Income Taxes (Details 1) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Deferred tax liabilities -
Deferred tax liabilities	$ 12,127,000,000	$ 10,557,000,000
Deferred tax assets -
Deferred tax assets	3,473,000,000	3,153,000,000
Total deferred tax liabilities, net	8,654,000,000	7,404,000,000
Portion included in prepaid expenses (accrued income taxes), net	125,000,000	117,000,000
Deferred state tax assets	86,000,000	91,000,000
Valuation allowance	(56,000,000)	(58,000,000)
Accumulated deferred income taxes	8,809,000,000	7,554,000,000
Asset retirement obligations-asset [Member]
Deferred tax assets -
Deferred tax assets	546,000,000	509,000,000
Unbilled Revenues [Member]
Deferred tax assets -
Deferred tax assets	110,000,000	126,000,000
Accelerated depreciation [Member]
Deferred tax liabilities -
Deferred tax liabilities	7,882,000,000	6,833,000,000
Deferred costs [Member]
Deferred tax assets -
Deferred tax assets	55,000,000	100,000,000
Property basis differences [Member]
Deferred tax liabilities -
Deferred tax liabilities	1,256,000,000	1,150,000,000
Leveraged lease basis differences [Member]
Deferred tax liabilities -
Deferred tax liabilities	277,000,000	263,000,000
Employee benefit obligations [Member]
Deferred tax liabilities -
Deferred tax liabilities	499,000,000	485,000,000
Deferred tax assets -
Deferred tax assets	1,594,000,000	1,179,000,000
Under recovered fuel clause [Member]
Deferred tax liabilities -
Deferred tax liabilities	82,000,000	179,000,000
Premium on reacquired debt [Member]
Deferred tax liabilities -
Deferred tax liabilities	111,000,000	109,000,000
Regulatory assets associated with employee benefit obligations [Member]
Deferred tax liabilities -
Deferred tax liabilities	1,198,000,000	814,000,000
Regulatory assets associated with asset retirement obligations [Member]
Deferred tax liabilities -
Deferred tax liabilities	546,000,000	509,000,000
Other deferred tax liabilities [Member]
Deferred tax liabilities -
Deferred tax liabilities	276,000,000	215,000,000
Federal effect of state deferred taxes [Member]
Deferred tax assets -
Deferred tax assets	393,000,000	386,000,000
State effect of federal deferred taxes [Member]
Deferred tax assets -
Deferred tax assets	1,000,000	50,000,000
Over recovered fuel clause [Member]
Deferred tax assets -
Deferred tax assets	33,000,000	40,000,000
Other property basis differences [Member]
Deferred tax assets -
Deferred tax assets	134,000,000	119,000,000
Cost of removal [Member]
Deferred tax assets -
Deferred tax assets	40,000,000	52,000,000
Tax credit carryforward [Member]
Deferred tax assets -
Deferred tax assets	129,000,000	192,000,000
Other comprehensive losses [Member]
Deferred tax assets -
Deferred tax assets	81,000,000	69,000,000
Other deferred tax assets [Member]
Deferred tax assets -
Deferred tax assets	$ 357,000,000	$ 331,000,000

The sum of the tax effects as of the balance sheet date of the amounts of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws ( before the valuation allowance, if any, to reduce such sum amount to net realizable value). Includes any tax benefit realized in deferred tax assets for significant impacts of tax planning strategies.

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For entities that net deferred tax assets and tax liabilities, represents the unclassified net amount of deferred tax assets and liabilities as of the balance sheet date, which result from applying the applicable enacted tax rate to net temporary differences and carryforwards pertaining to assets or liabilities. A temporary difference is a difference between the tax basis of an asset or liability and its carrying amount in the financial statements prepared in accordance with generally accepted accounting principles that will reverse in ensuing periods.

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- Definition

The sum of the portions of deferred tax assets as of the balance sheet date for which, based on the weight of available evidence, it is more likely than not will not be realized through future reductions of tax-based income.

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- Definition

The cumulative amount of all deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A taxable temporary difference is a difference between the tax basis and the carrying amount of an asset or liability in the financial statements prepared in accordance with generally accepted accounting principles that will result in taxable amounts in one or more future periods.

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- Definition

Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise separates deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets are classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, are classified according to the expected reversal date of the temporary difference.

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