Derivative Instruments And Hedging Activities (Amount Of Derivative Gain Or Loss Recognized In Income) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Revenue [Member]
Realized mark-to-market gains (losses)	$ 2	$ 1	$ (2)	$ 1
Unrealized mark-to-market gains (losses)	(5)		(5)
Total net mark-to-market gains (losses)	(3)	1	(7)	1
Fuel and Purchased Energy Expense [Member]
Realized mark-to-market gains (losses)
Unrealized mark-to-market gains (losses)
Total net mark-to-market gains (losses)
Total Earnings [Member]
Realized mark-to-market gains (losses)	2	1	(2)	1
Unrealized mark-to-market gains (losses)	(5)		(5)
Total net mark-to-market gains (losses)	$ (3)	$ 1	$ (7)	$ 1