Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Potomac Electric Power Co [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	$ (31)	$ (41)
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(25)	(22)
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(6)	(18)
Potomac Electric Power Co [Member] | Other [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total		(1)
Delmarva Power & Light Co/De [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(21)	(20)
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(21)	(19)
Delmarva Power & Light Co/De [Member] | Other [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total		(1)
Atlantic City Electric Co [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(12)	(14)
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total	(12)	(13)
Atlantic City Electric Co [Member] | Other [Member]
Related Party Transaction [Line Items]
(Payable to) Receivable from Related Party, Total		$ (1)