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Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($) | Mar. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Low [Member] |  |
Commodity Contracts |  |
Electricity physical forwards | $ 12.24 | $ 14.60
Natural gas financial swaps | 1.04 | 0.95
High [Member] |  |
Commodity Contracts |  |
Electricity physical forwards | 75.70 | 69.00
Natural gas financial swaps | 4.10 | 4.64
Weighted Average [Member] |  |
Commodity Contracts |  |
Electricity physical forwards | 50.85 | 45.00
Natural gas financial swaps | 1.80 | 1.82
Assets [Member] |  |
Commodity Contracts |  |
Electricity physical forwards | 4,000,000 | 3,000,000
Natural gas financial swaps | 0 | 0
Total commodity contracts | 4,000,000 | 3,000,000
Liabilities [Member] |  |
Commodity Contracts |  |
Electricity physical forwards | 69,000,000 | 84,000,000
Natural gas financial swaps | 5,000,000 | 7,000,000
Total commodity contracts | $ 74,000,000 | $ 91,000,000

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- Definition Electricity physical forward purchase + References No definition available. + Details
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