Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail) (USD $)	3 Months Ended						9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 PHI [Member]	Sep. 30, 2014 Potomac Electric Power Co [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member]	Sep. 30, 2014 Leased Equipment and Fleet Vehicles [Member]	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]
Commitments and Contingencies [Line Items]
Derivative portfolio guarantee	$ 13,000,000
Obligations under guarantee	51,000,000	10,000,000	13,000,000	15,000,000	13,000,000
Lease term range							1 to 4 years	3 to 8 years
Fair value of leased equipment and vehicles						$ 0