Asset Impairments - Narrative (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2019 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Deferred Income Taxes and Tax Credits				$ 681	$ (108)	$ (362)
Impairment of Intangible Assets, Finite-lived		$ 25
Impairment of Long-Lived Assets Held-for-use				201	50	573
Certain Distributed Energy Companies [Member]
Property, Plant and Equipment [Line Items]
Equity Method Investment, Other than Temporary Impairment	$ 164
Net income (loss) attributable to noncontrolling interests	96
Deferred Income Taxes and Tax Credits	(46)
Income (Loss) from Equity Method Investments	(15)
Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Net Assets				725
Impairment of Long-Lived Assets Held-for-use				0
ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Net Assets				1,893
Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets to be Disposed of			$ 460
Pepco Holdings LLC [Member]
Property, Plant and Equipment [Line Items]
Deferred Income Taxes and Tax Credits				(7)	30	252
Impairment of Intangible Assets, Finite-lived		$ 25
Impairment of Long-Lived Assets Held-for-use				0	0	52
Exelon Generation Co L L C [Member]
Property, Plant and Equipment [Line Items]
Net income (loss) attributable to noncontrolling interests				92	73	88
Deferred Income Taxes and Tax Credits				361	(451)	(2,023)
Impairment of Long-Lived Assets Held-for-use				$ 201	$ 50	$ 510
Exelon Generation Co L L C [Member] | Certain Distributed Energy Companies [Member]
Property, Plant and Equipment [Line Items]
Equity Method Investment, Other than Temporary Impairment	164
Net income (loss) attributable to noncontrolling interests	96
Deferred Income Taxes and Tax Credits	(46)
Income (Loss) from Equity Method Investments	$ (15)
Exelon Generation Co L L C [Member] | Antelope Valley [Member]
Property, Plant and Equipment [Line Items]
Capacity Of Facility Of Company Owned Solar Distribution Generation Facilities | MW				242
Net Assets				$ 725
Impairment of Long-Lived Assets Held-for-use				0
Exelon Generation Co L L C [Member] | ExGen Renewables IV, LLC [Member]
Property, Plant and Equipment [Line Items]
Net Assets				$ 1,893
Exelon Generation Co L L C [Member] | Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets to be Disposed of			$ 460