Commitments and Contingencies - Merger Commitment (Details) $ in Millions	Mar. 31, 2019 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,481
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	74
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	48
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	16
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 Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	117
Pepco Holdings Inc [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Pepco Holdings Inc [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Pepco Holdings Inc [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	17
Pepco Holdings Inc [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	29
Pepco Holdings Inc [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	123
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	320
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	264
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	6
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	90
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 Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	91
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	28
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	1
Pepco Holdings Inc [Member] | Potomac Electric Power Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	71
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 Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	72
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	12
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	5
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	12
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 Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	101
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	10
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Other1 [Member]
Other Commitments [Line Items]
Other Commitment	0
Pepco Holdings Inc [Member] | Atlantic City Electric Company [Member] | Remaining Commitment [Member]
Other Commitments [Line Items]
Other Commitment	$ 7