v2.4.0.6

Derivative Instruments (Details 3) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Realized gain (loss) on derivatives | $ (50) |  | $ 83 |  | $ 5 |
Unrealized gain (loss) | 30 | [1] | (56) | [1] | 87 | [1]
Summary of Derivative Instruments by Risk Exposure [Abstract] |  |  |  |  |  |
Power contracts included in operating revenues | (20) |  | (19) |  | 7 |
Natural gas contracts included in fuel and purchased energy expense | 138 |  | 276 |  | 109 |
Interest rate swaps included in interest expense | 7 |  | (7) |  | (24) |
Gain (Loss) on interest rate derivatives, net | 145 |  | 223 |  | 0 |
Gain (Loss) on Derivative Instruments, Net, Pretax | (20) | [1] | 27 | [1] | 92 | [1]
Interest Rate Swap [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Realized gain (loss) on derivatives | (193) |  | (31) |  | (32) |
Unrealized gain (loss) | 55 | [1] | (199) | [1] | 8 | [1]
Commodity Option [Member] |  |  |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |  |  |
Realized gain (loss) on derivatives | 143 |  | 114 |  | 37 |
Unrealized gain (loss) | $ (25) | [1] | $ 143 | [1] | $ 79 | [1]
[1] | In addition to changes in market value on derivatives not designated as hedges, changes in unrealized gain (loss) also includes de-designation of interest rate swap cash flow hedges and related reclassification from AOCI into income, hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.

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- Definition Interest rate swaps included in interest expense + References No definition available. + Details
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- Definition Natural gas contracts included in fuel and purchased energy expense + References No definition available. + Details
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- Definition Power contracts included in operating revenues + References No definition available. + Details
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5618551-113959 + Details
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- Definition Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44 -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 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5618551-113959 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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