Asset Impairments - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) MW	Mar. 31, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 8	$ 7
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	8	$ 7
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	717
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	$ 717
Impairment of Long-Lived Assets Held-for-use	0
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	1,865
ExGen Renewables IV, LLC [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	$ 1,865