Early Plant Retirements - Implications of Potential Early Plant Retirement on Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies	$ 1,425	$ 1,456
Property, plant and equipment, net	82,584	80,233
Exelon Generation Co L L C [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies	978	1,026
Property, plant and equipment, net	22,214	$ 24,193
Exelon Generation Co L L C [Member] | Braidwood [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies	84
Nuclear Fuel, Net of Amortization	120
Property, plant and equipment, net	1,397
Construction in Progress, Gross	31
Asset retirement obligation	(570)
Exelon Generation Co L L C [Member] | LaSalle [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies	106
Nuclear Fuel, Net of Amortization	285
Property, plant and equipment, net	1,590
Construction in Progress, Gross	30
Asset retirement obligation	(954)
Exelon Generation Co L L C [Member] | Braidwood LaSalle [Member] | Facility Closing [Member]
Implications of Potential Early Plant Retirement [Line Items]
Materials and supplies	190
Nuclear Fuel, Net of Amortization	405
Property, plant and equipment, net	2,987
Construction in Progress, Gross	61
Asset retirement obligation	$ (1,524)