Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	$ 494	$ 478
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	125	105
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	299	304
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	23	19
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	2	2
Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	45	48
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	43	46
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	1	1
Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	1	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	320	320
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	298	303
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	22	17
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	0	0
Accrual For MGP Investigation And Remediation [Member] | Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Total environmental investigation and remediation reserve	$ 0	$ 0