Derivative Instruments And Hedging Activities (Net Unrealized Derivative Gain (Loss) Deferred As A Regulatory Asset Or Liability) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Regulatory Clause Revenues, Under-Recovered [Member]
Net Unrealized Gain (Loss) Deferred as a Regulatory Liability (Asset)	$ (1)	$ (3)	$ (1)	$ (9)
Net Realized Loss Recognized in Fuel and Purchased Energy Expense	(2)	(4)	(5)	(10)
Power Delivery [Member]
Net Unrealized Gain (Loss) Deferred as a Regulatory Liability (Asset)	(4)	(9)	(6)	(21)
Net Realized Loss Recognized in Fuel and Purchased Energy Expense	$ (3)	$ (5)	$ (14)	$ (18)