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Derivatives (Notional Volumes of Commodity Swaps and Forward Contracts Designated for Regulatory Deferral) (Details) - Designated as Hedging Instrument [Member] - Regulatory Deferral Hedge [Member] - Commodity swaps and forwards [Member] bbl in Millions, T in Millions, MMBTU in Millions | 12 Months Ended
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Dec. 31, 2017 MMBTU T bbl
Coal [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Mass | T | 1
Coal [Member] | 2019-2021 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Mass | T | 1
Fuel [Member] | 2018 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 30
Fuel [Member] | 2019-2021 [Member} |
Derivative [Line Items] |
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU | 14
CrudeOilMember | 2018 [Member} |
Derivative [Line Items] |
DerivativeNonmonetaryNotionalAmountVolume | bbl | 0
CrudeOilMember | 2019-2021 [Member} |
Derivative [Line Items] |
DerivativeNonmonetaryNotionalAmountVolume | bbl | 1

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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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- Definition Nominal energy measure used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Definition Nominal mass used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Definition Nominal volume used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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