Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($)
Other Commitments [Line Items]
Derivative portfolio guarantee	$ 13,000,000
Obligations under guarantee	$ 52,000,000
Minimum [Member]
Other Commitments [Line Items]
Lease term range	1 year
Lease term range	3 years
Maximum [Member]
Other Commitments [Line Items]
Lease term range	4 years
Lease term range	8 years
PHI [Member]
Other Commitments [Line Items]
Obligations under guarantee	$ 9,000,000
Potomac Electric Power Co [Member]
Other Commitments [Line Items]
Obligations under guarantee	13,000,000
Delmarva Power & Light Co/De [Member]
Other Commitments [Line Items]
Obligations under guarantee	16,000,000
Atlantic City Electric Co [Member]
Other Commitments [Line Items]
Obligations under guarantee	14,000,000
Leased Equipment and Fleet Vehicles [Member]
Other Commitments [Line Items]
Fair value of leased equipment and vehicles	$ 0