Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Regulatory Assets
Regulatory Assets, Current	$ 583	$ 494
Regulatory Asset, Long-term	5,424	5,466
Total Regulatory Assets	6,007	5,960
Regulatory Liabilities
Regulatory Liabilities, Current	721	670
Regulatory Liabilities, Long-term	5,038	4,670
Total Regulatory Liabilities	5,759	5,340
Regulatory Balancing Accounts, Assets
Regulatory Assets
Regulatory Assets, Current	351	223
Regulatory Asset, Long-term	92	69
Energy Derivatives
Regulatory Assets
Regulatory Assets, Current	224	264
Regulatory Asset, Long-term	457	487
Other
Regulatory Assets
Regulatory Assets, Current	8	7
Regulatory Asset, Long-term	236	298
Regulatory Liabilities
Regulatory Liabilities, Current	9	9
Regulatory Liabilities, Long-term	7	4
Deferred Income Taxes - Net
Regulatory Assets
Regulatory Asset, Long-term	2,097	2,020
Pensions and Other Postretirement Benefits
Regulatory Assets
Regulatory Asset, Long-term	1,672	1,703
Unamortized Investments - Net
Regulatory Assets
Regulatory Asset, Long-term	483	484
Unamortized Loss on Reacquired Debt
Regulatory Assets
Regulatory Asset, Long-term	238	249
Nuclear-Related Investment - Net
Regulatory Assets
Regulatory Asset, Long-term	149	156
Regulatory Balancing Accounts, Liabilities
Regulatory Liabilities
Regulatory Liabilities, Current	712	661
Regulatory Liabilities, Long-term	1,054	864
Costs of Removal
Regulatory Liabilities
Regulatory Liabilities, Long-term	2,742	2,697
Asset Retirement Obligations
Regulatory Liabilities
Regulatory Liabilities, Long-term	$ 1,235	$ 1,105

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- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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