Commitments and Contingencies - Merger Commitment (Details) $ in Millions	Jun. 30, 2019 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,211
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	75
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	50
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	15
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member]
Other Commitments [Line Items]
Other Commitment	513
Pepco Holdings Inc [Member] | Rate credits
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Energy efficiency
Other Commitments [Line Items]
Other Commitment	117
Pepco Holdings Inc [Member] | Charitable contributions
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Delivery system modernization
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings Inc [Member] | Green sustainability fund
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings Inc [Member] | Workforce development
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings Inc [Member] | Other
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings Inc [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	116
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	320
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Rate credits
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Energy efficiency
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Charitable contributions
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Delivery system modernization
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Green sustainability fund
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Workforce development
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Other
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	86
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] | Rate credits
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Energy efficiency
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Charitable contributions
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Delivery system modernization
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Green sustainability fund
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Workforce development
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Other
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	69
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] | Rate credits
Other Commitments [Line Items]
Other Commitment	72
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Energy efficiency
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Charitable contributions
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Delivery system modernization
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Green sustainability fund
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Workforce development
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Other
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	11
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] | Rate credits
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Energy efficiency
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Charitable contributions
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Delivery system modernization
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Green sustainability fund
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Workforce development
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Other
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Remaining commitment
Other Commitments [Line Items]
Other Commitment	$ 6