Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail) - Jun. 30, 2015 - USD ($)	Total
Commitments and Contingencies [Line Items]
Derivative portfolio guarantee	$ 13,000,000
Obligations under guarantee	53,000,000
PHI [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	11,000,000
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	13,000,000
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	16,000,000
Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	13,000,000
Leased Equipment and Fleet Vehicles [Member]
Commitments and Contingencies [Line Items]
Fair value of leased equipment and vehicles	$ 0
Minimum [Member]
Commitments and Contingencies [Line Items]
Lease term range	1 to 4 years
Maximum [Member]
Commitments and Contingencies [Line Items]
Lease term range	3 to 8 years