Commitments and Contingencies - Merger Commitment (Details) $ in Millions	Mar. 31, 2021 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,123
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	52
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	24
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	17
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	11
Pepco Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	513
Pepco Holdings Inc [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	79
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	320
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	64
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	120
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	53
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	89
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	7
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	$ 4