
Severance Costs					$ 81
Severance Liability	81		81
Facility Closing [Member] | Midwest Asset Group [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Severance Costs					$ 81
Severance Liability	$ 81		$ 81