Commitments and Contingencies - Schedule of Spent Nuclear Fuel Obligation (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 1,199	$ 1,171
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	1,199	1,171
Spent Nuclear Fuel One Time Fee		277
Nuclear Plant [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,075	1,052
Nuclear Plant [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	1,075	1,052
Fitzpatrick [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	124	119
Fitzpatrick [Member] | Exelon Generation Co L L C [Member]
Spent Nuclear Fuel Obligation [Line Items]
Spent Nuclear Fuel Obligation, Noncurrent	$ 124	$ 119