Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As Regulatory Asset Or Liability) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Delmarva Power & Light Co/De [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized loss arising during the period	$ (3)	$ (13)	$ (20)
Net realized loss recognized during the period	(16)	(22)	(26)
Delmarva Power & Light Co/De [Member] | Power Delivery [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized loss arising during the period			(9)
Net realized loss recognized during the period		(5)	(13)
PHI [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized loss arising during the period	(6)	(13)	(20)
Net realized loss recognized during the period	(16)	(22)	(26)
PHI [Member] | Power Delivery [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized loss arising during the period			(9)
Net realized loss recognized during the period		$ (5)	$ (13)