Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As A Regulatory Asset Or Liability) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Net unrealized losses arising during the period included in Regulatory assets	$ (4)	$ (1)
Net realized losses recognized in Fuel and purchased energy expense	(7)	(7)
Power Delivery [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net realized losses recognized in Fuel and purchased energy expense		$ (2)