Asset Impairments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				$ 500	$ 33
Net income (loss) attributable to noncontrolling interests	$ 75		$ 53	99	(153)
Deferred income taxes and amortization of investment tax credits				(163)	33
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				493	18
Net income (loss) attributable to noncontrolling interests	74		$ 53	98	(153)
Deferred income taxes and amortization of investment tax credits				(142)	$ (54)
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
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]
Impairment of Long-Lived Assets Held-for-use				0
Generation New England [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	350	$ 500
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	$ 350	$ 500
Midwest Asset Group [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				0
Midwest Asset Group [Member] | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				$ 0