Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies [Line Items]
Derivative portfolio guarantee	$ 13
Obligations under guarantee	56
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
PHI [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	10
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	15
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	18
Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Obligations under guarantee	$ 13