Commitments and Contingencies - Narrative (Details) $ in Millions				3 Months Ended							9 Months Ended		12 Months Ended
	Oct. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Mar. 23, 2016 USD ($) MW	Sep. 30, 2020 USD ($) MGPSite Open_claim	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 MW	Sep. 30, 2020 USD ($) MGPSite Open_claim MW	Sep. 30, 2019 MW	Dec. 31, 2022 MW	Dec. 31, 2019 USD ($)
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				$ 2,924							$ 2,924
Accrual for Environmental Loss Contingencies, Gross				494							494			$ 478
Liability for Asbestos and Environmental Claims, Gross				91							91			83
Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				2,359							2,359
Accrual for Environmental Loss Contingencies, Gross				125							125			105
Liability for Asbestos and Environmental Claims, Gross				91							91			83
Contributions from parent				64
Commonwealth Edison Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				$ 223							$ 223
Mgp Site Contingency Monitoring Count | MGPSite				21							21
Accrual for Environmental Loss Contingencies, Gross				$ 299							$ 299			304
Deferred Prosecution Agreement payments				200							200			0
Estimated Litigation Liability, Current, Due within 30 days				100							100
Estimated Litigation Liability, Current, Due within 90 days				100							100
Contributions from parent				239	$ 124	$ 125	$ 63	$ 61	$ 63
Increase in Restricted Cash				100
Commonwealth Edison Co [Member] | Deferred Prosecution Agreement Payments [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Deferred Prosecution Agreement payments				200							200
Contributions from parent		$ 100
PECO Energy Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				$ 180							$ 180
Mgp Site Contingency Monitoring Count | MGPSite				8							8
Accrual for Environmental Loss Contingencies, Gross				$ 23							$ 23			19
Contributions from parent				17		231	29		145
Baltimore Gas and Electric Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				$ 5							$ 5
Mgp Site Contingency Monitoring Count | MGPSite				4							4
Accrual for Environmental Loss Contingencies, Gross				$ 2							$ 2			2
Contributions from parent				258	26		$ 104
Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				49							49
Accrual for Environmental Loss Contingencies, Gross				45							45			48
Contributions from parent				135	215	144		264	19
Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				23							23
Accrual for Environmental Loss Contingencies, Gross				43							43			46
Contributions from parent				125		137		$ 115	$ 14
Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				$ 16							$ 16
Mgp Site Contingency Count | MGPSite				1							1
Accrual for Environmental Loss Contingencies, Gross				$ 1							$ 1			$ 1
Contributions from parent				6	$ 100	$ 6
Open Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross				$ 27							$ 27
Open Asbestos Related Personal Injury Claims | Open_claim				274							274
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Liability for Asbestos and Environmental Claims, Gross				$ 64							$ 64
Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				513							513
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				320							320
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				120							120
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				89							89
West Lake [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross				280							280
West Lake [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Accrual for Environmental Loss Contingencies, Gross				30							30
Accrual for Environmental Loss Contingencies, Component Amount				90							90
Other Solar Projects [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Business Acquisition, Expected New Generation Mwh | MW			37
Other Commitment			$ 135	118							$ 118
Other Non-Financial Commitment | MW											27
Other Solar Projects [Member] | Pepco Holdings Inc [Member] | Exelon Generation Co L L C [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Commitment				118							$ 118
Wind Assets [Member] | Pepco Holdings Inc [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Other Non-Financial Commitment | MW			100
Wind Assets [Member] | Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Purchase Commitment | MW			120							40		40
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Increase in Restricted Cash	$ 100
Subsequent Event [Member] | Commonwealth Edison Co [Member] | Deferred Prosecution Agreement Payments [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Deferred Prosecution Agreement payments				$ 200							$ 200
Contributions from parent	$ 100
Subsequent Event [Member] | Wind Assets [Member] | Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Commitments And Contingencies Additional Narrative Information [Line Items]
Purchase Commitment | MW													40