Commitments and Contingencies - Schedule of Spent Nuclear Fuel Obligation (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,208	$ 1,199
Spent Nuclear Fuel One Time Fee		34
Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,208	1,199
Spent Nuclear Fuel One Time Fee		277
Nuclear Plant [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,082	1,075
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,082	1,075
Fitzpatrick [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	126	124
Fitzpatrick [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 126	$ 124