Commitments And Contingencies (Environmental Matters) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		1 Months Ended			1 Months Ended		3 Months Ended
	Jan. 31, 2011 gal	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012 PHI [Member]	Mar. 31, 2013 PHI [Member]	Dec. 31, 2012 PHI [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Jan. 31, 2011 Potomac Electric Power Co [Member] gal	Mar. 31, 2013 Potomac Electric Power Co [Member]	Mar. 31, 2013 Atlantic City Electric Co [Member]
Commitments And Contingencies [Line Items]
EPA costs to date to clean up site		$ 6								$ 6
Estimated costs remaining to remediate the site		6								6
Quantity of mineral oil spill (gallons)	4,500							4,500
Civil penalty and Supplement Environmental Projects cost				1			1
Investment in finance leases held in trust		869	1,237		869	1,237
Tax payment made	74
Income tax penalties	1
Interest expense assessed relating to disallowed deductions	28
Non-cash charge (after-tax)		377							377	377
Maximum tax penalty percentage		20.00%
Federal income tax benefits		192
Percentage of disallowed tax benefits associated with leases		100.00%
Potential interest on potential tax liability related to disallowed tax benefits		50
Deposit of additional taxes and related interest		$ 242