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Derivatives (Notional Volumes of Foreign Exchange Swaps and Forward Contracts Related to Commodity Contracts) (Details) - Regulatory Deferral Hedge [Member] - Foreign Exchange Swaps and Forward Contracts [Member] - Fuel [Member] $ in Millions | Dec. 31, 2016 USD ($)
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2017 |
Derivative [Line Items] |
Derivative, Notional Amount | $ 224
Derivative, Average Forward Exchange Rate | 1.0722
Derivative, Percent of USD Required to Purchase | 120.00%
2017 to 2020 |
Derivative [Line Items] |
Derivative, Notional Amount | $ 240
Derivative, Average Forward Exchange Rate | 1.1138
Derivative, Percent of USD Required to Purchase | 44.00%

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Average contractual rate at which a foreign currency can be purchased or sold. + References No definition available. + Details
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