Commitments and Contingencies - Schedule of Commitments and Obligations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Commitments and Contingencies [Line Items]
Guarantees associated with disposal of Conectiv Energy assets	$ 13
Guaranteed lease residual values	19
Total	32
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	5
Total	5
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