Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As A Regulatory Asset Or Liability) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Pepco Holdings Inc [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized (loss) gain arising during the period	$ (1)	$ (1)	$ (5)	$ (2)
Net realized loss recognized during the period	(4)	(4)	(11)	(11)
Delmarva Power & Light Co/De [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized (loss) gain arising during the period		(1)	(4)	(2)
Net realized loss recognized during the period	(4)	(4)	(11)	(11)
Power Delivery [Member] | Pepco Holdings Inc [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net realized loss recognized during the period		(1)		(3)
Power Delivery [Member] | Delmarva Power & Light Co/De [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net realized loss recognized during the period		$ (1)		$ (3)