Mergers, Acquisitions and Dispositions Commitment and Contingencies Table (Details) - USD ($) $ in Millions	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016
Other Commitments [Line Items]
Other Commitment	$ 513	$ 137
Pepco Holdings LLC [Member]
Other Commitments [Line Items]
Other Commitment			$ 444
Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	323
Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	126
Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	86
Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	111
Rate Bill Credits [Member]
Other Commitments [Line Items]
Other Commitment	259
Rate Bill Credits [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	259
Rate Bill Credits [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	91
Rate Bill Credits [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	67
Rate Bill Credits [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	101
Energy Efficiency Program [Member]
Other Commitments [Line Items]
Other Commitment	111
Energy Efficiency Program [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	0
Energy Efficiency Program [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Energy Efficiency Program [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Energy Efficiency Program [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Charitable Contributions [Member]
Other Commitments [Line Items]
Other Commitment	50
Charitable Contributions [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	50
Charitable Contributions [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	28
Charitable Contributions [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	12
Charitable Contributions [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	10
Delivery System Modernization [Member]
Other Commitments [Line Items]
Other Commitment	22
Delivery System Modernization [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	0
Delivery System Modernization [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Delivery System Modernization [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Delivery System Modernization [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Green Sustainability Fund [Member]
Other Commitments [Line Items]
Other Commitment	14
Green Sustainability Fund [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	0
Green Sustainability Fund [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Green Sustainability Fund [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Green Sustainability Fund [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Workforce Development [Member]
Other Commitments [Line Items]
Other Commitment	24
Workforce Development [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	0
Workforce Development [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Workforce Development [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Workforce Development [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	0
Other1 [Member]
Other Commitments [Line Items]
Other Commitment	33
Other1 [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Other Commitments [Line Items]
Other Commitment	14
Other1 [Member] | Potomac Electric Power Company [Member]
Other Commitments [Line Items]
Other Commitment	7
Other1 [Member] | Delmarva Power and Light Company [Member]
Other Commitments [Line Items]
Other Commitment	7
Other1 [Member] | Atlantic City Electric Company [Member]
Other Commitments [Line Items]
Other Commitment	$ 0