v2.4.0.6

Acquisitions, Divestitures and Discontinued Operations (Sale of Blue Spruce and Rocky Mountain) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 08, 2010	Dec. 06, 2010
Acquisitions, Divestitures and Discontinued Operations [Abstract]
Operating revenues										$ 92	$ 101
Gain on disposal of discontinued operations						209				209	0
Income from discontinued operations before taxes										43	35
Less: Income tax expense									0	59	0
Discontinued operations, net of tax expense	0	0	0	0	162	19	4	8	0	193	35
Ownership percentage before divestiture of business													100.00%
Proceeds from Divestiture of Business													739
Other Asset Sales (Textuals) [Abstract]
Cash Proceeds From Sale Of Undivided Interest In Power Plant Assets												215
Gain (Loss) on Disposition of Assets									$ 0	$ 119	$ 0
Undivided Interest Percentage In Power Plant Asset												25.00%

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Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Tax effect allocated to a disposal group that is classified as a component of the entity reported as a separate component of income before extraordinary items. Includes the tax effects of the following: income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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