Commitments and Contingencies - Schedule of Environmental Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 478	$ 496
Exelon Generation Co L L C [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	105	108
Commonwealth Edison Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	304	329
PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	19	27
Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	2	5
Pepco Holdings LLC [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	48	27
Potomac Electric Power Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	46	25
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	320	356
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	303	327
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	17	25
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	4
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