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Fair Value of FInancial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($) | Dec. 31, 2018 | Dec. 31, 2017
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Minimum [Member] |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Electricity physical forward purchase | $ 14.60 | $ 7.79
Natural gas financial swaps | 0.95 | 1.26
Fnancial swaps - electricity | 20.75 | 7.79
Maximum [Member] |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Electricity physical forward purchase | 69.00 | 41.23
Natural gas financial swaps | 4.64 | 2.92
Fnancial swaps - electricity | 35.46 | 29.74
Weighted Average [Member] |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Electricity physical forward purchase | 45.00 | 30.95
Natural gas financial swaps | 1.82 | 1.90
Fnancial swaps - electricity | 28.63 | 21.74
Assets [Member] |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Electricity physical forward purchase | 3,000,000 | 0
Natural gas financial swaps | 0 | 0
Fnancial swaps - electricity | 0 | 0
Total commodity contracts | 3,000,000 | 0
Liabilities [Member] |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Electricity physical forward purchase | 84,000,000 | 130,000,000
Natural gas financial swaps | 7,000,000 | 9,000,000
Fnancial swaps - electricity | 0 | 0
Total commodity contracts | $ 91,000,000 | $ 139,000,000

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- Definition Electricity physical forward purchase + References No definition available. + Details
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- Definition Fnancial swaps - electricity + References No definition available. + Details
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- Definition Natural gas financial swaps + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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