Capacity of facility of company owned solar distribution generation facilities.

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Asset Impairments - Narrative (Details) $ in Millions	3 Months Ended				12 Months Ended
Asset Impairments - Narrative (Details) $ in Millions	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairments					$ 591	$ 201	$ 50
Net income (loss) attributable to noncontrolling interests					(9)	92	74
Deferred Income Taxes and Tax Credits					$ 309	681	(108)
Certain Distributed Energy Companies [Member]
Impaired Long-Lived Assets Held and Used [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]
Impaired Long-Lived Assets Held and Used [Line Items]
Capacity Of Facility Of Company Owned Solar Distribution Generation Facilities \| MW					242
Asset impairments			$ 0
Generation New England [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairments				$ 0
Impairment of Long-Lived Assets to be Disposed of	$ 500
Generation Midwest [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets to be Disposed of	0
Exelon Generation Co L L C [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairments					$ 563	201	50
Net income (loss) attributable to noncontrolling interests					(10)	92	73
Deferred Income Taxes and Tax Credits					$ 78	$ 361	$ (451)
Exelon Generation Co L L C [Member] \| Certain Distributed Energy Companies [Member]
Impaired Long-Lived Assets Held and Used [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]
Impaired Long-Lived Assets Held and Used [Line Items]
Capacity Of Facility Of Company Owned Solar Distribution Generation Facilities \| MW					242
Asset impairments			$ 0
Exelon Generation Co L L C [Member] \| Generation New England [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairments				$ 0
Impairment of Long-Lived Assets to be Disposed of	500
Exelon Generation Co L L C [Member] \| Generation Midwest [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets to be Disposed of	$ 0