Commitments And Contingencies (Environmental Matters) (Detail) (USD $)	1 Months Ended				12 Months Ended			3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended			12 Months Ended	1 Months Ended	12 Months Ended			3 Months Ended
	Jan. 31, 2012	Dec. 31, 2011		Jan. 31, 2011 gal	Dec. 31, 2012		Dec. 31, 2011 District Of Columbia [Member]	Mar. 31, 2013 Subsequent Event [Member]	Mar. 31, 2013 Subsequent Event [Member] Minimum [Member]	Mar. 31, 2013 Subsequent Event [Member] Minimum [Member]	Mar. 31, 2013 Subsequent Event [Member] Maximum [Member]	Mar. 31, 2013 Subsequent Event [Member] Maximum [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Jan. 31, 2011 Potomac Electric Power Co [Member] gal	Dec. 31, 2011 Potomac Electric Power Co [Member]	Feb. 28, 2012 Pepco Energy Services [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Dec. 31, 2012 PHI [Member]	Mar. 31, 2013 PHI [Member] Subsequent Event [Member]	Mar. 31, 2013 PHI [Member] Subsequent Event [Member] Maximum [Member]
Commitments And Contingencies [Line Items]
EPA costs to date to clean up site					$ 6,000,000													$ 6,000,000
Estimated costs remaining to remediate the site					6,000,000													6,000,000
Quantity of mineral oil spill (gallons)				4,500											4,500
Civil penalty and supplement environmental projects cost													1,000,000
Penalty charges related to release of oil in U.S. waters		5,000														5,000
Civil penalty														40,000		40,000
Civil charge																	10,000
Investment in finance leases held in trust		1,349,000,000	[1]		1,237,000,000	[1]													1,200,000,000
Tax payment made	74,000,000
Income tax penalties				1,000,000
Interest expense assessed relating to disallowed deductions				28,000,000
Current annual tax benefits																			43,000,000
Federal and state income tax benefits					489,000,000
Percentage of disallowed tax benefits associated with leases																			100.00%
Additional federal and state taxes								600,000,000	170,000,000	170,000,000	200,000,000	200,000,000							600,000,000
Potential interest on potential tax liability related to disallowed tax benefits					144,000,000			150,000,000	50,000,000	50,000,000	60,000,000	60,000,000
Maximum tax penalty percentage																				20.00%	20.00%
Reduced pre-tax earnings							$ 1

[1] Excludes the credit ratings of collateral posted by the lessees in these transactions.