Derivative Instruments (Gain/(Loss) Recognized In Income For Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Gain/(loss) recognized in income on derivative instruments	$ (1)	$ (1)	$ (1)	$ (1)
Commodity Contracts [Member] | Operating Revenue [Member]
Gain/(loss) recognized in income on derivative instruments	(2)	(1)	1	(1)
Commodity Contracts [Member] | Fuel For Electric Generation [Member]
Gain/(loss) recognized in income on derivative instruments			(2)
Commodity Contracts [Member] | Cost Of Gas Sold [Member]
Gain/(loss) recognized in income on derivative instruments	1		1
Commodity Contracts [Member] | Purchased And Interchange Power [Member]
Gain/(loss) recognized in income on derivative instruments			$ (1)