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Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $) | Sep. 30, 2012 | Dec. 31, 2011
--- | --- | ---
Minimum [Member] |  |
Assets from price risk management activities: [Abstract] |  |
Natural gas financial swaps | $ 3.70 |
Liabilities from price risk management activities: |  |
Electricity financial swaps | 6.05 |
Natural gas financial swaps | 3.29 |
Maximum [Member] |  |
Assets from price risk management activities: [Abstract] |  |
Natural gas financial swaps | 5.41 |
Liabilities from price risk management activities: |  |
Electricity financial swaps | 51.68 |
Natural gas financial swaps | 4.94 |
Weighted Average [Member] |  |
Assets from price risk management activities: [Abstract] |  |
Natural gas financial swaps | 4.33 |
Liabilities from price risk management activities: |  |
Electricity financial swaps | 39.44 |
Natural gas financial swaps | 4.03 |
Fair Value, Inputs, Level 3 [Member] |  |
Assets from price risk management activities: [Abstract] |  |
Natural gas financial swaps | 4,000,000 | 0
Liabilities from price risk management activities: |  |
Electricity financial swaps | 33,000,000 | 29,000,000
Natural gas financial swaps | $ 51,000,000 | $ 50,000,000

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- Definition Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of natural gas. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of electricity. + References No definition available. + Details
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