Asset Impairments - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) MW	Jun. 30, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 33	$ 9
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	18	$ 9
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	710
Impairment of Long-Lived Assets Held-for-use	$ 0
Antelope Valley [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Capacity Of Facility Of Company Owned Solar Distribution Generation Facilities | MW	242
Long-lived assets	$ 710
Impairment of Long-Lived Assets Held-for-use	0
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	1,840
ExGen Renewables IV, LLC [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	1,840
Generation New England [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	0
Generation New England [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 0