Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As Regulatory Asset Or Liability) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
PHI [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gain (loss) arising during the period	$ 2	$ (4)
Net realized loss recognized during the period	(4)	(7)
Delmarva Power & Light Co/De [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gain (loss) arising during the period	2	(4)
Net realized loss recognized during the period	$ (4)	$ (7)