Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 483	$ 478
Exelon Generation Co L L C [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	121	105
Commonwealth Edison Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	293	304
PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	23	19
Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	2	2
Pepco Holdings LLC [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	44	48
Potomac Electric Power Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	42	46
Delmarva Power & Light Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Accrual For MGP Investigation And Remediation [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	314	320
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	293	303
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	21	17
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Pepco Holdings LLC [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power & Light Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0