Impairment of Long-Lived Assets - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) MW	Jun. 30, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	$ 9	$ 41
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	9	$ 41
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	740
Impairment of long-lived assets	$ 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	$ 740
Impairment of long-lived assets	0
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	1,950
ExGen Renewables IV, LLC [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Long-lived assets	$ 1,950