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Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($) | Jun. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Low [Member] |  |
Commodity Contracts |  |
Electricity physical forward | $ 12.25 | $ 14.25
Natural gas financial swaps | 1.70 | 1.85
Fnancial swaps - electricity | 15.83 | 8.57
High [Member] |  |
Commodity Contracts |  |
Electricity physical forward | 35.56 | 54.73
Natural gas financial swaps | 3.15 | 4.92
Fnancial swaps - electricity | 29.94 | 33.60
Weighted Average [Member] |  |
Commodity Contracts |  |
Electricity physical forward | 27.90 | 38.18
Natural gas financial swaps | 2.14 | 2.64
Fnancial swaps - electricity | 24.37 | 25.10
Assets [Member] |  |
Commodity Contracts |  |
Electricity physical forward | 0 | 0
Natural gas financial swaps | 0 | 1,000,000
Fnancial swaps - electricity | 2,000,000 | 1,000,000
Total commodity contracts | 2,000,000 | 2,000,000
Liabilities [Member] |  |
Commodity Contracts |  |
Electricity physical forward | 143,000,000 | 112,000,000
Natural gas financial swaps | 11,000,000 | 9,000,000
Fnancial swaps - electricity | 1,000,000 | 0
Total commodity contracts | $ 155,000,000 | $ 121,000,000

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