Derivative Instruments (Effect of Derivative Instruments on Consolidated Statements of Income) (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Gain/(Loss) Recognized in Income on Derivative Instruments	$ (1)	$ 4	$ (1)	$ 10
Commodity Contracts [Member] \| Operating Revenue [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments	(1)	2	(1)	5
Commodity Contracts [Member] \| Fuel for Electric Generation [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments		1		3
Commodity Contracts [Member] \| Purchased And Interchange Power [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments		$ 1		$ 2

- Definition

The amount of net gains and losses recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

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