Commitments And Contingencies (PHI's Cross-Border Energy Lease Investments) (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2011	Mar. 31, 2012	Dec. 31, 2011
Commitments And Contingencies [Line Items]
Estimated current annual tax benefits		$ 48,000,000
Investment in finance leases held in trust		1,362,000,000	1,349,000,000
Federal and state income tax benefits		522,000,000
Tax payment made	74,000,000
Income tax penalties	1,000,000
Interest expense associated with the disallowed deductions	28,000,000
Additional federal and state taxes	785,000,000	658,000,000
Potential tax liability in the event of a total disallowance		785,000,000
Potential interest on potential tax liability related to disallowed tax benefits		127,000,000
Maximum tax penalty percentage			20.00%
Pepco Holdings Inc [Member]
Commitments And Contingencies [Line Items]
Investment in finance leases held in trust		$ 1,400,000,000