Property, Plant and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012 MW	Dec. 31, 2011
Property Plant And Equipment Disclosure [Line Items]
Present value of future minimum lease payments	$ 152,000,000
Semi-annual payments	8,000,000
Description of lease term	Over a 25-year period that began in December 1994
Guaranteed residual value due at end of lease term	1
Approximate annual commitments, 2014	15,000,000
Approximate annual commitments, 2015	15,000,000
Approximate annual commitments, 2016	15,000,000
Approximate annual commitments, 2017	15,000,000
Approximate annual commitments, 2018	15,000,000
Approximate annual commitments, thereafter	16,000,000
Generating capacity		790
Decommissioning costs		3,000,000	2,000,000
Impairment losses, pre-tax	4,000,000	12,000,000
Asset retirement obligation	2,000,000
Buzzard Point and Benning Road [Member]
Property Plant And Equipment Disclosure [Line Items]
Asset retirement obligation	2,000,000	9,000,000
Subsidiaries [Member]
Property Plant And Equipment Disclosure [Line Items]
Jointly owned plant, net book value ownership	12,000,000	13,000,000
Impairment losses, pre-tax	4,000,000	12,000,000
Impairment losses, after-tax	3,000,000	7,000,000
Conectiv Energy [Member]
Property Plant And Equipment Disclosure [Line Items]
Asset retirement obligation	6,000,000
Minimum estimated costs for closure of the operations	2,000,000
Maximum estimated costs for closure of the operations	3,000,000
Annual post-closure operations, maintenance and monitoring period	30 years
Potomac Electric Power Co [Member]
Property Plant And Equipment Disclosure [Line Items]
Semi-annual payments	8,000,000
Description of lease term	Over a 25-year period that began in December 1994
Guaranteed residual value due at end of lease term	1
Approximate annual commitments, 2014	15,000,000
Approximate annual commitments, 2015	15,000,000
Approximate annual commitments, 2016	15,000,000
Approximate annual commitments, 2017	15,000,000
Approximate annual commitments, 2018	15,000,000
Approximate annual commitments, thereafter	16,000,000
Atlantic City Electric Co [Member]
Property Plant And Equipment Disclosure [Line Items]
Jointly owned plant, net book value ownership	$ 8,000,000	$ 8,000,000