Commitments and Contingencies Merger Commitment (Details) $ in Millions	Sep. 30, 2018 USD ($)
Other Commitments [Line Items]
Other Commitment	$ 3,386
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	91
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	43
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	13
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	9
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	259
Pepco Holdings Inc [Member] | Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	122
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	138
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment	315
Pepco Holdings Inc [Member] | Pepco Holdings LLC [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
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	94
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	75
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	84
Pepco Holdings Inc [Member] | Delmarva Power and Light Company [Member] | Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	67
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