Asset Impairments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				$ 541	$ 567
Net income (loss) attributable to noncontrolling interests	$ 26		$ 68	126	(85)
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use				537	552
Net income (loss) attributable to noncontrolling interests	26		68	125	$ (85)
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
Contracted Wind Project
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	45
Net income (loss) attributable to noncontrolling interests	21
Contracted Wind Project | Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	45
Net income (loss) attributable to noncontrolling interests	$ 21