Related Party Transactions - Schedule of Related Party Transactions Included in Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Atlantic City Electric Co [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	$ (13)	$ (15)
Atlantic City Electric Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(13)	(15)
Delmarva Power & Light Co/De [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(20)	(22)
Delmarva Power & Light Co/De [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(19)	(22)
Delmarva Power & Light Co/De [Member] | Other [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(1)
Potomac Electric Power Co [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(29)	(32)
Potomac Electric Power Co [Member] | PHI Service Company [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	(23)	(25)
Potomac Electric Power Co [Member] | Pepco Energy Services [Member]
Related Party Transaction [Line Items]
Payable to Related Party (current) (a) PHI Service Company	$ (6)	$ (7)