Commitments and Contingencies - Environmental Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended			1 Months Ended		3 Months Ended	6 Months Ended
	Jan. 31, 2011 gal	Mar. 31, 2013	Jun. 30, 2013	Mar. 31, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2012 PHI [Member]	Jun. 30, 2013 PHI [Member] Maximum [Member]	Jun. 30, 2013 PHI [Member] Minimum [Member]	Jun. 30, 2013 PHI [Member] Brandywine Fly Ash Disposal Site [Member] Maximum [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]	Jun. 30, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Minimum [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Brandywine Fly Ash Disposal Site [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
Period of capping of the right-of-way									90 days
Cost of implementation of a closure plan and cap								less than 1 million						less than 1 million
Maximum cost of implementation of a closure plan and cap							6						6
Tax payment made	74
Income tax penalties	1	0
Interest expense assessed relating to disallowed deductions	28
Non-cash charge (after-tax)		377		377								377
Maximum tax penalty percentage		20.00%	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
Period of capping of the right-of-way															90 days