Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	28.00%	25.00%	18.00%	24.00%
Production tax credits	$ 45	$ 66	$ 208	$ 229
Deferred income tax benefit associated with convertible investment tax credits	9	26	17	56
Income tax benefit associated with employee benefits		24		24
Deferred state tax benefit related to recent state tax law changes			64
Consolidated effect of reversal of valuation allowance related to certain state investment tax credits			26
Reduction of liability for unrecognized tax benefits			248
Reduction of accrued net interest receivable			131
Cash received from a final settlement with a taxing authority	$ 278		$ 278

The net amount of decreases in accrued interest receivable resulting from settlements with taxing authorities.

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Deferred income tax benefit related to the difference between the financial statement and tax bases of renewable property.

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Deferred state tax benefit related to recent state tax law changes reflected in the Corporate and Other Segment.

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Income tax benefit related to employee benefits

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions.

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The amount of the additional liability or refund received or expected based on a final settlement with a taxing authority.

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The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities.

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-Name FASB Interpretation (FIN)

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The amount of the change in the period in the valuation allowance for a specified deferred tax asset.

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