Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As A Regulatory Asset Or Liability) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized losses arising during the period included in Regulatory assets		$ (9)	$ (20)
Net realized losses recognized in Fuel and purchased energy expense	(5)	(13)	(41)
Power Delivery [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized losses arising during the period included in Regulatory assets	(13)	(20)	(18)
Net realized losses recognized in Fuel and purchased energy expense	$ (22)	$ (26)	$ (11)