Commitments and Contingencies - Schedule of Commitments and Obligations (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Commitments and Contingencies [Line Items]
Guarantees associated with disposal of Conectiv Energy assets	$ 13
Guaranteed lease residual values	20
Total	33
PHI [Member]
Commitments and Contingencies [Line Items]
Guarantees associated with disposal of Conectiv Energy assets	13
Guaranteed lease residual values	3
Total	16
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Guaranteed lease residual values	6
Total	6
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Guaranteed lease residual values	6
Total	6
Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Guaranteed lease residual values	5
Total	$ 5