Derivative Instruments and Hedging Activities - Net Unrealized Derivative Gain (Loss) Deferred as Regulatory Asset or Liability (Detail) (Other Derivative Activity [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gain (loss) arising during the period	$ 4	$ (6)	$ (13)
Net realized loss recognized during the period	(4)	(16)	(22)
Delmarva Power & Light Co/De [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized gain (loss) arising during the period	1	(3)	(13)
Net realized loss recognized during the period	$ (4)	$ (16)	$ (22)