Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 486	$ 496
Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	108	108
Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	320	329
PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	27	27
Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	5	5
Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	26	27
Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	24	25
Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	1	1
Accrual For MGP Investigation And Remediation [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	347	356
Accrual For MGP Investigation And Remediation [Member] | Exelon Generation Co L L C [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Commonwealth Edison Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	318	327
Accrual For MGP Investigation And Remediation [Member] | PECO Energy Co [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	25	25
Accrual For MGP Investigation And Remediation [Member] | Baltimore Gas and Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	4	4
Accrual For MGP Investigation And Remediation [Member] | Pepco Holdings LLC [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Potomac Electric Power Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Delmarva Power and Light Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	0	0
Accrual For MGP Investigation And Remediation [Member] | Atlantic City Electric Company [Member]
Accrual For Environmental Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Gross	$ 0	$ 0